LIBRARY 

UNIVERSITY  OF  CALIFORNIA 
DAVIS 


TEXT-BOOK 

OF 

PHYSIOLOGICAL  CHEMISTRY 

IN  THIRTY  LECTURES 


BY 

EMIL   ABDERHALDEN 

O.  PROFESSOR    FUR    PHYSIOLOGIE    DBS    PHYSIOLOGISCHEN    INSTITUTS 

DER    TIERARZTLICHEN    HOCHSCHULE   BERLIN    UND 

UNIVERSITATS-PROFESSOR 

TRANSLATED  BY 

WILLIAM   T.   HALL,  S.B. 

INSTRUCTOR    IN    CHEMISTRY,    MASSACHUSETTS    INSTITUTE 
OF   TECHNOLOGY 

AND 

GEORGE  DEFREN,  M.S. 

CONSULTING    CHEMIST 


FIRST  EDITION 
SECOND    THOUSAND 


NEW  YORK 

JOHN  WILEY  &  SONS 

LONDON:  CHAPMAN  &  HALL,  LIMITED 

1911 


LIBRARY 


COPYBIGHT,    1908, 

BY 
WILLIAM  T.  HALL 


Stanhope  ipress 

F.    H.    G1LSON     COMPANT 
BOSTON.      U.S.A. 


AUTHOR'S  PREFACE. 


THE  following  lectures  are  not  intended  to  embrace  all  the  results  of 
physiological-chemical  investigation.  On  the  contrary,  the  aim  has 
been  to  discuss  only  those  discoveries  which  are  known  to  be  of  general 
interest  and  importance.  All  isolated  facts,  of  however  great  significance 
for  the  individual  investigator  in  the  field,  of  which  the  value  is  not 
fully  established  and  where  the  connection  to  other  observations  is  not 
clearly  known,  have  been  intentionally  omitted.  The  lectures  should 
lead  to  individual  thought  and  serve  to  incite  further  investigation  and 
at  the  same  time  give  one  a  general  survey  of  the  field  covered  by  physi- 
ological chemistry.  Corresponding  to  this  purpose,  great  care  has  been 
used  with  regard  to  selecting  the  literature  upon  which  the  lectures  are 
based.  It  is  evident  that  within  the  space  allotted  only  a  limited 
number  of  researches  could  be  cited.  The  "  Zentral  blatter  "  with  their 
abstracts  and  especially  Asho  and  Spiro's  "  Ergebnisse  der  Physiologic  " 
must  serve  to  fill  in  the  gaps.  Methods  and  descriptions  of  individual 
compounds  are  not  discussed  in  detail.  It  is  not  possible  for  any  one  to 
work  well  from  brief  descriptions.  Practical  laboratory  experience  is 
necessary,  and  cannot  be  replaced  by  anything  else.  The  reader  is 
referred  to  Felix  Hoppe-Seyler's  "  Handbuch  der  physiologisch-chemi- 
schen  Analyse  "  for  all  such  particulars. 

E.  ABDERHALDEN. 


271685 

in 


TRANSLATOR'S  PREFACE. 


ONE  of  the  chief  difficulties  which  arose  in  the  preparation  of 
this  translation  was  with  regard  to  the  proper  spelling  of  the  com- 
pounds mentioned.  Many  of  them  have  not  been  described  much  in 
English,  so  that  English-speaking  scientists  are  often  better  acquainted 
with  the  German  orthography.  Some  of  the  chemical  compounds  have 
been  spelled  in  three  different  ways  by  writers  of  good  English.  This 
would  almost  lead  one  to  believe  that  there  is  no  good  authority  in 
English  for  the  spelling  of  chemical  names.  Many  writers  have  followed 
the  German  spelling  as  nearly  as  possible  in  describing  compounds  which 
have  hitherto  been  mentioned  only  in  German  literature.  This  must 
necessarily  lead  to  confusion,  particularly  because  the  ending  e  in  German 
usually  signifies  the  plural,  whereas  it  does  not  in  English.  The  Chemical 
Society  of  London  in  its  Abstracts  has  mentioned  nearly  every  sub- 
stance touched  upon  in  this  book  and  has  adopted  certain  rules  for 
spelling  which  its  abstractors  are  required  to  follow.  These  rules  have, 
in  the  main,  been  adopted  by  the  American  Chemical  Society  and  the 
American  Chemical  Journal.  According  to  these  rules,  —  (1)  All  hy- 
droxyl  derivatives  of  hydrocarbons  should  end  in  ol,  thus  glycerol, 
resorcinol  and  mannitol  rather  than  glycerine,  resorcin  and  mannite. 
(2)  Compounds  which  are  not  alcohols  and  have  names  ending  in  ol 
should  be  written  ole,  as  anisole,  indole.  (3)  When  a  substituent  is  one  of 
the  groups  NH2,  NHR,  NR-j,  NH  or  NR  its  name  should  end  in  ine,  thus 
aminopropionic  acid  and  not  amidopropionic  acid.  (4)  The  ending  ine 
should  be  reserved  for  these  basic  substances,  as  aniline  instead  of  anilin, 
and  the  termination  in  should  be  reserved  for  glycerides,  glucosides, 
bitter  principles  and  proteins,  such  as  palmitin,  amygdalin  and  albumin. 
It  seems  to  us  that  these  are  the  best  rules  for  English-speaking  chemists 
to  follow  at  present.  The  rules  cited  are  those  which  pertain  particu- 
larly to  the  substances  described  in  these  lectures. 

In  two  cases  we  have  intentionally  deviated  from  the  practice  of  the 
above-mentioned  chemical  journals.  We  have  used  the  word  ferment  to 
designate  "that  which  is  capable  of  causing  fermentation"  (Century  Dic- 
tionary) and  have  not  attempted  to  distinguish  between  ferments  and 
enzymes.  This  distinction  was  based  upon  an  error,  as  Buchner  has  so 
positively  shown,  and  has  led  to  much  confusion.  Again,  we  have  fol- 
lowed the  author  rather  than  the  chemical  journals  with  regard  to  the 


vi  TRANSLATOR'S   PREFACE. 

use  of  the  words  protein  and  proteid.  While  this  book  was  in  press  the 
"Joint  Recommendations  of  the  Committees  on  Protein  Nomenclature" 
was  published  in  Science,  in  which  the  first  recommendation  was  that  the 
word  proteid  should  be  abolished.  They  would  call  what  Dr.  Abder- 
halden  designates  as  proteids  the  conjugated  proteins.  The  confusion 
with  regard  to  the  word  proteid  has  arisen  from  the  fact  that  some  writers 
have  designated  as  proteids  the  whole  protein  group,  while  others  have 
used  the  word  only  for  these  compound  proteins.  It  was  too  late  to 
adopt  the  recommended  nomenclature,  as  many  of  the  plates  were  already 
cast.  It  seems  probable,  however,  in  view  of  the  rapid  progress  which  is 
now  being  made  in  this  branch  of  chemistry  that  before  long  we  shall  be 
able  to  adopt  a  chemical  classification  of  the  proteins  which  shall  be 
better  than  any  yet  proposed. 

It  has  not  seemed  best  to  give  all  of  the  titles  to  the  papers  cited  in 
the  footnotes.  Most  of  these  titles  which  appear  in  the  original  lectures 
are  in  German,  and  in  some  cases  they  were  evidently  taken  from  the 
Centralblatt  and  are  German  translations  of  English  titles.  It  seemed 
sufficient  to  give  merely  the  abbreviated  titles  of  the  journals  where  the 
references  could  be  found  with  the  volume  and  page.  The  abbreviations 
used  are,  in  the  main,  those  adopted  by  the  American  Chemical  Society 
in  their  Chemical  Abstracts,  the  principal  ones  being  given  in  the  front  of 
this  book. 

Dr.  Abderhalden  has  kindly  looked  over  all  of  the  "page  proof"  and 
has  suggested  numerous  changes  bringing  the  literature  in  some  cases  up 
to  1908.  Professor  F.  Jewett  Moore  of  the  Massachusetts  Institute  of 
Technology  as  well  as  Dr.  Percy  G.  Stiles  of  Simmons  College  and  the 
Institute  of  Technology  have  also  read  all  of  the  proof  and  have  rendered 
invaluable  aid  by  their  many  suggestions  and  criticisms.  If  this  trans- 
lation meets  with  the  same  friendly  reception  that  has  been  accorded  to 
the  original,  credit  is  due  fully  as  much  to  each  of  these  two  gentlemen 
as  to  either  one  of  the  translators. 

WILLIAM  T.  HALL. 

MASSACHUSETTS  INSTITUTE  OF  TECHNOLOGY, 
July  11,  1908. 


ABBREVIATIONS  USED  IN  FOOTNOTES. 


ABBREVIATED  TITLE.  FULL  TITLE. 

Allgem.  med.  Zentr Allgemeine  medizinische  Zentralzeitung. 

Am.  Chem.  J American  Chemical  Journal. 

Am.  J.  Physiol American  Journal  of  Physiology. 

Ann.  Phil Liebig's  Annalen  der  Chemie. 

Ann.  chim.  phys Annales  de  chimie  et  de  physique. 

Ann.  de  chim Annales  de  chimie. 

Ann.  inst.  Pasteur Annales  de  1 'institute  Pasteur. 

Ann.  Phil Annals  of  Philosophy. 

Arch.  Anat.  Physiol Archiv  fur  Anatomic  und  Physiologic. 

Arch,  exper.  Path.  Phann Archiv  fur  experimentelle  Pathologic  und  Pharma- 

kologie. 

Arch,  exper.  Path.  Therapie Archiv  fur  experimentelle  Pathologic  und  Therapie. 

Arch.  Gynak Archiv  fiir  Gynakologie. 

Arch.  Hyg Archiv  fiir  Hygiene. 

Arch.  Kinderheilk Archiv  fiir  Kinderheilkunde. 

Arch.  klin.  Med Archiv  fur  klinische  Medizin. 

Arch.  path.  Anat Archiv  fiir  pathologische  Anatomie  und  Physiolo- 
gic und  fiir  klinische  Medizin. 

Arch.  Pharm Archiv  der  Pharmacie. 

Arch,  physiol.  Ges Archiv  der  physiologischen  Gesellschaft. 

Beitr Beitrage.     See  Hofmeister. 

Ber Berichte  der  deutschen  chemischen  Gesellschaft. 

Ber.  Berl.  Akad.  Wissensch Berichte  der  Berliner  Akademie  der  Wissenschaften, 

Ber.  deut.  hot.  Ger Berichte  der  deutschen  botanischen  Gesellschaft. 

Berl.  klin.  Wochschr Berliner  klinischer  Wochenschrift. 

Biochem.  Zentr Biochemischer  Zentralblatt. 

Bot.  Ztg Botanische  Zeitung. 

Brit.  Med.  J British  Medical  Journal. 

Bull.  soc.  chim.. .  '. Bulletin  de  la  societe  chimique  de  Paris. 

Centralbl Chemischer  Centralblatt. 

Compt.  rend Comptes-rendus  hebdomadaires  des  stances  de  1'aca- 

demie  des  sciences. 
Compt.  rend.  soc.  biol Comptes-rendus     hebdomadaires     des     stances     et 

memoirs  de  1'academie  des  sciences. 

Deut.  Arch.  klin.  Med Deutsche  Archiv  fur  klinische  Medizin. 

Deut.  med.  Wochschr Deutsche  medizinische  Wochenschrift. 

Ergeb.  Physiol.  (Asherand  Spiro).Asher  and  Spiro's  Ergebnisse  der  Physiologic. 

Hofmeister's  Beitr Beitrage  zur  chemischen  Physiologic  und  Pathologic. 

vii 


viii  ABBREVIATIONS  USED  IN  FOOTNOTES. 

ABBREVIATED  TITLE.  FULL  TITLE. 

J.  Anat.  Physiol.- Journal  of  Anatomy  and  Physiology. 

J.  Exper.  Med Journal  of  Experimental  Medicine. 

J.  Chem.  Soc Journal  of  the  Chemical  Society,  London. 

J.  pharm.  chim Journal  de  pharmacie  et  de  chimie. 

J.  Physiol The  Journal  of  Physiology. 

J.  pr.  Chem Journal  fur  praktische  Chemie. 

Med.  Klinik Medizinische  Klinik. 

Mem.  couronn.  acad.  roy.  Belg.  .  .Me'moirescouronne'sde  l'acade*mie  royale  de  Belgique. 

Monatsh Monatshefte  fur  Chemie  und  verwandte  Teile  der 

Wissenschaf  ten . 
Munch,  med.  Wochschr Miinchener  medizinische  Wochenschrift. 

Pfliiger's  Arch Pfliiger's  Archiv  f iir  die  gesammte  Physiologic  des 

Menschen  und  der  Tiere. 

Pharm.  Zentr Pharmazeutische  Zentralblatt. 

Phil.  Trans.  Roy.  Soc Philosophical  Transactions  of  the  Royal  Society  of 

London. 

Pr.  Chem.  Soc Proceedings  of  the  London  Chemical  Society. 

Pr.  Physiol.  Soc Proceedings  of  the  Physiological  Society. 

Pr.  Roy.  Soc Proceedings  of  the  London  Royal  Society. 

Pr.  Roy.  Soc.  Edinburgh Proceedings  of  the  Edinburgh  Royal  Society. 

Sitzber.  Akad.  Wiss.  Berl Sitzungsberichte  der  konigliche  Preussischen  Aka- 

demie  der  Wissenschaften  zu  Berlin. 

Sitzber.  Akad.  Wiss.  Wien Sitzungsberichte  der  konigliche  Akademie  der  Wis- 
senschaften zu  Wien. 

Sitzber.  Gesel.  Morph.  u.  Physiol.  Sitzungsberichte  der  Gesellschaft  fur  Morphologie 
Miinchen und  Physiologic  in  Miinchen. 

Sitzber.  kgl.  Gesel.  Wiss.  Upsala.  .Sitzungsberichte  der  koniglichen  Gesellschaft  der 

Wissenschaften  zu  Upsala. 

Sitzber.  physikal.  med.  Gesel.  Sitzungsberichte  der  physikalisch-medische  Gesell- 
Wurzburg schaft  zu  Wurzburg. 

Sitzber.  Miinchener  Akad Sitzungsberichte  der  koniglichen  bayerischen  Aka- 
demie der  Wissenschaften  zu  Miinchen. 

Skand.  Arch.  Physiol Skandinavisches  Archiv  fur  Physiologie. 


Trans.  Chem.  Soc Transactions  of  the  Chemical  Society. 


Verb.  Ges.  Naturforsch.  Aerzte.  .  .Verhandlung   der   Gesellschaft   deutscher  Naturfor- 

scher  und  Aerzte. 
Virchow's  Arch Archiv  fur  pathologische  Anatomic  und  Physiologie 

und  fur  klinische  Medizin. 

Z.  allg.  Biol Zeitschrift  fiir  allgemeine  Biologic. 

Z.  allg.  Physiol Zeitschrift  fiir  allgemeine  Physiologie. 

Z.  Biol Zeitschrift  fiir  Biologic. 

Z.  Elektrochem Zeitschrift  fur  Elektrochemie. 

Z.  exper.  Path.  Therap Zeitschrift     fur     experimentelle     Pathologic     und 

Therapie. 


ABBREVIATIONS  USED  IN  FOOTNOTES.  ix 

ABBREVIATED  TITLE.  FULL  TITLE. 

Z.  Hyg Zeitschrift  fiir  Hygiene  und  Infektionskrankheiten. 

Z.  innere  Med Zeitschrift  fiir  innere  Medizin. 

Z.  klin.  Med Zeitschrift  fiir  klinische  Medizin. 

Z.  physikal.  Chem Zeitschrift  fiir  physikalische  Chemie. 

Z.  physiol.  Chem Hoppe-Seyler's      Zeitschrift      fur      physiologischen 

Chemie. 

Z.  rat.  Med Zeitschrift  fur  rationelle  Medizin. 

Zentr.  Bakt.  u.  Parasitienkunde .  .  Zentralblatt  fiir  Bakteriologie  und  Parasitienkunde. 

Zentr.  med.  Wissensch Zentralblatt  fur  die  medizinische  Wissenschaften. 

Zentr.  Physiol Zentralblatt  fiir  Physiologic. 

Zentr.    Stoffwechs.  Verdauungs-     Zentralblatt  fiir  Stoffwechsel  und  Verdauungskrank- 
krankheit heiten. 


TABLE  OF  CONTENTS. 


LECTURE  I 

PAGE 

INTRODUCTION  . .  1 


LECTURE  II 

CARBOHYDRATES.        I.        IN    GENERAL  —  MONOSACCHARIDES  —  GLUCOSAMINE  — 

GLUCURONIC  ACID  ....  13 


LECTURE  III 
CARBOHYDRATES.     II.     POLYSACCHARIDES 36 

LECTURE  IV 

CARBOHYDRATES.     III.     METABOLISM  OF  CARBOHYDRATES  IN  PLANT  AND  ANIMAL 

ORGANISMS 50 

LECTURE   V 

CARBOHYDRATES.    IV.     BUILDING  UP  AND  BREAKING  DOWN  OP  CARBOHYDRATES 

IN  THE  ANIMAL  ORGANISM 76 

LECTURE   VI 
FATS  —  LECITHIN  —  CHOLESTEROL 101 

LECTURE   VII 

ALBUMINS  OR  PROTEINS.     I.     ELEMENTARY  COMPOSITION  —  SIMPLE  SUBSTANCES 

OR  MIXTURES  —  CLASSIFICATION 119 

LECTURE   VIII 
ALBUMINS  OR  PROTEINS.    II.     THE  COMPONENTS  OF  PROTEIN 146 

LECTURE   IX 

ALBUMINS  OR  PROTEINS.     III.     COMPOSITION   OF   INDIVIDUAL   PROTEINS  —  CON- 
STITUTION     171 

xi 


xii  TABLE   OF  CONTENTS. 

LECTURE   X 

PAGE 

ALBUMINS  OR  PROTEINS.    IV.     DEGRADATION  AND  FORMATION   OF    PROTEIN   IN 

THE  ANIMAL  AND  VEGETABLE  ORGANISMS 193 

LECTURE   XI 

ALBUMINS  OR  PROTEINS.     V.    DECOMPOSITION  OF  PROTEIN  IN  THE  TISSUES  —  THE 

END-PRODUCTS  OF  ALBUMIN  METABOLISM 221 

LECTURE   XII 
ALBUMINS  OR  PROTEINS.    VI.     METABOLIC  END-PRODUCTS 251 

LECTURE   XIII 

THE   NUCLEOPROTEIDS   AND   THEIR   CLEAVAGE-PRODUCTS 275 

LECTURE   XIV 
MUTUAL  RELATIONS  BETWEEN  FATS,  CARBOHYDRATES,  AND  ALBUMINS.    1 301 

LECTURE   XV 
MUTUAL  RELATIONS  BETWEEN  FATS,  CARBOHYDRATES,  AND  ALBUMINS.     II.    LAW 

OF   ISODYNAMICS 331 

LECTURE   XVI 

INORGANIC  FOODS.    I.     IMPORTANCE    OF    INORGANIC    SUBSTANCES  AS  BUILDING 

MATERIAL  OF  THE  CELLS  AND  TISSUE.  —  WATER,  SALTS 349 

LECTURE   XVII 
INORGANIC  FOODS.    II 380 

LECTURE   XVIII 
OXYGEN 408 

LECTURE   XIX 
ANIMAL  OXIDATIONS 439 

LECTURE   XX 
FERMENTS 461 

LECTURE   XXI 
THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.     1 484 


TABLE  OF  CONTENTS.  xiii 

LECTURE  XXII 
THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.    II 511 

LECTURE   XXIII 
THE   BLOOD.    COAGULATION.    COMPOSITION 535 

LECTURE  XXIV 
BLOOD  AND  LYMPH • 558 

LECTURE   XXV 
THE  ELIMINATION  OP  METABOLIC  PRODUCTS  FROM  THE  BODY 579 

LECTURE  XXVI 
THE  RELATION  OF  THE  ORGANS  TO  ONE  ANOTHER 596 

LECTURE   XXVII 
GENERAL  METABOLISM.    I 620 

LECTURE  XXVIII 
GENERAL  METABOLISM.    II 644 

LECTURE   XXIX 
OUTLOOK.    1 663 

LECTURE  XXX 
OULTOOK.    II .679 


PHYSIOLOGICAL   CHEMISTEY. 


LECTURE  I. 
INTRODUCTION. 

PHYSIOLOGICAL  chemistry  forms  an  important  branch  of  the  large 
field  of  investigation  included  under  physiology.  It  has,  for  one  thing, 
the  task  of  determining  the  chemical  composition  of  the  material  from 
which  the  separate  tissues  in  the  living  organism  are  formed.  A  knowl- 
edge of  the  chemical  construction  of  the  different  organs  gives  us  the 
answer  to  certain  questions,  and  forms  the  basis  for  further  inquiry. 
It  is  perfectly  clear  that  the  organism  must  receive  in  its  nourishment  all 
those  elements  of  which  its  tissues  are  composed.  With  the  knowledge  of 
the  composition  of  the  separate  organs,  we  obtain,  by  comparing  their 
functions,  certain  interesting  views  regarding  the  significance  of  the  dif- 
ferent substances  which  take  part  in  their  formation.  Closely  related  to 
such  problems  stands  the  investigation  of  metabolism.  This  has  become 
almost  exclusively  the  domain  of  the  physiological  chemist.  We  desire, 
first  of  all,  to  know  as  much  as  possible  concerning  the  nutriment  that  the 
organism  receives,  and  especially  as  regards  its  utilization  in  metabolism. 
We  obtain  an  insight  into  such  processes  by  carefully  studying  the  excre- 
tions from  the  organism.  The  physiological  chemist  has  long  since  passed 
beyond  these  boundaries.  His  foremost  task  is  now  to  ascertain  what 
becomes  of  each  separate  group  of  food-stuffs  in  the  organism,  in  what 
way  it  reaches  the  tissues,  and  how  the  cells  utilize  the  different  substances 
in  their  metabolism  and  are  built  up  by  them.  For  a  long  time  we  have 
not  been  content  with  merely  contrasting  the  income  with  the  outgo  of 
the  organism.  A  final  goal  of  physiological-chemical  research  will  be 
attained,  when  we  are  able  to  follow,  in  every  separate  phase,  each  and 
every  food-stuff  from  the  time  of  its  introduction  into  the  alimentary 
canal  throughout  its  entire  stay  in  the  tissues  until  it  is  finally  eliminated; 
so  that  a  whole  chain,  without  any  missing  links,  of  all  the  different  trans- 
formations and  complicated  processes  will  lie  exposed  to  our  view.  We 
are  still  very  far  from  the  solution  of  this  problem.  To  be  sure,  in  recent 
years  certain  progress  has  been  made  in  our  knowledge  of  metabolism,  and 
indeed  here  and  there  the  advance  of  pure  chemistry  has  placed  certain 


2  LECTURE  I. 

interesting  biological  discoveries  upon  a  firm  foundation;  yet,  neverthe- 
less, the  investigations  of  the  physiological  chemist  are  obliged  to  halt  for 
the  present  before  the  individual  cell.  Here  for  a  time  is  our  boundary, 
but  that  it  will  not  prove  insurmountable  is  shown  by  recent  investigations. 

Physiological  chemistry  seeks  to  accomplish  still  another  result.  We 
desire  to  know  not  merely  the  manner  in  which  each  separate  substance 
passes  through  the  body,  and  how  it  is  broken  down,  but  we  also  wish  to 
know  its  relations  to  the  other  compounds  which  are  likewise  introduced 
into  the  body.  This  is  true  especially  for  our  organic  food-stuffs.  We 
wish  to  know  whether  they  can  mutually  replace  and  supplement  one 
another,  and  whether  it  is  possible  for  a  representative  of  one  class  of 
foods  to  exercise  a  function  usually  assumed  by  another. 

Beyond  these  limits,  physiological  chemistry  sets  itself  a  number  of 
other  tasks  which  are  now  only  just  beginning  to  be  attacked.  As  little 
as  we  are  content  with  the  discovery  of  the  anatomical  structure  of  a 
definite  organism,  but  seek  to  understand  clearly  its  ontogenesis  and 
phylogenesis,  just  so  little  should  we  be  satisfied  to  trace  in  the  case  of  a 
single  individual,  or  in  only  one  species,  all  of  the  processes  which  may 
be  referred  back  to  chemical  decompositions.  Comparative  physiological- 
chemical  research  is  called  upon  to  explain  clearly  certain  important 
processes  which  now  appear  enigmatical  to  us.  On  the  other  hand,  com- 
parative chemical  investigation  concerning  the  nature  of  the  bodies  and 
the  metabolism  of  individuals  belonging  to  different  animal  species,  will 
give  a  new  support  for  purely  morphological  research.  The  gradual 
evolution  in  the  entire  animal  kingdom  takes  place  step  by  step  parallel 
to  an  ever  more  delicate  and  ever  more  marked  specialization  of  the  single 
organs.  In  many  cases  where  the  histology  of  an  organ  permits  some 
doubt  to  arise  as  to  where  it  belongs,  the  determination  of  its  function 
often  gives  a  clear  decision. 

More  and  more  the  investigation  of  physiological-chemical  processes  in 
the  animal  organism  extends  beyond  its  more  narrow  field.  For  a  long 
time  it  has  been  evident  that  there  is  no  sharp  boundary  between  the 
animal  and  vegetable  kingdoms.  More  and  more  it  becomes  recognized 
that  the  line  once  drawn  was  an  entirely  artificial  one.  We  now  know 
that  countless  processes  take  place  in  plant  and  animal  organisms  which 
are  common  to  both.  The  more  this  uniformity  has  found  expression, 
the  more  sharply  defined  have  become  the  differences  in  the  metabolism 
of  the  different  members  of  each  kingdom.  Everywhere  there  are  tran- 
sition stages,  and  nowhere  do  we  meet  with  sudden  changes.  To-day  there 
is  no  longer  any  doubt  but  that  a  complete  understanding  of  the  pro- 
cesses transpiring  within  the  animal  organism  is  only  possible  when  atten- 
tion is  paid  as  well  to  those  changes  taking  place  in  plant  organisms.  We 
desire  to  know,  moreover,  the  source  of  each  article  of  food,  how  it  has  been 


INTRODUCTION.  3 

formed,  and  to  what  extent  the  animal  cell  is  able  to  build  it  up  for  itself. 
In  such  problems  as  these  we  meet  with  deep-seated  differences  in  the 
chemism  of  plant  and  animal  cells. 

Physiology  and  physiological  chemistry  were  at  one  time  a  single  field 
of  investigation.  The  latter,  owing  to  the  remarkable  progress  of  the 
exact  sciences  chemistry  and  physics,  has  now  developed  to  such  an  impor- 
tant branch  of  natural  science  that  it  is  altogether  impossible  to-day  for 
any  one  scientist  to  master  thoroughly  in  all  its  details  the  whole  field 
of  physiology.  Little  by  little,  there  has  developed  a  sharp  distinction 
between  pure  physiology  and  physiological  chemistry.  It  is  clear  that 
an  artificial  separation  of  two  such  closely  related  fields  of  investiga- 
tion must  work  to  disadvantage  for  the  development  of  each,  so  that  it  is 
fortunate  to  find  it  recognized  more  and  more  that  the  whole  science  of 
physiology  can  only  develop  satisfactorily  when  there  is  an  intimate 
exchange  of  ideas  between  investigators  in  the  two  fields.  The  chemical 
decompositions  in  the  tissues  do  not  take  place  beside  the  "  physiological 
processes,"  but  are  bound  up  with  them.  In  no  single  case  can  we  carry 
out  any  distinction  in  such  a  sense;  and  with  those  organs  in  which  the 
relations  between  the  functions  and  the  metabolism  are  not  known,  this  is 
chiefly  because  of  our  limited  knowledge  concerning  the  latter.  In  this 
connection  we  need  only  recall  the  whole  nervous  system. 

Finally  we  must  mention  the  fact  that  physiological  chemistry  is  con- 
stantly approaching  new  fields  of  investigation  which  a  few  years  ago 
apparently  had  almost  no  connection  with  it.  We  have  in  mind  here  the 
great  field  of  infectious  diseases  and  the  changes  in  the  metabolism  of  the 
cells  which  they  occasion.  The  apparently  great  gap  existing  between 
the  methods  of  protecting  the  organism  against  the  substances  produced 
by  micro-organisms  and  the  products  given  off  by  the  cells  under  normal 
conditions  is  at  last  bridged  over  by  means  of  certain  analogies  and  numer- 
ous transitions.  Pathology  also,  in  a  broad  sense,  seeks  to  unite  itself 
more  and  more  with  the  field  of  physiological  chemistry.  Many  a  path- 
ological process  has  afforded  us  a  desired  physiological  experiment,  and 
conversely  it  is  possible  to  obtain  by  comparing  physiological  and  path- 
ological processes  a  clearer  conception  of  the  latter.  It  becomes  more  and 
more  evident  that  pathological  changes  in  the  tissues  and  cells  should  not 
be  judged  entirely  from  a  morphological  standpoint.  We  can  easily  under- 
stand that  a  disturbance  in  the  metabolism  of  the  cell,  if  continued  long 
enough,  can  make  itself  evident  in  the  outer  appearance.  On  the  other 
hand,  it  is  perfectly  conceivable  that  a  definite  functional  disorder  may 
exist  without  the  anatomist  being  able  to  localize  it  by  the  means  at  his 
disposal.  In  no  case  does  it  follow  necessarily  that  the  limit  of  discern- 
ible degeneration  is  a  measure  for  any  given  functional  disturbance. 
Again,  an  abnormal  morphological  change  may  cause  but  a  slight  dis- 


4  LECTURE  I. 

turbance  in  the  metabolism  of  the  cell.  At  present  we  are  very  far  from 
gaining  insight  into  the  physiological  processes  concerned  in  cell-metab- 
olism, and  still  less  should  we  expect  to  obtain  already  a  clear  picture  of 
pathological  disturbances.  This  opens  up  for  us  a  particularly  enticing 
field  for  further  investigation,  the  foundations  of  which  must  rest  upon 
physiological  chemistry.  It  is  apparent  from  this  cursory  glance  that  the 
tasks  of  physiological  chemistry  are  extremely  varied. 

In  order  to  be  able  to  form  a  correct  judgment  of  results  brought  for- 
ward in  a  field  of  investigation,  it  is  necessary  to  decide  in  the  first  place 
whether  the  methods  employed  are  satisfactory  and  rest  upon  a  firm 
basis.  The  methods  used  by  the  physiological  chemist  are  for  the  most 
part  those  of  pure  chemistry.  Such  experience  forms  the  basis  of  his 
work.  We  shall  soon  see  that  in  spite  of  the  fact  that  in  many  cases 
perfectly  similar  methods  are  employed,  there  is  a  marked  difference  in  the 
two  fields  of  investigation.  Chemistry,  we  know,  is  an  exact  science. 
This  designation  means,  more  than  anything  else,  that  the  chemist  arrives 
at  his  conclusion  by  carrying  out  from  case  to  case  a  direct  proof,  in  a 
perfectly  objective  manner.  If  he  discovers  a  new  substance,  he  is  able 
by  various  processes  to  so  purify  it  that  by  its  crystalline  appearance,  the 
results  of  analysis,  its  melting-point,  molecular  weight,  etc.,  and  by  a  study 
of  the  substances  he  can  form  from  it,  he  can  decide  whether  it  is  a  simple 
substance  or  a  mixture.  Finally,  he  can  decompose  the  substance,  it  may 
be  by  hydrolysis,  or  perhaps  by  oxidation,  or  by  reduction,  thus  transform- 
ing it  into  constituents  of  known  composition,  or  into  some  other  well- 
known  compound,  and  in  this  way  eventually  establish  its  composition  in 
all  its  details.  But  even  after  all  this  work  the  chemist  is  not  satisfied. 
He  is  not  absolutely  positive  that  he  has  a  substance  of  definite  constitu- 
tion until  he  has  succeeded  in  effecting  its  synthesis.  To  be  sure,  meta- 
physical speculations  also  play  an  important  part  in  the  domain  of  pure 
chemistry,  and  rightly.  This  has  long  since  been  shown  to  be  justifiable 
on  account  of  the  fruitfulness  of  such  speculations.  The  chemist  must 
never  forget,  however,  where  the  facts  end  and  where  the  hypothesis 
begins. 

Let  us  see  now  how  the  physiological  chemist  conducts  his  proofs.  One 
might  be  tempted  to  believe  that  an  insight  into  the  chemical  processes 
which  take  place  in  the  organism  would  be  obtained  soonest  if  we  chose  for 
our  study  the  simplest  form  of  organized  being,  the  single  cell,  i.e.,  a  unicell- 
ular individual.  A  little  thought,  however,  shows  us  that  the  morphological 
unity  of  the  cell  corresponds  to  an  uncommonly  complicated  cell-mechan- 
ism. Each  cell-unit  here  takes  up  nutriment,  decomposes  and  assimilates 
it,  and  eventually  breaks  it  down  to  deposit  at  last  the  final  products  of 
metabolism.  All  of  these  processes  take  place  in  a  single  minute  cell. 
From  this  point  of  view,  every  morphological  differentiation  must  in  a 


INTRODUCTION.  5 

certain  sense  be  regarded  as  a  simplification  of  the  functional  processes. 
The  more  localized  the  separate  functions  are,  and  the  more  they  pertain 
to  certain  organs  only,  the  greater  becomes  the  possibility  of  our  succeed- 
ing in  studying  them  by  themselves  and  explaining  them.  In  this  sense 
the  most  suitable  objects  for  our  study  are  those  highly  complicated  beings, 
the  vertebrates. 

In  order  to  show  the  value  of  the  results  obtained  by  physiological- 
chemical  investigation,  a  few  examples  may  be  cited  briefly.  We  will 
disregard  here  that  part  of  the  field  which  concerns  itself  with  the  knowl- 
edge of  the  separate  components  of  our  food  and  the  substances  which  go 
to  form  our  tissues.  In  such  cases  it  is  evident  that  the  physiological 
chemist  will  make  use  of  the  same  methods  for  determining  the  value  of 
his  work  as  does  the  pure  chemist.  He  will,  furthermore,  proceed  in  pre- 
cisely the  same  way  as  we  have  described  for  a  chemical  investigation,  and 
will  thus  establish  the  proof  for  the  constitution  of  a  definite  compound. 
Here  physiological  chemistry  is  constantly  receiving  much  aid  from  the 
field  of  pure  chemistry,  and  in  fact  this  part  of  the  work  has  been 
developed  by  trained  chemists. 

We  will  choose  here,  as  an  example,  a  question  which  has  been  asked 
repeatedly,  namely  this:  What  becomes  of  a  definite  compound  after  it 
is  introduced  into  the  animal  organism,  in  what  way  is  it  broken  down, 
and  in  what  form  is  it  finally  excreted?  We  will  use  for  our  illustration 
a  very  important  discovery,  rich  in  results,  which  we  owe  to  Wohler. 
This  scientist  was  interested  to  learn  what  became  of  benzoic  acid  after  it 
was  introduced  into  the  intestine.  He  was  unable  to  detect  it  in  the 
urine,  nor  could  he  find  there  any  substance  which  he  recognized  as 
one  of  its  lower  derivatives.  On  the  other  hand,  he  did  find  in  the  urine 
another  acid,  hippuric  acid,  which  is  closely  related  to  benzoic  acid.  This 
is  formed,  as  we  shall  see  later  on,  by  the  combination  of  benzoic  acid  with 
glycocoll,  the  latter  substance  being  formed  by  the  hydrolysis  of  albumin. 
Hippuric  acid  on  being  boiled  with  strong  mineral  acids  or  alkalies  is 
decomposed  into  these  two  constituents.  Wohler,  by  establishing  the 
fact  that  the  benzoic  acid  which  he  introduced  into  the  organism  left  it  in 
the  form  of  hippuric  acid,  proved  for  the  first  time  that  syntheses  may  take 
place  in  animal  organisms.  In  this  way  the  path  was  broken  and  the  ob- 
struction to  the  development  of  physiological  chemistry  which  had  existed 
for  years  was  removed.  Up  to  that  time  it  was  regarded  as  an  established 
fact  that  only  plant  cells  were  capable  of  accomplishing  synthetical  work, 
while  those  of  the  animal  organism  could  only  effect  decomposition. 
This  first  observation  of  Wohler  was  particularly  fruitful,  and  inspired 
a  great  deal  of  similar  work,  so  that  to-day  we  are  perfectly  justified  in 
ascribing  complicated  syntheses  to  the  action  of  the  animal  cells.  If  we 
attempt  to  subject  Wohler's  method  of  proof  to  close  critical  analysis,  we 


6  LECTURE  I. 

find,  first  of  all,  that  it  is  indirect  in  character.  Here. we  meet  with  the  most 
remarkable  point  in  all  physiological-chemical  investigation.  A  very 
large  part  of  it  is  based  upon  indirect  proofs.  Its  inadequacy  is  clearly 
shown  if  we  choose  for  illustration,  instead  of  the  above  very  transparent 
example,  something  more  complicated,  such  as,  for  example,  the  question 
now  in  the  foreground  of  general  interest  with  regard  to  the  formation  of 
sugar  from  other  sources  than  carbohydrates.  By  extirpating  the  pan- 
creatic gland  of  a  dog,  its  carbohydrate  metabolism  may  be  so  disturbed 
that  sugar  is  constantly  eliminated  in  the  urine,  and  one  would  naturally 
think  a  priori  that  in  such  a  case  it  would  be  possible  to  determine  with- 
out difficulty  whether,  for  example,  albumin  or  fat  can  cause  secretion  of 
sugar  in  the  urine.  As  a  matter  of  fact,  this  secretion  of  sugar  continues 
even  after  all  carbohydrates  are  completely  eliminated  from  the  nourish- 
ment. We  may  assume  this  to  prove  that  albumin  and  fat  can  cause 
secretion  of  sugar  in  the  urine.  Although  we  are  justified  in  drawing  such 
a  conclusion,  it  is  not  necessarily  a  correct  one.  A  result  from  a  given 
experiment  can  lead  to  different  conclusions  according  to  the  standpoint 
assumed  by  the  individual  investigator.  In  this  case  it  is  possible  to 
explain  the  continued  secretion  of  sugar  in  another  way.  The  animal 
organism  possesses  constant  reserves.  Their  extent  has  only  recently 
been  realized.  From  them,  and  especially  from  carbohydrate  stores,  the 
sugar  may  have  its  source.  The  conclusion  that  the  animal  cell  is  capa- 
ble of  forming  sugar  from  other  sources  than  the  carbohydrates  can  only 
be  drawn  with  certainty  after  it  has  been  established  that  the  organism 
has  no  more  carbohydrates  at  its  disposal.  Not  till  this  has  been  clearly 
shown  will  the  above  conclusion  rest  upon  a  firm  basis.  It  remains  still 
undecided,  even  if  the  carbohydrates  as  sugar-formers  are  fortunately 
excluded,  as  to  whether  fats  and  albumins  belong  to  this  class  of  com- 
pounds. Now  it  has  been  often  observed  that  in  feeding  albumin  to  a  dog 
with  no  pancreas  the  elimination  of  nitrogen  runs  practically  parallel 
to  that  of  sugar.  This  repeatedly  established  relation  between  the  break- 
ing down  of  albumin  and  the  formation  of  sugar  has  been  given  as  a  direct 
proof  for  the  formation  of  sugar  from  albumin,  and  in  fact  one  might 
be  tempted  to  assume  that  this  is  actually  a  direct  demonstration. 
E.  Pfliiger,  whom  we  have  to  thank  for  a  detailed  critical  review  of  all  the 
work  in  this  field,  is  of  an  altogether  different  opinion.  If  we  assume  as 
correct  that  the  elimination  of  sugar  and  of  nitrogen  increases  at  an  equal 
rate,  we  are  still  far  from  being  justified  in  assuming  that  the  increase  in 
sugar  is  directly  due  to  the  breaking  down  of  the  albumin  which  is  taking 
place.  The  cells  of  a  dog  with  no  pancreas,  and  those  of  a  diabetic,  have 
not  lost  entirely  the  power  of  consuming  sugar,  and  in  all  cases  a  part  of 
the  sugar  formed  is  burned  up.  If  now  albumin  be  fed,  it  will  also  be 
burned;  in  other  words,  there  will  be  set  free  in  the  tissues  of  the  organism 


INTRODUCTION.  7 

a  definite  number  of  heat  units  which  it  can  use  in  performing  its  func- 
tions. By  means  of  the  calories  of  heat  coming  from  the  albumin  the 
organism  is  spared  a  corresponding  amount  which  were  otherwise  taken 
from  non-nitrogenous  material.  We  may  assume  that  the  cells,  which 
moreover  are  capable  of  consuming  sugar  only  with'  great  difficulty,  now 
do  not  use  so  much  of  it.  -More  and  more  unchanged  sugar  circulates  in 
the  tissues  and  in  the  blood,  and  since  the  kidneys,  as  we  shall  see  later, 
are  sensitive  to  the  slightest  increase  of  sugar  in  the  blood  over  the  normal 
and  serve  to  remove  all  such  excess,  it  follows  that  there  must  necessarily 
be  an  increase  in  the  elimination  of  sugar.  According  to  this  hypothesis 
the  action  of  albumin  is  an  indirect  one  as  regards  the  sugar.  Naturally 
this  explanation  is  not  necessarily  the  correct  one.  We  have  mentioned 
these  experiments  and  the  two  explanations  of  the  results  obtained  briefly 
in  order  to  show  by  a  somewhat  complicated  example  how  varied  the  con- 
clusions may  be  that  are  drawn  with  regard  to  an  apparently  simple  prob- 
lem. It  would  not  be  difficult  to  cite  numerous  other  examples  to  illustrate 
this  point.  Later  on  we  shall  repeatedly  come  back  to  these  indirect  proofs 
and  mention  again  and  again  the  fact  that  it  is  of  fundamental  importance 
for  the  further  development  of  all  physiological-chemical  investigation 
that  it  should  always  be  clearly  and  sharply  recognized  as  to  what  extent 
we  are  justified  in  speaking  of  facts,  and  at  what  place  the  indirect  con- 
clusions, corresponding  to  the  still  unsettled  part  of  our  field  of  investiga- 
tion, begin.  When  such  a  gap  is  discovered,  it  is  our  duty  not  to  rest  satisfied 
until  all  of  the  conclusions  have  been  subjected  here  also  to  direct  proof. 

Before  taking  up  the  discussion  of  ways  and  means  to  accomplish  this 
end,  we  will  turn  back  once  more  to  the  synthesis  of  hippuric  acid  in  the 
animal  organism.  This  was  established  indirectly,  and  its  assumption 
rests  solely  upon  probability.  After  introducing  benzoic  acid  into  the 
organism  of  a  mammal  we  find  a  corresponding  increase  in  the  amount  of 
hippuric  acid  in  the  urine.  It  is  a  fact  that  hippuric  acid  can  be  formed 
from  benzoic  acid  and  glycocoll.  The  chemist  is  able  to  make  hippuric 
acid  in  the  laboratory  from  these  two  components,  but  under  conditions 
which  it  is  impossible  to  realize  in  our  tissues.  It  requires  a  high  tempera- 
ture, considerable  pressure,  and  the  exclusion  of  water.  We  have,  how- 
ever, long  since  been  forced  to  the  conclusion  that  the  cells  have  the  power 
of  causing  chemical  reactions  to  take  place  which  require  entirely  dif- 
ferent conditions  when  carried  out  in  a  test  tube.  We  are  satisfied  if  an 
observed  chemical  process  does  not  outwardly  contradict  our  general 
experience.  We  base  our  explanations  of  the  chemical  decompositions 
taking  place  in  the  animal  organism  upon  the  results  of  chemical  research, 
and  seek  to  go  farther  and  bridge  over  all  the  large  gaps  which  we  meet 
with  everywhere  on  account  of  our  insufficient  knowledge  of  metabolic 
processes.  Here  also  we  must  be  conscious  that  we  are  only  speaking  of 


8  LECTURE  I. 

probabilities,  and  in  no  case  should  it  be  credited  as  if  resting  upon  facts 
established  experimentally.  Analogies  in  many  cases  are  without  doubt 
very  valuable,  and  often  form  the  skeleton  upon  which  we  can  build  further. 

We  receive  a  new  impulse  and  gain  a  new  point  of  view  with  every 
advance  made  by  pure  chemistry  concerning  substances  of  physiological 
interest.  Our  task  is  to  utilize  each  discovery  thus  made  and  to  give  it  a 
strictly  objective  test  with  regard  to  its  application  to  the  processes  taking 
place  in  the  tissues.  Here  again  we  meet  all  too  frequently  with  hypotheses 
which  are  stated  as  facts.  We  hardly  need  to  mention  how  extraordinarily 
restraining  the  direct  amalgamation  of  these  entirely  different  elements  is 
for  a  healthy  progress  in  the  knowledge  of  chemical  processes  in  the  animal 
organism.  For  these  reasons  Wohler's  experiment  proves  positively 
merely  that  when  benzoic  acid  is  introduced  into  the  system  it  causes  an 
increased  elimination  of.  hippuric  acid.  It  must  remain  an  open  question 
as  to  whether  the  benzoic  acid  introduced  stands  in  direct  relation  to  the 
other  acid  or  merely  indirectly  causes  its  formation.  In  this  particular 
case,  however,  the  latter  case  seems  scarcely  probable,  although  we  must 
make  such  a  limitation  unless  we  propose  to  draw  our  conclusions  beyond 
the  realms  of  fact. 

We  must  now  mention  an  important  aid  which  the  chemist  makes 
use  of  constantly  in  his  experiments,  which  are  often  indirect  in  nature. 
We  refer  to  the  control  experiment.  It  is  clear  that  there  is  nothing 
to  be  gained  by  merely  feeding  an  animal  with  benzoic  acid  and  deter- 
mining subsequently  the  amount  of  hippuric  acid  eliminated.  We  must 
first  learn  how  much  hippuric  acid  the  animal  in  question  eliminates  under 
normal  conditions.  If  the  experiment  is  to  be  made  convincing,  the  amount 
of  hippuric  acid  contained  in  the  urine  of  one  and  the  same  animal  fed 
uniformly  must  first  be  determined  and  this  continued  for  several  days. 
Then  for  a  time  a  little  benzoic  acid  should  be  added  to  the  food,  which 
otherwise,  must  remain  qualitatively  and  quantitatively  the  same  as  before, 
and  again  the  hippuric  acid  be  determined  in  the  urine.  If  now  the  experi- 
ment be  continued  for  another  period  of  several  days  in  which  no  benzoic 
acid  is  fed  to  the  animal,  then,  if  the  whole  experiment  is  consistent,  it 
will  be  possible  to  determine  whether  the  benzoic  acid  stands  in  any 
relation  to  the  elimination  of  hippuric  acid. 

The  uncertainty  of  the  significance  of  experiments  made  with  animals 
is  in  many  cases  greatly  increased  by  the  fact  that  individual  variations 
often  play  an  important  part.  Many  contradictions  to  be  found  in  the 
literature  are  due  solely  to  the  fact  that  the  experiments  were  not  carried 
out  long  enough.  We  must  not  only  require  that  such  experiments  should 
be  carried  out  in  a  single  individual  for  quite  a  length  of  time,  but  in  dif- 
ferent individuals  of  the  same  animal  species  as  well.  It  is,  furthermore, 
of  great  value  to  make  experiments  with  different  species  of  animals,  for 


INTRODUCTION.  9 

frequently  they  behave  altogether  differently  physiologically.  It  is 
apparent  already  from  these  brief  remarks  what  great  demands  are  laid 
upon  the  experimentation  of  the  physiological  chemist.  He  always  has  to 
deal  with  complicated  processes.  He  is  acquainted  usually  only  with  the 
initial  and  the  final  products  of  the  metabolism,  and  is  compelled  to  clear 
up  theoretically  the  whole  chain  of  transformations  which  are  necessary 
for  the  formation  of  the  latter  from  the  former.  Here  and  there  it  is 
possible  to  get  hold  of  intermediate  steps,  and  thus  we  encroach  more  and 
more  upon  the  great  domain  of  the  unknown. 

A  considerable  advance  in  the  subject  was  made  when  experimentation 
was  begun  upon  surviving  organs  rather  than  upon  the  whole  organism. 
Here  the  initial  and  end  products  are  more  closely  related,  or  at  least 
apparently  so,  although  here  also,  as  soon  as  the  change  in  cell  substance 
begins  really  to  take  place,  the  complication  is  naturally  practically  as 
great  as  in  following  one  substance  through  the  whole  body.  Experimen- 
tation with  surviving  organs  has  in  itself  quite  a  number  of  advantages. 
In  many  cases  we  are  able  to  change  an  indirect  proof  into  a  direct  one. 
We  are  able  to  work  out  accurately  the  composition  of  a  definite  organ. 
We  can  definitely  decide  the  question  as  to  whether  it  has  stored  up  in  it 
sufficient  amounts  of  definite  substances  to  cause  the  formation  of  certain 
compounds,  and  thus  determine  positively  whether  the  organ  makes  use  of 
a  substance  introduced  into  it  in  a  definite  process. 

Let  us  return  again  to  our  hippuric  acid  hypothesis.  It  is  possible  to 
establish  which  organ  is  capable  of  carrying  it  out.  G.  Bunge  and  O. 
Schmiedeberg  have  shown  that  the  kidneys  of  mammals,  or  more  accu- 
rately those  of  a  dog,  are  capable  of  forming  hippuric  acid  from  glycocoll 
and  benzoic  acid.  They  caused  a  dog  to  bleed  to  death,  cut  out  its  kidneys, 
and  introduced  defibrinated  blood  through  the  arteries  of  the  kidneys  and 
allowed  it  to  flow  out  through  the  renal  veins.  On  introducing  glycocoll 
and  benzoic  acid,  there  appeared  hippuric  acid  in  the  blood  and  in  the 
liquid  emptying  out  through  the  ureter.  A  control  experiment  with  the 
second  kidney  showed  that  it  as  well  as  the  blood  from  the  first  kidney  was 
free  from  hippuric  acid.  If  benzoic  acid  but  no  glycocoll  was  introduced 
into  the  blood,  the  amount  of  hippuric  acid  formed  was  extremely  small. 
The  conclusion  to  be  drawn  from  this  experiment  is  that  benzoic  acid 
effects  the  formation  of  hippuric  acid  because  it  is  itself  used  in 
the  synthesis.  However,  this  fact  is  not  yet  absolutely  proved.  The 
objection  may  still  be  raised  that  hippuric  acid  may  arise  from  another 
source.  The  formation  of  this  acid  is,  at  best,  a  very  complicated  process. 
We  have,  on  the  one  hand,  the  kidney  containing  a  very  complex  tissue, 
and,  on  the  other  hand,  the  blood  with  its  constituents.  As  a  matter  of 
fact,  it  was  not  possible  to  effect  the  above  synthesis  after  the  red 
corpuscles  were  removed  from  the  blood. 


10  LECTURE  I. 

Another  significant  advance  in  the  knowledge  of  chemical  processes  which 
take  place  in  the  animal  organism  was  caused  by  the  discovery  that  it  was 
possible  to  work  out  certain  processes  by  means  of  extracts  of  tissue.  We 
are  furthermore  fortunately  able  in  many  cases  to  isolate  the  active  prin- 
ciple. The  great  advantage  of  such  experiments  is  clear  from  the  fact  that 
an  extremely  small  amount  of  these  products,  called  ferments,  is  capable  of 
causing  considerable  change  without  itself  appearing  in  the  end  products  of 
the  reaction.  It  has  been  attempted  to  effect  the  hippuric  acid  synthesis  in 
this  way  by  means  of  a  ferment  which  has  been  isolated  from  the  kidneys. 
This  has  not  yet  been  done  satisfactorily.  An  instructive  example  of 
great  significance  as  regards  the  use  of  such  tissue  extracts  and  of  the 
ferments  obtained  from  them  is  found  in  the  recent  experiments  to  form 
uric  acid  from  the  purine  bases,  investigations  made  by  Horbaczewski, 
Wiener,  Spitzer,  Schittenhelm,  and  Burian.  The  first-mentioned  has 
shown  that  purine  bases  added  in  the  presence  of  oxygen  to  an  animal  organ 
which  has  been  macerated  to  a  paste  causes  an  increase  of  uric  acid.  Against 
this  experiment  the  objection  may  be  raised  that  it  is  not  conclusive.  The 
paste  itself  contains  some  purine  bodies  and  perhaps  substances  of  unknown 
nature  which  stand  in  close  relation  to  uric  acid.  The  purine  bases  added 
may  in  some  way  have  an  indirect  action  upon  the  given  synthesis.  The 
proof  becomes  much  more  satisfactory  if  instead  of  using  the  whole  organ, 
we  make  use  of  a  ferment  extracted  from  it.  To  be  sure,  the  nature  of  this 
ferment  is  not  known,  but  we  know  its  action.  We  can  free  it  completely 
from  purine  substances,  and  furthermore  we  require  but  a  small  amount  of 
it.  It  is  of  great  significance  with  regard  to  our  conclusions,  that  it  is  pos- 
sible here  to  follow  the  experiment  quantitatively.  We  can  weigh  accu- 
rately the  amount  of  purine  bases  added,  and  similarly  the  amount  of  uric 
acid  formed,  so  that  we  are  now  able  to  establish  sharply  the  relation 
between  the  purine  bases  and  the  uric  acid.  This  method  has  still  further 
advantages.  It  has  been  possible  to  identify  certain  intermediate  products 
formed  in  the  transformation  of  certain  purine  bases  into  uric  acid,  and  to 
establish  the  fact  that  certain  organs  possess  ferments  which  are  capable  of 
breaking  down  the  uric  acid  formed.  In  this  way  it  is  at  once  possible  to 
establish  clearly  the  complete  metabolism  of  purine  substances.  It  would, 
of  course,  be  unsafe  to  apply  the  results  of  such  experiments  without  further 
investigation  to  the  processes  taking  place  in  the  living  organism.  It  is 
perfectly  conceivable  that  the  conditions  prevailing  in  the  tissues  may  be 
entirely  different  from  those  prevailing  in  the  fermentation  experiments 
carried  out  artificially.  Such  a  limitation  holds  for  all  investigations 
carried  out  with  ferments,  and  especially  those  with  digestive  ferments.  In 
such  experiments  the  ferments  develop  their  action  under  entirely  changed 
conditions.  We  can  merely  imitate  the  temperature;  further  than  this  we 
are  practically  helpless.  In  the  alimentary  canal,  for  example,  absorption 


INTRODUCTION.  11 

takes  place  immediately  hand  in  hand  with  the  hydrolysis  of  food  by  the 
ferments  of  the  digestive  juices.  The  decomposition  products  are  imme- 
diately taken  away.  We  are  still  entirely  ignorant  of  the  manner  in  which 
each  individual  ferment  does  its  work,  how  the  different  ferments  assist 
one  another,  and  how  their  work  is  influenced  by  other  factors.  At  all 
events,  it  is  evident  that  the  decomposition  of  food  takes  place  much  more 
rapidly  than  in  a  test  tube.  All  the  products  of  the  decomposition  remain 
in  the  latter  case,  and  serve  to  hinder  the  further  action  of  the  ferment,  or 
perhaps  even  cause  it  to  act  in  a  different  direction.  On  the  other  hand,  in 
the  test  tube  we  are  often  able  to  identify  products  which  otherwise  escape 
our  observation  owing  to  the  rapid  absorption  in  the  bowels.  It  is  possible 
here  also  to  draw  conclusions  only  by  combining  experiments ;  that  is,  on 
the  one  hand  we  will  study  digestion  as  accurately  as  possible  in  the  test 
tube,  following  it  up  in  its  separate  phases,  and,  on  the  other  hand,  we  must 
attempt  to  identify  the  products  of  digestion  in  the  bowels  themselves;  in 
this  way  we  gradually  draw  a  picture  of  the  entire  process  of  digestion. 
In  an  entirely  similar  manner  the  metabolism  of  purine  substances  must 
be  studied  in  the  whole  organism  in  order  to  find  out  how  far  the  facts 
thus  ascertained  agree  with  the  results  of  experiments  with  ferments. 

We  must  consider  still  another  important  condition,  namely,  the  concept 
of  quantity.  In  physiological-chemical  experiments  this  is  too  frequently 
neglected.  Its  importance  is  perfectly  obvious.  We  must  always  require 
that  every  chemical  process  taking  place  in  the  organism  be  followed 
quantitatively.  Qualitative  experiments  are  prone  to  lead  to  great  errors, 
and  it  is  never  possible  to  recognize  clearly  by  means  of  them  the  relation 
between  individual  products.  We  must  always  know  how  much  of  this 
or  that  substance  has  been  changed  over  into  a  definite  product.  Often- 
times a  minor  process  will  otherwise  be  considered  the  essential  one  simply 
because  it  was  easy  of  discovery,  whereas  the  main  change  may  be  entirely 
overlooked. 

It  is  almost  superfluous  to  mention  the  fact  that  the  methods  employed 
must  be  suitable  for  the  problem  to  be  investigated.  Every  investigation  in 
the  field  of  physiological  chemistry  must  start  out  with  a  critical  examina- 
tion of  the  value  of  available  methods.  We  must  clearly  recognize  the 
sources  of  error  and  take  them  into  consideration,  especially  when  definite 
conclusions  are  to  be  drawn  from  any  discovery.  The  methods  are  the 
foundation  pillars  in  every  experimental  investigation.  Every  advance  is 
closely  dependent  upon  them,  so  that  we  must  lay  great  stress  upon  their 
final  development.  The  great  importance  in  the  improvement  of  methods 
too  often  falls  into  the  background,  especially  in  physiological-chemical 
investigation,  and  apparently  more  weight  is  laid  upon  the  more  or  less 
fruitful  hypotheses.  It  must  not  be  forgotten,  however,  that  essentially 
new  facts  are  usually  closely  connected  with  the  discovery  of  new  methods. 


12  LECTURE  I. 

The  latter  alone  cause  the  science  to  progress  upon  a  solid  foundation. 
They  assure  an  objective  investigation,  and  above  all  else  one  that  is 
free  from  prej  udgment .  Certainly  hypotheses  and  speculations  are  of  great 
value,  and  their  importance  should  not  be  underestimated.  They  form 
the  framework  upon  which  we  can  build  further.  The  facts,  however, 
should  never  be  adjusted  in  accordance  with  them.  The  facts,  and  never 
the  hypotheses  must  always  be  decisive.  This  warning  is  not  unnecessary, 
for  in  contrast  to  the  exact  sciences  such  as  chemistry  and  physics, 
here  in  physiological-chemical  investigation  the  hypotheses  step  boldly 
into  the  foreground,  especially  in  questions  concerning  metabolism,  and 
in  particular  that  of  the  cell  substance. 

We  make  these  few  preliminary  remarks  in  order  to  show  at  the  start 
the  nature  of  our  lectures  and  the  principles  which  are  authoritative.  It 
will  be  our  aim  to  define  as  sharply  as  possible  what  discoveries  are  to  be 
regarded  as  well-established  facts  and  at  what  place  the  probability 
proofs  are  justifiable.  Above  all  else  we  shall  strive  to  follow  every 
separate  food-stuff  from  its  introduction  into  the  organism  to  its  complete 
breaking  down  and  the  elimination  of  the  end-products  in  order  thus  to 
obtain  a  comprehensive  view  of  its  behavior  in  the  organism  and 
its  participation  in  metabolism.  We  shall  intentionally  consider  the 
building  materials  and  composition  of  the  separate  organs  only  in 
special  cases.  This  knowledge  we  acquire  in  studying  metabolism. 
A  consideration  of  the  quantitative  relations  in  which  the  different  sub- 
stances are  present  would  be  of  use  to  us  only  when  the  separate  values 
are  based  upon  a  broad  foundation  and  upon  a  great  many  observations. 
For  the  present  our  methods  are  not  adequate  to  give  us  a  satisfactory 
picture  of  the  building  up  of  the  separate  tissues.  Neither  is  our 
knowledge  sufficient  to  permit  the  valuation  of  the  results  for  compara- 
tive studies,  nor  are  we  in  general  in  a  position  to  draw  conclusions 
with  regard  to  the  functions  of  certain  organs  from  a  knowledge  of 
their  composition.  In  the  special  cases  where  this  is  possible  we  shall 
speak  of  it. 


LECTURE  II. 

CARBOHYDRATES.1 
I. 

IN  GENERAL  —  MONOSACCHARIDES  —  GLUCOSAMINE  —  GLUCURONIC 

ACID. 

THE  carbohydrates  are  extremely  abundant  in  nature.  They  take  a 
prominent  share  in  the  building  up  of  the  vegetable  kingdom,  and  play  an 
important  part  as  food  in  animal  economy ;  while  on  the  other  hand,  com- 
pared with  the  protein  bodies,  they  scarcely  come  into  consideration  at  all 
as  building  materials  for  the  animal  tissues  and  cells.  The  most  important 
representatives  of  this  class  of  bodies  have  been  known  for  a  long  time, 
especially  cane  sugar,  which  before  the  beginning  of  the  Christian  era  was 
obtained  in  India  in  a  solid  form  by  boiling  down  the  juice  of  the  sugar- 
cane. To-day,  besides  the  sugar-cane,  the  sugar-beet 2  forms  an  important 
raw  material.  Again,  grape-sugar  has  been  known  for  a  long  time,  and 
was  first  discovered  in  honey  although  prepared  pure  for  the  first  time 
by  Marggraf  in  the  middle  of  the  eighteenth  century.  In  the  year  1615 
Bartolleti 3  isolated  a  third  member  of  this  group  from  milk,  namely 
milk-sugar.  If  we  add  to  these  cellulose  and  starch  we  have  named 
all  of  the  members  of  the  carbohydrate  group  which  were  known  up  to 
the  time  that  the  study  of  organic  chemistry  as  we  know  it  to-day  began 
as  a  result  of  the  experiments  of  Lavoisier  and  Scheele.  If  we  disregard 
a  few  isolated  although  very  important  observations  —  e.g.,  Kirch- 
hoff's  discovery  that  starch  was  changed  into  grape-sugar  by  boiling  with 
dilute  acids,4  and  that  the  same  process  could  be  brought  about  by  a  sub- 
stance found  in  grain  or  malt 5  —  very  little  was  known  in  chemistry, 
and  consequently  in  physiology,  concerning  carbohydrates  up  to  within 
very  recent  times,  and  this  period  of  darkness  disappeared  only  with  the 
important  investigations  of  Kiliani  and  of  Emil  Fischer  especially. 


1  The  following  references  cover  this  field: —  Emil  Fischer:  Ber.  23,  2114  (1890). 
E.  0.  V.  Lippmann:  Die  Chemie  der  Zuckerarten  (1904).  B.  Tollens:  Kurzes 
Handbuch  der  Kohlehydrate  (1898). 

3  Discovered  by  Marggraf  (1747);  Ber.  Berlin.  Akad.  Wissensch.  79,  1749. 

3  Encyclopaedia  dogmatica,  1615. 

4  J.  d.  Pharm.  74,  199  (1811). 

5  Schweigger's  J.  14,  389  (1814). 

13 


14  LECTURE  II. 

In  the  course  of  the  following  discussion  we  shall  see  how  closely  the 
development  of  the  chemistry  of  carbohydrates  follows  the  general  develop- 
ment of  chemistry,  and  especially  that  of  stereochemistry  and  the  theory 
of  structure,  and  what  a  comprehensive  outlook  dawned  all  at  once 
for  the  whole  field  of  biology. 

The  carbohydrates  are  all  composed  of  the  elements  carbon,  hydrogen, 
and  oxygen,  and  these  are  the  same  elements  that  are  found  in  fats.  The 
two  classes  of  compounds,  however,  contain  these  elements  in  different 
relative  amounts.  Oxygen  and  hydrogen  in  the  former  are  present  in  the 
ratio  1 : 2,  which  is  the  same  as  in  water.  This  is  the  reason  that  the 
name  carbohydrates  has  been  given  to  the  group.  Many  other  compounds 
which  do  not  belong  to  the  sugar  group,  for  example  acetic  and  lactic 
acids,  are,  however,  also  composed  of  the  same  elements  and  -in  the  same 
ratio.  Formerly,  the  carbohydrates  were  defined  as  containing  six,  or  a 
multiple  of  six,  carbon  atoms.  This  limitation  was  shown  to  be  incorrect 
by  the  discovery  of  sugars  containing  less  than  six  atoms  of  carbon,  and  by 
the  synthesis  of  sugars  with  seven,  eight,  and  nine  carbon  atoms.  It  is  in 
fact  impossible  to  give  a  sharply-defined,  satisfactory  definition  of  a  carbo- 
hydrate, for  to  some  extent  the  individual  members  of  the  group  have  very 
different  properties  from  one  another.  In  general,  the  carbohydrates  are 
aldehyde  or  ketone  derivatives  of  polyatomic  alcohols. 

As  is  the  case  with  almost  all  branches  of  physiological  chemistry,  so 
here,  as  has  already  been  indicated,  it  was  only  possible  to  obtain  a  clear 
idea  of  the  formation  and  transformations  of  carbohydrates  in  the  animal 
and  vegetable  organisms  after  the  compounds  in  question  had  been  pre- 
pared synthetically.  It  was  Emil  Fischer  who  first  succeeded  in  this 
effort,  by  preparing  from  glycerol  —  the  same  glycerol  which  we  shall 
meet  with  again  in  the  discussion  of  fats  —  by  gentle  oxidation,  a  sub- 
stance with  the  typical  properties  of  a  sugar.  This  compound,  called 
glycerose,  contains,  to  be  sure,  only  half  as  much  carbon  as  grape-sugar.  As 
it  was  found  possible  to  prepare  by  the  action  of  dilute  alkali  upon  two 
molecules  of  glycerose  a  true  sugar  with  six  atoms  of  carbon,  there  was 
no  longer  any  doubt  that  glycerose  was  to  be  regarded  as  a  member  of 
the  carbohydrate  group.  This  synthesis  is  of  especial  value  to  us,  as  it 
establishes  a  relation  between  the  fats  and  the  sugars.  Finally,  it  was 
even  possible  to  effect  the  synthesis  from  the  elements;  for  starting  with 
formaldehyde,  CH^O,  Emil  Fischer  succeeded  by  polymerization 
(6  x  CH2O  =  C6Hi2O6)  in  obtaining  the  same  sugar  as  that  made  from 
the  glycerose  prepared  from  glycerol.1 

This  complete  synthesis  is  particularly  interesting  to  us,  because  some  time 


1  Ber.  23,  2114  (1890);  Die  Chemie  der  Kohlehydrate  und  ihre  Bedeutung  fur  die 
Physiologic,  Berlin,  1894;  Synthesen  in  der  Purin-imd  Zuckergruppe,  Braunschweig, 
1903. 


CARBOHYDRATES.  15 

before  this  Adolf  v.  Baeyer  *  had  explained  in  exactly  the  same  way  the 
formation  of  carbohydrates  in  plants.  According  to  this  conception,  which 
up  to  the  present  time  has  not  been  proved  absolutely,  the  leaves  contain- 
ing chlorophyll  reduce  the  carbon  dioxide  of  the  air  to  formaldehyde,  and 
the  latter  is  transformed  into  sugar  by  condensation.  The  formation  of 
sugars  containing  a  different  number  of  carbon  atoms  can  be  similarly 
explained  with  the  help  of  the  same  hypothesis.  It  is,  indeed,  perfectly 
possible  that  the  building  up  of  the  higher  sugars  by  nature  takes  place 
through  the  same  intermediate  stages  as  have  been  observed  in  the  arti- 
ficial synthesis. 

Now,  an  accurate  examination  showed  that  the  sugar  obtained  from 
glycerose,  or  from  formaldehyde,  containing  six  atoms  of  carbon  was  not 
identical  in  all  its  properties  with  grape-sugar.  It  was,  therefore,  given 
a  special  name,  acrose.  Biot 2  made  the  important  discovery  that  cane- 
sugar  rotates  the  plane  of  polarized  light.  This  property,  which  other 
sugars  found  in  nature  likewise  show,  was  quickly  utilized  technically 
for  the  quantitative  determination  of  cane-sugar  in  cane-juice,  etc.3  It 
proved  to  be  also  of  considerable  aid  in  distinguishing  the  different 
kinds  of  sugar  from  one  another.  Now  acrose  does  not  have  this  property : 
it  does  not  rotate  the  plane  of  polarized  light.  The  reason  for  this  is  that 
acrose  is  composed  of  components  each  having  the  opposite  effect  upon 
polarized  light,  and  as  a  matter  of  fact  it  is  possible  to  decompose  acrose 
into  these  unlike  individuals.  According  to  the  conditions  of  the  experi- 
ment, it  may  be  changed  into  fruit-sugar  or  mannose  or  grape-sugar. 
Herewith  the  final  step  in  the  artificial  synthesis  of  sugars  such  as  occur 
in  nature  was  accomplished. 

The  optical  activity  of  almost  all  natural  products  —  a  property  which  for 
a  long  time  served  to  distinguish  natural  products  sharply  from  artificial 
ones,  and  gave  support  to  the  theory  that  a  special  force  peculiar  to  a  living 
organism  was  necessary  for  the  production  of  such  compounds,  until  at  last 
here  also  successful  synthetical  chemistry  made  a  breach  in  the  wall  which 
had  been  considered  as  impregnable — was  first  explained  by  the  well-known 
fruitful  hypothesis  of  Le  Bel  and  van  't  Hoff 4  (1874).  These  two  scien- 
tists independently  traced  the  asymmetry  of  the  molecule,  which  Pasteur  5 


1  Ber.  3,  63  (1870). 

2  Compt.  rend.  10,  264;  16,  619  (1843). 


3  Clerget:  Compt.  rend.  16,  1000  (1843);  22,  1138  (1846);  23,  256  (1846);  26,  240 
(1848). 

4  Cf.  van't  Hoff:  Die  Lagerung  der  Atome  im  Raume.    Dix  anne*e  dans  Thistoire 
d'une  throne.     La  chimie  dans  1'espace  (1875).     K.  Auwers:  Die  Entwicklung  der 
Stereochemie  (1890). 

5  Lecons  de  chimie  professes  en  1860.  Paris,  1861.    See  also  H.  Landolt:  Das  optische 
Drehungsvermogen    organischer   Substanzen    und   dessen    praktische    Anwendungen, 
Braunschweig,  1898.     A.  Werner:  Lehrbuch  der  Stereochemie,  Jena,  1904. 


16  LECTURE  II. 

had  ingeniously  brought  forward  in  order  to  explain  the  optical  difference 
between  dextro-tartaric  and  laevo-tartaric,  acids,  to  the  individual  carbon 
atom.  This  atom  is  in  combination  with  four  different  masses.  Every 
asymmetric  carbon  atom  in  a  compound  causes  the  possibility  of  two 
optical  isomers,  one  rotating  the  plane  of  polarized  light  to  the  right,  and 
the  other  to  the  left.  We  can  illustrate  this  best,  according  to  van 't  Hoff, 
by  imagining  the  valences  or  affinities  of  the  carbon  atom  extending  to- 
wards the  apexes  of  a  tetrahedron  in  the  center  of  which  the  carbon  atom 
itself  is  placed. 


Fig.  1. 

(Ri,  R2,  RS,  R4,  are  the  four  different  masses  with  which  the  carbon 
atom  is  combined.) 

The  above  drawing  represents  this  kind  of  isomerism.  The  two  forms 
are  in  the  same  relation  to  one  another  as  an  object  and  its  reflected 
image,  or  as  a  right  and  left  glove;  i.e.,  they  cannot  be  superposed  one  upon 
the  other,  so  that  the  corresponding  parts  will  all  coincide.  There  are, 
then,  three  possible  modifications  in  the  case  of  every  carbon  compound 
containing  an  asymmetric  carbon  atom,  namely,  two  optically  active  forms, 
and  one  which  is  inactive,  being  composed  of  an  equal  number  of  molecules 
of  each  of  the  other  two  forms.  In  the  last  case  the  two  asymmetric 
carbons,  although  both  active,  have  an  equal  and  exactly  opposite  effect 
upon  polarized  light,  so  that  they  neutralize  one  another. 

If  these  assumptions  are  correct,  then  if  there  are  two  or  more  asymmet- 
ric carbon  atoms  in  the  molecule,  the  number  of  possible  optical  isomers 
must  increase  regularly  and  amounts  to  2n  where  n  is  the  number  of  asym- 
metric carbon  atoms.  This  theory  has  been  confirmed  empirically 
to  a  most  remarkable  degree,  and,  indeed,  in  no  part  of  chemistry  has 
the  work  of  Le  Bel  and  van 't  Hoff  been  so  strongly  supported  as  in  the 
development  of  carbohydrate  chemistry  according  to  this  point  of  view 
by  Emil  Fischer. 

In  advance,  it  may  be  mentioned,  for  example,  that  there  are  several 
different  sugars  having  the  empirical  formula  CeH^Oe.  Of  these  we  need 
mention  only  d-glucose,  mannose,  and  galactose.  Now  all  of  these  sugars 
contain,  as  shown  by  the  following  general  structural  formula,  no  less  than 
four  asymmetric  carbon  atoms: 


CARBOHYDRATES. 

COH 
*CH.OH 
*CH.OH 
*CH.OH 
*CH.OH 

CHo.OH 


17 


According  to  the  rule  given  above,  24  =  16  different  compounds  should 
exist  having  such  a  structure.  There  is  really  no  doubt  concerning  this, 
for  already  no  less  than  twelve  isomers  representing  six  optical  pairs  have 
been  isolated.  For  each  one  of  these  the  geometric  constitution  is  ex- 
plained by  the  theory,  and  the  configuration  of  each  single  molecule 
represented  by  a  definite  structural  formula.  The  following  is  a  summary 
of  the  configuration  formulae  given  by  Fischer  to  the  hexoses,1  in  which 
the  asymmetric  carbon  atoms  are  marked  with  an  asterisk. 


COH 

H—  *OH 

1 

COH 

HO—  *H 

1 

COH 

HO—  *—  H 

i 

COH 

H—  *—  OH 

1 

H—  *—  OH 

1 

HO—  *—  H 

i 

H—  *—  OH 

i 

HO—  *—  H 

I 

HO—  *—  H 

1 

H—  *—  OH 

i 

HO—  *—  H 

i 

H—  *—  OH 

1 

HO—  *—  H 

CH2.OH 

/-Mannose 

H—  *—  OH 

CH2OH 
d-Mannose 

HO—  *—  H 

CH2OH 

Z-Glucose 

H—  *—  OH 

CH2OH 
d-Glucose 

COH 
HO—  *—  H 
H—  *OH 

HO—  *—  H 

1 

COH 
H—  *—  OH 
HO*—  H 

H—  *OH 

I 

COH 
H—  *—  OH 
H—  *—  OH 

HO—  *—  H 

I 

COH 
HO—  *—  H 
HO—  *—  H 

H—  *—  OH 

I 

H—  *—  OH 

CH2OH 
Z-Idose 

HO—  *—  H 

CH2OH 

c?-Idose 

H—  *—  OH 

CH2OH 

Z-Gulose 

HO—  *—  H 

CH2OH 

c?-Gulose 

The  configuration  formulae  for  sugars  with  less  carbon  have  also  been  worked  out. 


18 

LECTURE 

II. 

COH 

1 

COH 

1 

COH 

i 

COH 

HO—  *—  H 
H—  *—  OH 

H—  *—  OH 

1 

H—  *—  OH 
HO—  *—  H 

HO—  *—  H 

1 

H—  *—  OH 
H—  *—  OH 

H—  *—  OH 

i 

_       H 
HO—  *—  H 

HO—  *—  H 

1 

HO—  *—  H 

CH2OH 

Z-Galactose 

H—  *—  OH 

CH2OH 
d-Galactose 

HO—  *—  H 

CH2OH 
Z-Talose 

H—  *—  OH 

CH2OH 
d-Talose 

COH 

1 

COH 

1 

COH 

COH 

i 

HO—  *—  H 

1 

H—  *—  OH 

1 

H—  *—  OH 

i 

HO—  *—  H 

i 

HO—  *—  H 
HO—  *—  H 
HO—  *— 
CH2OH 

H—  *—  OH 
H—  *—  OH 
H—  *—  OH 
CH2OH 

HO—  *—  H 
HO—  *—  H 
HO—  *—  H 
CH2OH 

H—  *—  OH 
H—  *—  OH 
H—  *—  OH 
CH2OH 

Not  yet  prepared. 

The  detailed  discussion  here  of  these  purely  chemical  problems  is  com- 
pletely justified  on  account  of  the  great  significance  which  these  investiga- 
tions have  for  biology,  and  as  a  matter  of  fact  it  will  not  be  possible  to 
understand  clearly  the  metabolism  of  carbohydrates  without  having  a 
thorough  knowledge  of  such  structure  questions  as  we  have  briefly  touched 
upon.1 

The  ways  and  means  by  which  sugars  rich  in  carbon  are  prepared  syn- 
thetically from  those  with  fewer  carbon  atoms  are  not  without  interest 
for  biology.  All  the  compounds  represented  on  the  preceding  page  con- 
tain an  aldehyde  group,  and  aldehydes  are  capable  of  combining  with 
hydrocyanic  (prussic)  acid.  By  saponifying  the  cyanhydrins  and  sub- 
sequent reduction,  a  new  sugar  is  obtained,  as  E.  Fisher  and  later  Kiliani 2 
showed,  which  contains  more  carbon  than  the  original  sugar.  In  this  way, 
it  is  possible  to  prepare  not  only  hexoses  from  the  simplest  members  of 
the  carbohydrate  group,  but  sugars  with  seven,  eight,  and  nine  atoms  of 

1  Since  we  shall  meet  with  the  same  point  of  view  in  the  case  of  other  classes  of 
substances,  especially  the  proteins,  the  student  is  advised  to  refer  to  some  of  the  books 
on  the  subject. 

a  Ber.  18,  3066  (1885);  19,  221,  767,  and  1128  (1886). 


CARBOHYDRATES.  19 

carbon  as  well.1    There  appears  really  to  be  no  limit  to  the  applicability  of 
the  synthesis. 

Perhaps  this  synthesis  throws  some  light  upon  the  formation  of  the 
different  sugars  in  plant  organisms,  for  it  must  be  often  necessary  for 
them  to  build  up  from  sugars  containing  a  small  number  of  carbon  atoms 
those  with  more  carbon.  The  possibility  of  such  transformations  shows 
that  there  is  no  sharp  distinction  between  the  separate  sugar  groups  contain- 
ing different  numbers  of  carbon  atoms,  and  unites,  both  chemically  as  well  as 
biologically,  the  different  classes  to  a  large  unit  which  becomes  even  more 
closely  related  by  reason  of  the  fact  that  the  artificial  representatives  of 
the  same  group  such  as  grape-sugar,  mannose,  and  fruit-sugar,  can  be 
changed  into  one  another  by  successive  oxidation  and  reduction. 

The  large  number  of  sugars  prepared  synthetically,  some  of  which  have 
not  yet  been  found  in  nature,  together  with  the  natural  sugars  are  sub- 
divided into  groups.  We  distinguish,  in  the  first  place,  between  the  more 
simple  sugars  called  monosaccharides  and  compound  sugars  called  poly- 
saccharides.  The  latter  may  be  regarded  as  formed  from  two  or  more 
molecules  of  the  former  with  elimination  of  water,  and,  as  a  matter  of 
fact,  the  simpler  sugars  may  be  formed  from  them  by  hydrolysis. 

The  monosaccharides  again  are  divided  into  subclasses  governed  by  the 
number  of  carbon  atoms  in  the  molecule.  Thus  we  have  a  diose  (glycol 

HCO 
aldehyde,  or  glycolose,     |  )     which  is  the  simplest  possible  sugar, 

CH2OH 

and  trioses,  tetroses,  pentoses,  hexoses,  heptoses,  etc.  We  have  seen,  further- 
more, that,  in  general,  a  sugar  is  a  polyatomic  alcohol  containing  either  a 
ketone  or  aldehyde  group.  Corresponding  to  this,  from  the  trioses  on,  we  dis- 
tinguish between  al doses  (aldehyde  alcohols)  and  ketoses  (ketone  alcohols). 
Again,  an  important  type  which  we  frequently  meet  with  in  nature  is  that  of 
the  methyl  derivatives  of  these  sugars;  thus  we  have  fucose  (from  rockweed, 
known  botanically  as  fucus),  rhodeose  (from  jalap)  and  rhamnose  (pre- 
pared from  numerous  plants),  which  are  all  designated  as  methyl  pentoses. 

Of  all  the  numerous  sugars,  but  few  are  found  in  the  animal  organism, 
and  only  a  few  play  any  considerable  part  as  forms  of  nourishment,  al- 
though we  must  admit  that  our  present  knowledge  concerning  the  phys- 
iological significance  of  numerous  sugars  found  distributed  throughout 
the  vegetable  kingdom,  partly  free  and  partly  combined  with  other 
substances,  is  still  far  from  being  complete.  Members  of  the  last-men- 
tioned class  of  substances,  the  number  of  which  is  extremely  large  are 
known  as  glucosides,  and  as  such  we  designate  all  substances  which  are 
more  or  less  readily  decomposed  into  a  sugar  on  the  one  hand  and  a  com- 
pound either  aromatic  or  aliphatic  in  nature  on  the  other.  Such  decom- 

1  Emil  Fischer:  Ann.  270,  64  (1892). 


20  LECTURE  II. 

positions  may  be  effected  by  ferments  (emulsin,  myrosin,  betulase,  etc.) 
as  well  as  by  chemical  reagents.  Thus,  for  example,  amygdalin  breaks 
down  by  the  action  of  emulsin  into  two  molecules  of  grape-sugar,  one 
molecule  of  benzaldehyde,  and  one  of  hydrocyanic  acid: 

C2oH27NOii  +  2  H2O  =  2  C6H12O6  +  C6H5CHO  +  HCN. 

The  structure  of  these  compounds  has  been  cleared  up  perfectly  by  Emil 
Fischer,1  who  succeeded  in  making  sugar  combine  with  alcohol  and  similar 
substances  by  the  mere  action  of  dilute  hydrochloric  acid.2  The  glucosides 
are  in  fact  compounds  perfectly  analogous  to  the  polysaccharides,  both 
being  formed  by  the  combination  of  two  molecules  of  simpler  compounds 
with  loss  of  water,  although  in  the  former  case  the  molecules  reacting  are 
unlike,  whereas  in  the  case  of  polysaccharides  only  sugar  molecules  are 
concerned.  Not  only  monosaccharides,  but  polysaccharides  take  part 
in  the  formation  of  true  glucosides,  as  Emil  Fischer  showed  in  the  case 
of  amygdalin.3  Such  observations  are  of  great  value  for  biology,  as  they 
permit  us  to  consider  the  formation  of  such  large  classes  of  substances 
from  a  single  point  of  view. 

The  significance  of  the  glucosides  in  the  narrower  sense  of  the  economy 
of  the  animal  organism  has  up  to  the  present  time  been  but  slightly  inves- 
tigated. Without  doubt  a  part  of  the  sugar  contained  in  the  organism  is 
in  such  a  form,  and  perhaps  this  enables  such  sugar  to  escape  combustion. 
It  is  only  recently  that  such  substances  have  been  carefully  studied.  The 
investigations  of  Thierfelder 4  upon  cerebron,  a  substance  isolated  by 
means  of  indifferent  solvents  from  the  human  brain,  may  be  mentioned  in 
this  connection.  On  being  subjected  to  hydrolysis  this  substance  took  up 
two  molecules  of  water  and  formed  one  molecule  of  cerebronic  acid,  one  of 
sphingosine  and  one  of  galactose: 

C48H93N09  +  2  H2O  =  C25H5oO3  +  Ci7H35NO2  +  C6H1206. 

A  similar  glucoside  is  the  glycoproteid  prepared  by  Schulz  and  Ditthorn  5 
from  the  albuminous  glands  of  the  frog,  which  on  being  subjected  to 
hydrolysis  yields  among  other  products  an  amido-sugar,  galactosamine,  a 
result  which  is  closely  analogous  to  the  finding  of  glucosamine  by  Fried- 
rich  Miiller  6  in  the  mucin  substances  of  the  human  respiratory  organs. 


1  Ber.  26,  2400  (1893). 

2  For  example:  C6H12O6  +  CH3OH  =  C6HnO6  .  CH3  +  H2O. 

3  Emil  Fischer:  Ber.  28,  1508  (1895).    From  amygdalin  the  yeast-enzyme  splits  off 
one   molecule  of   sugar,  and   forms  a  new  glucoside  called  mandelonitrile-glucoside, 
which  emulsin  decomposes  completely  into  sugar,  benzaldehyde,  and  hydrocyanic  acid. 

4  Z.  physiol.  Ch.  43,  21  (1904)  and  44,  366  (1905). 

5  Ibid.,  29,  373  (1900);  32,  428  (1901). 

6  Sitzungsber.    Gesellsch.    Forderung  gesamt.   Naturwissensch.    zu  Marburg.  1896, 
6;  1898,  6. 


CARBOHYDRATES.  21 

Later  on,  when  we  come  to  consider  the  proteins,  we  shall  have  to  take  up 
these  substances  in  detail. 

From  the  group  of  glucosides,  furthermore,  there  are  derived  a  great 
many  compounds,  some  of  which  have  strong  toxic  properties  and  are  very 
important  drugs,  their  pharmaceutical  value  having  been  discovered  purely 
empirically.1  Of  this  large  group  of  such  compounds  we  shall  mention 
only  the  saponin  substances,  phloridzin,  salicin,  helleborin,  and  the  digitalis 
glucosides  (digitalin,  digitonin,  digitoxin)2.  Finally,  it  may  be  stated 
that  alizarin,  the  well-known  red  dye,  likewise  occurs  in  nature  as  a  gluco- 
side  (ruberythric  acid)  in  madder  root  (Rubia  tinctoruiri).  This  gluco- 
side  has  lost  most  of  its  practical  importance  on  account  of  the  famous 
synthesis  of  alizarin  by  Graebe  and  Liebermann  (1868).  This  synthesis 
was  considered  a  great  triumph  of  chemical  investigation,  and  awakened 
many  bright  dreams  for  the  future.  Even  then  it  was  suggested  that  the 
time  was  near  at  hand  when  foods  could  be  produced  practically  by 
synthetic  methods.  Although  this  hope  has  not  yet  been  fully 
realized,  nevertheless,  such  syntheses  as  that  of  alizarin  have  an  indirect 
effect  upon  the  production  of  foods  because  whenever  a  natural  substance 
is  replaced  by  an  artificial  one  a  considerable  amount  of  acreage  is 
released. 

As  far  as  the  animal  organism  is  concerned,  the  hexoses  are  the  most 
important  representatives  of  the  monosaccharides,  and  for  a  long  time  they, 
and  the  corresponding  polysaccharides,  were  the  only  carbohydrates  to  be 
considered  at  all.  It  was  not  until  1892  that  a  sugar  with  five  molecules  of 
carbon  corresponding  to  the  formula  CsHioOs  was  discovered.  In  that 
year  Jastrowitz 3  found  a  specimen  of  human  urine  showing  strong  reducing 
properties  but  which  fermented  little  if  any,  and  was  moreover  optically 
inactive.  Salkowski3  then  showed  that  a  pentose  was  present.  In  the 
same  year  Kossel,4  by  the  hydrolysis  of  yeast-nucleic-acid  with  hydrochloric 
acid,  obtained  furfurol,  and  soon  afterwards  Hammarsten  5  made  similar 
observations  in  studying  the  nucleoproteid  obtained  from  the  pancreas; 
later  on  Salkowski 6  followed  the  matter  still  further,  and  proved  finally 
that  pentoses  are  present  in  the  above-mentioned  products.  Sugars, 
then,  of  the  five  carbon  series,  have  been  detected  one  after  another  in 
various  products  found  in  the  body,7  especially  in  the  nucleoproteids.  The 

1  See  text-books  on  pharmacology  for  the  physiological  and  pharmacological  action 
of  these  substances. 

2  For  other  special  cases,  see  van  Rijn:  Die  Glykoside,  Berlin,  1900. 

3  Zent.    med.  Wissensch.  19  and  35,  pp.  337  and  593  (1892). 

4  "Ueber   die  Nucleinsaure, "  Verhandl.  physiol.  Gesellsch,  Berlin,  and    in    Arch. 
Physiol.  Anat.  1893,  157. 

5  Z.  physiol.  Chem.  19,  19  (1894). 

6  Ibid.  27,  507  (1899). 

7  Z.  klin.  Med.  34,  160  (1898). 


22  LECTURE  II. 

pentoses  accordingly  take  part  in  the  construction  of  animal  tissue.  The 
only  pentose  which  has  been  isolated  from  the  organs  and  closely  studied 
is  that  from  the  pancreas-proteids,  which  C.  Neuberg x  has  identified 
as  /-xylose  with  the  following  configuration: 

0  OH  H  OH 
HC— C— C— C— CH2OH 
H  OHH 

It  belongs,  therefore,  to  the  aldoses. 

Recently  Wohlgemuth  2  has  isolated  the  same  pentose  from  liver-pro- 
teid.3  According  to  other  investigations,  it  appears  that  the  pentoses  in  the 
animal  organism  are  limited  to  the  class  of  nucleoproteids,  and  in  fact 
that  the  carrier  of  the  pentoses  is  not  the  albumin,  but  rather  the  other 
component  of  the  compound  protein.  This  was  shown,  namely,  by  the 
experiments  of  Ivar  Bang,4  who  succeeded  by  warming  pancreas-nucleo- 
proteid  with  dilute  caustic  potash  in  decomposing  it  into  albumin  and  into 
a  product  free  from  albumin,  the  so-called  guanylic  acid.  This  latter  con- 
tains the  Z-xylose.  Guanylic  acid  is  decomposed  by  boiling  with  mineral 
acids  into  guanine,  glycerol,  and  pentose;  it  may  therefore  be  considered 
as  glycerophosphoric  acid  in  which  the  hydroxyl  groups  are  partly  re- 
placed by  guanine  and  partly  by  pentose.  As  to  whether  the  pentose  is 
similarly  combined  in  the  other  nucleoproteids  has  not  yet  been  established. 

The  quantity  of  pentoses  contained  in  the  separate  organs  varies  greatly 
and  depends  directly  upon  the  amount  of  nucleic  substances  present. 
Grund  5  estimates  the  percentage  of  pentoses  (calculated  as  xylose)  present 
in  certain  organs  as  follows: 


Pancreas      2 .48 

Liver 0 .56 

Thymus 0.56 

Submaxillary  Gland 0.53 

Thyroid  Gland 0.50 

Kidneys 0.49 

Spleen 0.46 

Brain .  0.22 

Muscle  .  0.11 


The  values  represent  the 
percentage  of  pentose  (cal- 
culated as  xylose)  in  the 
dry  substance. 


As  has  already  been  mentioned,  the  first  pentose  was  discovered  in 
urine  and  formed  by  metabolism  in  the  human  organism.     The  disease 


Ber.  35,  1467  (1902). 

Z.  physiol.  Chem.  37,  475  (1903). 

For  further  particulars  and  other  literature,  see  Neuberg  in  Ergeb.  Physiol. 
(Asher  and  Spiro),  3,  Abt.  I,  p.  373. 

Z.  physiol.  Chem.  31,  411   (1900-1901). 

Ibid.  35,  111  (1902).  See  also  Bendix  and  Ebstein:  Z.  allg.  Physiol.  2,  Heft 
1  (1902). 


CARBOHYDRATES.  23 

causing  the  elimination  of  this  substance  is  called,  if  we  adopt  the  suggestion 
of  Salkowski,  pentosuria.  Up  to  the  present  time  about  a  dozen  cases 
are  known.  Pentosuria  is  distinctly  different  from  true  diabetes.  It 
exists  for  years  without  showing  the  clinical  indications  of  the  latter 
metabolic  disturbance.  In  rare  cases  the  elimination  of  pentose  has  been 
detected  in  diabetes  also,1  but  it  is  not  known  that  there  is  any  connection 
between  the  two  diseases.  The  amount  of  pentose  eliminated  varies  in 
individual  cases  between  0.2  and  1  per  cent. 

It  is  a  striking  fact  that  the  pentoses  eliminated  in  urine  are,  as  a  rule, 
optically  inactive.  Luzzato,2  alone,  has  described  an  optically  active 
pentose.  The  question  next  arises  as  to  the  source  of  pentose  in  urine. 
First  of  all,  Bial  and  Blumenthal 3  have  proved  that  pentosuria  is  inde- 
pendent of  the  composition  of  the  diet  and  especially  as  regards  the  amount 
of  pentoses  in  it.  They  have  also  shown  that  with  persons  afflicted  with 
the  disease  the  combustion  of  carbohydrates,  and  thus  also  of  Z-arabinose, 
is  perfect.  Pentoses  in  urine,  therefore,  do  not  find  their  source  in  the 
food.  The  next  possibility  which  would  suggest  itself  is  that  perhaps 
they  arise  from  the  breaking  down  of  tissue  and  especially  of  the 
nuclei.  If  this  supposition  were  correct,  we  should  expect  that  the  pentose 
found  in  urine  would  be  the  same  as  that  found  in  the  organs,  namely, 
inactive  xylose.  This  now  is  not  the  case,  as  Neuberg  4  has  shown,  for 
the  pentose  in  urine  is  arabinose,  and  curiously  enough  almost  always  the 
inactive,  racemic  form.  Furthermore,  this  pentose  for  the  most  part  does 
not  exist  free  in  the  urine,  but  is  combined  with  urea.  For  the  present,  we 
can  only  formulate  hypotheses  concerning  its  formation.  Above  all,  we 
are  ignorant  as  to  why  the  pentose  should  nearly  always  be  eliminated  in 
an  inactive  form. 

The  five-carbon  sugars  are  much  more  widely  distributed  in  the  vege- 
table kingdom  than  in  the  animal.  Up  to  the  present  time  they  have 
not  been  identified  with  certainty  in  a  free  state,  but  on  the  other  hand 
they  appear  to  be  deposited  in  the  nucleoproteids  of  certain  plants  in  the 
same  manner  as  in  animals,  for  Osborne  and  Harris  5  have  isolated  tritico- 
nucleic  acid  from  wheat  flour.  This  manner  of  occurrence  is  inappreciable 
as  compared  with  that  of  high  molecular  pentosans,  i.e.,  polysaccharides 
of  the  pentoses.  These  substances  are  extremely  widely  distributed,  and 
take  part  in  various  ways  in  the  building  up  of  plants.  By  their  hydrolytic 
cleavage  the  simpler  members  of  this  series  are  obtained.  Not  only  the 
pentoses  are  found  as  pentosans,  but  we  have  methyl-pentosans  as  well 


Kiilz  and  Vogel:  Z.  Biol.  1895,  185. 
Hofmeister's  Beitrage,  6,  87  (1904). 
Deut.  med.  Wochenschr.  22  (1901). 
Ber.  33,  2243  (1900). 
Z.  physiol.  Chem.  36,  85  (1902). 


24 


LECTURE  II. 


(especially  the  polysaccharides  of  fucose),  which  are  found  everywhere  in 
sea-moss.  The  fucose  pentosans  are  furthermore  found  in  gum-arabic, 
cerasin,  and  gum-tragacanth,  in  the  leaves  of  plane  and  linden  trees,  in  pine 
and  beechwood,  etc.  The  rhamnoses,  first  found  in  quercitrin,  the  coloring 
principle  contained  in  the  bark  of  dyer's  oak  (Quercus  tintoria),  are  also 
widely  distributed.  Most  pentosans,  however,  are  derived  from  the 
simple  pentoses.  The  most  important  of  these  are  Z-arabinose,  which  is 
obtained  from  different  gums;  and /-xylose,  also  called  wood  sugar  because 
it  is  the  most  important  mother  substance  of  lignin  (xylogen) .  Xylogen 
is  also  found  in  oat-,  rye-  and  wheat-straw,  etc.  The  pentosans  in 
general  are  by  no  means  simple  compounds,  and  yield  on  being  sub- 
jected to  hydrolysis  all  sorts  of  different  sugars  of  the  five  and  six  carbon 
series.  Doubtless  there  are  a  great  many  intermediary  products  lying 
between  the  simpler  and  more  involved  complexes.  As  regards  their 
physiological  function  in  the  plant  organism,  our  knowledge  is  still  very 
limited.  We  shall  see  later  on  that  they  are  of  importance  for  the 
nourishment  of  animal  organisms,  particularly  the  herbivora.  The  fol- 
lowing table  will  give  some  idea  concerning  the  occurrence  of  pentosans, 
the  values  being  given  in  terms  of  pentose: 


Per  cent. 

Per  cent. 

Meadow  hay 

21   64 

Bruised  barley                .    .    . 

7  96 

Molasses  fodder 

15  98 

Sesame  cake     

3  87 

Rape  cake 

11  50 

Table  turnip     

1  .13 

Turnip 

2  26 

Spinach      

1  .02 

Oil-seed  cake 

9  07 

Sauerkraut   

0.96 

Acrospires 

14  12 

Coffee  beans      

6.5 

Rice  flour                     .       ... 

5.73 

As  regards  the  formation  of  pentoses  in  plant  organisms,  we  have  no 
experimental  data.  Chemically,  we  can,  as  has  already  been  mentioned, 
easily  account  for  it  in  three  ways.  The  simplest  explanation  is  that  of 
the  formation  from  formaldehyde,  which  is  hypothetically  the  first  assim- 
ilation product  of  the  carbonic  acid  in  the  air  by  the  green  leaves.  Five 
molecules  of  the  aldehyde  will  condense  to  form  one  molecule  of  pentose 
(5  X  CH2O  =  C5HioO5).  It  is  also  conceivable,  that  glycerose  obtained 
by  the  oxidation  of  glycerol  is  the  starting-point,  and  from  thence  by  the 
third  method  of  building  up  a  sugar,  namely,  the  addition  of  carbon 
atoms,  the  pentoses  may  be  formed.  Finally  it  is  possible  that  the 
pentoses  are  formed  by  the  breaking  down  of  higher  sugars.  At  all  events 
this  relatively  simple  class  of  chemical  compounds  shows  to  what  ex- 
tremely diverse  purposes  the  vegetable  organism  is  capable  of  building 
itself  up. 


CARBOHYDRATES.  25 

We  know  absolutely  nothing  with  regard  to  the  formation  of  sugars  of 
the  five  carbon  series  in  the  animal  organism  and  concerning  their  signifi- 
cance in  the  organism.  It  would  seem  most  likely  that  the  source  of  their 
presence  is  to  be  sought  in  the  diet,  although  such  a  relationship  has  not 
yet  been  definitely  traced. 

We  now  come  to  that  group  of  monosaccharides  which  is  most  important 
for  the  animal  organism,  namely,  the  hexoses  of  the  general  formula 
C^H1206-  We  have  already  seen  that,  according  to  the  rule  of  Le  Bel  and 
van  't  Hoff,  there  are  sixteen  possible  isomeric  aldehydes  having  this  gen- 
eral formula.  We  need  consider  here  only  the  mannoses,  the  glucoses,  the 
galactoses,  and  the  fructoses.  Before  taking  up  these  sugars  in  detail  we 
will  mention  some  of  the  more  important  general  reactions  of  sugars  to 
the  extent  necessary  for  us  to  understand  the  physiological  behavior  of 
different  kinds  of  sugars. 

The  simple  sugars,  in  accordance  with  their  aldehyde  or  ketone  nature, 
are  very  readily  oxidized.  They  reduce,  therefore,  metallic  oxides  on 
warming  their  alkaline  solutions.  Some  of  the  qualitative  and  quanti- 
tative methods  of  analysis,  such  as  those  of  Fehling,  Trommer,  and 
Bottcher,  are  based  upon  this  property. 

On  heating  a  solution  of  sugar  in  caustic  soda,  or  potash,  a  decomposition 
takes  place  (Moore's  test).  The  liquid  turns  brown,  and  among  other 
substances,  lactic  acid,  catechol,  and  formic  acid  are  formed. 

If  half  a  cubic  centimeter  of  a  dilute,  aqueous  solution  of  d-glucose  is 
treated  with  a  few  drops  of  a  ten  per  cent  solution  of  a-naphthol  in  alco- 
hol and  then  one  cubic  centimeter  of  concentrated  sulphuric  acid  cau- 
tiously added,  the  zone  of  contact  becomes  reddish  violet  in  color.  On 
shaking,  the  mixture  assumes  this  color  (Molisch).  This  test  is  often 
used  for  detecting  the  presence  of  sugar  in  proteins,  etc.,  and  depends  upon 
the  formation  of  furfurol  by  the  action  of  the  concentrated  sulphuric  acid 
upon  the  sugar. 

If  a  sugar  solution  is  evaporated  to  dryness  and  the  residue  heated 
somewhat,  or  if  the  sugar  itself  is  at  once  exposed  to  direct  heat,  carboni- 
zation takes  place  with  a  characteristic  odor.  The  mass  is  called  caramel. 

An  important  reaction,  and  one  which  has  become  of  great  consequence 
in  the  investigation  of  the  different  kinds  of  sugars,  is  the  combining  of 
many  sugars  with  hydrazines  in  acetic  acid  solution,  water  being  eliminated 
and  hydrazones  formed.  The  most  important  of  these  compounds  are 
those  with  phenyl-hydrazine.1  If  an  approximately  ten  per  cent  aqueous 
solution  of  glucose,  for  example,  is  treated  with  a  solution  of  phenyl- 
hydrazine  in  acetic  acid  and  then  heated  on  the  water-bath  for  ten  or 
fifteen  minutes,  fine  yellow  needles  are  deposited  whose  composition 

1  Emil  Fischer:  "  Verbindungen  des  Phenylhydrazins  mit  den  Zuckerarten,"  Ber. 
17,  579  (1884),  and  20,  821  (1887). 


26  LECTURE  II. 

corresponds  to  the  formula  Ci8H22N4O4.  This  compound  is  known  as 
glucosazone.1  It  is  formed  by  the  action  of  two  molecules  of  phenyl- 
hydrazine  upon  one  molecule  of  sugar,  and  in  fact  the  reaction  takes  place 
in  two  stages.  First  the  sugar  combines  with  one  molecule  of  the  base, 
forming  a  hydrozone  as  follows: 

CH2(OH)  [CH(OH)]3CHOH  .  CHO  +  C6H5NH  .  NH2  = 
CH2(OH)  [CH(OH)]3  .CHOH  :  N  .  NH  .  C6H5  +  H2O. 

* 

As  this  compound  is  very  readily  soluble  in  water,  this  phase  of  the 
reaction  is  not  noticeable  in  the  reaction  with  glucose.2  Then  on  warm- 
ing with  an  excess  of  phenyl-hydrazine,  the  alcoholic  group  marked  with 
an  *  undergoes  a  peculiar  oxidation.  The  group  is  changed  into  carbonyl, 
CO,  and  is  thus  capable  of  combining  with  a  second  molecule  of  phenyl- 
hydrazine,  to  form  an  ozazone  of  the  formula: 

CH2OH[CH(OH)]3  .  C  -  CH 

II        II 
C6H5  .  HN  .  N      N  .  NH  .  C6H5 

As  we  shall  soon  see,  fruit-sugar  (fructose)  instead  of  being  an  aldehyde, 
is  a  ketone  with  the  following  structure: 

CH2OH 

1° 

HO— C— H 
H— C— OH 

H— C— OH 

I 

CH2OH 

Now  it  is  possible  to  obtain  exactly  the  same  glucosazone  from 
fructose  as  from  d-glucose,  but  in  this  case  the  two  stages  of  the  reaction 
take  place  in  the  reverse  order;  the  ketone  being  first  acted  upon  then  by 
oxidation  an  aldehyde  is  formed,  which  reacts  with  a  second  molecule  of 
phenyl-hydrazine,  as  shown  by  the  following  scheme: 

CH2(OH)  [CH(OH)]3  .C      CH2(OH) 

II  * 

C6H5  .  HN  .  N 

CH2OH  .  [CH(OH)]3  .  C  -  CH 

II        II 
C6H5  .  HN  -  N      N  .  NH  .  C6H5 


1  Similarly  we  speak  of  galactosazone,  arabinosazone,  xylosazone,  maltosazone,  etc. 

2  With  mannose  °  difficultly  soluble  phenylhydrazone  is  formed  and  can  be  isolated. 


CARBOHYDRATES.  27 

Natural  and  artificial  sugars  which  reduce  Fehling's  solution  (includ- 
ing milk  sugar  and  maltose)  give  the  above  reaction.  The  products 
obtained  are  very  characteristic,  and  are  the  most  valuable  means  that 
we  possess  for  recognizing  and  separating  the  sugars. 

An  important  property  of  the  natural  sugars  which  has  been  mentioned 
already  is  their  optical  activity.  Quantitative  methods  for  the  analysis 
of  sugars  are  based  upon  this  property,  and  it  serves  for  classifying  the 
sugars  as  well.  Thus  the  dextro-rotary  dextrose  was  first  designated  as 
d-glucose,  and  laevo-rotary  laevulose  as  Mructose.  Emil  Fischer  then 
proposed  a  different  method  of  nomenclature  which  shows  the  relation  of 
the  compounds  to  one  another.  The  monoses  derived  from  a  d-,  /-,  or 
i-monose  are  also  designated  by  the  letters  d-,  1-,  and  i-,  even  when  they 
possass  a  rotary  power  opposite  in  sign  to  that  indicated  by  these  letters. 
In  this  way  laevulose  is  now  designated  as  d-fructose,  because  of  its  close 
relation  to  d-glucose,  or  dextrose. 

The  most  interesting  reaction  of  sugar  from  a  biological  standpoint  is 
its  ability  to  undergo  fermentation.  Thus  different  yeasts  cause  dextrose' 
to  break  down  into  alcohol  and  carbon  dioxide  (alcoholic  fermentation) : 

C6Hi2O6  =  2  C2H5OH  +  2  CO2. 

On  the  other  hand,  bacterium  lactis  converts  it  into  ordinary  lactic 
acid  (lactic  acid  fermentation) : 

C6H1206  =  2  C3H603. 

Finally  dextrose  may  be  converted  into  butyric  acid,  carbon  dioxide,  and 
hydrogen  by  the  action  of  certain  microbes  (butyric  acid  fermentation) : 

C6Hi2O6  =  C4H8O2  +  2  CO2  +  2  H2. 

At  this  place  we  shall  not  take  up  these  processes  in  further  detail.  We 
shall  later  on  find  opportunity  for  showing  how  great  an  influence  the 
stereo-configuration  of  the  different  sugars  has  upon  their  fermentability, 
and  how  Emil  Fischer  by  the  aid  of  fermentation  studies  was  able  to 
formulate  hypotheses  and  arrive  at  conclusions  which  are  of  great 
biological  importance  and  form  the  foundation  of  our  whole  knowledge 
concerning  fermentation  reactions. 

It  remains  still  to  show  certain  relations  between  the  sugars  and  two 
other  classes  of  compounds,  namely,  their  reduction  products  (the  corre- 
sponding alcohols)  and  their  oxidation  products  (the  acids).  The  former 
relation  is  at  once  apparent  from  the  following  summary:  glucose  is  the 
aldehyde  of  sorbite,  mannose  of  mannite,  and  galactose  of  dulcite,  while 
fructose  is  the  ketone  of  mannite.  By  oxidation  we  obtain: 

From  glucose,  first  the  monobasic  gluconic  acid,  then  by  further 
oxidation  the  dibasic  saccharic  acid. 


28 


LECTURE  II. 


From  mannose,  the  monobasic  mannonic  acid  and  then  the  dibasic 
manno-saccharic  acid. 

From  galactose  the  monobasic  galactonic  acid  and  then  the  dibasic 
mucic  acid. 

Fructose  behaves  quite  differently  on  oxidation.  In  the  case  of  the 
above-mentioned  sugars,  which  are  all  aldoses,  acids  are  obtained  by 
oxidation  having  the  same  number  of  carbon  atoms  as  the  original  sugars. 
Fructose,  on  the  other  hand,  is  a  ketone,  and  on  being  oxidized  breaks  down 
into  compounds  containing  a  smaller  number  of  carbon  atoms. 

These  reactions  are  naturally  not  peculiar  to  hexoses,  and  for  the  simpler 
or  higher  monosaccharides  there  are  corresponding  alcohols  as  well  as 
monobasic  and  dibasic  acids.  Thus  we  have  for  example: 


Bioses : 


Trioses : 


Alcohol 
CH2OH 

CH2OH 
Glycol 

CH2OH 


HOH 


H2OH 
Glycerol 


Tetroses : 


Sugar  Monobasic  Acid  Dibasic  Acid 

CHO  CO  .OH  CO  .  OH 

I  I  I 

CH2OH  CH2OH  CO  .  OH 

Glycolose          Glycollic  Acid    Oxalic  Acid 
(Glycolaldehyde) 


CHO 

CO.  OH 

CO.  OH 

CHOH 

CHOH 

CHOH 

CH2OH 

CH2OH 

COOH 

Glycerose 

Glyceric  Acids 

Tartronic  Acid 

(Glyceraldehyde) 

COOH 
CHOH 
CHOH 

COOH 

Tartaric 
Acids  (4) 


Erythritol  was  discovered  by  Lamy  (1852)  in  the  algae  Protococcus 
vulgaris.  It  is  optically  inactive. 

In  the  group  of  the  pentoses,  it  has  already  been  stated  that  arabinose 
corresponds  to  the  alcohol  arabitol  and  the  two  acids,  arabonic  and  1-trioxy- 
glutaric,  while  with  xylose  we  have  the  alcohol  xylitol  and  two  correspond- 
ing acids.  Although  these  last  alcohols  and  acids  have  up  to  the  present 


CH2OH 

CHO 

CO.  OH 

CHOH 

CHOH 

CHOH 

CHOH 

CHOH 

CHOH 

CH2OH 

CH2OH 

CH2OH 

d-  and  l- 

d-  and  l- 

Erythric 

Erythritol 

Erythrose 

Acids 

CARBOHYDRATES.  29 

time  not  been  found  in  nature,  yet  a  native  alcohol  adonitol,  obtained  in  an 
optically  inactive  form  from  Adonis  vernalis,  corresponds  to  rhibose,  a 
sugar  of  the  pentose  series  and  which  has  only  been  prepared  synthetically. 

In  the  case  of  the  sugars  containing  more  than  six  atoms  of  carbon  and 
which  up  to  the  present  time  have  only  been  obtained  artificially,  the 
seven-carbon  alcohols  perseitol  and  volemitol  are  found  in  nature.  The 
former  is  present  in  the  unripe  seeds,  leaves,  and  pericarp  of  Per  sea  gratis- 
sima,  while  the  latter  is  contained  in  Lactarius  volemus,  and  has  recently 
been  prepared  from  the  rhizomes  of  several  species  of  Primula. 

Of  the  four  above-mentioned  hexoses,  glucose,  galactose,  fructose  and 
mannose,  only  the  first  three  are  found  in  the  animal  organism.  d-Mannose 
is  found  only  in  the  vegetable  kingdom  partly  as  such  (for  example,  in 
the  sap  of  Japanese  Amorphophallus  Konjako),  to  some  extent  as  glucoside- 
like  compounds  (thus,  strophantobiose  decomposes  into  d-mannose  and 
rhamnose),  and  finally  very  extensively  in  anhydride-like,  condensation 
products  known  as  mannans. 

Fructose  occurs  similarly  in  the  vegetable  kingdom,  and  likewise  either 
free  or  combined.  In  the  former  state  it  is  seldom  found  pure,  but  usually 
is  mixed  with  other  sugars  as  a  component  of  many  fruits.  Fructose  is 
formed,  furthermore,  by  the  hydrolysis  of  many  vegetable  substances  ; 
thus,  of  inulin,  the  reserve-substance  in  the  tubers  of  dahlia,  helianthus, 
sweet  potato,  elecampane,  etc. 

Its  most  important  occurrence  is  in  cane  sugar,  by  the  hydrolysis  of 
which  one  molecule  of  d-glucose  and  one  molecule  of  d-fructose  are 
obtained.  This  mixture  is  known  as  invert  sugar. 

In  the  products  of  the  animal  kingdom,  fructose  is  not  often  found.  In 
honey  it  occurs  together  with  glucose.  It  is  sometimes  to  be  found  in  the 
urine  after  one  has  eaten  considerable  fruit.  In  rare  cases  it  is  found  in 
larger  amounts  in  the  urine  of  a  diabetic.  That  fructose  occurs  normally 
in  animal  tissues  is  extremely  doubtful.1 

Grape  sugar,  d-glucose,  glucose  or  dextrose,  as  it  is  variously  called, 
plays  without  question  the  most  important  role  of  all  the  monosaccharides 
in  the  animal  system.  It  is  this  form  which  carbohydrates  in  general 
assume  before  absorption  and  assimilation.  As  d-glucose  the  greater  part 
of  the  carbohydrate  is  conducted  from  organ  to  organ,  from  the  place  of 
storage  to  the  place  of  consumption.  Glucose  is  always  present  in  the 
blood,  and  the  amount  varies  only  within  narrow  limits,  averaging  from 
0.05  to  0.1  per  cent  in  different  animals.2  These  figures,  however,  are  not 
accurate,  because  glucose  is  not  the  only  sugar  that  is  found  in  blood.  On 

1  Cf.  Adler  and  Adler:  Pfluger's  Arch.  110,  99  (1905);  Neuberg   and   Strauss:  Z. 
physiol.  Chem.  36,  233  (1902);    Rudolf  Ofner:   Monatsh.  26,  1153  (1904);   26,  1165 
(1905);  and  Z.  physiol.  Chem.  45,  359  (1905). 

2  See  Lecture  XXIII. 


30  LECTURE  II. 

the  other  hand,  it  is  not  true,  as  Asher  and  Rosenfeld1  have  recently 
shown,  that  the  greater  part  of  the  glucose,  or  perhaps  all  of  it,  is  present 
in  a  combined  state.  Glucose  from  blood  diffuses  through  a  parchment 
membrane,  even  when  the  outer  liquid  is  a  blood  deficient  in  sugar,  made 
so  by  the  action  of  yeast.  Glucose  is  also  present  in  certain  organs  (mus- 
cles). It  is  often  hard  to  decide  whether  the  glucose  found  was  pre-formed, 
or  whether  it  has  been  produced  secondarily  from  a  carbohydrate  of  higher 
molecular  weight  by  hydrolytic  fermentation.  Normal  human  urine  fre- 
quently contains  glucose,  but  always  in  very  small  quantities.  It  may 
appear  in  larger  amounts  after  a  diet  rich  in  carbohydrates,  especially  after 
large  amounts  of  grape  sugar  have  been  taken  into  the  system.  This  is 
spoken  of  as  alimentary  glucosuria.2 

The  elimination  of  considerable  quantities  of  sugar  in  the  urine  has 
been  observed  after  the  introduction  of  numerous  chemical  substances  into 
the  system,  as,  for  example,  strychnin,  curari,  phosphorus,  etc. 

The  most  interesting  form  of  glycosuria  is  that  produced  by  phloridzin 
and  known  as  phloridzin-diabetes.  Phloridzin  3  is  a  glucoside  obtained 
from  the  root-bark  of  apple,  pear,  cherry,  and  plum  trees,  and  yields  by 
hydrolysis  glucose  and  phloretin: 


phloretin 

The  phloretin  is  decomposed  further  into  phloroglucinol  and  phloretic 
acid: 

Ci5H1405  +  H20  =  C6H3(OH)3  +  C6H1003 

phloroglucinol    phloretic  acid 

We  shall  consider  these  artificially-produced  glucosurias  at  another 
place. 

Glucosuria  has  been  observed,  furthermore,  by  Hofmeister  4  when  he 
fed  starch  to  starved  dogs.  Bohm  and  Hoffmann  5  have  described  the 
appearance  of  large  amounts  of  sugar  in  the  urine  of  cats  which  were 
confined  and  protected  from  cooling  off  by  coverings.  Glucosuria  can 
also  be  produced  by  a  cold. 

Glucose  is  very  widely  distributed  in  the  vegetable  kingdom  partly  as 
such,  partly  in  large  storage  deposits  in  the  form  of  starch,  and  partly  as 


1  Asher  and  Rosenfeld:  Zentr  Physiol.  19,  449  (1905). 

2  Concerning  sugar  in  urine,  see  Pfliiger,  Schondorf,  and  Wenzel;  Pfliiger's  Arch.  105, 
121  (1904).     It  is  to   be  remembered  that  chloroform,  for  example,  when  boiled  in 
alkaline  solution  shows  a  strong  reducing  power. 

3  J.  S.  Stass:  Ann.  30,  192  (1840). 

4  Arch.  exp.  Path.  Pharm.  26,  355  (1890). 
6  Ibid.  8,  271  and  375  (1878). 


CARBOHYDRATES.  31 

the  framework-substance  in  all  varieties  of  cellulose.  Finally  it  takes 
part  in  the  formation  of  a  great  number  of  glucosides. 

The  last  member  of  this  series  which  we  have  to  consider  is  galactose. 
Up  to  the  present  time  it  has  never  been  detected  with  certainty  in  the 
free  state.  It  is  found  as  a  constituent  of  certain  vegetable  glucosides, 
for  example,  digitonin  and  sapotoxin. 

On  the  other  hand,  numerous  polymers  of  galactose,  the  so-called  galac- 
tanes,  are  known,  some  of  which  yield  galactose  alone  on  hydrolysis,  while 
some  give  other  sugars  as  well. 

In  the  animal  organism,  galactose  is  present  chiefly  in  milk-sugar,  but 
similarly  it  has  been  obtained  by  the  hydrolysis  of  cerebron  (see  page  20) . 
We  know  very  little  concerning  the  formation  of  galactose  or  of  milk- 
sugar.  There  are,  as  has  been  mentioned,  certain  well-known  higher 
sugars  in  the  vegetable  kingdom  which  yield  galactose,  but  it  is  very 
questionable  that  there  is  any  direct  connection  between  the  galactose  in 
the  nourishment  and  that  of  milk-sugar.  We  shall  come  back  to  this 
point  in  the  discussion  of  the  latter  compound. 

At  this  place  we  will  consider  two  compounds  which  are  very  closely 
related  to  glucose,  namely,  glucuronic  acid  and  glucosamine  (chitosamine) . 

Glucuronic  acid  (also  written  glycuronic)  is  a  derivative  of  glucose. 
Schmiedeberg  and  Meyer  1  suspected  this,  for  they  realized  that  the  com- 
pound combined  the  properties  of  an  acid,  an  aldehyde,  and  a  polyvalent 
alcohol.  It  was  not  proved,  however,  until  Thierf elder2  succeeded  in 
changing  glucuronic  acid  into  d-saccharic  acid,  and  Fischer  and  Piloty3 
effected  its  synthesis  from  d-saccharic  acid.  By  the  work  of  the  last 
named,  the  configuration  was  established,  as  shown  by  the  following 
summary: 

CHO                          CO .  OH  CHO 

HCOH  HCOH  HCOH 

HOCH  HOCH  HOCH 

HCOH  HCOH  HCOH 

HCOH  HCOH  HCOH 

CH2OH  CO  .OH  CO  .  OH 

d-Glucose  d-Saccharic  acid          d-Glucuronic  acid 


1  Z.  physiol.  Chem.  3,  422  (1879). 

2  Ibid.  11,  389  (1887). 

3  Ber.  24,  521  (1891). 


32  LECTURE  II. 

Glucuronic  acid  itself  is  not  crystalline,  but  on  boiling  its  solution, 
glucurone  lactone,  CeH8O6,  crystallizes  out: 

CHO  .  CHOH  .  CH  .  CHOH  .  CHOH  .  CO. 

I O 

Glucuronic  acid  does  not  occur  free  in  the  animal  organism,  and  the 
uncombined  acid  has  not  yet  been  positively  identified  in  the  vegetable 
kingdom.  Its  derivatives  are  always  present  to  a  slight  extent  in  urine, 
in  the  blood,  and  in  the  liver.1  It  has  always  been  found  present  in  ester- 
like  coupling  with  various  compounds  from  which  the  glucuronic  acid  may 
be  prepared  by  saponifying  reagents.  In  normal  urine  we  find  phenol-, 
indoxyl-,  and  skatoxyl-glucuronic  acids.  These  compounds  are  of  much 
less  importance  than  those  well-known  compounds  of  glucuronic  acid  with 
different  substances  introduced  into  the  body.  Glucuronic  acid  pairs  with 
members  of  the  aliphatic  series  (alcohols,  aldehydes,  ketones,  etc.)  and  also 
of  the  aromatic  series.  The  best  known  of  these  compounds  are  those  with 
camphor  and  chloral,  although  the  number  of  conjugated  d-glucuronic 
acids  that  have  been  studied  is  very  large.2  According  to  their  entire 
behavior  they  may  be  regarded  as  glucosides. 

Up  to  the  present  time,  the  way  in  which  glucuronic  acid  is  formed  has 
not  been  clearly  decided.  Again,  we  know  nothing  regarding  the  amount 
formed  under  normal  conditions,  for  it  is  highly  probable  that  the  acid  is 
oxidized  further  in  the  organism  when  no  compound  capable  of  combining 
with  it  is  present.  It  would  seem  most  probable  that  it  is  formed  from 
glucose,  but,  as  Emil  Fischer3  has  stated,  it  is  difficult  to  understand  a 
direct  transformation  here.  It  is  hard  to  see  why  in  such  a  case  the 
oxidation  should  take  place  at  the  primary  alcohol  group  rather  than  at 
the  readily-oxidizable  aldehyde  group.  Emil  Fischer  assumes,  therefore, 
that  by  the  introduction  of  substances  such  as  camphor,  there  is  an  inter- 
mediate combination  with  the  glucose  so  that  the  aldehyde  group  is  thus 
protected  from  oxidation.  Then  by  oxidation  of  the  free  primary  alcohol 
group,  the  glucuronic  acid  compound  is  formed. 

Thierf elder  4  called  attention  to  another  source  of  glucuronic  acid  by 
showing  that  when  camphor  and  chloral  hydrate  are  fed  to  hungry  dogs 
the  corresponding  conjugated  acid  is  eliminated  in  the  urine.  It,  therefore, 


1  Paul  Mayer  and  Carl  Neuberg:  Z.  physiol.  Chem.  29,  256  (1900).  Paul  Mayer:  ibid. 
32,  518  (1901).  Lepine  and  Boulud:  Compt.  rend.  133,  138  (1901);  134,  398  (1902); 
141,  453  (1905). 

*  Hildebrandt  has  recently  studied  a  large  number  of  these  compounds.  See  sum- 
mary in  article  by  Neuberg  on  Pentoses  and  Glucuronic  Acid,  Ergeb.  Physiol.  (Asher 
and  Spiro),  3  Abt  I,  p.  373. 

3  E.  Fischer  and  O.  Piloty:  Ber.  24,  521  (1891). 

4  Z.  physiol.  Chem.  10,  163  (1886). 


CARBOHYDRATES.  33 

seemed  probable  that  the  glucuronic  acid  was  formed  from  decomposed 
albumin.  According  to  recent  investigations  concerning  the  reserve 
stores  of  sugar  in  the  starved  organism,  especially  of  glycogen,  all  such 
conclusions  have  become  doubtful.  Furthermore,  the  whole  question 
of  the  formation  of  glucuronic  acid  from  albumin  coincides  with  that  of 
carbohydrates  from  proteins.  At  another  place  we  shall  discuss  this 
problem  in  detail.  On  the  other  hand,  an  observation  made  by  Salkowski 
and  Neuberg1  is  worthy  of  mention  here.  They  found  that  glucuronic 
acid  when  exposed  to  intense  putrefaction  goes  over  into  the  aldopentose, 
l-xylose,  with  the  splitting  off  of  carbonic  acid. 

CHO  COH 

HCOH  HCOH 

HOCH  HOCH 

HCOH  HCOH 

HCOH  H2COH 


io. 


OH 
d-Glucuronic  acid  Z-Xylose 

We  have  met  with  Z-xylose  before.  It  is  found  in  the  nucleoproteids  of 
the  pancreas  and  liver,  and  is  perhaps  the  sole  pentose  occurring  in  the 
animal  organism.  This  observed  transformation  connects  the  aldo- 
hexose,  glucose,  with  the  aldopentose,  xylose.  It  is  indeed  conceivable  that 
the  formation  of  xylose  in  the  animal  system  may  take  place  in  a  similar 
way.  For  the  present  we  have  no  precise  knowledge  about  this  process, 
and  we  know  just  as  little  regarding  the  place  of  formation  of  glucuronic 
acid,  i.e.,  in  what  part  of  the  body  the  compound  is  synthesized.  It  is 
extremely  probable  that  it  is  not  limited  to  a  single  organ.2 

Glucuronic  acid  is  to  be  considered  as  a  substance  which  protects  the 
organism  against  the  action  of  various  kinds  of  substances  some  of  which 
are  formed  in  the  body  while  some  are  brought  into  contact  with  the  cells 
of  the  body  from  the  outside.  It  combines  with  these  substances  and 
makes  them  harmless.  We  shall  subsequently  meet  with  other  compounds 
(glycocoll,  sulphuric  acid)  which  perform  the  same  task.  The  poisons 
thus  neutralized  are  almost  always  substances  which  cannot  be  destroyed 
in  the  organism  by  direct  oxidation.  Glucuronic  acid  may  combine 
directly  with  these  poisons,  that  is,  without  the  latter  undergoing  any 


1  Z.  physiol  Chem.  36,  261  (1902). 

2  Julius  Pohl:  Arch.  exp.  Path.  Pharm.  41,  97  (1898). 


34  LECTURE  II. 

other  change.  This  is,  for  example,  the  case  with  substances  containing 
an  hydroxyl  group.  Thus,  trimethyl  carbinol  introduced  into  the  system 
is  eliminated  in  the  urine  as  a  conjugated  glucuronic  acid:1 

(CH3)3  .  COH  +  C6H-i007  =  (CH3)3  .  CO.C6H906  +  H20 

Many  compounds,  however,  are  not  chemically  suitable  for  coupling 
with  glucuronic  acid.  They  are  prepared  for  combination  by  the  action 
of  the  animal  body  either  by  reduction,  by  oxidation,  by  hydration,  or  by 
the  two  last-named  processes  acting  together.  Thus,  for  example,  chloral 
hydrate  2  and  butylchloral  hydrate  3  are  reduced.  The  former  is  changed 
into  trichlorethyl  alcohol,  and  this  combines  with  glucuronic  acid,  the 
conjugated  acid  being  eliminated  in  the  urine.  The  compound  formed  is 
known  as  urochloralic  acid: 


C13C  .  CH  +  2  H  =  C13C  .  CH2OH  +  H2O, 

XOH 
C13C  .  CH2OH  +  C6H10O7  =  C13C  .  CH2O  .  C6H9O6  +  H2O. 

A  preliminary  oxidation  takes  place  in  the  case  of  o-nitrotoluol  4  it  being 
changed  in  the  organism  of  the  dog  to  nitrobenzyl  alcohol: 

NO2  .  C6H4  .  CH3  +  O  =  NO2  .  C6H4  .  CH2OH, 
NO2  .  C6H4CH2OH  +  C6Hi007  =  N02  .  C6H4  .  CH2O  .  C6H9O6  +  H2O. 

Many  camphor  varieties  undergo  a  similar  preliminary  oxidation. 

In  other  cases  the  animal  organism  causes  the  poisonous  substance  to 
take  on  water,  and  oxidation  may  take  place  simultaneously.  An  example 
of  this  is-  found  in  the  transformation  of  thujone  into  thujone  hydrate,5 
which  then  unites  with  glucuronic  acid: 

OC10H17OH  +  C6H1007  =  OC10H170  .  C6H9O6  +  H20. 
Camphene  6  is  changed  into  camphene  glycol: 

Ci0H16  +  O  +  H20  =  HO  .  Ci0H16  .  OH. 

As  the  above  equations  show,  the  fundamental  principle  of  the  coupling 
is  in  all  cases  the  same,  except  that  sometimes  the  poison  can  unite  directly 
with  the  glucuronic  acid  (or  glucose  —  see  above)  ,  while  otherwise  this 

Thierfelder  and  von  Mering:  Z.  physiol.  Chem.  9,  511  (1885). 

von  Mering:  ibid.  6,  480  (1882).    von  Mering  and  Musculus:  Ber.  8,  662  (1875). 

Kiilz:  Pfliiger's  Arch.  28,  506  (1882);  33,  221  (1883). 

Jaffe":  Z.  physiol.  Chem.  2,  47  (1878-79),  and  Ber.  12,  1092  (1878). 

Emil  Fromm  and  Hermann  Hildebrandt:  Z  physiol.  Chem.  33,  579  (1901). 

Fromm,  Hildebrandt,  and  Clemens:  ibid.  37,  189  (1902-03). 


CARBOHYDRATES.  35 

union  is  possible  only  after  the  animal  organism  itself  has  produced  some 
change  in  the  objectionable  substance.1 

Quite  different  from  glucuronic  acid  in  its  properties  is  the  compound 
d-glucosamine,  also  known  as  chitosamine.  It  was  first  prepared  in  large 
amounts  from  the  chitin  of  lobster  shells,2  and  later,  as  has  been  mentioned, 
from  mucin  substances  and  as  a  cleavage  product  of  proteins.  The  con- 
stitution of  glucosamine  has  been  recently  cleared  up  by  Fischer  and 
Leuchs.3  It  is  to  be  regarded  as  a  derivative  of  either  d-glucose  or  d- 
mannose,  in  which  the  hydroxyl  of  the  a  position  is  replaced  by  the  amido 
group,  NH2-  Its  configuration  is  the  following: 


H          H         OH 

I  I  I 

CH2(OH)—   C       -   C       •   C   --CH(NH2)  .  CHO 

H 


OH       01 


Glucosamine  is  a  very  interesting  compound.  It  forms  an  intermediate 
step  between  the  hexoses  and  the  hydroxy-a-amino  acids,  which  we  will 
soon  meet  with  as  cleavage  products  of  the  proteins,  so  that  glucosamine, 
in  a  sense,  forms  a  bridge  between  the  proteins  and  the  carbohydrates. 
At  present  we  know  nothing  concerning  the  physiological  significance  of 
glucosamine.  It  does  not  occur  free  in  the  above-mentioned  substances, 
but  in  a  polymeric  form  either  alone  or  with  other  sugars. 

Finally  there  remains  one  other  amino-sugar  to  mention  which  we  have 
already  touched  upon,  namely,  galactosamine.  It  was  discovered  by  Schulz 
and  Ditthorn  and  represents  a  component  of  the  glucoproteids  in  the  albu- 
minous gland  of  the  frog.  Its  constitution  is  not  known  at  present. 


1  Cf.  Fromm's  Die  chemischen  Schutzmittel  des  Tierkorpers  bei  Vergiftungen,  Strass- 
burg,  1903. 

2  Ledderhose:  Z.  physiol.  Chem.  2,  213  (1878-79);  4,  139  (1880).     H.  Steudel:  ibid. 
34,  353  (1902). 

3  Ber.  35,  3787  (1902);  36,  24  (1903). 


LECTUKE   III. 

CARBOHYDRATES. 
II. 

POLYSACCHARIDES. 

THE  polysaccharides,  or  compound  sugars,  which  we  now  have  to 
consider,  can  be  regarded,  as  we  have  seen,  as  glucosides  of  sugar  itself;  in 
other  words,  they  are  formed  from  simpler  sugars  with  elimination  of 
water;  and,  conversely,  by  the  action  of  hydrolyzing  agents  (chemicals  or 
ferments),  they  may  be  broken  down  into  their  separate  components,  i.e., 
simple  sugars.  In  discussing  the  monosaccharides,  we  often  found  oppor- 
tunity to  point  out  how  widely  distributed  these  complicated  sugars  are, 
for  the  simple  sugars  themselves  in  some  cases  only  occur  in  nature  in  this 
state.  Biologically  this  group  assumes  a  distinctive  position.  The  animal 
and  vegetable  organisms  store  their  reserves  of  carbohydrates  in  this 
form.  On  the  other  hand,  many  representatives  of  the  class  may  be 
looked  upon  as  the  intermediary  products  between  the  more  complicated 
and  simpler  sugars,  and  owe  their  origin  to  a  progressive,  spontaneous 
hydrolysis.  In  the  center  of  all  these  processes  of.  transformation  taking 
place  in  the  animal  organism,  we  find  the  hexoses,  especially  glucose; 
whether  a  complicated  sugar  molecule  such  as  starch  breaks  down,  or 
whether  such  a  one  as  glycogen  is  formed,  for  example.  In  the  plant 
organism  the  relations  are  to  some  extent  similar,  except  that  here,  as  has 
been  previously  mentioned,  the  sugars  of  the  five-carbon  series  are  more 
common.  It  is,  however,  still  an  open  question  as  to  whether  the 
simple  pentoses  here  take  such  a  central  position  in  the  metabolism 
of  carbohydrates  as  the  hexoses  in  the  animal  system,  for  up  to  the 
present  time  the  pentoses  are  known  almost  exclusively  in  the  form  of 
polysaccharides  (pentosans,  etc.),  concerning  the  formation  of  which  our 
knowledge  is  still  very  limited. 

The  group  of  polysaccharides  is  subdivided,  according  to  the  number  of 
sugar  molecules  which  enter  into  their  composition,  into  di-,  tri-,  tetrasac- 
charides,  etc.,  and  the  true  polysaccharides. 

The  disaccharides  1  consist  of  two  molecules  of  the  simple  sugar  minus 

1  Here  only  the  hexobioses  are  considered,  i.e.,  those  composed  of  two  molecules  of 
hexose.  There  are  also  bioses  built  up  of  sugars  containing  fewer  carbon  atoms,  for 
example,  gluco-apiose,  which  is  built  up  from  /?-oxymethyl-tetrose  (apiose)  and  glucose, 
and  is  obtained  from  the  glucoside  in  Petroselinum  apiin.  Again,  we  have  the  mano- 
rhamnoses  prepared  from  strophanthin. 

36 


CARBOHYDRATES.  37 

one  molecule  of  water.      This  conception  corresponds  to  the  empirical 
formulae: 

Ci2H22Oii  =  (C6H1206)2  -  H20     or     Ci2H22On  +  H2O  =  2  (C6Hi2O6). 

They  correspond  in  their  behavior  to  the  monosaccharides.  Cane- 
sugar  is  an  exception  to  this  rule,  as  its  alkaline  solution  is  not  capable  of 
reducing  metallic  oxides,  whereas  the  other  disaccharides  retain  entirely 
the  properties  of  the  aldehyde  alcohols.  The  exceptional  behavior  of 
cane-sugar  has  been  ascribed  to  a  protected  position  of  its  aldehyde  and 
ketone  groups. 

To  this  group  belong  sugars  which  are  found  in  nature  as  such,  besides 
other  sugars  which  are  formed  by  cleavage  from  sugars  of  higher  molecular 
weight.  Cane-sugar,  milk-sugar,  and  maltose  are  of  especial  importance, 
whereas  the  remaining  members  of  the  group  are,  according  to  their 
occurrence  and  importance,  of  only  limited  interest.  Worthy  of  men- 
tion are  trehalose,  first  found  in  ergot  of  rye ;  gentiobiose,  obtained  from 
gentianose  by  partial  hydrolysis  produced  by  invertin  or  very  dilute 
sulphuric  acid;  and  cellose  (cellobiose),  which  is  believed  to  stand  in  the 
same  relation  to  cellulose  as  maltose  to  starch,  but  has  not  yet  been  found 
in  the  vegetable  kingdom.  Melibiose  is  another  hexobiose,  and  is  formed 
by  partial  inversion  of  either  melitriose  or  of  rafrinose,  either  by  the  action 
of  dilute  acids  or  by  certain  varieties  of  yeast. 

Before  discussing  the  above-mentioned,  more  important  disaccharides, 
we  must  mention  two  other  hexobioses  which  have  been  obtained  in  a 
peculiar  manner,  namely,  isomaltose  and  isolactose.  The  former  was 
synthesized  by  Emil  Fischer  from  grape-sugar  by  the  action  of  cold,  fuming 
hydrochloric  acid,  and  is  said  to  be  formed,  on  the  other  hand,  together 
with  maltose  by  the  breaking  down  of  starch.  It  must  be  mentioned, 
however,  that  the  identification  of  isomaltose  in  most  cases  has  not  been 
entirely  satisfactory,  so  that  we  are  still  unable  to  tell  much  about  the 
building  up  and  breaking  down  of  carbohydrates  in  plant  and  animal 
organisms,  and  especially  because  it  seems  probable  that  quite  a  number 
of  different  products  have  been  designated  as  maltose  by  various  inves- 
tigators. Isomaltose  excited  the  interest  of  biologists  in  particular  when, 
in  1898,  A.  C.  Hill l  succeeded  in  obtaining  it  from  grape-sugar  by  the  aid 
of  the  maltoglucase  of  yeast,  and  likewise  by  the  so-called  taka-diastase 
from  Aspergillus  oryzae.  Hill  added  the  ferment  to  concentrated  solutions 
of  grape-sugar,  and  showed  that  the  fermentation  reaction  was  to  some 
extent  a  reversible  process.  Hill  himself  regarded  the  product  formed 


1  J.  Chem.  Soc.  73,  634  (1898) ;  Ber.  34,  1380  (1901) ;  Proc.  Chem.  Soc.  19,  99  (1901) ; 
17,  184  (1901). 


38  LECTURE  III. 

as  maltose.  Emmerling  1  showed,  however,  that  isomaltose  was  chiefly 
present  in  this  case.  Later  on  we  shall  take  up  the  syntheses  produced 
by  the  action  of  ferments  more  in  detail,  as  well  as  their  biological  impor- 
tance.2 

Isolactose  occupies  a  quite  similar  position,  and  has  been  obtained  by 
Fischer  and  Armstrong  3  from  a  mixture  of  d-glucose  and  d-galactose  under 
the  influence  of  lactoglucase. 

Cane-sugar,  also  known  as  sucrose,  saccharose,  and  saccharobiose,  is  of 
great  importance  for  plant  and  animal  organisms.4  It  plays  an  important 
part  in  the  reserve-stores  of  all  Phanerogamia,  and  is  found  chiefly  in 
tissues  containing  no  chlorophyll,  although  it  is  present  in  smaller  quan- 
tities in  all  parts  of  the  plant.  It  occurs  to  the  greatest  extent  in  the 
stalk  of  the  sugar-millet  (sorghum)  and  sugar-cane,  in  the  sap  of  certain 
kinds  of  palm,  that  of  the  sugar-maple,  the  birch  and  the  carob  tree  (St. 
John's  bread).  Considerable  amounts  are  found  in  the  ripe  fruits  and 
leaves  of  various  growths.  At  present  the  sugar-beet  is  cultivated  exten- 
sively on  account  of  the  cane-sugar  it  contains,  and,  together  with  the 
sugar-cane,  forms  the  source  of  practically  all  commercial  sugar. 

This  important  food  and  condiment  has  never  been  positively  identified 
in  the  animal  organism.  It  is  certain  that  it  takes  no  part  in  intermediary 
metabolism.  This  follows  from  the  fact  that  cane-sugar  introduced  into 
the  veins  is  not  utilized,  but  passes  off  unchanged  in  the  urine.  In  order 
for  this  sugar  to  be  of  value  to  the  animal  organism,  it  must  first  be 
subjected  to  hydrolysis  in  the  digestive  tract.5 

Cane-sugar,  as  proved  by  Liebig  in  the  year  1834,  corresponds  in  its 
composition  to  the  formula  Ci2H22On.  It  decomposes  under  the  action 
of  hydrolytic  agents  into  one  molecule  of  d-fructose  and  one  of  d-glucose. 
Since  the  d-fructose  in  this  mixture  rotates  the  plane  of  polarized  light  more 
to  the  left  than  d-glucose  does  to  the  right,  the  product  is  Isevorotary,  that 
is  to  say,  in  the  opposite  direction  as  compared  with  cane-sugar,  which  is 
strongly  dextrorotary.  For  this  reason  this  mixture  of  equal  parts  of  the 
two  hexoses  obtained  by  the  cleavage  of  cane-sugar  is  called  invert-sugar, 
and  the  process  is  spoken  of  as  inversion*  Its  formation  was  first  studied 
by  Dubrunfaut  7  in  1830.  Mixtures  of  fruit-  and  grape-sugars,  moreover, 
occur  very  extensively  in  nature  (honey,  fruit,  etc.). 

1  Ber.  34,  600  and  2206  (1901). 

2  See  lecture  on  Ferments. 

3  Ber.  35,  3144  (1902). 

4  E.  Schulze  and  S.  Frankfurt:  Z.  physiol.  Chem.  20,  511  (1895). 

5  Claude  Bernard:  "Legons  sur  le  Diabete,"  p.  249  (1877).     Fritz  Voit:  Deut.  Arch, 
klin.  Med.  58,  523  (1897). 

6  This  term  is  also  used  in  general  to  denote  the  hydrolytic  decomposition  of  com- 
pound carbohydrates  into  simple  sugars.     The  opposite  change  is  called  reversion. 

7  Compt.  rend.  25,  308  (1847);  29,  51  (1849);  42,  901  (1856). 


CARBOHYDRATES.  39 

Milk-sugar,  also  called  lactose  or  lactobiose,  occurs  similarly  in  nature, 
and  was  described  as  long  ago  as  1615  by  Fabricio  Bartoletti  in  the 
"  Encyclopaedia  dogmatica,"  and  described  in  1700  by  Testi  and  in  1715 
by  Vallisneri  as  a  newly-discovered  medicine.  Milk-sugar  is  found  in  vary- 
ing amounts  in  the  milk  of  all  mammals.  During  confinement  it  is  often, 
found  in  small  quantities  in  the  urine.1  Similarly  in  calving  it  has  been 
detected  in  the  urine  for  several  days  before  and  after  the  birth.  Again 
after  weaning,  sugar  is  wont  to  pass  off  through  the  kidneys.  Recently, 
Porcher  2  has  carefully  studied  the  origin  of  the  lactose  in  milk.  He  found 
that  extirpation  of  the  breast-glands  of  milch-goats  and  cows  soon  caused 
a  marked  increase  in  the  amount  of  sugar  in  the  blood,  while,  at  the  same 
time,  glucose  appeared  in  the  urine.  These  experiments  make  it  seem 
very  probable  that  the  milk-sugar  is  first  formed  in  the  breast,  and  appar- 
ently from  glucose  alone,  and  not  out  of  the  glucose  and  galactose  in  the 
food 

Milk-sugar  has  never  been  found  in  the  vegetable  kingdom.3  On 
being  subjected  to  hydrolysis  it  breaks  up  into  one  molecule  of  glucose 
and  one  of  galactose.  By  oxidizing  it  with  nitric  acid,  mucic  acid, 
COOH  .  (CHOH)4  .  COOH,  is  formed. 

Maltose,  also  called  malt-sugar,  maltobiose,  ptyalose,  and  cerealose, 
occupies  a  quite  different  position  from  the  above  two  disaccharides.  It 
is  a  cleavage  product  of  starch,  and  in  fact  an  intermediary  product  which 
usually  is  immediately  hydrolyzed  further  as  fast  as  it  is  formed.  It  is 
true  that  small  amounts  of  maltose  are  met  with  now  and  then  in  plant 
organisms,  and  it  is  quite  possible  that  it  is  here  also  a  transitory  product 
in  the  metabolism  of  carbohydrates.  Recent  investigations  make  it  seem 
probable  that  maltose  is  also  found  as  a  glucoside  in  the  vegetable  kingdom. 

In  animal  organs  (liver,  blood,  etc.)  maltose  has  been  repeatedly  found, 
although  always  in  small  amounts;  and  furthermore,  in  many  cases  the 
methods  of  identification  have  not  been  entirely  satisfactory.  The  most 
important  manner  of  formation  is  by  the  action  of  a  ferment  upon  starch. 

As  long  ago  as  1785  Irvine,  and  in  1815  KirchhoftV  observed  that  extract 
of  malt  was  capable  of  breaking  down  starch.  The  sugar  formed  was 
recognized  first  by  Dubrunfaut 5  in  1822.  The  active  principle  in  malt, 
the  so-called  diastase,  was  first  isolated  by  Payen  and  Persoz.6  Starch 


1  Cf.  Franz  Hofmeister:  Z.  physiol.  Chem.  1,  101   (1877-78).     P.  Kaltenbach:  ibid. 
2,  360  (1878-79).     F.  A.  Lemaire:  ibid.  21,  442  (1895-96). 

2  Ch.  Porcher:  Compt.  rend.  141,  73  and  467  (1905). 

3  Bouchardat  [Compt.  rend.  73,  462  (1871)]  claimed  to  have  found  milk-sugar  in  the 
ripe  fruit  of  achras  sapota,  but  this  has  not  been  confirmed. 

4  Schweigger's  J.  15,  389. 

5  Ann.  chim.  phys.  3,  21  and  178. 

6  Ibid.  2,  53,  56,  73,  and  337. 


40  LECTURE  III. 

does  not  decompose  into  maltose  alone,  but  quite  a  number  of  other  prod- 
ucts are  formed  at  the  same  time.  The  whole  process  of  dissolving  the 
starch  by  the  action  of  diastase  has  been  made  the  subject  of  countless 
studies.  A  large  number  of  intermediate  products  have  been  isolated 
and  provided  with  special  names,  but  it  would  be  out  of  place  to  discuss 
here  all  the  transformation  products  that  have  been  described,  for  their 
manner  of  formation  and  their  chemical  characteristics  are  not  yet  accu- 
rately known.  The  reason  for  this  is  mainly  that  we  are  in  doubt  con- 
cerning the  homogeneity  of  the  starting  material,  the  starch  itself,  and 
know  still  less  concerning  diastase. 

Ferments,  corresponding  in  their  action  to  this  malt-diastase,  are  widely 
distributed  in  nature,  and  take  an  important  part  in  the  metabolism  of 
carbohydrates  in  plants.  They  give  back  to  the  metabolism  of  the  plant 
its  reserve-stores,  the  insoluble  starch. 

The  animal  organism,  as  well,  is  known  to  contain  ferments  which  dis- 
solve starch  and  convert  it  into  sugars,  and  in  this  process  maltose  is 
formed  as  an  intermediate  product,  which  then  breaks  down  into  two 
molecules  of  grape-sugar.  Later  on  we  shall  have  to  consider  such  trans- 
formations in  detail.  It  may  be  mentioned  here,  however,  that  in  the 
breaking  down  of  glycogen,  the  stored  carbohydrate  of  the  animal  system, 
maltose  has  also  been  observed. 

Polysaccharides  which  are  anhydrides  of  three  and  four  sugar  molecules 
are  also  known  and  have  been  accurately  described,  while  in  the  case  of  the 
more  complicated  compound  sugars  we  know  nothing  at  present  concern- 
ing the  number  of  sugar  molecules  which  take  part  in  their  formation. 
We  know  of  a  trisaccharide,  rhamninose,  which  is  composed  of  two  pentoses 
and  one  hexose;  this  is  obtained  in  the  decomposition  of  a  glucoside 
obtained  in  the  fruit  of  Rhamnus  injectoria,  the  xanthorhamnin.  Rham- 
ninose breaks  down  into  two  molecules  of  rhamnose  and  one  molecule  of 
d-glucose.  Trisaccharides  composed  of  three  molecules  of  hexose  are 
more  widely  distributed  in  nature.  Of  these  we  will  mention  raffinose 
(also  known  as  melitriose  or  gossypose)  which  is  found  in  different  plants 
and  in  the  sugar-beet.  A  tetrasaccharide,  stachyose,  (manna-tetrasac- 
charide),  is  known,  and  was  first  obtained  from  the  manna  of  ash.  On 
being  treated  with  dilute  mineral  acids  it  takes  on  water,  and  is  decom- 
posed into  one  molecule  of  d-fructose,  one  of  d-glucose,  and  two  of 
d-galactose. 

The  higher  polysaccharides  have  been  studied  but  little.  We  know 
merely  that  the  complete  hydrolysis  of  these  compounds  gives  mono- 
saccharides  as  final  products.  We  know  nothing,  however,  concerning 
the  number  of  molecules  of  simple  sugar  which  take  part  in  their  forma- 
tion. To  the  widely  different  substances  of  this  large  group  the  general 
formula  (CeHioOs^  is  given,  which  signifies  that  the  compound  is  com- 


CARBOHYDRATES.  41 

posed  of  z-molecules  of  sugar  anhydrides.  The  attempt  has  frequently 
been  made  to  determine  the  molecular  weight  of  many  of  these  compounds. 
Thus  with  starch,  the  formula  derived  in  this  way  has  been  given  as 
CisHsoOis  on  the  one  hand,  and  as  C360H6ooO3oo  on  the  other.  We  will 
meet  with  the  same  difficulty  when  we  come  to  study  the  proteins. 

The  following  substances  belong  to  this  group :  starch,  inulin,  cellulose, 
gums,  vegetable  mucilages,  and  glycogen.  They  are,  with  the  possible 
exception  of  glycogen  and  inulin,  all  known  only  in  the  amorphous  state. 
Water  dissolves  some  of  them  completely,  others  merely  swell,  while  the 
remainder  are  unaffected.  The  solutions  do  not  taste  sweet,  but  are 
optically  active.  In  general  they  will  not  diffuse  through  a  parchment 
membrane,  and  for  this  reason  they  are  also  called  saccharo-colloids. 
Chemically  they  are  indifferent  compounds,  and  will  not  combine,  .for 
example,  with  phenyl-hydrazine.  With  the  exception  of  dextrin,  they  will 
not  reduce  metallic  oxides  in  alkaline  solution. 

These  various  higher  polysaccharides  differ  widely  in  biological  signifi- 
cance. Thus  starch  and  glycogen,  which  on  account  of  their  similar 
nature  may  be  designated  as  vegetable  and  animal  glycogens,  are  found 
to  be  the  most  important  reserve-substances  of  the  carbohydrate  group 
that  occur  in  the  vegetable  and  animal  kingdoms  respectively.  Inulin 
has  a  similar  nature.  The  gums  and  vegetable  mucilages,  on  the  other 
hand,  fulfill  an  entirely  different  purpose.  They  serve,  at  least  to  some 
extent,  to  close  up  injuries,  and  correspond  to  the  wound-secretions  of 
animals.  Then  again,  those  substances  classed  together  under  the  name  of 
cellulose  have  a  still  different  significance.  They  are  found  extensively 
in  the  vegetable  world,  and  form  in  general  the  chief  constituents  of  the 
walls  of  plant  cells;  or  at  least  this  is  true  from  the  mosses  and  ferns  up 
through  the  whole  order  of  phanerogams,  while  in  the  studies  concerning 
bacteria,  fungi,  and  algae,  the  conclusions  drawn  have  not  been  uniform.1 
A  peculiar  position  is  occupied  by  the  dextrins,  which  it  is  now  certain 
are  not  individual  substances,  but  very  complicated  mixtures.  As  we 
have  already  seen,  they  are  to  be  looked  upon  as  the  decomposition 
products  of  starch. 

Now,  after  this  brief  introduction,  we  shall  turn  our  attention  to  the  indi- 
vidual representatives  of  this  class.  Sharply  distinct  in  its  entire  behavior 
from  all  the  other  higher  polysaccharides,  is  cellulose.  It  is  perfectly  insol- 
uble in  the  ordinary  solvents,  water,  alcohol,  ether,  etc.  There  is,  in  fact, 
only  one  good  solvent  known  for.  cellulose,  and  this  is  an  ammoniacal 
solution  of  copper  oxide  (Schweitzer's  reagent).  If  cellulose  is  treated 
with  concentrated  sulphuric  acid  at  ordinary  temperatures,  first  of  all  the 
sulphuric  acid  ester  of  cellulose  is  formed.  If  this  sulphuric  acid  solution 

1  For  the  chemical  composition  of  the  cell  membranes  of  different  cryptogams,  see 
Karl  Miiller:  Z.  physiol.  Chem.  45,  265  (1905). 


42  LECTURE  III. 

is  diluted  with  water  and  boiled,  glucose  is  formed.  Cellulose  is  found 
almost  exclusively  in  the  vegetable  kingdom.  In  the  animal  world  it  has 
only  been  identified  with  certainty  in  the  shells  of  the  tunicata.1  In  the 
cell  walls  of  plants  there  are  found  not  only  sugars  of  the  cellulose  group, 
but  other  complicated  carbohydrates  as  well,  which,  on  being  subjected  to 
hydrolysis,  sometimes  yield  glucose,  sometimes  no  glucose  at  all,  besides 
other  sugars  (arabinose,  xylose,  etc.).  These  substances  have  been 
designated  by  Schulze  as  hemicelluloses.2  In  building  up  the  cell  walls, 
furthermore,  the  pentosans,  which  yield  only  pentoses  on  hydrolysis,  also 
take  an  active  part. 

As  is  well  known,  the  cell  walls  undergo  changes  with  age  which  at  first 
are  manifest  externally  only  by  greater  rigidity.  We  speak  of  lignification. 
This  process  has  been  made  the  subject  of  much  careful  investigation 
without  ever  being  clearly  explained.  Erdmann  3  assumes  that  "  wood  " 
is  formed  from  cellulose  by  its  combination  with  other  substances  which 
are  perhaps  of  an  aromatic  character.4 

Exuding  from  the  various  tissue-complexes  (medullary-,  wood-,  and 
bark-parenchyma)  of  the  cell  membranes  come  the  different  gums.  They 
are  very  widely  distributed  in  nature,  and,  by  breaking  them  down  with 
dilute  acids,  usually  galactose  and  arabinose  are  formed.  Naturally  this 
group  cannot  be  regarded  as  homogeneous.  Especially  well  known  are 
gum-arabic  and  cherry-gum.  To  this  class  belongs  agar-agar  (obtained 
from  East- Asiatic  algffi) ,  which  has  become  important  as  a  culture  medium 
for  bacteria.  Again,  the  common  vegetable  mucilages  are  included,  being 
different  from  the  gums  only  by  their  insolubility,  or  difficult  solubility, 
in  water. 

We  now  come  to  those  members  of  the  carbohydrate  group  which  the 
animal  and  vegetable  organisms  temporarily  withdraw  from  the  general 
metabolism  in  order  to  be  able  to  make  use  of  them  at  any  time  by  trans- 
forming them  back  into  simple  sugars.  We  have,  in  cane-sugar,  already 
met  with  such  a  reserve-substance  for  plants.  At  least  an  equally  impor- 
tant part  is  taken  by  the  starches5  (amylum)  which  are  found  in  the 
seeds,  roots,  bulbs,  tubers,  pith  of  trees  in  winter  (especially  in  vegetation 
robbed  of  their  leaves  at  this  season  of  the  year),  etc.  The  amount  of 
starch  present  in  some  of  these  stores  may  amount  to  even  eighty  per  cent 
of  the  dry  substance.  Amylum  occurs  in  the  form  of  stratified  granules, 


1  C.  Schmidt:   J.  pr.  Chem.  38,  433  (1846).     Franchimont:  Ber.  12,  1938  (1879). 
Winterstein:  Ber.  26,  362  (1893). 

2  Schulze,  Steiger,  and  Maxwell:  Z.  physiol.  Chem.  14,  227  (1890).     Schulze:  ibid. 
16,  387  (1892);  19,  38  (1894);  Ber.  22,  1192  (1889),  and  24,  2271  (1891). 

3  J.  Erdmann:  Ann.  Suppl.  5,  223  (1867). 

4  Cf.  Viktor  Grafe:  Monatsh.  25,  987  (1904). 

6  Cf.  Brown  and  Heron,  Ann.  199,  165  (1879). 


CARBOHYDRATES.  43 

differing  in  form  and  size  with  different  plants.  The  concentric  rings 
represent  its  gradual  growth.  Starch  is  scarcely  changed  at  all  by  cold 
water,  but  warm  water  makes  the  grains  swell  up  and  finally  burst,  form- 
ing starch-paste.  Starch-paste  does  not  reduce  metallic  oxides  in  alkaline 
solutions.  A  very  rapid  swelling  is  brought  about  at  ordinary  temper- 
atures by  means  of  concentrated  solutions  of  metallic  salts.  Even  with 
dilute  alkalies  a  starch-paste  may  be  prepared  in  a  short  time.  A  well- 
known  test  for  starch  is  the  indigo-blue  coloration  produced  by  iodine 
solutions  in  the  presence  of  hydriodic  acid  or  an  iodide.  The  color- 
ation is  not  permanent  on  boiling,  but  reappears  on  cooling.  The 
presence  of  substances  capable  of  being  oxidized  by  iodine  (caustic  alkali, 
sulphurous  acid,  arsenious  acid,  etc.)  will  prevent  the  appearance  of  this  test, 
the  blue  color  only  being  obtained  when  such  impurities  have  been  oxidized. 
All  varieties  of  starch  do  not  give  a  blue  color  with  iodine;  some  of  them 
give  a  reddish-brown  color,  and  with  others  the  color  is  that  of  red  wine. 

At  present  we  do  not  know  a  great  deal  concerning  the  significance  of 
these  different  colorations;  it  is  positively  certain,  however,  that  starch 
cannot  be  regarded  as  a  chemical  individual.  The  conception  "  starch  " 
comprises  a  large  group  of  substances  of  similar  physical  and  chemical 
properties,  which  form  a  unit  on  account  of  their  common  biological  signifi- 
cance. An  attempt  has  been  made  to  get  an  idea  concerning  the  structure 
of  starches  by  studying  their  decomposition  products.  On  boiling  them 
with  dilute  acids,  glucose  is  obtained.  If  the  acid  is  allowed  to  act  in 
the  cold,  or  with  only  gentle  heating,  a  hydration  product  is  produced 
which  is  known  as  "  soluble  starch."  By  the  action  of  cold,  dilute  mineral 
acids  for  several  weeks,  or  by  an  hour's  treatment  with  4  per  cent,  sul- 
phuric acid  at  80°  C.,  the  so-called  "  amylodextrin  "  is  obtained,  and, 
on  further  hydrolysis  of  the  latter,  dextrins  are  formed,  while,  as  just 
mentioned,  the  final  product  is  grape-sugar.  We  stated  in  connection 
with  maltose  that  a  similar  breaking  up  of  the  starch  molecule  could  be 
effected  by  ferments,  in  this  case  diastatic  ferments.  It  was  also  men- 
tioned then,  that  at  present  we  are  not  able  to  deduce  a  picture  of  the 
starch  formation  from  a  study  of  the  great  number  of  intermediate  products 
obtained  by  partial  hydrolysis  and  designated  in  the  literature  with  par- 
ticular names.  We  must  be  satisfied,  for  the  time  being,  with  the  knowl- 
edge that  amylum  contains  a  large  number  of  anhydride-like  grape-sugar 
molecules,  and  by  taking  on  water  it  is  decomposed,  step  by  step,  into 
smaller  molecules,  and  finally  into  the  basal  component  glucose.  We 
shall  find,  later  on,  that  the  proteins  are  quite  similarly  constituted. 
Soluble  starch,  amylodextrin,  dextrin,  etc.,  correspond  to  the  albumoses  and 
peptones,  while  glucose,  the  elementary  building  material,  corresponds  to 
the  amino-acids.  A  similar  analogy  is  found  with  the  fats,  although  here 
the  relations  are  much  simpler. 


44  LECTURE  III. 

In  discussing  fruit-sugar  we  met  with  a  reserve-carbohydrate,  inulin, 
which  in  its  biological  relations  completely  corresponds  to  starch.  It 
is  found  in  the  roots  of  Inula  Helenium,  the  bulbs  of  dahlias,  etc.,  and  is 
different  from  starch  in  so  far  as  it  yields  on  hydrolysis  fructose  instead 
of  glucose.  Furthermore,  inulin  dissolves  in  warm  water  without  forming 
a  paste;  iodine  colors  it  yellow,  and  diastatic  ferments  do  not  attack  it. 

Finally,  in  many  lichens,  especially  in  Iceland-moss,  another  kind  of 
starch  is  recognized  which  likewise  is  colored  yellow  by  iodine;  it  dissolves 
in  hot  water,  and  yields  glucose  upon  complete  hydrolysis.  This  is  lichenin, 
and,  like  inulin,  it  is  not  effected  by  diastatic  ferments. 

Besides  these  carbohydrates  which  are  found  in  the  reserve-stores  of 
plants,  others,  such  as  amylin,  lavosin,  cerosin,  and  secalin,  are  found  in 
grain-seeds.  These  substances  yield,  as  a  result  of  hydrolytic  decom- 
position, sometimes  glucose  and  sometimes  fructose.  In  the  constructive- 
tissue  of  Lupinus  luteus  is  found  galactin,  a  carbohydrate  of  this  group 
yielding  only  galactose  upon  complete  hydrolysis.  Again,  in  the  class  of 
graminese,  palms,  liliacese,  amaryllidacese,  iridese,  and  also  in  the  many 
dicotyledons,  we  meet  with  the  so-called  reserve-celluloses.  We  under- 
stand by  the  term  reserve-carbohydrates,  substances  which  appear  as  solid 
deposits  on  the  cell-membrane  of  constructive  tissue  in  seeds. 

The  dextrins  are  usually  regarded  as  forming  a  particular  class  in  the 
group  of  carbohydrates.  They  are,  as  has  been  stated,  decomposition 
products,  and  are  obviously  mixtures  of  substances  with  different  molecular 
weights.  They  form  a  transition  stage  between  the  "  reserve-carbohy- 
drates "  and  the  "  metabolic  carbohydrates."  By  further  hydrolysis 
they  yield  molecules  of  glucose. 

Glycogen  is  to  the  animal  organism  what  starch  is  to  plants.  We  have 
to  thank  the  French  scientist  Claude  Bernard  1  for  its  discovery,  who  in 
1848  noticed  the  high  sugar  content  of  liver,  and  found  sugar  only  absent 
from  it  after  prolonged  starvation.  A  few  years  later,  the  same  inves- 
tigator succeeded  in  showing  that  the  sugar  observed  in  liver  was  not 
directly  present  as  such,  but  was  formed  gradually  from  a  preliminary 
state.  He  established  the  fact  that  by  taking  the  liver  from  a  dog  right 
after  it  is  killed,  the  blood  being  washed  off  and  the  washing  continued 
in  running  water  for  forty  minutes,  then  the  last  wash-water  will  no  longer 
show  the  presence  of  sugar.  Even  if  a  piece  of  such  liver  is  boiled  in 
water,  no  sugar  will  be  dissolved  out  of  it.  If,  however,  the  liver  is  allowed 


1  See  Bernard  and  Barreswil:  Compt.  rend.  27,  514  (1848);  also  E.  F.  W.  Pfliiger: 
"Das  Glykogen  und  seine  Beziehungen  zur  Zuckerkrankheit,"  Bonn,  Martin  Hager 
(1905)  and  Max  Cremer:  "Physiologic  des  Glykogens,"  in  Ergeb.  Physiol.  (Asherund 
Spiro)  1,  803  (1902),  Wiesbaden,  published  by  T.  F.  Bergmann.  A  complete  summary 
of  Bernard's  work  is  found  in  "L'ceuvre  de  Claude  Bernard,"  Paris,  T.  B.  Bailliere 
et  Fils. 


CARBOHYDRATES.  45 

to  stand  for  twenty-four  hours,  a  considerable  quantity  of  sugar  will  then 
be  found  present.  This  suggested  to  Bernard  that  a  substance  must  be 
present  in  liver  which  is  difficultly  soluble  in  water,  but  yielded  sugar  by 
the  action  of  the  liver  substance,  and  this  must  be  "  living,"  as  the  fol- 
lowing experiment  showed.  After  thoroughly  washing  the  liver,  half  of 
it  was  boiled,  and  from  this  it  was  not  possible  to  obtain  any  more  sugar, 
whereas  sugar  was  slowly  formed  in  the  other  piece.  Bernard  not  only 
assumed  the  presence  of  a  complicated  substance  in  the  liver  from  which 
the  sugar  was  formed,  but  he  actually  succeeded  in  isolating  such  a  sub- 
stance.1 The  method  employed  by  him  for  the  preparation  of  glycogen 
is  essentially  the  same  as  that  of  to-day.  It  depends  upon  the  fact  that 
alcohol  precipitates  glycogen  from  an  alkaline  solution  of  the  organ.  By 
dissolving  it  again  in  caustic  potash  and  reprecipitating  by  alcohol,  it  is 
easy  to  purify  the  crude  glycogen.  In  this  way  August  Kekule 2  succeeded 
in  preparing  glycogen  free  from  nitrogen  and  ash. 

We  shall  later  find  that  this  skillful  investigator,  Bernard,  not  only  dis- 
covered glycogen,  but  to  him  is  also  due  the  credit  of  clearly  recognizing 
its  biological  significance. 

Glycogen  is  closely  related  to  starch  not  alone  by  acting  as  a  reserve 
carbohydrate,  but  also  as  regards  its  formation.  It  is,  however,  not  iden- 
tical with  starch,  but  sharply  distinct  from  it.  In  common  with  the  other 
members  of  this  complicated  group  of  carbohydrates,  its  empirical  formula 
is  represented  by  (CeHioOs)^  It  is  a  fine,  white,  amorphous  powder. 
We  know  absolutely  nothing  concerning  its  molecular  weight.3  It  swells 
in  cold  water  and  apparently  dissolves,  although  the  solution  shows  a 
distinct  opalescence.  That  an  actual  solution  is  not  formed  is  shown  by 
the  fact  that  the  glycogen  will  not  diffuse  through  a  parchment  membrane. 
Furthermore,  Gatin-Gruzewska 4  has  recently  shown  that  glycogen  in 
water  behaves  exactly  like  a  colloid,  migrating  towards  the  anode.  Gly- 
cogen is  dextrorotary.  Its  solutions  are  colored  by  iodine  yellowish- 
brown,  reddish-brown  to  deep  red  according  to  the  concentration.  An 
alkaline  solution  of  copper  oxide  dissolves  it,  but  the  solvent  is  not 
reduced.5 

Quite  like  the  other  polysaccharides,  glycogen  is  decomposed  by 
boiling  with  dilute  mineral  acids  into  its  simplest  component,  which  in 
this  case  is  exclusively  grape-sugar.  The  breaking  down  of  the  complex 

1  Claude  Bernard:  Le£ons  sur  la  Physiologie  et  la  Pathologie  du  Systeme  nerveux, 
vol.  i,  p.  467  (1857).     See  also  Gazette  medicale,  28,  III  (1857). 

2  Pharm.  Zentrb.  p.  300  (1858). 

3  Z.  Gatin-Gruzewska :  Wanderung  des  Glykogens  unter  dem  Einfluss  des  elektrischen 
Stromes.     Pfliiger's  Arch.  103,  287  (1904). 

4  Pfliiger's  Arch.  103,  282  (1904). 

5  Concerning  its   quantitative   estimation,   see   E.  F.  W.  Pfliiger,    loc.  cit.  pp.  61 
and  67,  et  seq. 


46  LECTURE  III. 

molecule  can  take  place,  as  with  starch,  step  by  step,  and  quite  anal- 
ogous products  are  obtained  here.  Diastatic  ferments  likewise  attack 
glycogen.  Among  the  decomposition  products  obtained  by  hydrolysis, 
dextrin  and  maltose  have  been  identified  with  certainty.  In  its  other 
relations  it  is  exactly  similar  to  starch,  and  here  as  in  the  case  of  the 
compounds  of  higher  molecular  weight  formed  from  it  (the  dextrins,  for 
example) ,  we  have  no  guarantee  concerning  their  individuality,  and  sim- 
ilarly we  do  not  really  know  whether  glycogen  itself  is  a  simple  com- 
pound or  a  mixture. 

We  do  not  yet  know  with  sufficient  certainty  whether  glycogen  as  such 
is  deposited  in  the  tissues,  or  whether  at  least  a  part  of  it  may  not  be 
present  in  a  combined  state. 

Glycogen  is  widely  distributed  in  the  animal  kingdom,  and  is  found  in 
all  sorts  of  different  tissues.1  One  of  its  chief  sources  is  the  liver,  in  which 
it  is  deposited  in  the  cell-substance.  The  nucleus  is  always  free  from  it. 
The  amount  present  depends  greatly  upon  the  condition  of  nourishment 
of  the  animal.  The  liver  contains  this  polysaccharide  even  in  its  early 
stages  of  development,2  although  perhaps  in  small  amounts.  It  is  also 
found  in  organs  corresponding  to  the  liver  in  many  invertebrates,  thus,  in 
crabs,  mollusks,  etc. 

Detailed  studies  have  been  made  concerning  the  distribution  of  glycogen 
in  the  liver  of  the  Gasteropoda.  It  was  found  that  the  content  of  glycogen 
was  dependent  upon  precisely  the  same  conditions  as  with  Vertebrata. 
In  the  case  of  Limax  and  Helix  the  entire  glycogen  content  could  be  made 
disappear  at  the  end  of  twenty  to  twenty-one  days.  After  feeding,  it 
reappeared  in  the  course  of  nine  or  ten  hours.  It  is  first  deposited  in  the 
connective  tissue,  and  then  in  the  epithelium  of  the  liver.  Starvation 
alone  causes  it  to  disappear.  With  the  gasteropods  the  liver  is  the  only 
place  in  which  glycogen  is  deposited  to  any  extent;  in  the  other  organs 
the  amount  is  hardly  worthy  of  consideration. 

Also  in  the  lower  organisms,  other  than  mollusks  and  gasteropods, 
glycogen  is  widely  distributed.  Bernard  found  it  in  the  larvae  of  flies, 
the  grubs  of  many  insects,  in  earth-worms  and  tape- worms,  etc.  Other 
authors  have  mentioned  its  occurrence  in  Echinoderms,  Holothuria, 
Polyps,  Sponges,  etc. 

Glycogen  has  likewise  been  identified  in  Protozoa  (Vorticella,  Opalina, 


1  For  the  microchemical  detection  of  glycogen,  see  Dietrich  Barfurth:   "Verglei- 
chende  histochemische  Untersuchungen  liber  das  Glykogen,"  Arch,  mikro.  Anat.  26, 
259  (1895),  and  Edgar  Gierke:  "Das  Glykogen  in  der  Morphologic  des  Zellstoffwechsels," 
Habilib-Schrift,  G.  Fischer,  Jena,  1905. 

2  E.  Pfliiger:   Ueber  den  Glykogenhalt  der  fotalen  Leber,  Pfliiger's  Arch.  95,  19 
(1901),  and  Glykogengehalt  der  fotalen  Leber  und  die    Jodreaktion  des  Glykogens," 
ibid.  102,  305  (1904). 


CARBOHYDRATES. 


47 


Chilodon,  Amoeba,  Rhizopoda)  and  also  in  fungi.1  Clautrian,2  as  well  as 
Harden  and  Young,3  has  carefully  determined  and  studied  the  amount  of 
glycogen  in  yeast. 

The  identification  of  the  glycogen  has  in  many  cases  not  been  perfect, 
and  it  is  an  open  question  as  to  whether  some  of  the  supposed  glycogen  has 
not  been  an  entirely  different  substance.  At  all  events,  these  substances 
belong,  according  to  their  biological  relations,  to  the  glycogen  or  starch 
group,  or,  as  we  may  say,  to  the  group  of  reserve-carbohydrates.4 

In  the  vertebrates  the  muscles  also  serve  to  store  glycogen.  The  various 
muscles  contain  different  amounts,  as  shown  by  the  following  table:5 


Animal. 

Muscle. 

Glycogen. 

Doe  I 

Biceps  brachii    

Per  cent. 
1  0  17 

Quadriceps  femoris  

(  0.53 

Dog  II 

Biceps  brachii 

(  0  25 

Quadriceps  femoris 

'  0  32 

Dog  III 

Dorsal  musculature 

(  0  135 

Adductors  posterior      

1  0  077 

Rabbit  I  

Dorsal  musculature      

50.417 

Adductors  posterior 

t  0  444 

It  is  found  not  only  in  striated  but  also  in  smooth  muscle  and  in  the 
muscle  fibrils.  The  glycogen  content  in  the  muscles  is  dependent  upon 
the  condition  of  nourishment.  We  shall  soon  see  that  the  glycogen  of 
muscles  has  a  particular  function,  and  stands  in  direct  relation  to  the 
performance  of  work  by  the  musculature.  Even  in  invertebrates,  glycogen 
is  not  lacking  in  the  muscular  apparatus,  and  performs  the  same  function. 

Glycogen  occurs  furthermore,  in  the  pancreas,  in  the  small  glands  of 
the  digestive  apparatus,  the  lungs,  kidneys,  sexual  glands,  brain,  epithe- 
lium, connective-tissue,  and  blood- 8  and  lymph  vessels. 

B.  Schondorff  7  has  determined  the  amount  of    glycogen  in  different 


1  Errera:  "Das  Epiplasma  der  Ascomyceten  und  das  Glykogen  der  Pflanzen,"  Briissel 
(1882),  and  Compt.  rend.  101,  253  (1885). 

2  Clautrian:  "Chemische  Untersuchungen  iiber  Glykogen,"  Mem.   couronn.  Acad. 
Roy.  Belg.  p.  53  (1895). 

s  Trans.  Chem.  Soc.  81  (1902). 

*  Concerning  the  occurrence  of  glycogen  under  pathological  conditions,  see  O. 
Lubarsch  in  O.  Lubarsch  und  R.  Ostertag:  Ergebnisse,  1,  Jahr.  2,  166  (1895). 

5  August  Cramer:  Z.  Biol.  24,  78  (1888). 

8  It  is  a  much  disputed  question  whether  blood-plasma  itself  contains  glycogen,  or 
whether  the  glycogen  in  blood  is  to  be  traced  merely  to  that  of  the  white  blood-corpuscles. 
It  looks  as  if  glycogen  might  be  present  in  the  plasma,  though  ordinarily  its  presence 
is  limited  to  the  leucocytes. 

7  Pfliiger's  Arch.  99,  191  (1903). 


48 


LECTURE  III. 


organs  of  dogs  which  were  well  fed  with  carbohydrates  and  meat  shortly 
before  their  death.  The  following  table  gives  a  summary  of  the  results 
obtained: 

PER    CENT  OF  GLYCOGEN  IN  THE   ORGANS. 


Dog  I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Blood  . 

005 

0  002 

0  0061 

Liver  ... 

4  35 

7  60 

18  69 

17  10 

16  38 

9  89 

7  30 

Muscle  

0  72 

0  88 

2  54 

3  23 

3  72 

2  53 

0  76 

Bone   

0  18 

0  39 

1  00 

1  31 

1  76 

0  97 

0  27 

Viscera  

0  03 

0  08 

1  47 

1  51 

1  72 

1  01 

0  20 

Skin  

0.38 

0  20 

0  73 

0  84 

1  60 

0  92 

0  09 

Heart  

0.12 

0  10 

0  58 

0  72 

1  21 

0  49 

0  23 

Brain  

0.04 

0  23 

0  27 

0  23 

0  20 

0  25 

0  20 

100  grams  of  glycogen  in  the  body  are  distributed  in  the  different  parts   of  the 
dog  as  follows: 


Dog  I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Average. 

Blood 

0.04 

0.01 

0.001 

0.015 

Liver 

20.09 

26.37 

53.54 

56.74 

38.53 

2l'.  95 

48.54 

37.97 

Muscle 

62.55 

58.31 

31.22 

29.00 

38.93 

53.76 

35.83 

44.23 

Bone 

5.36 

10.32 

6.81 

7.29 

12.88 

11.30 

10.77 

9.25 

Viscera 

0.38 

1.10 

5.21 

4.31 

5.32 

7.30 

3.03 

3.81 

Skin  . 

11.38 

3.76 

3.00 

2.48 

4.01 

5.38 

1.42 

4.49 

Heart 

0.17 

O.Q8 

0.14 

0.12 

0.28 

0.18 

0.19 

0.17 

Brain 

0.04 

0.06 

0.07 

0.05 

0.05 

0.13 

0.23 

0.09 

It  is  evident  from  the  above  table  that  the  amount  of  glycogen  present 
in  the  different  organs  varies  greatly.  At  all  events,  it  is  never  possible  to 
draw  conclusions  concerning  the  amount  of  glycogen  present  in  any  given 
organ  from  a  knowledge  of  the  amount  contained  in  another  organ  or 
even  in  the  whole  body. 

Besides  the  carbohydrates  which  have  been  mentioned  up  to  this  point, 
there  are  quite  a  number  of  other  compounds  belonging  to  the  group  of 
polysaccharides  which  have  been  observed  in  blood,  in  milk,  and  es- 
pecially in  urine.  They  have  been  designated  partly  as  animal  gums/  and 
partly  as  dextrin-like  substances,2  etc.  The  last-mentioned  are  found  in 
large  quantities  in  the  urine  of  diabetics,  although  it  is  quite  possible  that 
such  products  may  be  present  to  some  extent  even  in  normal  urine,  because 
boiling  it  with  mineral  acids  causes  the  formation  of  humin  substances, 

1  H.  A.  Landwehr:  Zent.  med.  Wissensch.  21,  369  (1885).     See  also  K.  Baisch:  Z. 
physiol.  Chem.  18,  193  (1894);  19,  339  (1895);  and  20,  249  (1895). 

2  Cf.  K.  v.  Alfthan:  Helingfors.  Osakeyhtio  Weilin  und  Goos  Aktiebolag.  1904. 


CARBOHYDRATES.  49 

which  points  to  the  presence  of  carbohydrates.1  Our  knowledge  concern- 
ing these  products  is  still  indefinite,  and  the  same  may  be  said  concerning 
their  biological  significance.  It  seems  possible  that  in  the  case  of  these 
complicated  carbohydrates  in  urine  we  have  to  do  with  products  which 
have  escaped  a  complete  breaking  down. 

At  this  place  we  may  mention  the  acid  recently  observed  by  P.  A. 
Levene  2  in  the  preparation  of  nucleic  acid  from  the  spleen,  which  of  itself 
has  no  reducing  power,  but  acquires  it  after  being  boiled  with  acids. 
Levene  called  it  glucothionic  acid,  and  regards  it  as  a  sulphuric  acid 
ester.  It  is  not  yet  determined  what  the  nature  of  the  carbohydrate 
component  is:  John  A.  Mandel  and  P.  A.  Levene  3  succeeded  in  obtaining 
this  acid  also  from  the  kidneys,  liver,  pancreas,  and  milk  glands,  although 
only  in  very  small  amounts.  Apparently  such  sulphuric  acid  compounds 
of  carbohydrate-like  substances  are  quite  widely  distributed  in  the  organ- 
ism. Nothing  is  definitely  known  as  to  the  relation  that  chondroitin-sul- 
phuric  acid  4  (prepared  from  cartilage  and  amyloid)  bears  to  this  group, 
and  we  are  equally  ignorant  concerning  the  significance  of  these  products. 

Our  knowledge  concerning  jecorin,  first  described  by  Drechsel 5  and 
found  by  him  in  the  liver  of  a  horse  and  later  in  that  of  a  dolphin,  and 
finally  by  Baldi 6  in  the  same  organ  and  spleen  of  other  animals,  in  the 
muscles  and  blood  of  the  horse  and  in  the  human  brain,  is  still  very  indef- 
inite. Its  constitution  is  unknown,  but  it  contains  sulphur,  phosphorus, 
and  a  carbohydrate  complex  which  Manasse  7  states  to  be  glucose.8  It  is 
probably  not  a  chemical  individual,  but  rather  a  mixture  of  quite  dif- 
ferent products.  At  present  there  is  not  much  known  concerning  its 
significance.9 

1  Cf.  Emil  Abderhalden  and  Fritz  Pregl:  Z.  physiol.  Chem.  46,  19  (1905). 

2  Z.  physiol.  Chem.  37,  400  (1903). 

3  Z.  physiol.  Chem.  45,  386  (1905). 

4  Carl  Th.  Morner:  Z.  physiol.  Chem.  20,  357  (1895).  See  also  Skand.  Arch.  Physiol. 
1,  210  (1899);  Z.  physiol.  Chem.  23,  311  (1897).     N.  P.  Krawkow:  Arch.  exp.  Path. 
Pharm.  40,  195  (1898).     R.  Oddi:  ibid.  33,  376  (1894).  O.  Schmiedeberg:  ibid.  28,  355 
(1891).     A.  Orgler  and  C.  Neuberg:  Z.  physiol.  Chem.  37,  407  (1903). 

5  E.   Drechsel:   Ber.    sachs    Gesell.    Wissensch.    1886,   p.    44,   and    "  Beitrage  zur 
Chemie  erniger  Seetiere,"  Z.  Biol.  33,  85  (1896). 

8  Baldi:  Arch.  Physiol.  1887,  Suppl.  p.  100. 

7  Z.  physiol.  Chem.  20,  478  (1895). 

8  B.  Bing.     Skand:  Arch.  Physiol.  9,  166  (1900). 

9  See  also  J.  Meinertz:  Z.  physiol.  Chem.  46,  376  (1905),  and  M.  Siegfried  u.  H.  Mark: 
ibid.  46,  492  (1905). 


LECTURE   IV. 
CARBOHYDRATES. 

III. 
METABOLISM  OF  CARBOHYDRATES  IN  PLANT  AND  ANIMAL  ORGANISMS. 

FORMERLY  the  biology  of  plants  occupied  a  sharply  distinct  field  from 
that  of  the  animal  organism.  The  two  kingdoms  were  believed  to  be 
opposed  to  one  another  with  regard  to  the  transformations  of  energy  and 
of  force  taking  place  within  each.  Plants  were  alone  held  to  be  capable  of 
building  up  organic  substances,  i.e.,  to  be  capable  of  effecting  syntheses. 
The  animal  system,  on  the  other  hand,  served  to  break  down  such  sub- 
stances. In  this  way  the  animal  and  vegetable  worlds  acted  in  conjunction 
and  formed  a  large  unit.  However,  the  more  scientists  penetrated  into 
the  intricacies  of  vegetable  and  animal  metabolism,  and  in  proportion  to 
the  comparative  studies  made,  the  more  it  became  evident  that  there  was 
no  sharp  line  to  be  drawn  between  these  two  fields.  When  Wohler  in  1824 
discovered  that  benzoic  acid  introduced  into  the  animal  body  was  not 
consumed  nor  eliminated  as  such,  but  was  to  be  found  in  the  urine  com- 
bined with  glycocoll  in  the  form  of  hippuric  acid,  the  path  was  broken, 
and  for  the  first  time  a  synthetical  process  was  recognized  as  taking  place 
in  the  animal  organism. 

In  the  following  period,  as  we  shall  see,  a  large  number  of  such  syntheses 
were  discovered  as  taking  place  in  the  organism  of  animals,  and  to-day 
there  is  no  longer  any  doubt  but  that  synthetical  processes  play  an 
important  part  therein.  To  be  sure,  in  importance,  and,  as  far  as  we  know, 
in  variety  also,  they  are  far  in  the  background  as  compared  to  the  synth'eses 
in  plant  organisms.  On  the  other  hand,  plants  utilize  oxygen  and  produce 
carbon  dioxide  from  more  complicated  compounds ;  in  other  words,  they 
break  down  substances.  In  this  way  physiology  has  given  a  new  and  pow- 
erful support  to  the  well-known  common  morphological  outlines  of  the  two 
kingdoms,  so  that  to  some  extent  the  two  fields  have  been  placed  upon  a 
common  basis  although  each  retains  a  certain  degree  of  independence. 

Nothing  supported  the  old  conception  of  the  sharp  distinction  between 
the  synthetical  processes  of  plants  on  the  one  hand,  and  the  catabolic  pro- 
cesses taking  place  in  animal  organisms  on  the  other  hand  more  than  the 

50 


CARBOHYDRATES.  51 

formation  of  carbohydrates  in  plants.1  No  synthesis  is  more  wonderful 
than  this.  It  determines  the  whole  metabolism  of  the  plant;  it  forms 
the  support  upon  which  rests  the  whole  development  or  extinction  not 
only  of  plants  but  of  the  animal  world.  By  means  of  it  the  great  mass  of 
carbon  which,  in  the  form  of  carbon  dioxide,  is  apparently  withdrawn 
from  metabolism  as  the  final  product  in  the  combustion  of  organic  sub- 
stances, is  carried  back  to  it;  thus  the  sugar  synthesis,  or  what  is  commonly 
spoken  of  as  the  assimilation  of  carbonic  acid  by  the  organs  of  the  plant 
containing  chlorophyll,  forms  an  important  stage  in  the  carbon  cycle. 
The  great  deposits  of  coal,  and  the  rocks  which  underlie  the  surface  of 
the  earth  in  vast  layers,  and  are  to  a  considerable  extent  composed  of 
carbonates  (principally  of  calcium  and  magnesium),  belong  to  this  cycle. 
The  coal  is  formed  from  plant  residue  which  formerly  thrived  on  the 
carbon  dioxide  of  the  air;  and  by  burning  coal,  carbon  dioxide  is  again 
formed,  so  that  the  cycle  can  again  take  place.  Carbon  dioxide  found 
combined  with  bases  such  as  lime  and  magnesia  likewise  originated  from 
the  atmosphere.  It  is  temporarily  removed  from  the  cycle  only  to  return 
to  it  when,  for  example,  it  is  replaced  by  the  action  of  another  acid,  such 
as  silicic  acid.  Oxygen,  for  the  greater  part,  also  makes  the  cycle  with 
carbon. 

The  only  important  source  of  the  carbon  contained  in  plants  is,  in  fact, 
as  Ingenhousz  2  and  then  Theodor  de  Saussure  3  first  showed,  the  carbon 
dioxide  of  the  air.  It  is  true  that  it  has  been  observed  that  roots  can 
take  up  carbonic  acid  from  carbonates  and  bicarbonates  in  the  soil,  but 
the  amount  thus  available  is  very  slight.  Carbon  dioxide  is  taken  up 
for  the  most  part  through  the  stomata  (breathing-pores)  of  the  leaves. 
The  assimilation  depends  within  certain  limits  upon  the  amount  of  car- 
bon dioxide  in  the  atmosphere,  the  temperature  of  the  leaf,  and  the 
intensity  of  the  illumination.4  For  every  temperature  there  is  a  definite 
amount  of  carbon  dioxide  assimilation;  in  general,  the  optimum  lies 
between  20°  and  30°  C. 

In  spite  of  numerous  studies,  it  is  still  a  problem  as  to  what  is  first 
formed  from  the  carbon  dioxide.  At  present  we  understand  merely  the 


1  Concerning  the  assimilation  of  carbonic  acid,  consult  the  text-books  on  botany,  e.g., 
W.  Pfeffer's     "  Pflanzenphysiologie,  Ein  Handbuch  der  Lehre  vom  Stoffwechsel  und 
Kraftwechsel  in  der  Pflanze,"  published  by  Engelmann  in  Leipsic.  —  Friedrich  Czapek: 
"Biochemie  der  Pflanzen,"  published  by  Fischer  in  Jena. 

2  Ingenhousz:  "Experiments  upon  Vegetables,"  London,  1779,  and  "Essays  on  the 
Foods  of  Plants  and  the  Renovation  of  Soils  "  (1796). 

3  T.    de    Saussure:   "Recherches   chimiques    sur   la   ve"ge"tation,"   Paris,    1804.— 
Edmund  O.  v.  Lippmann:  "DieChemie  der  Zuckerarten."  —  T.  Sachs:    "Geschichte 
des  Botanik." —  A.  Hansen:  "Geschichte  der  Assimilation." 

4  F.  Frost  Blackman  and  Gabrielle  L.  C.  Matthaei:  Proc.  Roy.  Soc.  London,  76,  402 
(1905). 


52  LECTURE  IV. 

outward  conditions  under  which  the  carbonic  acid  assimilation  takes 
place.  We  know  that  cells  containing  chlorophyll  are  absolutely  indis- 
pensable to  the  process.  In  order  to  disturb  the  condition  of  equilibrium 
in  the  carbon  dioxide  molecule  and  in  those  of  the  water  required  to  form 
the  assimilation  products  of  carbon  dioxide  —  in  each  of  these  compounds 
the  affinity  of  carbon  and  hydrogen  for  oxygen  is  completely  saturated  — 
energy  is  necessary.  The  plant  cells  perform  work  in  transforming 
kinetic  energy  into  potential  energy.  It  has  been  known  for  a  long  time, 
and  proved  experimentally,  that  cells  containing  chlorophyll  are  not  of 
themselves  capable  of  assimilating  carbonic  acid.  The  process  takes 
place  only  by  the  aid  of  light.  The  light  vibrations  of  the  ether  furnish 
the  energy.  All  the  rays  of  white  light  are  not  active  in  this  respect. 
In  fact,  the  so-called  chemical,  or  actinic  rays,  of  the  ultra-violet  and 
similarly  the  peculiar  heat  rays  of  the  infra-red  part  of  the  spectrum 
have  little  or  no  power  of  furnishing  the  cells  with  the  energy  necessary 
for  assimilation.  The  most  active  rays  are  the  red,  orange,  and  yellow.1 
These  relations  have-  been  established  by  the  work  of  Engelmann.2 
The  essential  moment,  therefore,  in  the  formation  of  organic  substances 
in  the  plant  cell  is  the  transformation  of  radiant  energy  into  chemical 
energy,  a  process  which,  as  far  as  we  know,  takes  place  exclusively  in 
cells  containing  chlorophyll.  Chlorophyll  takes  part,  thereby,  in  an 
important  phase  in  the  energy  cycle.  By  its  help,  kinetic  energy  is  trans- 
formed into  potential  energy,  and  when  later  the  plant  is  eaten  by  the 
animal,  this  is  eventually  changed  back  into  kinetic  energy.  Yet  even  in 
the  vegetable  world  the  last-mentioned  process  plays  an  important  part, 
for  we  know  of  whole  groups  of  plants  which  are  not  able  to  assimilate 
carbon  dioxide  themselves;  these  are  the  parasites  which  contain  no  chloro- 
phyll, and,  as  regards  their  metabolism,  they  are  closely  related  to  the 
animal  organism;  while  on  the  other  hand,  we  have  species  belonging  to 
the  animal  kingdom  (vorticella,  certain  Flagellata,  planarians,  hydra,  etc.), 
which  assimilate  carbonic  acid,  and  set  free  oxygen,  thus  imitating  plants 
in  their  metabolism.  It  has  been  found  that  the  assimilation  of  carbonic 
acid  in  such  cases  is  also  due  to  the  presence  of  the  same  agent,  chlorophyll, 


1  The  maximum  assimilation  for  the  bluish-green,  fresh-water  algae  and  the  red  sea- 
algae  is  effected  by  rays  in  other  parts  of  the  sun's  spectrum.     Engelmann  has  shown 
(loc.  cit.}  that  the  light  rays  act  more  strongly  in  proportion  as  they  are  absorbed  by 
the  color.     In  general,  light  complementary  to  the  color  of  the  plant  is  most  active  upon 
assimilation.     Spectroscopic   analysis  shows  that  of  light  passing  through   different 
depths  of  water,  the  red  rays  are  strongly  absorbed,  while  the  green  and  bluish-green 
are  less  so.     This  explains  why  at  greater  depths  of  water,  the  red  and  yellow  forms 
prevail  rather  than  those  which  are  blue  or  bluish-green  in  color.     Cf.  W.  Engelmann: 
Arch.  Physiol.  Suppl.  1902,  p.  333.     Gaidukow:  ibid.  p.  214. 

2  Th.  W.  Engelmann:  Bot.  Ztg.  1882,  419;  1883,  1,  1884,  80;  1886,  64;  1887,  393, 
Pfliiger's  Arch.  25,  285  (1881);  ibid.  26,  537  (1887);  27,  485  (1882);  30,  95  (1883). 


CARBOHYDRATES.  53 

which  is  present  in  plants;  and  in  fact,  the  chlorophyll  is  not  deposited  free 
in  the  tissues  of  these  animals,  but  the  chlorophyll-bearers  are  those  algse 
which  exist  together  with  the  animal  cell  and  have  a  commensal  existence. 
This  sort  of  parasitism  is  met  with  very  frequently,  for  instance  in 
lichens,1  which  are  composed  of  fungi  and  algae.  Again,  we  find  the  same 
sort  of  symbiosis  in  higher  organisms.  Undoubtedly,  for  example,  the 
bacteria  found  in  the  alimentary  canal  illustrate  this  relation;  they  serve, 
as  we  shall  see  later  on,  to  convert  carbohydrates  (cellulose,  etc.)  into  a 
form  capable  of  absorption. 

By  means  of  carbonic  acid  alone,  the  cell  cannot  build  up  organic  sub- 
stances; hydrogen,  which  forms  an  integral  component  of  all  the  com- 
plicated compounds  of  the  carbohydrate  series  which  the  plant  organism 
produces,  is  lacking.  Hydrogen  is  obtained  by  the  plant  chiefly  from 
water  in  the  soil.  Herein  the  plant  finds  another  source  of  oxygen.  The 
way  in  which  the  plant  cells  utilize,  by  the  help  of  chlorophyll  and  the 
sun's  rays,  this  carbonic  acid  and  water,  or,  in  other  words,  -  the  first 
products  formed,  is  still  a  matter  of  conjecture.  -We  know  merely  that 
all  syntheses  start  with  a  reduction  process;  oxygen  is  set  free.  In  fact, 
we  can  follow  the  assimilation  of  carbonic  acid  either  by  determining  the 
loss  of  carbonic  acid  in  a  gas  mixture,  or  by  determining  the  oxygen 
evolved.  The  latter  can  be  observed  directly  by  immersing  the  parts  of 
a  plant  in  water.  Engelmann 2  ingeniously  made  use  of  bacteria  as  a 
reagent  for  oxygen.  If,  for  example,  a  thread  of  algse  and  some  aerobic 
bacteria  are  placed  under  an  air-tight  cover-glass,  it  will  be  noticed  at 
first  that  the  latter  are  very  lively.  If,  now,  the  preparation  is  kept  in  the 
dark  the  motion  of  these  bacteria  will  cease  altogether  after  a  time,  show- 
ing that  all  the  oxygen  has  been  consumed.  Then,  on  bringing  the  prep- 
aration to  the  light,  the  bacteria  begin  to  become  most  active  because  the 
thread  of  algse  has  begun  to  assimilate  carbon  dioxide  and  water  with 
elimination  of  oxygen.  By  means  of  this  very  sensitive  test  as  little  as 
one  billionth  part  of  a  milligram  of  oxygen  may  be  detected.  Engelmann, 
as  already  stated,  has  by  means  of  this  method  studied  the  different  parts 
of  the  solar  spectrum,  testing  it  with  regard  to  its  effect  upon  plant  assim- 
ilation. Beyerinck  3  later  in  a  similar  way  made  use  of  the  luminescence 
of  certain  bacteria,  which  also  depends  upon  the  presence  of  free  oxygen, 
for  the  detection  of  carbonic-acid  assimilation. 

With  regard  to  the  synthetical  products  first  formed  by  the  plant, 


1  Schwendener:  Nagelis  Beitrage  z.  wissensch.  Botanik  H.  2,  3,  and  4,  Leipsic,  1860- 
1868.  — de  Bary:  "Die  Erscheinung  der  Symbiose,"  Strassburg,   1879.     O.  Hertwig: 
"Die  Symbiose  oder  das  Genossenschaftsleben  in  Tierreich,"  Jena,  1883. 

2  Bot.  Ztg.  loc.  cit. 

3  Ibid.   (1890)  744.     See  also  Hans  Molisch:  "Die  Lichtenwicklimg  in  den  Pflan- 
zen,  Naturwissenschaftliche  Rundschau,  20,  505  (1905). 


54  LECTURE  IV. 

different  conjectures  have  been  made,  and  the  same  is  true  concerning 
the  action  of  chlorophyll.  Some  conceive  it  to  have  the  action  of  a  fer- 
ment,1 others  consider  it  as  closely  related  to  the  first  assimilation  product 
assuming  that  it  combines  with  the  carbonic  acid. 

As  long  as  we  know  practically  nothing  concerning  the  formation  of 
chlorophyll,  and  still  less  about  the  plasma  of  the  plant  cell  itself,  and  as 
long  as  we  are  unable  to  isolate  satisfactorily  any  of  the  first  products  of 
the  assimilation,  the  discussion  of  all  such  possibilities  has  only  a  relative 
value.  For  the  present  we  can  restrict  ourselves  to  those  hypotheses 
which  seem  plausible  from  a  chemical  standpoint.  At  the  same  time  it 
does  not  follow  necessarily  that  the  plant  organism  carries  out  its  syntheses 
in  such  a  way,  nor  that  the  intermediate  products  which  we  assume  are 
actually  formed  in  the  living  plant  cell.  Above  all,  the  impression  should 
not  be  left  that  the  assimilation  of  carbonic  acid  can  take  place  only  in  one 
direction.  It  is  indeed  possible,  and  in  fact  probable,  that  other  primary 
products  of  assimilation  exist.  It  is  undoubtedly  certain  that  one  of  the 
first  products  of  the  assimilation  is  a  carbohydrate,  whether  grape-sugar, 
starch,  or  perhaps  a  simpler  sugar  with  fewer  than  six  carbon  atoms  in  the 
molecule.  At  all  events,  —  and  this  is  of  greatest  importance  for  under- 
standing the  whole  metabolism  of  plants,  and  indirectly  that  of  the  animal 
organisms,  —  the  carbohydrates  stand  at  the  center  of  all  the  synthetical 
processes  taking  place  in  the  plant  organism.  We  shall  see  later  on  that 
the  fats,  the  albumins,  and  many  other  highly  complicated  compounds, 
evidently  originate  from  carbohydrates,  whether  by  constructive  or 
destructive  processes,  or  both  acting  together. 

In  discussing  the  first  synthesis  produced  in  the  plant  cell  we  meet  with 
a  highly  important  problem  which  we  have  already  briefly  touched  upon.2 
All  the  carbon  compounds  which  are  either  directly  or  indirectly  produced 
by  animal  or  plant  organisms,  are  optically  active;  that  is  to  say,  they 
possess  at  least  one  asymmetric  carbon  atom.  As  we  have  already  seen, 
most  of  these  compounds  are  found  in  nature,  only  in  the  optically- 
active  state.  Now,  the  plant  cell  in  carbon  dioxide  receives  a  carbon 
compound,  which  does  not  contain  an  asymmetric  carbon  atom.  The 


1  Jean  Friedel  (Compt.  rend.  132,  1138  (1901))  has  tried  to  support  this  view  by 
experiments.     He  brought  together  the  glycerol  extract  from  fresh  leaves  with  finely 
powdered  leaves  which  had  been  rapidly  and  carefully  dried,  and  found  oxygen  was 
evolved  by  the  action  of  light,  and  carbonic  acid  taken  up.     The  experiments,  however, 
are  not  conclusive,  and  have  not  been  corroborated.     Cf.  M.  Harroy:  Compt.  rend.  138, 
890  (1901).—  R.  O.  Herzog:  Z.  physiol.  Chem.  35,  459  (1902).    Again,  Bach  and  Chodat 
have  published  a  great  deal  of  work  summarized  in  Biochem.  Zentrbl.  1,  11,  417,  and 
I,  12,  457  (1903). 

The  relations  are  so  complicated  that  it  is  hard  to  draw  a  conclusion  at  the  present 
time  concerning  the  work  of  these  scientists. 

2  Cf.  p.  15. 


CARBOHYDRATES.  55 

beginning  of  all  the  asymmetry  in  the  organic  world  is  centered  in  the 
assimilation  of  the  carbon  dioxide,  for  evidently  it  is  here  in  the  plant 
cell  that  the  first  asymmetric  synthesis  is  carried  out  which  continues 
constantly  in  the  production  of  only  asymmetric  compounds.1  It  is 
indeed  possible  that  chlorophyll,  which  is  itself  asymmetrically  consti- 
tuted, plays  an  important  part  in  this  asymmetric  synthesis.  The  first 
appearance  of  asymmetry  is,  however,  unexplained.  Its  existence  evi- 
dently coincides  with  the  formation  of  the  first  cell.  It  is  possible,  on 
the  other  hand,  that  the  plant  cell  produces  first  of  all  an  inactive  com- 
pound, for  example,  an  inactive  sugar,  and  that  asymmetry  first  develops 
by  the  cleavage  of  this  compound.2  The  animal  organism  receives  in  turn 
with  its  food,  this  asymmetry  of  its  body-substance  from  the  plant 
world,  partly  directly,  as  in  the  case  of  the  herbivora,  and  partly 
indirectly,  as  in  the  case  of  the  carnivora.  We  shall  find,  moreover, 
that  these  relations  are  so  suited  to  the  animal  organism  that  it  some- 
times directly  disintegrates  racemic  compounds,  and  in  many  cases  utilizes 
only  one  component  and  discards  the  other  unchanged. 

The  first  observed  assimilation  product  of  the  carbon  dioxide  and  water 
was  starch,  easily  recognized  by  means  of  the  iodine  reaction.  For  a  long 
time  it  was  held  to  be  the  primary  product  of  assimilation.  Gradually  it 
became  a  recognized  fact  that  starch  is  a  product  formed  secondarily  from 
more  simple  components,  and  little  by  little  the  opinion  gained  ground 
that  d-glucose  was  to  be  regarded  as  the  primary  product  of  assimilation. 
This  assumption  was  supported  by  the  discovery  that  leaves  which  have 
been  preserved  in  the  dark  are  capable  of  forming  starch  directly  if  solu- 
tions containing  hexoses  are  placed  upon  them.  In  general,  the  following 
compounds  are  assimilated:  —  d-glucose,  d-mannose,  d-galactose,  and 
d-fructose.  Other  similar  compounds  may  be  utilized;  thus,  mannitol 

1  Cf.  Emil  Fischer:  "Die  Chemie  der  Kohlehydrate  und  ihre  Bedeutung  fur  die 
Physiologic." 

2  Cf.  A.  Byk:  Z.  physiol.  Chem.  49,  641  (1904).     Byk  seeks  to  trace  the  formation 
of  asymmetry  back  to  circularly-polarized  light  which  maybe  produced  by  the  reflection 
of  plane-polarized  daylight  by  the  surface  of  the  sea.     The  revolution  of  the  plane  of 
polarization  by  the  magnetism  of  the  earth  makes  it  impossible  for  equal  amounts  of 
the  two  forms  of  light  to  exist  at  any  point  on  the   earth,  or  upon  the  whole  surface 
of  the  earth,  or  for  any  considerable  period.     It  is  indeed  possible  that  such  may  be 
the  explanation  of  the  asymmetry  of  the  first  cells,  but  it  is  scarcely  probable  that  it 
accounts  for  the  continuous  production  of  asymmetric  molecules,  for  it  is  unreasonable 
to  assume  that  one  and  the  same  kind  of  light  is  permanently  in  excess  at  one  and  the 
same  point  on  the  earth's  surface;  and  it  would  seem  likely,  furthermore,  that  compo- 
nents of  unlike  optical  products  would  be  formed  in  different  localities.     Again,  Byk's 
proof  that  by  means  of  circularly-polarized  light  racemic  compounds  can  be  split  off  is 
not  perfectly  satisfactory.     Furthermore,  chlorophyll  itself  has  optical  properties.     It 
undoubtedly  changes  the  sun's  rays  of  short  wave  lengths,  which  have  no  effect  upon 
the  assimilation,  into  active,  longer  wave  lengths. 


56  LECTURE  IV. 

by  leaves  of  the  Oleacese,  dulcite  by  those  of  the  Evonymus;  and  interest- 
ingly enough  it  has  been  found  in  the  case  of  all  the  plants  examined  that 
the  assimilation  takes  place  with  those  carbohydrates  which  they  contain 
normally  as  reserve-substances. 

The  fact  that  the  volume  of  carbon  dioxide  absorbed  is  equal  to  that  of 
the  oxygen  evolved  *  has  been  cited  to  prove  that  a  carbohydrate  must  be 
the  first  assimilation  product.2  Again,  the  relations  of  the  heat  effect 
observed  coincides  very  satisfactorily  with  this  assumption.  On  the  other 
hand,  it  must  be  remembered  that  it  has  not  been  possible  to  carry  out 
exact  measurements  in  this  direction.  Side  by  side  with  the  assimilation 
of  carbon  dioxide  there  is  a  constant  absorption  of  oxygen  and  production 
of  carbon  dioxide.  Both  processes  stand  in  a  certain  relation  to  one 
another,  although  the  nature  of  this  has  never  been  determined.  It  has 
been  repeatedly  asserted  that  oils  and  fats  may  appear  as  the  first  pro- 
ducts of  assimilation.  Inclusions  of  oil  have  been  observed  frequently 
in  the  chromatophores  of  certain  plants;  for  example,  in  the  Musacese, 
Cactacese,  alga?,  and  especially  the  Vaucheria.3  By  the  decomposition  of 
the  fat  into  glycerol  and  fatty  acids,  and  the  simultaneous  partial  reduc- 
tion or  oxidation  of  these  cleavage  products,  sugars  could  be  formed  from 
the  glycerol,  and  vegetable  acids  from  the  fatty  acids.  It  was  soon  evi- 
dent, however,  that  these  fats  and  oils  were  not  primary  products  of 
assimilation,  but  rather  reserve-substances,  the  formation  of  which  can 
be  readily  traced  back  to  carbohydrates.  Equally  untenable  proved 
Liebig's  4  hypothesis  that  the  vegetable  acids  were  formed  as  the  first 
assimilation  products  from  which  the  carbohydrates  were  obtained 
secondarily.  At  present,  there  are  no  known  observations  which  are 
contrary  to  the  assumption  that  the  carbohydrates  represent  the  entrance 
of  the  carbon  from  carbon  dioxide  into  the  general  metabolism  of  the  plant. 

It  is  now  a  question  as  to  how  we  shall  explain  this  synthesis  of  carbo- 
hydrates —  d-glucose,  for  example  —  from  carbon  dioxide  and  water.  We 
have  already  mentioned  5  one  hypothesis,  namely,  the  assumption  of 
Baeyer  6  that  carbon  dioxide  by  reduction  is  changed  into  formaldehyde, 
and  by  the  condensation  of  the  latter  a  sugar  is  formed: 


C02  +  H2O 
Baeyer  originally  assumed  that  the  carbon  dioxide  absorbed  was  first 


1  Boussingault:  Compt.  rend.  53,  862  (1861),  and  Holle:  Flora,  118  (1877). 

2  This  might  take  place  as  follows:  6  CO2  +  6  H2O  =  C6H12Or>  +  6  O2. 

3  Paul  Fleissig:  "Ueber  die  physiologische  Bedeutung  der  olartigen  Einschliisse  in 
der  Vaucheria,"  Inaug.  Diss.  Basel,   1900. 

4  J.  Liebig:  Ann.  46,  58  and  66  (1843). 

5  Cf.  p.  15. 

6  Ber.  3,  63  (1870). 


CARBOHYDRATES.  57 

changed  into  carbon  monoxide  and  oxygen.  The  former  was  believed  to 
combine  with  chlorophyll  in  much  the  same  way  as  it  does  with  haemo- 
globin. 

Bach l  has  recently  modified  somewhat  this  suggestion  of  Baeyer.  Accord- 
ing to  him,  the  carbonic  acid  is  first  changed  into  percarbonic  acid,  water, 
and  carbon.  The  percarbonic  acid  is  then  decomposed  into  carbon 
dioxide  and  hydrogen  peroxide,  while"  the  latter  forms  with  carbon  and 
water  the  formaldehyde: 

3  H2CO3  =  2  H2CO4  +  H2O  +  C, 
2  H2CO4  =  2  CO2  +  2  H2O2  =  2  CO2  +  2  H2O  +  02, 
H2O  +  C  =  HCHO. 

Naturally,  a  great  many  attempts  have  been  made  to  isolate  formalde- 
hyde or  related  compounds  from  plants,  especially  from  the  green  leaves. 
This  has  not  been  accomplished,  however,  up  to  the  present  time  in  a  satis- 
factory way.2  On  the  other  hand,  nothing  has  been  shown  that  is  con- 
trary to  the  assumption  that  formaldehyde  does  actually  represent  the 
first  intermediate  product,  for  it  is  perfectly  possible  that  the  amount  of 
aldehyde  that  is  constantly  being  formed  is  so  extremely  small  that  it 
condenses  so  rapidly  that  it  escapes  detection.  It  has  been  brought 
forward  in  support  of  Baeyer's  theory  that  certain  plants  show  a  con- 
siderable resistance  towards  formaldehyde.  Thus  Treboux  3  found  that 
Elodea  canadensis  will  stand  a  0.001  per  cent  solution.  Algae  and  young 
plants  of  Sinapis  alba  are  said  to  be  strikingly  resistant  towards  formal- 
dehyde.4 

We  saw  in  considering  the  artificial  synthesis  of  carbohydrates  that 
it  was  possible  to  form  a  sugar  very  easily  from  formaldehyde,  and  we 
can  readily  understand  how,  according  to  the  number  of  molecules  of 
formaldehyde  entering  into  the  reaction,  sugars  containing  a  different 
number  of  carbon  atoms  in  the  molecule  may  be  obtained.  It  is,  how- 
ever, scarcely  probable  that  such  syntheses  take  place  in  this  simple  way. 
Thus,  for  example,  according  to  all  that  we  know  at  present,  it  is  hardly  to 
be  expected  that  pentoses  are  formed  directly  as  one  of  the  first  products 
of  the  condensation  of  formaldehyde.  Apparently  it  is  much  more  likely 
that  such  sugars  are  formed  by  the  breaking  down  of  higher  sugars 
especially  the  hexoses.  Such  a  process  is  likewise  easy  to  represent,  as,  in 


1  Arch.  sci.  phys.  nat.  Gen.  5,  401  (1898). 

2  H.  Euler:  Ber.  37,  3411  (1904).     Hans  and  Astrid  Euler:  Arkiv  for  Kemi.  1,  347 
(1904);  Ber.  39,  39  (1906),  and  ibid.  39,  45  (1906).     W.  Loeb:  Z.  Elektrochem.  11,  745 
(1905). 

3  Trehoux:  Flora,  73  (1903). 

4  R.  Bouillac:  Compt.  rend.  135,  1369  (1902).     Bouillac  and  Giustiniani:  ibid.  136, 
1155  (1903). 


58  LECTURE  IV. 

fact,  O.  Ruff  has  shown.1  He  prepared  d-gluconic  acid  by  the  oxida- 
tion of  d-glucose;  its  calcium  salt  he  allowed  to  stand  in  the  sunlight  in 
the  presence  of  ferric  acetate,  or  he  treated  it  with  hydrogen  peroxide 
and  thus  obtained  d-arabinose. 

CHO                           CO.OH  CHO 

HCOH  HCOH  HOCH 

HOCH  HOCH  HCOH 

HCOH  HCOH  HCOH 


HCOH  HCOH 

CH2OH  CH2OH  CH2OH 

d-glucose  d-gluconic  acid  d-arabinose 

At  all  events,  —  and  this  is  of  great  importance,  —  we  can  explain 
chemically  without  difficulty  the  formation  of  the  different  members  of 
the  carbohydrate  series  from  the  hexoses,  especially  d-glucose. 

Emil  Fischer2  has  suggested  that  the  glycerose  discovered  by  him  is 
perhaps  the  first  assimilation  product  of  carbonic  acid  by  the  plant  cells 
containing  chlorophyll.  By  the  combination  of  two  molecules  of  this,  it 
is  easy  to  understand  how  hexoses  may  be  formed.  Again,  glycerose  may 
be  of  great  importance  in  other  relations.  We  shall  mention  here  merely 
the  fact  that  it  is  closely  related  to  glycerol,  which  is  one  of  the  components 
of  the  fats;  and  on  the  other  hand,  that  from  this  point  of  the  carbon  dioxide 
assimilation  the  synthesis  of  albumin  may  start.  Glycerose,  as  we  shall 
show  more  fully  later  on,  stands  in  close  relation  to  certain  of  the  decom- 
position products  of  albumin,  namely  alanine,  serine,  and  cystine.  Naturally 
it  does  not  necessarily  follow  that  either  the  formation  of  the  fats  or  that 
of  the  proteins  must  begin  with  this  hypothetical  product  of  assimilation. 
It  is  indeed  possible  that  glycerose  appears  merely  as  one  of  the  decom- 
position products  of  d-glucose  or  starch,  and  then  is  used  for  syntheses 
by  the  plant  cell. 

All  of  these  possibilities  have  been  brought  forward  in  order  to  bring 
the  ground-plan  of  the  whole  carbon  assimilation  at  least  within  the  realms 
of  our  understanding,  and  to  show  the  far-reaching  value  that  purely 
chemical  investigations,  especially  those  of  Emil  Fischer,  have  upon  the 
science  of  biology;  for  it  is  by  this  means  only  that  the  most  important 
classes  of  substances  —  carbohydrates,  fats  and  proteins  —  have  been 
traced  back  to  a  common  source.  The  consideration  of  these  relations  is 


1  Ber.  31,  1573  (1898);  32,  550  (1899).     Otto  Ruff  and  Ollendorf:  ibid.  33,  1798 
(1900).     Cf.  A.  Wohl:  ibid.  26,  730  (1893) ;  33,  3666  (1899). 
3  Ber.  23,  2138  (1890). 


CARBOHYDRATES.  59 

of  great  importance;  and  a  detailed  discussion  is  justifiable,  furthermore, 
because  it  is  very  probable  that  also  in  the  animal  organism  chemical 
changes  take  place  by  means  of  which  a  substance  belonging  to  one  class 
is  changed  into  a  compound  of  another,  as,  for  example,  a  fat  into  a  car- 
bohydrate or  conversely. 

The  animal  organism  is,  in  its  entire  existence,  dependent  upon  this 
carbonic  acid  assimilation  by  the  plants,  for  in  this  way  it  obtains  all  the 
organic  compounds  of  complicated  structure.  Energy  originating  in  the 
sun  is  thus  obtained  by  the  animal  in  the  form  of  potential  energy,  from 
which  the  animal  derives  its  kinetic  energy  and  ability  to  perform  work. 
The  assimilation  by  the  plant  not  only  serves  to  furnish  organic  material 
for  the  animal  organism,  but  to  a  certain  extent  it  furnishes  the  oxygen 
which  it  requires  for  obtaining  the  kinetic  energy  again  by  combustion; 
the  assimilation  process  being  one  of  reduction  in  which  oxygen  is  con- 
stantly being  evolved.  The  oxygen  in  this  way  returns  to  the  general 
cycle  of  the  elements.  This  oxygen,  after  taking  part  in  the  metabolism 
of  the  animal,  escapes  chiefly  as  carbon  dioxide  and  water,  both  of  which  are 
again  utilized  by  the  plant  for  the  formation  of  other  organic  substances. 

Let  us  turn  now  to  those  carbohydrates  which  are  most  important  as 
food  for  the  animal  organism,  namely,  grape-sugar,  cane-sugar,  and  starch. 
From  the  last  two  compounds  the  animal  obtains  all  the  carbohydrates 
that  it  needs.  Let  us  follow  these  sugars  on  their  way  through  the  ali- 
mentary canal  to  their  absorption  and  final  assimilation.  As  an  example, 
we  shall  choose  starch,  because  it  is  here  that  the  relations  are  the  most 
complicated,  and  we  shall  be  able  to  treat  of  the  behavior  of  the 
simpler  sugars  in  connection  with  the  separate  phases  in  the  breaking 
down  of  the  starch. 

First   of   all  starch  —  or,  strictly  speaking,  the   food   containing  it  — 
is  ground  up  with  the  saliva  by  the  act  of  chewing.     The  saliva  con- 
tains a  diastatic  ferment,  ptyalin,1  which  converts  the  starch  into  dextrins 
and  finally  largely  into  maltose.2     The  latter  is  inverted  by  means  of  a 

1  Ptyalin  is  not  found  in  the  saliva  of  all  animals,  e.g.,  that  of  the  carnivora.     It 
would  be  well  to  drop  the  name  ptyalin  as  it  tends  to  give  one  the  impression  that 
there  is  only  one  ferment  found  in  the  saliva.      At   present  we  know  only  of   its 
action,  which  coincides  with  that  of  various  other  ferments  found  in  the  animal  and 
vegetable  kingdoms.     It  is  better,  therefore,  to  speak  of  a  diastatic  or  amylolytic  fer- 
ment.   We  would  be  justified  in  using  a  special  name  for  the  ferment  of  unknown  com- 
position only  when  it  has  an  unusual  action;  thus,  for  example,  if  the  diastase  in  saliva 
led  to  different  cleavage-products  of  starch  than  do  the  ferments  of  other  origin. 

2  The  earlier  assumption,  that  glucose  is  formed  directly,  has  been  shown  to  be  false. 
Cf.  J.  Seegen:  Zent.  med.  Wissensch.  14,  849  (1876),  and  Pfliiger's  Archiv.    19,  106 
(1879).     Otto  Nasse:  ibid.  14,  473  (1877).      Musculus  and  v.  Mering  :  Z.  physiol. 
Chem.  1,  395  (1877-78).     Ibid.  2,  403  (1878-79);  ibid.  4,  93  (1880).    von  Mering:  ibid. 
5,  185  (1881).     Brown  and  Heron:  Ann.  199,  165  (1879);  204,  228  (1880).     Kiilz  and 
Vogel:  Z.  Biol.  31,  108  (1895). 


60  LECTURE  IV. 

special  ferment,  called  glucase  (or  maltase).1  This  last  action  plays  a 
subordinate  part  in  the  total  action  of  the  saliva.  The  transformation 
of  the  starch  past  the  dextrin  stage  into  maltose  does  not  take  place  so 
simply  as  might  seem  possible.  A  great  many  intermediate  products  have 
been  described.  At  present  there  is  no  reason  for  going  into  the  details  here, 
partly  because  we  are  not  sure  whether  some  of  these  products  are  single 
substances,  or  mixtures  of  several  constituents. 

The  human  saliva,  or  rather  the  amylolytic  ferment  contained  in  it, 
does  not  attack  raw  starch  to  any  extent.  In  almost  every  case  the 
starch  has  already  undergone  a  process  of  change  which  greatly  facil- 
itates the  action  of  the  diastase  upon  it.  In  most  cases  the  starch  has 
been  cooked,  which  swells  the  grains.  The  fact  that  this  is  favorable  to 
the  action  of  the  diastase  can  be  easily  shown  by  the  following  experiment : 
In  one  test-tube  a  few  grains  of  ordinary  starch  are  mixed  with  saliva, 
while  in  another  the  same  saliva  is  allowed  to  act  for  an  equal  length  of 
time  upon  starch  paste.  If  at  the  end  of  a  certain  length  of  time  iodine  is 
added  to  test  for  unchanged  starch,  a  much  stronger  coloration  will  be 
obtained  in  the  first  tube  than  in  the  second.  If,  on  the  other  hand,  we 
test  for  the  sugar  2  formed,  we  shall  this  time  obtain  a  better  test  in  the 
other  test-tube. 

Leaving  the  mouth,  the  starch,  together  with  some  of  its  transformation 
products,  all  intimately  mixed  with  the  saliva,  reaches  the  stomach. 
For  a  long  time  it  was  believed  that  the  action  of  the  diastase  quickly 
stopped  here  on  account  of  the  acid  reaction  of  the  contents  of  the  stomach. 
Free  hydrochloric  acid  is  especially  unfavorable  to  the  action  of  diastase; 
as  little  as  0.03  per  cent  prevents  it  from  changing  starch  into  sugar. 
Recent  experiments3  have  shown,  however,  that  the  food  reaching  the 
stomach  is  not  immediately  mixed  with  the  gastric  juice  as  was  formerly 
assumed,  but  on  the  contrary  lies  out  of  contact  with  this  for  some  time. 
In  the  stomach  itself  there  has  not  been  found  any  agent  capable  of  con- 
verting carbohydrates  into  sugar,4  but,  on  the  other  hand,  a  not  incon- 
siderable absorption  of  the  simple  sugar  formed  is  known  to  take  place 
here. 

The  main  digestion  of  carbohydrates  is  effected,  however,  in  the  intes- 
tine by  the  action  of  a  diastase  from  the  pancreas.  By  means  of  it  the 
starch  —  which  for  the  greater  part  is  still  unchanged,  or  at  least  only  very 


1  M.  C.  Tebb:  J.  Physiol.  15,  421   (1894).     Hamburger:  Pfliiger's  Archiv.  60,  543 
(1895). 

2  Naturally,  the  saliva,  starch,  and  starch  paste  should  be  examined  for  sugar  at  the 
start. 

3  P.  Grutzner:  Pfliiger's  Arch.  106,  463  (1905). 

4  According  to  H.  Friedenthal,  the  stomach  juices  of  a  dog  contain  a  ferment  which 
acts  strongly  in  acid  solutions.     Archiv.  (Anat.  und)  Physiol.  1899,  Suppl.  383. 


CARBOHYDRATES.  61 

incompletely  broken  down  —  is  now  acted  upon  completely,  and  in  fact 
intermediate  products  are  formed  which  are  similar  to,  if  not  identical 
with,  those  produced  by  the  saliva.  The  cleavage  produced  by  the  pan- 
creatic diastase  is  believed  to  yield  finally  only  maltose.  This  last,  by  the 
action  of  a  particular  ferment,  gliLcase  (also  called  maltase) ,  is  eventually 
decomposed  into  molecules  of  d-glucose.  Here  in  the  intestine  the  breaking 
down  of  cane-sugar  also  takes  place  for  the  most  part.  By  means  of  the 
above-mentioned  ferments,  or  at  least  by  similar  ones,1  it  is  similarly 
inverted  into  its  two  components,  dextrose  and  laevulose  (d-glucose  and 
d-fructose).  In  this  way  the  carbohydrates  in  the  food  are  prepared 
for  absorption,  which  sets  in  as  fast  as  the  breaking  down  of  the 
carbohydrates  takes  place. 

We  must  now  touch  upon  the  question  as  to  whether  the  more  com- 
plicated carbohydrates,  such  as  the  dextrins,  for  example,  are  capable 
of  direct  absorption.  Under  normal  conditions  these  substances  are  not 
taken  up  by  the  intestine,  or  at  least  such  products  are  not  met  with 
beyond  the  intestines  in  the  assimilatory  tracts.2  Cane-sugar  and  mal- 
tose can  be  absorbed  directly.  They  are  taken  up  more  slowly  than  the 
simpler  sugars,  and  in  every  case  they  must  suffer  cleavage  before  they 
are  turned  over  to  the  blood;  for  if  cane-sugar,  avoiding  the  intestinal 
canal,  is  introduced  directly  into  the  blood,  it  suffers  no  further  change, 
but  is  eliminated  as  such  in  the  urine.3 

The  most  important  result  of  the  successive  changes  which  take  place  in 
the  intestinal  canal  as  regards  the  carbohydrates  which  we  have  studied 
up  to  this  point,  is  the  tendency  to  form  by  the  action  of  a  definite  ferment 
the  simplest  building  material,  especially  the  hexoses,  thus  giving  to  the 
system  a  uniform  material  from  which  it  can  construct  the  substances  of 
which  the  body  is  composed.  It  is  evident  from  what  has  been  said  that 
the  significance  of  the  alimentary  canal  and  of  all  the  different  organs 
connected  with  it  does  not  consist  solely  in  transforming  the  non-diffusible 
substances,  which  cannot  be  absorbed,  such  as  starch,  into  products 
which  are  diffusible.  Its  task  stretches  far  beyond  this  single  action.4 
The  molecules  which  are  naturally  foreign  to  the  animal  organism 
are  destroyed  and  converted  into  a  homogeneous  indifferent  material 

1  It  is  probable  that  the  same  ferment  does  not  act  upon  both  maltose  and  cane- 
sugar.     Cane-sugar  is  not  split  up  beyond  the  intestine,  while  maltose  appears  as  a 
product  from  glycogen  and  is  inverted. 

2  Von  Mering  (Arch.  f.  anat.  und  Physiol.  1877,  379,    413)  has  found  substances 
similar  to  dextrin  in  the   blood   of  the  portal  vein  after  a  diet  very  rich  in   carbo- 
hydrates.    It  has  not  been  shown  whether  this  is  a  normal  occurrence. 

3  Cf.  Fritz  Voit:  Deut.  Arch.  klin.  Med.  58,  523  (1897).     Ernst  Weinland:  Z.  Biol. 
47,  279  (1905). 

4  Cf.    Emil    Abderhalden:    Zentrb.    Stoffwechs.    Verdauungskrankheit,  6,  No.  24, 
647  (1904). 


62  LECTURE  IV. 

from    which    the    organism    is   able   to   build    up   its   own    individual 
carbohydrates. 

Before  we  attempt  to  follow  the  simple  sugars  on  their  way  to  the 
organs,  or,  in  other  words,  to  study  the  course  taken  in  their  absorption,  we 
must  consider  what  takes  place  in  the  case  of  a  few  compound  carbo- 
hydrates which  form  an  important  part  of  our  food.  We  refer  to  milk- 
sugar  which  occurs  in  milk,  and  the  numerous  carbohydrates  other  than 
starch  that  are  obtained  in  vegetable  nutriment,  cellulose  especially. 
Milk-sugar  is  unquestionably  decomposed  into  its  components  while  in 
the  bowels  in  the  case  of  animals  accustomed  to  milk  nourishment,  espe- 
cially during  the  age  of  suckling.1  On  the  other  hand,  in  many  animals 
there  seems  to  be  no  ferment  present  in  the  whole  of  the  alimentary  canal 
which  is  capable  of  splitting  up  milk-sugar.  What  happens  to  milk-sugar 
in  such  cases  is  not  clear  to  us  at  present;  probably  it  is  further  decom- 
posed in  the  wall  of  the  canal.  The  question  as  to  the  utilization  of  car- 
bohydrate introduced  into  the  organism  in  the  form  of  cellulose  is  a  very 
important  one.  Cellulose  plays  no  part  at  all  in  the  nourishment  of  the 
carnivora,  and  it  is  also  unessential  in  the  case  of  the  omnivora,  whereas 
in  the  case  of  the  herbivora  a  not  inconsiderable  part  of  the  carbohydrates 
contained  in  their  nourishment  is  in  the  form  of  cellulose.  Now,  this 
compound  is  not  acted  upon  by  the  saliva,  nor  by  the  juices  of  the  stomach, 
pancreas,  or  intestine,  provided  we  leave  out  of  consideration  the  action 
of  bacteria  which  are  ever-present.  It  is  here  that  the  activity  of  certain 
micro-organisms  present  in  the  intestines  comes  into  play,  and  this  forms 
to  some  extent  an  example  of  symbiosis.  The  fact  that  cellulose  is  actually 
subject  to  a  transformation  in  the  bowels  is  proved  by  our  being  unable 
to  find  in  the  fseces  the  whole  amount  of  cellulose  which  has  been  introduced 
into  the  system.2  Outside  of  the  organism,  it  has  been  found  possible  to 
dissolve  as  much  as  seventy  per  cent  of  cellulose  by  means  of  the  intestinal 
juices  from  a  horse;  these  are  rich  in  bacteria.3  Sugar  is  not  formed  by 
this  process,  but  a  considerable  amount  of  gas  is  evolved.  The  mixture 
produced  by  the  decomposition  has  an  acid  reaction.  These  products 
have  been  studied  by  Tappeiner.4  He  found  that  by  the  action  of  meat 


1  Cf.  Rohmann  and  Nagano:    Pfliiger's  Arch.  95   60  (1903);    Ernst  Weinland:    Z. 
Biol.  38,  16,  and  606  (1899);  40  (1900). 

2  The  food-value  of  cellulose  has  not  been  determined  definitely  even  as  regards  the 
herbivora.     Cf.  the  following  articles:  —  W.  Henneberg  and  F.  Stohmann:  "  Beitriige  zu 
einer  rationellen  Fiitterung  der  Wiederkauer,"  Braunschweig,  1860  and  1864.     Z.  Biol. 
21, 613  (1885).     v.  Knieriem:  ibid.  21,  67  (1885).     Weiske,  Schulze,  and  Flechsig:  ibid. 
22,  373  (1886).     E.  Wolff:  Landwirtsch.  Jahrbucher,  49,  Suppl.  Ill  (1887).     N.  Zuntz: 
Pfliiger's  Arch.  49,  477  (1891). 

3  Viktor  Hofmeister:  Arch,  wissensch.  und  prakt.  Heilkunde,  11,  1  and  2  (1885). 

4  Z.  Biol.  20,  52  (1884) ;  24,  105  (1888) ;  and  Hoppe-Seyler:  Z.  physiol.  Chem.  10,  401 
(1886). 


CARBOHYDRATES.  63 

extract  which  he  had  inoculated  with  bacteria  from  the  contents  of  the 
paunch  upon  absorbent  cotton-wool,  the  following  products  were  formed: 
carbonic  acid,  methane,  and  fatty  acids  (acetic,  butyric,  and  valeric 
acids).  It  is  perfectly  possible  that  the  breaking  down  of  the  cellulose 
takes  place  similarly  in  the  intestinal  canal.  The  behavior  of  cellulose 
here  has,  however,  never  been  entirely  explained.  It  is  also  possible  that 
perhaps  only  a  portion  of  the  cellulose  is  decomposed  in  this  way,  while 
another  portion  may  be  acted  upon  differently  perhaps  by  means  of  the 
epithelium  of  the  canal  itself,  being  transformed  in  such  a  way  that  it  can 
be  absorbed.  Not  only  the  herbivora  are  capable  of  utilizing  cellulose,  but 
the  omnivora  can  make  use  of  it  at  least  to  some  extent.  The  investiga- 
tions of  v.  Knieriem  have  shown  that  the  human  intestine  is  capable  of 
dissolving  a  part  of  the  tender  cellulose  from  young  vegetables.  As  much 
as  forty  per  cent  of  the  cellulose  introduced  into  the  system  could  not 
be  detected  in  the  faeces.1 

Cellulose,  especially  in  animals  possessing  a  long  intestine,  —  chiefly 
the  herbivora,  but  also  the  omnivora,  —  plays  still  another  characteristic 
part,  as  the  following  experiments  show.  If  rabbits  are  fed  with  food 
containing  no  cellulose,  they  soon  die.  This  is  due  to  the  fact  that 
when  cellulose  is  left  out  of  the  nourishment  the  intestine  no  longer  expe- 
riences a  certain  mechanical  irritation  to  which  it  has  become  accustomed. 
On  this  account  the  peristalsis  becomes  retarded,  then  the  contents  of  the 
intestines  accumulate,  whereby  putrefaction  ensues,  and  eventually  there 
is  inflammation  of  the  bowels.  That  this  explanation  is  correct,  is  shown 
by  the  fact  that  the  animals  experimented  with  continue  to  live,  if,  instead 
of  the  cellulose,  the  animals  are  fed  with  horn  shavings  which  are  perfectly 
indigestible.2 

The  bacteria  contained  in  the  stomach  and  intestines  attack  not  only 
cellulose  but  other  carbohydrates  as  well.  For  this  reason,  the  breaking 
down  of  the  more  complicated  carbohydrates  does  not  actually  take  place 
so  simply  as  has  been  depicted.  On  the  other  hand,  the  decomposition 
brought  about  by  means  of  bacteria  is,  in  general,  not  very  extensive,  and 
depends  very  much  upon  the  external  conditions.  The  products  formed  by 
their  action  are  chiefly  lactic  acid,  formic  acid,  acetic  acid,  butyric  acid,  and 
alcohol  with  evolution  of  carbon  dioxide,  hydrogen,  and  methane.8  There 
are,  furthermore,  other  micro-organisms  known,  as,  for  example,  Bacterium 4 
thermo,  which  break  down  starch  in  very  much  the  same  way.  as  this  is 
accomplished  by  the  diastase  in  saliva  and  pancreas,  thus  aiding  the 
conversion  of  amylum  into  sugar. 


1  Loc.  tit. 

2  von  Knieriem:   loc.  cit. 

3  Cf.  H.  Tappeiner:  Z.  Biol.  19,  228  (1883). 

4  J.  Wortmann:  Z.  physiol.  Chem.  6,  287  (1882). 


64  LECTURE  IV. 

The  question  has  often  been  raised  as  to  whether  the  micro-organisms 
of  the  alimentary  canal  are  absolutely  necessary  for  the  perfect  digestion 
of  the  food,  or  whether  they  should  be  regarded  as  true  parasites.  To 
decide  this  point,  Nuttall  and  Thierf elder 1  have  made  the  following  experi- 
ment: By  Caesarean  section,  they  removed  guinea  pigs  from  the  uterus 
of  the  mother  shortly  before  their  normal  birth,  taking  most  careful  anti- 
septic precautions,  and  placing  them  in  a  sterilized  cage.  Guinea  pigs, 
unlike  most  of  the  related  animals,  come  into  the  world  in  such  a  developed 
state  that  they  are  able  to  assimilate  properly  the  food  of  the  adult.  It 
was  found  possible,  as  proved  by  later  examination,  to  keep  these  little 
pigs  perfectly  sterile  during  the  entire  experiment  (eight  days)  and  to  feed 
them  with  sterile  food,  crackers  and  milk,  in  a  sterile  environment.  The 
animals  experimented  with  gained  in  weight  normally,  thus  proving  that 
the  animal  organism  could  thrive  when  bacteria  were  absent.  These 
experiments  were  especially  valuable  because  they  were  performed  with 
animals  which  are  particularly  likely  to  be  infested  with  bacteria  from 
their  vegetable  food.  It  may  be  said,  on  the  other  hand,  however,  that 
the  experiment  merely  shows  that  guinea  pigs  can  subsist  upon  crackers 
and  milk  in  the  absence  of  bacteria,  but  it  does  not  necessarily  follow  that 
the  result  would  have  been  the  same  if  a  food  rich  in  cellulose  had  been 
fed  them. 

Schottelius  2  has  arrived  at  quite  different  results  from  those  of  Nuttall 
and  Thierf  elder.  He  chose  for  his  experiments  chickens  which  were 
hatched  under  sterile  conditions,  kept  in  sterile  places,  and  fed  with  sterile 
food.  These  animals,  although  they  ate  abundantly,  had  continuous 
hunger,  and  declined  about  as  quickly  as  a  starving  animal.  As  soon  as 
bacteria  from  hen  faeces  were  mixed  with  the  food  the  animals  revived  and 
increased  in  weight.  Recently  Moro  3  has  carried  out  similar  experiments 
with  the  larvae  of  the  mud-frog  (Pelobates  juscus).  He  was  able  to  keep 
them  sterile  for  thirty-six  days.  It  was  found,  however,  that  if  the  sterile 
larvae  were  placed  in  water  containing  the  faeces  of  the  mother,  the 
increase  in  weight  and  general  development  was  much  more  rapid  than 
was  the  case  with  larvae  kept  sterile. 

In  discussing  the  carbohydrates  we  have  mentioned  the  fact  that  the 
five-carbon  sugars,  the  pentoses  or  their  condensation  products  the  pen- 
tosans  which  are  so  widely  distributed  in  the  vegetable  kingdom,  are  not 
unimportant  forms  of  nutriment,  especially  in  the  case  of  the  herbivora. 
The  researches  of  Stone  4  and  of  Weiske  5  have  shown  that  the  herbivora 


Z.  physiol.  Chem.  21,  109  (1895-96);  22,  62  (1896-97). 

Arch.  Hyg.  34,  210  (1899),  and  42,  48  (1902). 

Jahrb.  fur  Kinderheilkunde,  62,  H.  4  (1905). 

Am.  Chem.  J.  14,  9  (1902). 

Z.  physiol.  Chem.  20,  489  (1895). 


CARBOHYDRATES.  65 

can  utilize  up  to  fifty  or  sixty  per  cent  of  the  pentosans  contained  in 
vegetables.  In  these  experiments  a  mixture  of  pentosans  (araban, 
xylan,  methylpentosan)  was  fed  to  the  animals,  but  recently  Slowtzow  l 
has  fed  pure  xylan  to  rabbits.  In  the  excreta  from  17.1  to  66.8  per  cent 
of  the  pentosans  were  found  in  an  unchanged  condition.  The  remainder 
was  undoubtedly  utilized  in  the  system  after  having  been  converted  into 
the  simpler  sugars  (pentoses) . 

From  the  intestine  on,  the  simple  sugars  (e.g.,  d-glucose)  are  quickly 
absorbed,  whether  introduced  into  the  system  in  this  form,  or  obtained 
from  the  destruction  of  more  complicated  sugars.  There  are  two  ways  in 
which  the  nutriment  absorbed  by  the  intestine  can  reach  the  general  cir- 
culation. In  the  first  place  it  can  enter  directly  by  means  of  the  blood-ves- 
sels, in  this  case  the  branches  of  the  portal  vein.  This  is  the  path  taken  by 
salts,  carbohydrates,  and  proteins.  In  this  way  they  reach  the  liver,  there 
to  undergo  certain  important  transformations,  after  which  they  are  capable 
of  being  introduced  into  the  general  circulation  of  the  blood.  The  second 
path  is  by  way  of  the  lymphatics,  which  conduct  the  absorbed  sub- 
stances, especially  the  fats,  into  the  thoracic  duct,  from  which  they  are  led 
into  the  Vena  anonyma,  and  thus  into  the  general  circulation. 

The  experiments  showing  that  the  absorption  of  carbohydrates  as  a 
matter  of  fact  takes  place  in  the  first  manner  will  be  discussed  later  when 
we  come  to  consider  the  absorption  of  fats. 

In  order  to  get  some  idea  of  the  process  by  means  of  which  sugar  is 
transferred  to  the  circulatory  system,  and  in  order  to  understand  how 
large  amounts  of  carbohydrates,  e.g.  500  grams,  can  be  transferred  in  a 
relatively  short  time  to  the  blood-stream  (especially  into  the  portal  vein) 
without  materially  increasing  the  sugar  content  of  the  blood,  we  must 
remember  what  an  enormous  surface  for  absorption  is  presented  by  the 
extremely  fine  network  of  blood-capillaries.  Absorption  takes  place 
continuously  hand  in  hand  with  the  breaking  down  of  the  more  com- 
plicated carbohydrates  into  simpler  sugars.  Although  the  tiny  molecules 
of  sugar  are  absorbed  at  thousands  of  places  and  pass  into  the  blood,  and 
although  they  are  immediately  carried  away,  it  would  seem  that  there 
must  be  an  increase  in  the  amount  of  sugar  contained  in  the  blood  corre- 
sponding to  the  amount  absorbed.  That  this  is  not  the  case  —  the  normal 
amount  of  sugar  is  0.5  to  1.5  grams  per  liter  and  remains  constant  —  must 
be  due  to  the  fact  that  sugar  is  removed  from  the  blood  to  the  same  extent 
that  it  is  absorbed  by  it.  This  is,  as  a  matter  of  fact,  exactly  what  hap- 
pens, and  it  is  the  liver  which  regulates  the  exchange  of  carbohydrates  in 
the  whole  animal  system.  It  intercepts  the  absorbed  sugar,  and  keeps  the 
sugar  content  in  the  blood  constant.  By  means  of  the  activity  of  the 


1  Z.  physiol.  Chem.  34,  181  (1901).     See  also  Rudzinski :  ibid.  40,  317  (1904). 


66  LECTURE  IV. 

liver  cells,  the  molecules  of  d-glucose  are  made  to  unite  together  again 
with  loss  of  water  and  the  formation  of  a  new  polysaccharide,  glycogen. 
In  making  this  transformation  the  animal  organism  acts  precisely  like  the 
plant  in  forming  cellulose,  the  circulating  sugar  being  removed  from 
metabolism,  stored  up  and  protected  from  combustion  in  such  a  way 
that  at  any  given  moment  it  can  be  made  "  liquid  "  again.  This  stage 
in  the  metabolism,  of  carbohydrates  in  the  animal  system  can  be  demon- 
strated very  simply  by  means  of  the  following  experiment:  A  number 
of  rabbits  may  be  kept  from  food  for  a  length  of  time  until  it  is  known 
as  a  matter  of  experience  that  the  glycogen  content  of  the  organs,  espe- 
cially the  liver,  has  been  brought  as  low  as  possible.  This  is  the  case  at 
the  end  of  about  ten  days.  As  we  shall  see  later  on,  the  consumption  of 
glycogen  can  be  accelerated  greatly  by  muscular  work  (whether  by  actual 
body  work  —  e.g.  dogs  running  in  a  tread-mill  —  or  by  muscular  convul- 
sions produced  by  strychnine  poisoning),  and  thus  the  time  required  for 
the  experiment  greatly  shortened.  A  part  of  the  animals  experimented 
upon  are  then  fed  with  a  diet  rich  in  carbohydrates.  If  now  all  the 
animals  are  killed,  those  that  are  starving  as  well  as  those  which  have 
been  recently  fed  and  are  in  the  act  of  digesting  the  food,  the  former, 
when  subjected  to  quantitative  tests,  will  be  found  to  contain  only 
traces  of  glycogen  in  the  liver,  whereas  the  latter  will  contain  a  large 
amount.1  This  state  of  affairs  is  of  regular  occurrence,  so  that  to-day 
there  is  scarcely  any  one  who  doubts  that  there  is  a  direct  connection 
between  the  carbohydrates  taken  up  (the  absorbed  d-glucose)  and  the 
glycogen.2  The  fact  that  the  liver  actually  forms  glycogen  directly  from 
sugar  has  been  demonstrated  recently  by  Karl  Grube.3  Grube  passed  blood 
rich  in  sugar  through  the  liver  of  a  dog,  and  could  detect  a  slight  increase 
in  the  liver-glycogen.  It  is  another  question  as  to  whether  all  carbo- 
hydrates, for  example,  the  pentoses,  are  capable  of  forming  glycogen  in 
this  way.  We  shall  later  on  take  up  this  point  more  in  detail,  but  at  this 
place  it  is  of  interest  for  us  to  know  merely  how  the  more  important  carbo- 
hydrates in  food,  namely,  starch,  cane-sugar,  and  grape-sugar,  behave  in 
this  respect.  Starch,  as  we  have  already  seen,  is  decomposed  eventually 
into  molecules  of  d-glucose,  and  the  same  is  true  of  saccharose.  From  the 
latter,  however,  not  only  d-glucose  but  an  equal  amount  of  d-fructose  is 
formed,  the  latter  being  a  ketohexose.  The  question  that  now  arises  is, 

1  Cf.  F.  W.  Pavy:  Phil.  Transact,  for  1860,  p.  579,  and  Researches  on  the  Nature  and 
Treatment  of  Diabetes,  London,  1862.     Also  The  Physiology  of  Carbohydrates,  1894. 
See  also  Pfluger's  Das  Glycogen  und  seine  Beziehung  zur  Zuckerkrankheit,  and  Cremer's 
Physiologic  das  Glykogens,  Ergeb.  Physiol.  (Asher  u.  Spiro)  1,  p.  803  (1902.) 

2  Carl  Voit  has  furthermore  shown  that  subcutaneous  introduction  of  d-glucose  into 
rabbits  caused  an  increase  of  up  to  eight  per  cent  glycogen  in  the  liver.     Z.  Biol.  28, 
245,  288  (1891).     See  also  Erwin  Voit:  Z.  Biol.  25,  551  (1889). 

3  Pfliiger's  Arch.  107,  490  (1905). 


CARBOHYDRATES.  67 

Does  the  latter  become  changed  into  glycogen,  does  it  form  a  particular 
glycogen  of  its  own,  or  is  the  fructose  first  changed  into  d-glucose,1  and 
then,  in  common  with  the  other  glucoses,  changed  to  glycogen?  Until 
recently  it  was  quite  generally  assumed  that  the  last-mentioned  process 
was  carried  out,  but  now  certain  facts  have  become  known  which  will 
perhaps  lead  us  to  another  conception.  It  has  been  established  that, 
after  the  extirpation  of  the  pancreas  in  dogs,  not  only  does  sugar  appear 
in  the  urine,  but  at  the  same  time  the  formation  of  glycogen  in  the  liver  is 
interfered  with,  and  as  a  matter  of  fact  this  disturbance  is  much  more 
pronounced  when  rf-glucose  is  fed  to  the  dog  than  in  the  case  of  fructose. 
The  exact  significance  of  this  result  is  at  present  not  clear. 

When  the  food  is  rich  in  carbohydrates  the  liver  cannot  retain  all  of 
it  as  glycogen.  The  glycogen  stored  in  the  liver  of  man  amounts  at  the 
most  to  150  grams.  The  muscles  can  take  up  an  equal  amount  provided 
they  did  not  originally  contain  considerable.  As  this  is  often  the  case 
under  normal  conditions,  however,  we  must  answer  the  question  as  to 
what  becomes  of  the  sugar  which  is  not  disposed  of  as  glycogen.  A  direct 
consumption  of  large  amounts  of  sugar  is  not  to  be  thought  of;  and  on  the 
other  hand  the  sugar  content  of  the  organs,  and  of  the  blood  especially, 
never  exceeds  certain  well-established  limits  when  the  storage  places  for 
glycogen  have  been  filled.  Here  for  the  first  time,  we  meet  with  the 
question  of  the  transformation  of  one  food-stuff  into  another.  Sub- 
sequently we  shall  have  to  study  this  closely,  but  at  present  we  will  merely 
mention  that  the  excess  of  sugar  is  evidently  disposed  of  as  fat,  a  phenom- 
enon which  we  meet  with  in  the  vegetable  kingdom,  and  one  which  plays 
an  important  part  in  the  depositing  of  nutriment  in  latent  seeds,  and 
conversely  in  its  utilization  at  the  time  of  germination. 

Now  what  becomes  of  this  stored-up  glycogen?  As  we  have  seen,  the 
glycogen  gradually  disappears  if  nourishment  is  withheld  or  work  is 
performed.  It  was  Claude  Bernard  2  who  first  showed  this  relation  between 
glycogen  and  muscular  work.  He  found  that  the  livers  of  hibernating  ani- 
mals during  their  winter's  sleep  contained  large  amounts  of  glycogen,  and 
not  only  was  the  glycogen  contained  in  the  liver  cells,  but  also  in  the 
muscular  tissue  and  in  the  lungs.  As  soon  as  the  animals  awoke  and 


1  Such  a  transformation  is  explained  to  us  by  the  work  of  C.  A.  Lobry  de  Bruyn  and 
W.  Alberda  van  Ehenstein,  Ber.  28,  3078  (1895),  and  Rec.  trav.  chim.  14,  103,  156. 
These  two  authors  have  shown  that  glucose,  fructose,  and  mannose  can  be  easily  trans- 
formed into  one  another  in  alkaline  solution.     The  transformation  of  mannose  into 
glucose  is  equally  interesting  as  that  of  fructose  into  glucose,  for  the  former  is  used 
as  material  for  the  formation  of  glycogen.     Thus  in  Japan  a  natural  manna  is  found 
which  serves  the  inhabitant  in  the  same  way  as  starch  does  for  us.     Cf.  Low  and  Tsuji: 
Landwirtschaftliche  Versuchstationen,  45,  433.     Also  Haycraft:  Z.  physiol.  Chem.  19, 
137  (1894). 

2  Compt.  rend.  48,  673  (1859). 


68 


LECTURE  IV. 


began  to  move  about,  Bernard  noticed  that  the  glycogen  disappeared. 
He  furthermore  observed  that  when  the  muscular  tissues  of  well-nourished 
mammals  or  birds  were  at  rest  —  whether  voluntarily  so  or  as  a  result  of 
artificially  severing  the  nerves  in  them  —  the  glycogen  content  gradually 
increased,  only  to  disappear  again  when  the  muscles  were  set  at  work. 

Direct  experiments  were  carried  out  by  S.  Weiss.1  He  compared  the 
glycogen  content  of  a  frog's  hind  legs  of  which  one  had  been  tetanized 
almost  to  exhaustion  while  the  other  was  under  control  and  rested.  The 
glycogen  in  the  active  muscles  decreased  from  24.27  to  50.43  per  cent. 
Finally  Th.  Chandelon  2  has  carried  out  the  following  experiment:  In  a 
rabbit  he  severed  the  sciatic  and  crural  nerves,  and  at  the  end  of  from  2 
to  5  days  found  in  the  paralyzed  muscles  an  increase  in  glycogen  amount- 
ing to  from  5.51  to  172.4  per  cent.  Similarly  Marcuse 3  made  similar 
observations,  and  found  the  following  glycogen  values: 


EXPERIMENT. 

Per  cent  glycogen  in  the  — 

Unirritated    Muscles. 

Irritated  Muscles. 

I 

0.748 
0.749 
0.589 
0.542 

0.539 
0.461 
0.395 
0.341 

HI                                                               

IV                                                 

v                .          

Average      

0.657 

0.434 

Finally,  the  same  result  has  been  obtained  by  Edward  Klilz  4  in  another 
way.  He  caused  a  well-nourished  dog  to  draw  a  heavy  cart.  The  animal 
weighed  45.500  kilograms,  and  was  made  to  drag  the  cart  for  9  hours 
and  40  minutes.  The  dog  was  then  bled  to  death.  The  glycogen  deter- 
mination showed  the  presence  of  52.053  grams,  i.e.,  1.16  grams  per  kilogram 
of  the  dog's  weight.  A  well-nourished  dog  that  is  not  tired  shows  a 
glycogen  content  of  38  grams  per  kilogram.  For  comparison,  it  may  be 
mentioned  that  after  28  days  of  starvation  a  dog  of  about  the  same  size  as 
the  above-mentioned  showed  but  1.5  grams  of  glycogen  per  kilogram.  It 
is  evident,  therefore,  that  after  about  9§  hours  of  labor  the  glycogen  stores 
were  consumed  to  fully  as  great  an  extent  as  in  the  case  of  a  dog  starved 
for  28  days.  Kiilz  then  repeated  the  experiment  with  three  other  dogs  and 
with  the  same  result. 

A  further  confirmation  of  the  fact  that  the  carbohydrates  serve  as  an 
important  source  of  muscular  energy  is  shown  by  the  interesting  experi- 


1  Sitzber.  Akad.  Wiss.  Wien.  64,  Abt.  1. 

2  Pfliiger's  Arch.  13,  626  (1876). 

8  Pfluger's  Arch.  39,  425  (1886).     See  also  Edward  Manche,  Z.  Biol.  25,  163  (1889). 
4  Beitrage  zur  Kenntniss  des  Glykogens,  p.  41  (1891). 


CARBOHYDRATES.  69 

ment  of  Fick  and  Wislicenus.1  These  scientists  attempted  to  find  out 
what  substances  were  chiefly  decomposed  as  a  result  of  strenuous  mus- 
cular work.  At  that  time  Liebig's  2  theory  prevailed  that  the  muscles 
performed  work  at  the  cost  of  albuminous  substances,  and  they  decided 
to  test  this  experimentally.  If  Liebig's  theory  were  correct,  it  was  to  be 
expected  that  the  elimination  of  nitrogen  would  be  increased  as  a  result 
of  muscular  activity.  Fick  and  Wislicenus  climbed  Mount  Faulhorn,  1956 
meters  above  the  Lake  of  Brienz,  which  was  the  starting-point.  For  sev- 
enteen hours  before  the  start,  during  the  ascent  (which  required  six  hours), 
and  for  six  hours  following,  care  was  taken  to  eat  only  food  which  was  free 
from  nitrogen.  All  the  urine  passed  during  the  ascent  and  the  six  hours 
following  was  carefully  collected  and  the  nitrogen  accurately  determined. 
From  the  results  obtained  by  chemical  analysis  it  was  found  that  Fick  had 
decomposed  38.3  grams  of  albumin,  and  Wislicenus  37  grams.  These 
amounts  of  albumin  correspond  to  about  250  heat  units  in  each  case,  or 
106,000  kilograms  of  work.  If  we  estimate  the  actual  work  performed  in 
climbing  the  mountain  we  arrive  at  the  following  values.  Wislicenus 
weighed  76  kilograms.  By  simply  raising  this  weight  to  the  height  of  the 
mountain  peak,  76  X  1956  =  148,656  kilograms  of  work  was  performed. 
These  values  suffice  to  show  that  the  work  could  not  have  been  at  the  ex- 
pense of  albumin  alone.  This  fact  is  still  more  striking  when  we  remember 
that  the  above  value  of  albumin  in  heat  units  is  too  high,  for  it  is  based 
upon  the  assumption  that  the  carbon  is  completely  changed  to  CO2  and  the 
hydrogen  to  H2O.  Now,  as  a  matter  of  fact,  nowhere  near  this  amount  of 
energy  is  obtained  by  the  consumption  of  albumin  in  the  animal  organism, 
for  a  part  of  the  carbon,  some  of  the  hydrogen,  and  the  greater  part  of  the 
nitrogen,  are  eliminated  in  the  form  of  urea.  In  man,  the  amount  of  urea 
formed  is  as  a  rule  equal  to  one-third  the  weight  of  albumin  decomposed. 
Therefore  from  the  above  heat  value  of  albumin  we  must  deduct  one-third 
the  heat  of  combustion  of  the  same  weight  of  urea.  On  the  other  hand, 
as  a  matter  of  fact,  the  scientists  performed  much  more  work  than  we 
have  estimated.  Fick  and  Wislicenus  estimate  the  amount  of  work  per- 
formed by  their  circulatory  and  respiratory  apparatus  as  30,000  kilogram- 
meters.  Furthermore,  it  must  be  taken  into  consideration  that  in  every 
motion,  in  every  step,  work  is  performed  which  is  transformed  into  heat 
and  lost  as  far  as  the  work  performed  is  concerned.  According  to  Helm- 
holt  z,  only  one-fifth  of  the  actual  heat  of  combustion  is  transformed  into 
external  work.  It  is  perfectly  certain,  therefore,  that  we  can  safely  con- 
clude from  the  above  experiment  that  albumin  alone  is  not  the  source  of 
muscular  work,  but,  on  the  other  hand,  we  are  not  justified  in  concluding 

1  Vierteljahresschrift  des  Ziiricher  naturforschenden  Gesellsch.  10,  317  (1865). 
'  2  Chemische  Briefe  (1857).     Cf.  also  Ann.  163  1,  and  157  (1870);  C.  Voit:  Z.  Biol.  6, 
305  (1870);  Schenck:  Arch,  exper.  Path.  Pharm.  2,  21  (1874). 


70  LECTURE  IV. 

that  the  source  is  to  be  sought  entirely  in  substances  free  from  nitrogen. 
At  all  events,  however,  Liebig's  theory  is  untenable. 

It  remained  for  C.  Voit  *  to  establish  a  more  exact  proof  of  the  theory 
that  muscular  work  is  performed  chiefly  at  the  expense  of  substances  free 
from  nitrogen.  He  caused  a  dog  to  run  in  a  tread-mill,  and  compared  the 
amount  of  nitrogen  in  the  urine  which  was  passed  during  the  working 
period  with  that  passed  during  rest,  both  before  and  after  working.  It 
was  found  that  the  amount  of  nitrogen  eliminated  during  twenty-four 
hours  of  a  working  period  was  but  slightly,  if  at  all,  in  excess  of  that  elimi- 
nated during  the  resting  periods.  O.  Kellner  2  tried  a  similar  experiment 
with  horses,  and  obtained  the  same  results  when  the  animals  experi- 
mented upon  were  fed  with  an  abundance  of  carbohydrates.  If  this  was 
not  the  case,  the  amount  of  nitrogen  eliminated  was  considerably  more. 
Finally,  Voit 3  performed  corresponding  experiments  with  human  beings, 
and  determined  not  only  the  amount  of  nitrogen  eliminated,  but  at  the 
same  time  estimated  the  carbon  dioxide,  and  indirectly  the  absorption  of 
oxygen.4 

The  increased  absorption  of  oxygen  and  elimination  of  carbon  dioxide 
have  also  been  observed  in  direct  experiments  upon  the  muscles  themselves, 
by  comparing  the  amount  of  these  gases  contained  in  the  venous  blood  of 
a  resting  muscle  and  of  one  that  has  been  tetanized.5  The  inactive  muscle 
takes  up  more  oxygen  from  the  blood  than  it  gives  back  to  the  latter  in 
the  form  of  carbonic  acid  gas.  Obviously  the  muscular  cells  retain  oxygen 
in  some  form  or  other.  We  can,  in  fact,  speak  of  a  storing  up  of  oxygen. 
This  stored-up  oxygen  again  appears  after  violent  exercise,  for  then  the 
muscle  gives  up  to  the  blood  more  oxygen  as  carbon  dioxide  than  it  takes  up 
from  the  blood  as  free  oxygen.  Yet  it  is  also  true  that  the  muscle  takes 
up  more  oxygen  from  the  blood  during  exercise  than  in  periods  of  rest,  for 
venous  blood  contains  during  work  less  oxygen  and  more  carbonic  acid 
than  when  the  muscle  is  at  rest.  That  evidently  not  only  an  oxidation 
process  but  a  hydrolytic  decomposition  as  well  should  be  regarded  as  the 
source  of  muscular  work  will  be  shown  later. 

We  must  now  answer  the  question  as  to  how  the  glycogen  is  decom- 
posed and  in  what  way  it  is  utilized  in  muscular  work.  Furthermore, 
we  are  interested  to  know  what  connection  there  is  between  the  principal 

1  Z.  Biol.  2,  307  and  339  (1866). 

2  Landw.  Jahrb.  8,  701  (1879),  and  9,  651  (1880). 

3  Z.  Biol.  2,  307,  488  (1866). 

4  This  was  known  to  Lavoisier:    Seguin  and  Lavoisier:    Me"m.  acad.  Sciences,  688 
and  696  (1789).     See  also  Sonde"n  and  Tigerstedt:  Skand.  Arch.  Physiol.  6,  181  (1895). 
O.  Krummacher:   Z.  Biol.  33,  117  (1896)      Zuntz,  Frentzel,  and  Loeb:   Arch.   (Anat. 
und)  Physiol.  541  (1894).     Speck:  ibid.  465  (1895). 

5  Ludwig  and  Sczelkow:  Sitzber.  Akad.  Wiss.  Wien.  45,  171  (1862).     Max  v.  Frey  : 
Arch.  Anat.  Physiol.  533  (1885). 


CARBOHYDRATES.  71 

store  of  glycogen,  namely  liver-glycogen,  and  the  consumption  of  carbo- 
hydrates by  the  muscles.  According  to  all  our  experience  up  to  the 
present  time,  glycogen  is  not  directly  oxidized,  but  is  previously  decom- 
posed into  d-glucose.  This  is  shown  directly  by  the  experiments  of  J. 
Ranke  *  and  of  Otto  Nasse.2  The  former  examined  the  sugar  content  of 
the  hind  legs  of  a  number  of  frogs,  one  leg  being  tetanized  and  the 
other  at  rest.  Several  determinations  showed  0.058  per  cent  sugar  in 
the  dry  substance  of  the  resting  muscle,  and  0.082  per  cent  in  the  tetanized 
muscle.  The  sugar  content,  therefore,  was  increased  41  per  cent  in  the 
latter  case.  The  hydrolysis  of  glycogen  is  evidently  caused,  as  Magendie 3 
has  shown,  by  a  ferment  which  in  its  action  coincides  with  that  of  diastase, 
which  is  already  known  to  us.  In  the  liver  also  the  stores  of  glycogen  are 
decomposed  in  this  way.4  Here,  besides  d-glucose,  the  intermediate  products 
dextrin  and  maltose  have  been  detected.  They  are  probably  formed  in 
the  breaking  down  of  glycogen  in  the  muscles,  but  their  presence  has  never 
been  established  with  certainty.  The  fact  that  the  hydrolysis  of  glycogen 
in  the  liver  is  not  to  be  considered  as  a  result  of  the  activity  of  the  cells, 
but  rather  that  it  is  due  to  a  ferment  which  can  be  separated  from  the 
liver  cells,  was  clearly  shown  as  long  ago  as  1873  by  von  Wittich.5  He 
proved  that  it  was  possible  to  extract  by  means  of  glycerol  from  liver 
which  was  completely  freed  from  blood  and  hardened  by  alcohol  a  fer- 
ment which  was  capable  of  hydrolyzing  glycogen.  von  Wittich  showed 
that  this  ferment  belonged  to  the  liver  cells  rather  than  to  the  blood  by 
again  and  again  obtaining  the  diastatic  ferment  after  repeated,  thorough 
washings  of  the  liver.  It  is  also  possible,  as  Pavy  has  shown,  to  treat 
liver  with  alcohol,  dry  it,  and  preserve  it  indefinitely.  If  such  a  preparation 
is  digested  with  water,  the  diastatic  reaction  will  be  obtained  invariably. 
On  the  other  hand,  the  objection  may  be  raised  to  this  line  of  reasoning, 
that  the  formation  of  sugar  is  perhaps  due  to  the  action  of  micro-organisms, 
an  assumption  which  in  the  light  of  recent  experience  obtained  by  working 
with  organs  and  their  extracts  does  not  seem  improbable.6  E.  Salkowski,7 

Tetanus,  p.  168,  Leipsic,  1865. 

Pfliiger's  Arch.  2,  97  (1869). 

Compt.  rend.  23,  189  (1846). 

Musculus  and  v.  Mering:  Z.  physiol.  Chem.  2,  416  (1878-79).  E.  W.  Pavy:  The 
Physiology  of  Carbohydrates,  London,  1894.  Kiilz  and  Vogel:  Z.  Biol.  31,  108  (1895). 

Pfliiger's  Arch.  7,  28  (1873). 

For  an  explanation  of  the  other  view,  that  the  sugar  formation  from  glycogen  is 
caused  by  the  life  process  of  the  liver  cells,  see  M.  Foster:  Text-book  of  Physiology, 
appendix  by  Sheridan  Lea,  pp.  58,  98.  Noel  Paton:  Hepatic  Glycogenesis,  Trans.  Roy. 
Soc.  1894,  and  Phil.  Trans.  185  B,  233  (1894). 

7  Deut.  Med.  Wochschr.  No.  16,  1888;  Arch.  Physiol.  554  (1890);  Zent.  med.  Wis- 
sensch.  Jg.  27,  No.  13,  227  (1889).  See  also  Otto  Nasse:  Rostocker  Ztg.  No.  105  (1889). 
Salkowski:  Z.  klin.  Med.  p.  90  (1891),  and  Pfliiger's  Arch.  56,  339  and  351  (1894). 
Arthus  and  Huber:  Arch,  de  Physiol.  651  (1892). 


72  LECTURE  IV. 

however,  has  shown  that  this  sugar  formation  will  also  take  place  in 
chloroform  water.  Since  aqueous  solutions  of  chloroform  prevent  proto- 
plasmic action  including  the  action  of  micro-organisms,  this  experi- 
ment proves  that  the  formation  of  sugar  from  glycogen  is  not  due  to  the 
action  of  bacteria,  and  further  that  the  liver  cells  themselves  are  not  the 
cause,  but  that  the  hydrolysis  of  glycogen  is  to  be  traced  to  the  action  of 
a  soluble  ferment.  Salkowski  clearly  established  this  important  fact  by 
means  of  the  following  experiment:  He  removed  the  liver  from  a  rabbit 
which  had  taken  into  its  stomach  seventeen  hours  before  death  ten  grams 
of  cane-sugar  dissolved  in  water.  After  taking  out  the  gall  bladder  and 
the  large  bile  ducts,  the  liver  was  cut  up  into  fine  pieces  and  triturated. 
Two  portions  of  the  same  weight  of  liver-pulp  were  taken,  one  of  which 
was  placed  directly  in  a  bottle  filled  with  chloroform  water;  the  other 
portion  was  boiled  in  water  first,  and  then  treated  with  the  same  amount 
of  chloroform  water.  After  sixty-eight  hours'  digestion,  the  glycogen  and 
sugar  were  determined  in  each  of  the  extracts.  The  first  extract  showed 
a  large  amount  of  sugar  and  no  glycogen,  whereas  the  extract  of  the 
boiled  liver  contained  considerable  glycogen  and  only  very  little  sugar. 
In  the  first  experiment  there  were  found  48.28  grams  of  sugar;  in  the  second, 
3.65  grams. 

As  we  have  seen,  the  glycogen  content  of  the  liver  stands  in  a  definite 
relation  to  that  of  the  muscles.  After  the  muscles  have  performed  hard 
work,  we  find  that  not  only  does  the  glycogen  in  them  disappear,  but  that 
in  the  liver  as  well.  This  leads  us  to  believe  that  the  liver  serves  as  a 
central  storage  place  which  is  capable  of  feeding  all  the  other  stores  in  the 
organism.  The  transfer  of  the  liver-glycogen  takes  place  by  means  of 
the  blood,  and  in  the  form  of  d-glucose  as  we  have  seen.  Now  the  organism 
strives  to  a  remarkable  degree,  even  during  starvation,  to  maintain  a 
constant  amount  of  sugar  in  the  blood.  If  the  glycogen  in  the  muscles  is 
used  up,  the  muscle  cells  then  strive  to  form  glycogen  from  the  sugar  in 
the  blood.  This  would  cause  a  diminution  in  the  sugar  content  of  the 
blood,  except  for  the  fact  that  as  soon  as  this  sugar  is  removed,  then  hepatic 
glycogen  is  decomposed  into  d-glucose  and  removed  by  the  blood.1  It 
has  been  stated  that  the  higher  products  of  the  hydrolysis  of  glycogen, 
namely  dextrin  and  maltose,  are  likewise  transported  by  the  blood;  but 
how  far  such  observations  are  correct,  or  what  the  extent  to  which  this  takes 
place,  cannot  be  decided  at  present.  At  all  events,  such  statements  have 

1  The  assumption  made  by  J.  Seegen  (Die  Zuckerbildung  im  Tierkorper,  ihr  Umfang 
und  ihre  Bedeutung,  Berlin,  1890,  and  Studien  iiber  Stoffwechsel  im  Tierkorper,  Berlin, 
1887),  that  blood-sugar  is  formed  from  proteins  in  the  nourishment,  and  that  on  the 
other  hand  the  liver-glycogen  originates  from  the  fats,  is  not  supported  by  the  facts. 
Cf.  R.Bohm  and  F.  A.  Hoffmann:  Pfliiger's  Arch.  23,  205  (1880).  H.  Girard:  Pfliiger's 
Archiv.  41,  294  (1887).  E.  Cavazzani:  Arch.  Anat.  Physiol.  539  (1898). 


CARBOHYDRATES.  73 

lost  much  of  their  significance  since  it  has  become  known  that  the  blood- 
serum  contains  a  ferment  which  is  capable  of  converting  glycogen  and 
starch  into  dextrose.1  The  fact  that  the  muscles  are  capable  of  forming 
glycogen  from  glucose  has  been  proved  by  Kiilz.2  By  subcutaneous 
injection  of  sugar  into  frogs  with  extirpated  livers  he  was  able  to  establish 
the  fact  that  there  was  an  increase  of  muscle-glycogen. 

That  the  sugar  content  of  the  blood  is  directly  dependent  upon  the  liver 
is  shown  by  the  fact  that  ablation  of  the  liver  causes  the  amount  of  sugar 
in  the  blood  to  diminish  and  finally  disappear.3 

Although  we  have  outlined  the  way  carbohydrates  break  down  in  the 
alimentary  canal,  the  absorption  of  their  hydrolytic  products  and  their 
destiny  in  the  animal  organism  from  the  time  of  their  being  stored  up  as 
glycogen  on  to  their  change  back  into  d-glucose,  still  we  have  failed  to  give 
an  exact  picture  of  the  manner  in  which  the  glucose  formed  is  eventually 
consumed.  We  are,  indeed,  acquainted  with  the  end-products,  carbon 
dioxide  and  water,  and  know  that  an  oxidation  takes  place,  but  we  are  still 
in  doubt  concerning  the  intermediate  products.  The  destruction  of  the 
sugar  has  been  traced  by  Lepine  4  and  others  to  the  action  of  a  glucolytic 
ferment  in  the  blood  and  in  the  tissues.  Claude  Bernard  5  had  previously 
shown  that  the  sugar  content  of  blood  gradually  diminishes  on  standing. 
More  recently  it  has  been  found  that  ferments  of  similar  action  are  present 
in  almost  all  of  the  organs.  It  is  hard  to  decide  whether  in  all  cases  there 
is  no  cooperation  of  micro-organisms,  and  as  to  what  part  this  decom- 
position of  c?-glucose  plays  in  the  living  tissue.  At  all  events,  there  is  at 
present  no  justification  for  the  assumption  that  all  of  the  sugar  decomposi- 
tion is  caused  by  the  action  of  the  ferment  mentioned.  In  this  connection 
we  will  refer  to  the  work  of  Stoklasa.6  He  obtained  from  the  expressed 
juices  of  all  sorts  of  different  organs  (muscles,  liver,  lungs,  pancreas)  by 
precipitation  with  alcohol-ether,  ferments  which  produced  alcoholic  fermen- 
tation in  a  sterilized  sugar  solution  without  the  aid  of  bacteria.  The 
proportion  of  carbon  dioxide  and  alcohol  formed  was  the  same  as  in  the 
fermentation  brought  about  by  the  zymase  in  yeast.  The  decomposition 


1  M.  Bial:  Pfluger's  Arch.  52,  137  (1892),  and  54,  73  (1893).     Cf.  also  Rohmann, 
Ber.  25,  3654  (1892). 

2  Pfliiger's  Arch.  24,  64  (1881). 

3  Cf.  Tangl  and  Harley:  Pfliiger's  Arch.  61,  551  (1895).    Pavy  and  Siau:  J.  Physiol. 
29,  375  (1903).     Minkowski:  Arch.  exp.  Path.  Pharm.  21,  41  (1886).    Schenk:  Pfluger's 
Arch.  57,  553  (1894). 

4  Compt.  rend.  110,  742  (1890);  110,  1314;  112,  146  (1891);  112,  411;  112,  604;  112, 
1185  and  1414;  113,  118  (1891);  120,  139  (1895).  Lupine:  Le  ferment  glycolytique  et  la 
pathogenic  du  diabete,  Paris,  1891.  Cf .  Nasse  and  Framm :  Pfluger's  Arch.  63, 203  (1896). 

5  Lecons  sur  le  diabete  (1878). 

6  Hofmeister's  Beitr.  3,  460  (1903);  Ber.  36,  4058  (1903);  Pfluger's  Archiv.  101,  311 
(1904);  Zentr.  Physiol.  17,  465  (1903);  and  Ber  38,  664  (1905). 


74  LECTURE  IV. 

of  the  carbohydrate  did  not  stop  with  the  formation  of  the  products 
named,  but  acetic  and  formic  acids  were  formed  with  consumption  of 
oxygen.  It  is  at  present  hard  to  tell  what  part  the  alcoholic  fermentation 
plays  in  the  living  organism,  or  whether,  in  fact,  it  has  any  significance. 
At  all  events,  Stoklasa's  observations  include  the  possibility  of  energy 
being  produced  without  oxygen  being  supplied.  The  fact  that  the  animal 
organism  evidently  makes  use  of  such  simple  decompositions  as  a  source  of 
energy  is  shown  by  the  interesting  experiments  of  Hermann,  Pfliiger,  and 
Bunge.  Hermann  1  proved  that  a  piece  of  extirpated  muscle,  from  which 
no  more  oxygen  could  be  pumped  out,  could  work  in  an  atmosphere  free 
from  oxygen  and  produce  carbonic  acid.  Hermann  at  the  same  time 
detected  the  formation  of  an  acid  (lactic  acid).  Pfliiger2  succeeded  in 
keeping  a  frog  alive  for  twenty-five  hours  at  a  temperature  a  few  degrees 
above  the  freezing-point  of  water  in  an  atmosphere  free  from  oxygen, 
during  which  time  the  animal  evolved  a  considerable  amount  of  carbonic 
acid  gas.  Finally  G.  V.  Bunge3  showed  that  a  parasitic-worm  of  the  cat, 
Ascaris  mystax,  could  survive  for  four  or  five  days  in  a  medium  absolutely 
devoid  of  oxygen,  and  move  around  in  a  very  lively  manner  during  that 
time.  It  should  by  no  means  be  concluded  from  these  very  interesting 
experiments,  that  the  animal  organism  performs  its  muscular  work  solely 
at  the  expense  of  the  energy  set  free  by  hydrolytic  decompositions. 
The  amount  of  living  force  produced  in  this  way  would  be  altogether  too 
small.  On  the  other  hand,  it  is  conceivable  that  the  cell,  by  means  of  a 
partial  breaking  down,  that  is  to  say,  by  a  hydrolysis  and  subsequent 
oxidation  of  the  decomposition  products,  can  increase  when  necessary  the 
amount  of  energy  available.  Thus  100  grams  of  glucose  when  completely 
oxidized  to  carbon  dioxide  and  water  yield  3939  calories  (=  1,674,000 
kilogram-meters  of  work).  By  alcoholic  fermentation,  i.e.,  the  hydrolysis 
of  100  grams  glucose  into  carbon  dioxide  and  ethyl  alcohol,  only  372 
calories  (=  158,100  kilogram-meters  of  work)  are  liberated. 

As  a  result  of  work  the  muscular  tissue,  which  is  amphoteric,  becomes 
of  acid  reaction.  This  change  is,  at  least  to  some  extent,  due  to  the 
formation  of  lactic  acid.  Formerly  it  was  believed  that  there  was  a  direct 
connection  between  the  formation  of  the  latter  and  the  decomposition 
of  carbohydrates.  More  recently,  however,  this  view  has  been  strongly 
combated.  At  present  it  has  not  been  definitely  decided  as  to  what 
relation  the  lactic  acid  bears  to  the  performance  of  work  by  the  muscles. 
It  is  possible  that  its  presence  is  due  to  a  hydrolysis  caused  by  the 
absence  of  a  sufficient  amount  of  oxygen.  On  the  other  hand,  it  is  also 
conceivable  that  the  formation  of  lactic  acid  has  nothing  whatever  to  do 

1  Untersuchungen  iiber  den  Stoffwechsel  der  Muskeln,  Berlin,  1867. 

2  Pfliiger's  Arch.  10,  251  (1875). 

3  Z.  physiol.  Chem.  8,  48  (1883-84);  12,  565  (1888);  14,  318  (1889). 


CARBOHYDRATES.  75 

with  the  combustion  of  carbohydrates  in  the  muscle,  but  results  from  the 
breaking  down  of  protein.  We  shall  see  later  on  that  alanine,  which 
is  formed  by  the  hydrolysis  of  albumin,  stands  in  close  relation  to  lactic 
acid.1 

The  role  of  the  carbohydrates  in  the  animal  organism  is  by  no  means 
limited  to  the  production  of  muscular  energy.  Above  all  they  are  to  be 
considered  as  a  source  of  heat.  Thus  it  is  possible  to  cause  the  glycogen 
stores  to  disappear  by  merely  chilling  the  animal.2  The  carbohydrates, 
without  doubt,  take  an  active  part  in  the  life  process  of  the  individual 
cells.  They  take  part  also  in  their  building  up.  At  present  we  know 
nothing  concerning  the  way  they  occur  in  the  organism  and  concerning 
their  union  in  the  cell  complex.  We  have  already  mentioned  the  occur- 
rence of  pentoses,  especially  xylose,  which  is  in  the  nucleoproteids.  We 
shall  later  on  see  that  there  are  indications  of  the  hexoses  also  being  used 
as  building  material  for  the  nuclei  of  the  cells. 


1  Cf.  Astaschewsky:  Z.  physiol.  Chem.  4,  397  (1880).  Warren:  Pfliiger's  Arch.  24, 
391  (1881).  Heffter:  Arch,  exper.  Path.  Pharm.  31,  225  (1893).  Werther:  Pfliiger's 
Arch.  46,  63  (1890).  Spiro:  Z.  physiol.  Chem.  1,  111  (1877-78).  Zillesen:  Z.  physiol. 
Chem.  15,  387  (1891).  Araki:  Z.  physiol.  Chem.  15,  335  and  546  (1891),  and  Z. 
physiol.  Chem.  16,  453  (1892).  Hoppe-Seyler:  Z.  physiol.  Chem.  19,  476  (1894). 

a  E.  Kiilz:  Pflijger's  Arch.  24,  14  (1881). 


LECTURE  V. 

CARBOHYDRATES. 
IV. 

BUILDING  UP  AND  BREAKING  DOWN  OF  CARBOHYDRATES  IN  THE 
ANIMAL  ORGANISM. 

WE  found  in  the  last  lecture  that  the  blood  under  varying  physiological 
conditions  always  maintained  a  constant  sugar-content.  This  does  not 
increase  when  the  food  is  rich  in  carbohydrates,  nor  decrease  materially 
during  starvation.  This  phenomenon  is  explicable  only  by  the  assumption 
that  there  is  an  extraordinarily  delicate  regulating  mechanism  which 
works  on  the  one  hand  in  conjunction  with  the  organs  containing  the 
stored-up  sugar,  and  on  the  other  hand  with  the  places  where  sugar  is 
consumed.  If  for  any  reason  the  amount  of  sugar  in  the  blood  increases 
above  the  normal,  then  sugar  appears  in  the  urine.  This  may  take  place, 
for  example,  when  an  excessive  amount  of  sugar  has  been  introduced  into 
the  alimentary  canal.  In  such  a  case  it  is  not  always  possible  to  remove 
the  sugar  fast  enough  from  the  general  metabolism  by  converting  it  into 
glycogen  or  fat.  This  ability  of  storing  up  sugar  is  a  restricted  one.1 
The  maximum  amount  of  sugar  which  it  is  possible  for  the  system  to 
assimilate  is  known  as  the  limit  of  assimilation,  and  the  elimination  of 
sugar  which  takes  place  when  this  is  exceeded  is  spoken  of  as  alimentary 
glucosuria.  The  limit  varies  with  different  forms  of  sugar  and  for  different 
individuals.  In  general,  the  danger  of  giving  the  blood  an  over-supply  of 
sugar  under  normal  conditions  of  nourishment  is  but  slight,  because  under 
normal  conditions  the  bulk  of  the  carbohydrates  are  taken  into  the  system 
either  as  starch  or  as  cane-sugar.  There  is  no  danger  of  these  forms  of 
sugar  being  suddenly  broken  down  in  the  alimentary  canal;  on  the  con- 
trary, their  decomposition  always  takes  place  gradually  from  one  stage  to 
another  so  that  this  in  itself  serves  in  a  measure  to  regulate  the  absorption 
of  sugar. 

Under  certain  conditions  the  assimilation  limit  for  carbohydrates  can 
be  reduced  greatly  for  a  time.  This  is  particularly  true  of  the  central 
organ  of  carbohydrate  metabolism,  namely  the  liver.  Claude  Bernard  3 
recognized  the  fact  that  the  storing  up  of  sugar  in  the  form  of  glycogen 

1  Cf.  Franz  Hofmeister:  Arch.  exp.  Path.  Pharm.  25,  240  (1889). 
'  Legons  (Cours  du  semestre  d'hiver),  1854-55,  p.  289. 

76 


CARBOHYDRATES.  77 

and  its  transformation  into  glucose,  both  changes  being  functions  of  the 
liver  cells, —  partly  directly  and  partly  indirectly, —  were  dependent  upon 
the  nervous  system.  He  showed  this  by  means  of  the  following  classical 
experiment,  which  was  first  performed  upon  rabbits.  If  a  rabbit  is  injured 
at  a  certain  place  in  the  medulla,  sugar  appears  in  the  urine  after  a 
short  time.  This  region  is  bounded  above  by  the  origin  of  the  two  audi- 
tory nerves,  and  below  by  a  line  connecting  the  places  of  origin  of  the 
vagus  nerves.  The  experiment  is  carried  out  in  this  way:  After  tying 
the  rabbit,  the  point  of  a  trocar  is  placed  in  the  median  line  upon  the 
os  occipitale  exactly  at  the  Protuberantia  occipitalis  superior,  and  then 
pushed  through  carefully  until  the  Pars  basillaris  is  reached.  The  instru- 
ment thus  bores  through  the  skull,  the  cerebellum,  and  the  posterior 
and  median  columns  of  the  medulla.  Two  hours  after  the  operation 
sugar  appears  in  the  urine.  The  elimination  of  sugar,  however,  in  such 
cases  is  not  lasting,  usually  disappearing  at  the  end  of  five  or  six  hours. 
With  dogs,  however,  this  glucosuria  lasts  longer.  Claude  Bernard  in  one 
case  found  it  to  last  for  a  week.  In  such  cases  the  amount  of  sugar  con- 
tained in  the  urine  is  not  large,  usually  amounting  to  merely  two  or  three 
per  cent.1  Bernard  shows  the  cause  of  the  sugar  elimination  to  be  an 
excessive  amount  of  blood-sugar.  He  found,  instead  of  the  customary 
0.1  to  0.15  per  cent,  more  than  0.3  per  cent.  This  operation  also  has  the 
same  result  when  performed  with  birds  2  or  with  frogs.3 

An  observation  made  by  F.  W.  Dock  4  is  of  considerable  importance  for 
complete  understanding  of  this  kind  of  glucosuria.  He  found  that  the 
above  operation  succeeded  only  with  well-nourished  animals,  i.e.,  with  those 
which  possessed  stored-up  glycogen.  Naunyn  5  arrived  at  the  same  con- 
clusion. He  showed  that  the  success  of  the  so-called  "  diabetic  puncture  " 
depended  wholly  upon  the  state  of  nourishment  of  the  animal  experimented 
upon.  Dissection  of  the  animal  after  the  operation  always  showed  that  the 
liver  was  free  from  glycogen.  The  fact  that  the  liver  in  this  case  loses  the 
power  of  storing  up  sugar  in  the  form  of  glycogen  is  shown  by  the  following 
experiment:  If  a  solution  of  d-glucose  is  injected  into  the  mesenteric 
vein  of  a  dog  whose  liver  has  been  deprived  as  far  as  possible  of  glyco- 
gen by  starvation,  only  very  small  amounts  of  sugar  will  subsequently 
be  found  in  the  urine.  If  the  same  experiment  is  repeated  with  another 
animal  which  has  undergone  the  "  diabetic  puncture,"  a  marked  glucosuria 
ensues  soon  after  the  injection  of  the  sugar.8 


H4don:  Diabete,  Dictionnaire  de  Physiol.  4,  812. 

M.  Bernhardt:  Virchow's  Arch.  59,  407  (1874). 

M.  Schiff:  Untersuchungen  iiber  die  Zuckerbildung,  Wiirzburg,  1859. 

Pfliiger's  Archiv.  5,  571  (1872). 

Arch,  exper.  Path.  Pharm.  3,  85  (1875). 

Cf.  P.  Levine:  Zentr.  Physiol.  8,  397  (1894). 


78  LECTURE  V. 

The  question  now  arises  as  to  what  the  connection  is  between  the 
"  diabetic  puncture  "  and  the  flooding  of  the  organism  with  sugar.  Claude 
Bernard,  by  means  of  the  following  experiment,  showed  that  the  vagus 
nerves  participate  in  this.1  If  the  "  diabetic  puncture  "  is  performed 
after  cutting  these  nerves  at  the  neck,  it  is  as  effective  as  when  the  nerves 
remained  intact.  On  stimulating  the  peripheric  stumps  of  a  vagus  nerve, 
no  glucosuria  ensues.  It  appears  immediately,  however,  if  the  central  end, 
i.e.,  the  end  connected  with  the  medulla  oblongata,  is  stimulated.  In 
such  experiments  Bernard  showed  that  the  whole  body  of  the  animal 
experimented  upon  was  flooded  with  sugar.  The  greatest  quantity  was 
found  in  the  hepatic  veins.  Bernard  showed,  furthermore,  that  cutting 
the  vagus  nerves  at  the  neck  resulted  in  making  the  liver  free  from  sugar. 
He  concludes  from  all  these  experiments  that  in  the  medulla  oblongata 
there  is  a  center  which  regulates  the  transformation  of  sugar  by  the  liver. 
Communication,  i.e.,  the  excitement,  is  provided  by  means  of  the  vagus 
nerve.  The  sugar  formation  caused  by  stimulation  of  the  central  stump 
of  the  vagi  nerve,  Bernard  conceives  to  be  a  reflex  action;2  and  it  is  the 
pulmonary  branches  of  the  vagus  which  contain  the  fibers  acting  upon 
the  sugar  center,  for  if  the  vagi  are  cut  above  the  liver  and  below  the 
lungs,  no  influence  upon  the  sugar  formation  of  the  liver  was  observed. 

Now  how  does  this  sugar  center  exert  its  influence  upon  the  liver? 
Bernard  cut  through  the  spinal  cord  at  different  places  below  the  medulla 
oblongata,  and  found  that  the  path  of  communication  must  lie  in  the 
upper  parts  of  the  spinal  cord;  for  if  it  was  severed  below  the  lower  dorsal 
vertebrae,  the  sugar  formation  in  the  liver  was  not  affected.  C.  Eckhard,3 
who  confirmed  this  conclusion,  found  that  after  severing  both  the  vagi 
and  sympathetic  nerves  in  the  neck,  a  successful  diabetic  puncture  could 
be  made.  After  severing  the  splanchnic  nerves,  however,  it  ceased  to  be 
operative.  This  indicates  that  the  diabetic  puncture  acts  upon  the  trans- 
formation of  the  carbohydrates  in  the  liver  by  nerve  impluses  passing 
along  the  path  of  the  splanchnic  nerves. 

•  We  must  assume,  therefore,  that  the  sugar  formation  in  the  liver  is 
regulated  directly  by  a  center  in  the  medulla  oblongata.  The  vagi  nerves 
conduct  the  centripetal  impulses,  and  the  splanchnic  nerves  the  centri- 
fugal. Later  on,  when  we  come  to  discuss  digestion,  and  especially 
the  dependence  of  the  secretion  of  the  digestive  glands  upon  certain 
nervous  influences,  the  above  hypothesis  will  no  longer  appeal  to  us  as 
remarkable. 

Thus  far  we  have  left  the  matter  unsettled  as  to  whether  the  liver  alone 
gives  up  sugar  after  the  "diabetic  puncture,"  or  whether  the  sugar  in  the 


1  Cf.  C.  Eckhard:  Beit.  Anat.  Physiol.  8,  77  (1879). 

2  Cf.  E.  F.  Pfliiger:  Das  Glykogen,  loc.  cit.  386. 

3  Beitr.  Anat.  Physiol.  4,  138. 


CARBOHYDRATES.  79 

urine  also  comes  from  other  organs.  The  experiments  of  Moos1  and  of  Moritz 
Schiff 2  have  proved  that  only  the  sugar  formation  in  the  liver  is  affected. 
If  the  vessels  of  the  liver  are  all  tied,  the  diabetic  puncture  becomes 
inoperative.  This  is  particularly  well  shown  by  the  experiments  of  Schiff, 
who  took  eight  frogs  of  the  same  size,  and  produced  glucosuria  in  all  of 
them.  At  the  end  of  from  two  to  four  and  three-quarters  hours  sugar 
could  be  detected  in  the  urine.  The  livers  of  all  the  animals  experimented 
upon  were  then  exposed,  drawn  out  through  the  abdominal  wound,  and 
all  the  vessels  and  bile  ducts  encircled  with  a  slip-knot  of  thread.  In 
four  cases  the  knots  were  drawn  tight,  while  in  the  other  four  they  were 
not.  In  the  latter  case  the  glucosuria  continued,  while  in  the  former  it 
gradually  diminished,  so  that  at  the  end  of  three  hours  the  urine  was  free 
from  sugar. 

It  is  not  yet  clear  how  this  increased  sugar  formation  is  brought  about. 
There  are  several  conceivable  possibilities.  The  fact  that  the  glycogen 
stored  up  in  the  liver  is  suddenly  converted  into  glucose,  would  make  it 
seem  probable  that  the  diastatic  action  has  been  considerably  increased 
above  the  normal.  It  is  also  conceivable  that  there  is  an  increased  pro- 
duction of  diastase,  or,  on  the  other  hand,  it  is  possible  that  under 
normal  conditions  the  glycogen  is  not,  as  ordinaly  assumed,  deposited  in 
the  cells  as  a  foreign  body,  but  rather  in  the  form  of  a  loose  chemical 
combination,  and  that  the  diastase  begins  to  act  upon  glycogen  as  soon 
as  it  is  set  free.  By  exerting  certain  influences  upon  the  liver  cells,  - 
whether  by  the  diabetic  puncture,  or  whether  by  some  other  excitement 
of  the  sugar  center,  —  all  of  the  glycogen  is  perhaps  set  free  from  its 
loose  chemical  combination,  and  subjected  to  the  action  of  diastase,  which 
found  no  point  of  attack  as  long  as  the  glycogen  was  in  a  combined 
state.  Claude  Bernard  believed  that  the  increased  formation  of  glucose 
was  due  to  an  increased  blood  flow,  which  was  probably  caused  by  the 
fact  that  the  diabetic  puncture  had  an  effect  upon  the  vaso-motor  center. 
He  had  in  mind  the  increased  blood  flow  which  accompanies  the  increased 
secretion  of  saliva  by  the  submaxillary 3  gland  on  stimulating  the  fibers 
in  the  chorda  tympani.  R.  Heidenhain,  however,  has  shown  that  an 
increased  secretion  of  saliva  may  take  place  without  an  increase  in  the 
blood  flow,  and  that  the  chorda  tympani  evidently  possesses  certain  specific 
secretory  fibers.  Analogously,  it  is  possible  that  the  splanchnic  nerves 
contain  fibers  which  exert  an  influence  upon  the  formation  of  glucose  in 
the  liver. 

Closely  connected   with  the  so-called   "  diabetic   puncture "   we   have 
another  observation  to  consider.     If  a  one  per  cent,  solution  of  common 


1  Arch,  wissenschaftl.  Heilkunde,  4,  37. 

J  Untersuchungen  liber  die  Zuckerbildung  in  der  Leber,  p.  76,  Wiirzburg,  1859. 

3  Pfliiger's  Arch.  6,  309  (1872);  9,  335  (1874). 


80  LECTURE  V. 

salt l  is  introduced  into  the  vascular  system,  glucosuria  ensues.  If,  on 
the  other  hand,  the  splanchnic  nerves  are  severed,  the  salt  infusion 
becomes  ineffective.  Morphia 2  behaves  similarly.  Quite  recently  the 
exact  connection  between  these  experiments  and  the  glucosuria  produced 
by  the  "  diabetic  puncture  "  has  been  developed  by  Martin  H.  Fischer.3  He 
showed,  first  of  all,  that  instead  of  the  one-sixth-molar  solution  of  common 
salt  which  he  injected  into  the  circulatory  system  of  rabbits  at  the  rate  of 
75  to  100  c.c.  per  minute,  one-sixth-molar  solutions  of  other  sodium  salts 
—  e.g.,  NaBr,  Nal,  NaNO3  —  could  be  used  with  the  same  effect.4  Fischer 
showed,  furthermore,  that  the  cause  of  the  glucosuria  was  not  a  per- 
manent injury  produced  in  any  organ,  for  he  could  cure  the  disease 
by  the  use  of  a  solution  of  calcium  chloride.  A  renewed  injection  of  the 
common  salt  would,  however,  again  lead  to  glucosuria.  The  greater 
the  concentration  of  the  solution  of  sodium  salt  employed,  the  sooner 
the  sugar  appeared  in  the  urine. 

Fischer,  now,  sought  to  determine  upon  which  tissues  the  solution  of 
salt  acted  in  producing  this  glucosuria.  He  remembered  at  the  same  time 
the  experiments  of  Klilz,  who  observed  that  glucosuria  was  only  produced 
when  the  splanchnic  nerves  remained  intact.  Fischer  found  that  after 
cutting  these  nerves,  he  could  not  produce  glucosuria,  and,  furthermore, 
if  the  glucosuria  was  already  established  before  the  nerves  were  severed,  it 
would  disappear  shortly  after  the  operation.  This  suggested  the  thought 
that  probably  the  salt  solution  produced  some  such  action  as  that  pro- 
duced by  the  vagi  nerves  upon  the  sugar  center.  Fischer  sought  to  localize 
the  action  of  the  common  salt  as  much  as  possible.  For  this  purpose  he 
tied  the  axillary  artery  in  some  rabbits,  and  injected  the  solution  of  salt 
into  the  central  end  of  this  artery  so  that  the  salt  passed  on  through  the 
vertebral  artery  directly  to  the  medulla  oblongata.  When  the  salt  solu- 
tion was  injected  in  this  way,  the  sugar  appeared  in  the  urine  somewhat 
more  quickly  than  when  the  same  amount  of  the  same  solution  was  intro- 
duced into  a  peripheral  vessel.  Furthermore,  the  glucosuria  was  more 
severe  and  was  more  lasting.  As  much  as  7.3  per  cent  of  urine  sugar 
was  found  in  the  urine.  These  experiments  make  it  seem  probable  that 
the  salts  introduced  into  the  circulation  act  upon  the  same  center  as  that 
of  the  "  diabetic  puncture." 

There  are  other  poisons  known  which  will  produce  glucosuria,  strychnine, 
for  example.  The  poisonous  effect  of  this  substance  is  not  obtained, 
however,  if  the  spinal  cord,  with  the  exception  of  the  upper  portions,  is 
extirpated.  Since  strychnine  does  not  cause  elimination  of  sugar  in  the 


1  C.  Eckhard:  Beit.  Anat.  Physiol.  8,  77  (1879). 

2  Kiilz:  Eckhard's  Beitrage,  6,  177  (1872). 

1  University  of  California  Publications,  Physiology,  1,  77  (1903),  and  1,  87  (1904). 
4  LiCl,  KC1,  and  SrCl2,  produced  glucosuria;  NH4C1  did  not. 


CARBOHYDRATES.  81 

urine  of  frogs  with  extirpated  livers,  it  is  probable  that  the  glucosuria  is 
to  be  attributed  to  a  disturbance  of  the  liver  function.  It  might  be  sup- 
posed that  the  sugar  elimination  in  the  urine  is  a  result  of  the  tetanus 
produced  by  the  strychnine  poisoning.  That  this  is  not  the  case  is  shown 
by  the  fact  that  animals  poisoned  with  large  amounts  of  strychnine  —  large 
doses,  instead  of  producing  tetanus,  cause  paralysis  of  the  motor  nerves  — 
are  also  subject  to  glucosuria,  and,  as  a  matter  of  fact,  in  a  more  severe  form 
than  in  the  case  of  animals  with  tetanus,  caused  by  smaller  doses  of  strych- 
nine. The  simplest  explanation  of  this  last  fact  is  that  during  tetanus 
sugar  is  consumed.  Other  poisons,  such  as  phosphorus,  arsenic,  uranium 
salts,  corrosive  sublimate,  carbon  monoxide  (illuminating-gas),  amyl 
nitrite,  curari,  chloral,  nitrobenzene,  chloroform,  acetone  vapors,  ether, 
etc.,  will  also  cause  glucosuria.1  At  present  we  know  nothing  more  definite 
concerning  the  mode  of  action  of  these  various  substances.  It  should  not, 
however,  be  assumed  that  they  all  have  the  same  point  of  attack. 

The  glucosuria  produced  by  the  glucoside  phloridzin  has  been  studied 
with  especial  thoroughness.2  If  from  one  to  three  grams  of  this  sub- 
stance is  administered  to  a  dog  for  each  kilogram  of  its  body  weight, 
glucosuria  results.  In  the  case  of  starving  animals,  after  the  injection 
of  from  0.3  to  2.5  grams  of  phloridzin,  the  sugar  can  be  found  in  the 
urine.  Von  Mering,  the  discoverer  of  this  form  of  glucosuria,  also  studied 
the  effect  of  the  decomposition  products  of  phloridzin,  and  found  that 
phloretin  alone  was  active  in  this  respect,  whereas  phloroglucinol  and 
phloretic  acid  were  inactive. 

All  the  other  glucosurias  which  we  have  discussed  up  to  this  point  have 
been  caused  by  a  glucohemia,  i.e.,  a  flooding  of  the  organism  and  especially 
of  the  blood  with  sugar.  The  elimination  of  sugar  through  the  kidneys 
is  a  result  of  a  self-regulating  mechanism.  By  eliminating  the  excess  of 
sugar  the  organism  seeks  to  bring  the  sugar  content  of  the  blood  back  to 
the  normal.  Even  the  glucosuria  produced  by  phloridzin  has  been  ex- 
plained in  this  way,3  although  Mering  himself  and  many  other  later  inves- 
tigators have  failed  to  detect  any  increase  in  the  amount  of  sugar  contained 
in  the  blood  even  when  the  ureter  was  tied.  Phloridzin  glucosuria  is  also 

1  Cf.  Langendorff:  Arch.  Anat.  Physiol.  138  (1887).     F.  Giirtler:  Inaug.    Dissert. 
Konigsberg,    1886.      Araki:   Z.   physiol.   Chem.  17,  311   (1893).     Luchsinger:   Inaug. 
Dissert.  Zurich,  1875.    Senff :  Inaug.  Dissert.  Dorpat,  1869.    Straub:  Arch,  exper.  Path. 
Pharm.  38,  139  (1897).     Rosenstein:  ibid.  40,  363  (1898).     Araki:  Z.  physiol.  Chem. 
15,  351    (1891);  19,   422,  476    (1894);  also  Bernard:  LeQons  sur  la  diabete  et  la  gly- 
cosurie  animale.     Paris,  1877. 

2  v.  Mering:  Ueber  Diabetes  mellitus.  Verhandl.  Kongr.  innere  Med.,  1886  u.  1887; 
Z.  klin.  Med.  14,  405  (1888),  and  16,  431  (1889).   v.  Mering  and  Minkowski:  Zentr.  klin. 
Med.  10,  393  (1889).     Max  Cremer:  Z.  Biol.  29,  175  (1893).     Cremer  and  Ritter:  ibid. 
29,  256  (1893). 

3  Cf.  Pavy:   J.  Physiol.  20,  xix-xxii  (1896).     S.  Leone:  Gazz.  internaz.  di  med.  prat. 
Vol.  3,  21. 


82  LECTURE  V. 

shown  to  be  different  from  the  other  forms  by  the  investigations  under 
the  leadership  of  Minkowski,  carried  out  by  Andreas  Thiel l  and  by  von 
Mering.2  These  investigators  have  shown  that  geese  with  extirpated 
livers  eliminate  sugar  after  the  injection  of  phloridzin,  whereas  we  have 
seen  that  with  the  other  forms  of  glucosuria  it  is  essentially  the  liver  alone 
which  takes  part  in  the  sugar-formation. 

Much  more  important  than  the  results  of  these  last  experiments 3  is  the 
above-mentioned  fact  that  most  investigators  have  failed  to  find  any 
evidence  of  glucohemia  in  the  case  of  phloridzin-glucosuria.  The  con- 
clusion has,  therefore,  been  drawn  that  the  elimination  of  sugar  after 
phloridzin  poisoning  is  due  to  the  abnormal  permeability  of  the  kidney 
epithelium  for  sugar.  Thus  the  sugar  in  the  blood  would  become  less  and 
less,  and  indirectly  the  liver,  and  perhaps  the  other  places  where  glycogen 
is  stored,  would  be  compelled  to  give  up  sugar.  To  support  the  assump- 
tion, that  the  glucosuria  produced  by  phloridzin  is  of  a  renal  nature,  N. 
Zuntz  4  has  published  a  proof,  which  is  not,  however,  conclusive.  He 
injected,  by  means  of  a  trocar,  a  solution  of  phloridzin  through  the  walls 
of  the  renal  artery  into  the  blood-stream.  The  kidney  to  which  the  glu- 
coside  was  carried  directly  was  the  first  to  eliminate  sugar.  Pfliiger 5 
believes  that  it  is  not  impossible  that  the  first  separation  of  sugar  may  be 
due  to  a  decomposition  of  the  phloridzin  itself.  At  present  we  cannot  be 
sure  as  to  what  is  the  correct  explanation  of  phloridzin  glucosuria.  Only 
this  is  known,  —  the  matter  is  by  no  means  so  simple  as  has  been 
assumed.6  Above  all,  it  must  be  mentioned  that  starving  animals  will 
also  eliminate  sugar  after  the  introduction  of  phloridzin,  and  repeated 
additions  of  the  glucoside  result  in  renewed  glucosuria,7  and  to  such  a 
degree  that  the  question  as  to  whether  food  other  than  carbohydrates  can 
give  rise  to  the  sugar  formation  now  presents  itself. 

Our  knowledge  concerning  the  formation  of  sugar  in  the  animal  organism 
was  considerably  increased  by  the  discovery  of  von  Mering  and  Minkowski  8 
in  the  year  1889  that  dogs  always  suffered  from  severe  glucosuria  after 
complete  extirpation  of  the  pancreas.  If  a  small  part  of  the  pancreas  is  left 


1  Inaug.  Dissert.  Konigsberg,  1887. 

2  Loc.  cit.  Z.   klin.    Med.    14,  415  (1888).     Cf.  Minkowski   and  Thiel:    Arch.  exp. 
Path.  Pharm.  23,  142  (1887). 

3  For  a  critical  discussion  see  E.  Pfliiger:  Das  Glykogen  und  seine  Beziehungen  zur 
Zuckerkrankheit  (1905). 

4  Arch.  Anat.  Physiol.  1895,  570. 

5  Loc.  cit.  p.  539. 

6  Cf.  Carl  Jakobj:  Arch,  exper.  Path.  Pharm.  36,  213  (1895). 

7  Cf.  Lusk:   Z.  Biol.  42,  31  (1901).     O.  Loewi:    Arch,  exper.  Path.  Pharm.   47,  48 
(1902). 

8  Ibid.  26,  371  (1890).     O.  Minkowski:  Untersuchungen  iiber  den  Diabetes  mellitus, 
Leipzig,  1893. 


CARBOHYDRATES. 


83 


in  the  body,  the  glucosuria  is  either  prevented  or  lessened.  As  Pfliiger  l 
has  shown,  an  animal  which  has  been  wholly  deprived  of  its  pancreas 
behaves  outwardly  quite  differently  from  one  which  has  a  slight  residue  of 
the  gland  left  in  the  body.  Pfliiger  observed  that  after  a  total  extirpation 
the  sugar  elimination  invariably  appeared  within  the  first  twenty-four 
hours,  and  lasted  continuously  until  the  death  of  the  animal,  even  when  it 
received  no  further  nourishment.  The  symptoms  peculiar  to  a  partial 
extirpation,  such  as  polydipsia  (excessive  thirst),  polyphagia  (voracity), 
and  polyuria  (excessive  urination) ,  were  either  entirely  lacking  or  barely 
indicated.  Usually  the  elimination  of  sugar  takes  place  very  quickly  after 
the  extirpation  of  the  pancreas.  Thus  Bierry  and  Gatin-Gruzewska 
obtained  the  following  results  from  four  experiments: 


Weight  of 
Dog. 

End  of  Opera- 
tion. 

Appearance  of 
Dextrose. 

Experiment  No 

1     

10  kg. 

1  o'clock 

3  o'clock 

Experiment  No. 

2     

14  kg. 

4  o'clock 

5  .35  o'clock 

Experiment  No. 
Experiment  No 

3     
4                    

20kg. 
14.3  kg. 

1  o'clock 
10.30  o'clock 

3  .30  o'clock 
3  30  o'clock 

The  elimination  of  sugar  in  the  urine  has  likewise  been  observed  after 
total  pancreas  extirpation  in  Selachier,2  frogs  3  and  in  birds.4  The  results 
obtained  after  partial  extirpation  are  not  as  uniform.  Sometimes  gluco- 
suria is  observed,  sometimes  not.  This  might  indicate  that  all  the  parts 
of  the  pancreas  gland  are  not  of  the  same  nature,  so  that  in  one  operation 
more  of  the  tissue  which  partakes  in  the  sugar  formation  is  carried  away 
than  in  another.  Numerous  experiments  by  different  observers  in  this 
direction  have,  however,  established  the  fact  that  all  parts  of  the  pancreas 
tend  to  increase  the  sugar  content  of  the  system,  and  thus  prevent  gluco- 
suria. The  true  cause  of  the  divergence  in  the  results  obtained  by 
different  investigators  is  probably  to  be  traced  to  the  different  methods 
of  operation  employed.5  Indeed,  the  glucosurias  produced  by  partial  and 


1  Pfliiger's  Arch.  106,  181.     Cf.  Sandmeyer:  Z.  Biol.  31,  12  (1895).  Cf.  also  E.  W. 
Pfluger:  Das  Glycogen,  etc.,  loc.  cit. 

2  V.  Diamare:  Zentr.  Physiol.  20,  617  (1906). 

3  Cf.  Aldehoff:  Z.  Biol.  28,  293  (1891),  and  Marcuse:  Arch.  Anat.  Physiol.  539  (1894). 

4  W.  Kausch:   Arch,  exper.  Path.   Pharm.  37,  274  (1896);     39,    219    (1897).     O. 
Minkowski:    Arch,    exper.    Path.    Pharm.  31,    85    (1893).      Cf.    v.    Diamare:   Zentr. 
Physiol.  19,  545  (1905).     Cremer  and  Ritter:  Z.  Biol.  28,  459  (1891). 

5  Cf.  De  Renzi  and  Reale:  Berliner  klin.  Wochenschr.    No.  23  (1892).     J.  Thiroloix: 
Diabete-pancreatique,  p.  95  (1892).     von  Mering  and  Minkowski:  Diabetes  mellitus 
nach  Pancreasexstirpation,  p.  12  (Leipsic,  1899).     W.  Sandmeyer:  Z.  Biol.  31,  74  and 
85  (1894).     E.  He"don:  Travaux  de  physiologic,  1-150,  Paris,  1898. 


84  LECTURE  V. 

total  extirpation  of  the  gland  are  very  similar,  and  only  show  gradual 
differentiations.  Also,  it  must  not  be  forgotten  that  the  pancreatic 
gland,  like  other  organs,  is  in  its  entire  function  without  question 
dependent  upon  nervous  influences,  and  that  under  certain  conditions 
disturbances  and  injuries  in  the  region  of  the  nerves  which  are  connected 
with  the  pancreas  may  produce  glucosuria.  The  fact  that  the  operation 
of  itself  does  not  cause  elimination  of  sugar,  has  often  been  shown,  neither 
does  the  extirpation  of  the  solar  plexus,  or  at  least  not  permanently. 
Before  we  take  up  the  explanation  of  this  disturbance  in  the  metabolism 
of  carbohydrates  produced  by  extirpation  of  the  pancreas,  it  may  be  well 
to  describe  briefly  the  phenomena  exhibited  by  the  organism  after  it  has 
been  deprived  of  the  gland.  In  general,  dogs  do  not  survive  the  operation 
very  long;  at  best  they  can  be  kept  alive  only  two  or  three  weeks.  Pfliiger 
found  the  cause  of  death  to  be  extensive  suppuration.  According  to 
him,  it  was  not  the  lack  of  the  gland,  nor  the  glucosuria  produced,  which 
caused  the  death,  but  rather  that  the  wound  did  not  heal  on  account  of 
the  sugar  in  the  tissues.  That  this  view  is  correct  is  shown  by  the  fact 
that  if  a  piece  of  the  pancreatic  gland  is  left  in  the  abdominal  cavity,  gluco- 
suria ensues  only  after  this  piece  is  dead,  and  such  dogs  live  much  longer. 
By  dissection  of  such  a  dog,  Pfliiger  1  found  an  extensive  atrophy.  The 
individual  organs  did  not  show  much  signs  of  disease.  The  fatty  tissue 
had  disappeared.  The  liver  showed  a  remarkable  condition.  All  the  other 
organs,  except  the  brain,  heart,  and  kidneys,  which  retain  their  weight 
even  during  inanition,  had  lost  considerably  in  weight;  the  liver,  on  the 
contrary,  had  increased.  Its  weight  represented  4.77  per  cent  of  the  body 
weight.  Normally,  the  liver,  according  to  Pavy,2  amounts  to  from  3  to 
4.7  per  cent  of  the  body  weight,  and  after  28  days  of  starvation  the 
value  falls  to  1.5  per  cent.  The  composition  of  the  liver  was  found  to  be 
as  follows: 

Per  cent. 

Dry  substance  in  the  fresh  liver 24 . 2 

Fat  in  the  fresh  liver 2.7 

Fat  in  the  dry  substance      11.2 

Water  in  the  fresh  liver  after  extraction  of  the  fat      ...  78 . 3 

Dry  substance  in  the  fresh  liver  after  extraction  of  the  fat    .  21.7 

Nitrogen  in  the  fresh  liver 3.2 

Nitrogen  in  the  dry  liver      13.2 

Nitrogen  in  the  dry  liver  after  extraction  of  the  fat    .    .    .  14.9 


1  Pfliiger's  Archiv.  108,  115  (1905). 

5  Phil.  Trans,  for  1860,  p.  579.    Researches  on  the  Nature  and  Treatment  of  Diabetes, 
London,  1862. 


CARBOHYDRATES.  85 

The  liver  contained  0.0259  gram  of  glycogen.  This  shows  that  it  had 
retained  the  power  of  forming  glycogen. 

Pfliiger  also  examined  the  muscles,  and,  as  in  the  case  of  the  liver,  found 
values  which  were  not  different  from  the  normal.  The  only  striking  fact 
was  the  high  percentage  of  water.  In  spite  of  this  agreement  of  com- 
position in  the  case  of  the  liver  and  muscles  (which  obviously  play  the  most 
important  part  in  the  metabolism  of  carbohydrates)  with  the  values 
obtained  under  normal  conditions,  it  is  on  no  account  permissible  to  draw 
the  conclusion  that  as  a  matter  of  fact  there  has  been  no  change  in  the 
materials  which  go  to  make  up  these  tissues.  As  we  shall  see  subse- 
quently, our  methods  of  analysis  are  not  sensitive  enough,  and  our  knowledge 
of  the  cell-constituents  is  far  too  inadequate  for  us  to  attempt  to  answer 
such  questions  with  exactness.  It  is  of  importance,  first  of  all,  to  know 
that  so  far  as  we  are  now  able  to  judge,  the  liver,  like  the  organs  indis- 
pensable to  life  [e.g.,  the  brain,  heart,  and  kidneys],  is  protected  during 
inanition  at  the  cost  of  all  other  tissues.  From  this  the  conclusion  may 
be  drawn  that  evidently  the  liver  is  not  simply  cut  off  from  the  metabolism 
of  carbohydrates  during  the  whole  duration  of  glucosuria,  but,  on  the 
contrary,  is  continually  acting  vigorously.  It  gives  up  the  large  amounts 
of  sugar  which  are  found  in  the  urine,  and  in  it  evidently  takes  place,  as  we 
shall  see,  the  transformation  into  sugar  of  substances  not  belonging  to  the 
carbohydrate  group. 

The  fact  that  the  sugar  content  of  the  blood  rises  after  total  extirpation 
of  the  pancreas,  while  at  the  same  time  the  glycogen  content  of  the  organs, 
the  liver  especially,  remains  low,  is  a  matter  of  considerable  importance. 
A  true  glucohemia  naturally  ensues  which  causes  glucosuria.  Thus  the 
cause  is  the  same  as  in  all  the  other  cases  of  sugar  elimination,  which  have 
been  observed  up  to  the  present  time,  phloridzin  glucosuria  possibly 
forming  an  exception.  We  are  now  ready  to  take  up  the  question  as  to  what 
causes  the  glucohemia.  It  is  a  matter  of  fact  that  it  appears  as  soon 
as  the  pancreatic  gland  is  removed,  which  suggests  the  thought  that  the 
loss  of  the  function  of  this  gland  is  the  cause  of  the  observed  disturbance. 
First  of  all  we  must  remember  that  the  pancreas  plays  an  important  part 
in  the  digestion  taking  place  in  the  alimentary  canal.  We  have  seen  that 
the  breaking  down  of  starch  in  the  bowels  is  brought  about  principally  by 
the  action  of  the  diastase  from  the  pancreatic  gland.  On  the  other  hand, 
it  is  certain  that  on  taking  away  the  ferments  of  the  pancreas  the  absorption 
and  assimilation  of  all  the  remaining  foods,  and  consequently  the  whole 
metabolism,  must  suffer.  We  have  then  to  decide,  first  of  all,  whether  the 
glucosuria  produced  by  the  removal  of  the  pancreas  can  be  traced  to  the 
absence  of  the  digestive  ferments.  This  must  be  answered  in  the  nega- 
tive, because,  for  one  thing,  if  the  ducts  of  the  pancreas  are  ligated, 
glucohemia  does  not  develop.  Then  again  the  greater  part  of  the 


86  LECTURE  V. 

gland  may  be  removed,  and,  in  fact,  that  portion  directly  connected 
with  the  intestine,  and  glucosuria  does  not  take  place  as  long  as  a  small 
part  of  the  tissue  of  the  gland  still  remains  in  the  body.  A  further  proof 
that  pancreatic-glucosuria  is  not  intimately  connected  with  digestion  is 
shown  by  the  fact  that  in  the  case  of  total  extirpation  of  the  gland,  sugar 
still  appears  in  the  urine  after  prolonged  starvation,  i.e.,  after  the  stomach 
and  intestines  have  become  empty.  Furthermore,  it  is  not  possible  to 
influence  the  existing  glucosuria  by  feeding  the  gland  to  the  animal.  It  is 
interesting  that  after  a  partial  elimination  of  the  pancreas  the  assimilation 
limit  for  sugar  is  considerably  decreased.  This  is  shown  by  the  fact  that 
an  animal  experimented  upon  which  did  not  show  glucosuria  would 
eliminate  sugar  in  the  urine  when  the  amount  of  carbohydrates  fed  to  it 
was  increased,  especially  if  the  food  contained  glucose. 

It  is  particularly  significant  that  a  small  piece  of  the  gland  tissue 
usually  suffices  to  keep  the  entire  metabolism  of  carbohydrates  in  nor- 
mal paths.  This  was  shown  very  strikingly  by  the  experiments  of 
Minkowski,  which  proved  conclusively  that  it  was  not  the  severe  operation 
itself,  but  the  total  removal  of  the  pancreas  function,  that  caused  the 
great  disturbance  in  the  metabolism  of  carbohydrates.  In  dogs  the  lowest 
part  of  the  descending  branch  of  the  pancreas  does  not  grow  together  with 
the  duodenum,  but  lies  free  in  the  mesentery.  Minkowski  separated 
this  piece  from  the  remaining  tissue  of  the  pancreas  so  that  it  was  still  iri 
connection  with  the  mesentery  and  without  disturbing  its  supply  of  blood 
and  lymph  vessels.  This  piece  of  pancreas  was  then  drawn  out  through 
the  abdominal  cavity,  grafted  under  the  skin,  and  allowed  to  heal  to- 
gether with  the  wound.  After  the  animal  had  survived  this  operation, 
the  abdomen  was  again  opened,  and  all  of  the  rest  of  the  pancreas  removed 
from  the  body.  Thus  only  the  small  portion  of  the  gland  which  had  been 
transplanted  under  the  skin  remained  in  the  animal,  and  yet  glucosuria  did 
not  ensue.  If,  however,  this  part  of  the  pancreas  was  finally  removed, 
sugar  appeared  in  the  urine  at  once. 

The  fact  that,  in  many  cases,  a  small  portion  of  the  pancreas  left  in  the 
body  serves  to  prevent  the  appearance  of  glucohemia,  suggests  to  us 
other  possibilities.  It  is  perfectly  conceivable  that  the  pancreatic  gland 
serves,  like  the  liver,  for  example,  to  neutralize  injurious  substances,  and 
especially  those  which  interfere  with  the  metabolism  of  carbohydrates. 
When  the  pancreas  is  removed,  these  products  perhaps  pass  unhindered 
into  the  circulation,  and  prevent  the  normal  breaking  down  of  sugar.  If 
this  view  were  correct,  it  would  follow  that  the  injection  of  the  blood  from 
an  animal  suffering  from  glucosuria  into  the  circulation  of  a  healthy 
animal  would  inevitably  produce  the  same  disease.  That  this  is  not  the 
case  was  shown  by  the  direct  experiments  of  Minkowski  and  von  Mering. 

The  only  remaining  explanation  of  pancreatic-glucosuria  would  seem  to 


CARBOHYDRATES.  87 

lie  in  the  assumption  that  the  pancreatic  gland  produces  a  substance  which 
either  directly  or  indirectly  influences  the  metabolism  of  carbohydrates. 
It  is  altogether  out  of  the  question  to  imagine  that  the  sugar  in  the  blood 
undergoes  any  change  by  passing  through  the  gland.  The  regulation  of 
the  carbohydrate  metabolism  must  take  place  indirectly,  i.e.,  the  tissue  of 
the  pancreas  influences  in  some  way  or  other  the  organs  whose  task  it  is 
to  build  up  or  to  consume  the  sugar.  This  assumption  has  gradually 
gained  ground,  especially  after  the  experimental  explanation  of  Lepine 
concerning  pancreatic-glucosuria  had  been  found  untenable.  Lepine,1  as 
has  been  mentioned,  discovered  the  presence  of  a  ferment  in  the  blood 
which  was  able  to  decompose  sugar.  This  glucolytic  ferment  was  assumed 
to  be  produced  by  the  pancreatic  gland.  The  ferment  was  supposed  to  pass 
continually  through  the  thoracic  duct  into  the  blood  and  circulate  in  this 
attached  to  the  white  corpuscles.  Lepine  found  that  in  animals  deprived 
of  the  pancreas  there  was  a  considerable  diminution  of  the  amount  of  this 
ferment,  or,  in  other  words,  the  power  of  the  blood  to  consume  sugar 
was  considerably  diminished.  Thus  the  assumption  was  made  that  pan- 
creatic-glucosuria was  a  result  of  the  fact  that  the  ferment  was  not  formed 
after  the  pancreas  was  removed.  Lepine's  views,  however,  were  soon 
contradicted,  and  to-day  the  hypothesis  may  be  said  to  be  completely 
shattered.  De  Dominicis,2  for  one,  showed  that  in  animals  suffering  from 
pancreatic-glucosuria  there  was  no  diminution  in  the  elimination  of  sugar 
when  blood  from  the  portal  vein  of  normal  animals,  which  according  to 
Lepine  would  be  rich  in  the  ferment,  was  injected  into  them.  On  the 
contrary,  the  result  was  that  the  glucosuria  became  more  severe.  Arthus  3 
found  that  the  blood  contained  in  ligated  vessels  was  not  capable  of 
decomposing  sugar,  and  therefore  contained  no  glucolytic  ferment.  More- 
over, from  many  sides  it  has  been  shown  that  glucolysis  appears  as  a  post- 
mortem phenomenon,  and  that  it  has  any  connection  with  the  metabolism 
of  carbohydrates  in  the  living  organism  has  been  flatly  denied.  In  fact,  the 
whole  theory  of  glucolysis  in  the  blood  rests  upon  an  extremely  slight 
foundation,  and  a  great  deal  maybe  said  against  it.  Lepine  in  his  experi- 
ment failed  entirely  to  take  into  consideration  many  phenomena  which 
appear  after  extirpation  of  the  pancreas,  such  as,  for  example,  the  fact  that 
after  the  operation  the  liver  loses  its  glycogen.  In  this  connection, 
Marcuse's  4  observation  is  interesting  that  glucosuria  in  frogs,  resulting 
from  extirpation  of  the  liver,  disappeared  if  at  the  same  time  the  pancreas 
was  removed. 

In  the  last  lecture,  we  found  that  the  muscles  are  the  chief  consumers 


1  Compt.  rend.  113,  729  (1891);i6wf.  113,  1014  (1891). 

2  Wiener  med.  Wochschr.  42-45  (1898). 

3  Arch.  Physiol.  1891,  425;  1892,  337. 

4  Z.  klin.  Med.  26,  225  (1894).     Cf.  A.  Montuori:  Arch,  ital.'biol.  25  (1896). 


88  LECTURE  V. 

of  sugar.  Their  necessary  supply  of  carbohydrates  is  regulated  by  the 
liver.  It  would  seem  possible,  therefore,  that  the  function  of  the  liver 
might  be  disturbed  in  some  way  by  the  removal  of  the  pancreas.  The 
liver  stores  up  the  resorbed  sugar  in  the  form  of  glycogen.  It  might  seem 
possible  that  the  liver  in  an  animal  deprived  of  the  pancreas  is  no  longer 
able  to  retain  the  resorbed  sugar,  i.e.,  withdraw  it  from  the  general  metab- 
olism, so  that  in  this  way  the  blood  is  flooded  with  sugar.  Now  Pfliiger,  as 
we  have  seen,  showed  that  the  liver,  even  after  long-continued  glucosuria,  is 
still  capable  of  forming  glycogen.  At  least  the  ability  is  not  entirely  want- 
ing. Furthermore,  this  assumption  does  not  explain  the  fact  that  starving 
animals  also  exhibit  glucohemia.  This  latter  fact  suggests  to  us  another 
way  in  which  the  liver-function  may  be  disturbed,  namely,  with  regard  to 
the  decomposition  of  glycogen.  Hand  in  hand  with  the  consumption  of 
sugar  in  the  muscles,  there  takes  place  the  transformation  of  the  stored- 
up  glycogen  into  sugar.  An  extremely  fine  regulating  mechanism  pre- 
vents large  amounts  of  glycogen  being  suddenly  decomposed  in  such  a 
way  that  the  blood  would  be  flooded  with  sugar.  We  have  already  met 
with  this  regulation  in  discussing  the  glucosuria  produced  by  the  "  diabetic 
puncture,"  and  the  elimination  of  sugar  in  the  urine  caused  by  the  injection 
of  salt  solution  into  the  circulation.  We  saw  at  that  time  how  evident  it 
was  that  nervous  influences  had  a  great  deal  to  do  with  keeping  the  glycogen 
condition  of  the  liver  along  definite  paths.  What  is  unexplained  is  merely  how 
the  breaking  down  of  the  glycogen  takes  place.  It  is  a  result  of  diastatic 
action.  It  is  inexplicable  why  the  diastase,  which  is  evidently  present  in 
the  liver,  at  one  time  attacks  the  glycogen  and  at  another  leaves  it  alone, 
unless  we  assume  that  either  the  glycogen  is  present  in  a  condition  such 
that  it  cannot  be  acted  upon  by  the  ferment,  i.e.,  is  in  some  form  of  loose 
chemical  combination,  or  that  the  diastase  becomes  active  only  at  the 
time  it  is  required.1  We  are  acquainted  with  many  ferments,  as  we  shall 
eventually  see,  which  are  secreted  by  the  cells  in  an  inactive  condition. 
In  such  cases  the  presence  of  another  substance  usually  formed  by 
an  entirely  different  kind  of  cells  is  necessary  in  order  to  make  the 
ferment  "  active."  Such  processes  have  not  been  sufficiently  studied 
in  the  case  of  diastase.  We  may  assume,  however,  that  by  union  with 
some  sort  of  substance,  perhaps  the  protoplasm  of  the  cells,  the  diastase 
is  inactive  and  becomes  free  only  at  such  a  time  when  it  is  needed.  At 


1  The  assumption  that  the  breaking  down  and  building  up  of  glycogen  takes  place 
in  the  same  way  that,  for  example,  a  hydrolysis  or  a  synthesis  may  be  brought  about 
artificially  by  the  action  of  one  and  the  same  ferment  according  to  the  concentration 
ratio  (cf.  p.  38)  is  not  well  established  at  present,  for  the  products  formed  artificially 
are  not  those  expected,  but  their  isomers ;  and  furthermore,  it  is  not  known  that  the  living 
cell  contains  the  condition  established  in  chemical  experiments.  Cf.  Hofmeister's  Die 
Chemische  Organisation  des  Zelle.  Viewig  and  Sohn,  Braunschweig,  1901. 


CARBOHYDRATES.  89 

present  our  knowledge  in  this  direction  is  still  too  slight  for  us  to 
attempt  to  discuss  in  the  light  of  experimental  data  any  disturbance 
in  the  glycogen  decomposition.  We  merely  wish  to  point  out  the  possi- 
bility, and  to  suggest  that  there  is  a  certain  analogy  between  pancreatic- 
glucosuria  and  the  disturbances  in  the  formation  of  sugar  which  have 
been  taken  up  previously  (diabetic  puncture,  etc.). 

Glucohemia  might  also  become  established  by  the  failure  of  the 
muscles  to  consume  sugar.  Unfortunately  we  know  very  little  con- 
cerning the  manner  in  which  the  muscles  consume  sugar,  and  conse- 
quently practically  nothing  concerning  the  possibilities  of  disturbing 
this  function.  In  analogy  to  other  processes,  it  has  been  suggested  that 
this  may  also  be  due  to  the  action  of  a  ferment,  a  conception  which  is  per- 
fectly plausible,  for  we  have  here  to  deal  with  either  a  direct  or  indirect 
protoplasmic  action.  Recently  O.  Cohnheim  1  has  studied  this  problem. 
He  showed  that  the  juice  obtained  from  the  pancreatic  gland  by  high 
pressure  was  not  capable  of  decomposing  sugar.  On  the  other  hand, 
sugar  was  not  attacked  by  the  expressed  juice  from  the  muscles.  Cohn- 
heim found,  however,  that  on  bringing  together  the  juices  from  both  of 
these  organs,  glucolysis  took  place  at  once.  He  explained  this  fact  by 
considering  the  analogy  with  observations  made  with  other  ferments,  and 
assuming  that  the  muscles  produce  a  ferment  which  is  inactive,  i.e.,  inca- 
pable by  itself  of  attacking  sugar.  This  muscular  ferment  is  activated  by 
a  substance  obtained  from  the  pancreatic  gland  and  brought  to  it  by  the 
blood  circulation.  This  would  readily  explain  pancreatic-glucosuria.  It 
must  be  remembered,  however,  that  this  conception  does  not  explain  all 
of  the  phenomena  observed  in  pancreatic-glucosuria;  thus,  for  example, 
it  does  not  account  at  all  for  the  fact  that  the  glycogen  stores  of  the  liver 
disappear.  On  the  other  hand,  there  is  absolutely  no  reason  for  assuming 
that  the  pancreas  has  only  one  function  with  regard  to  the  metabolism  of 
carbohydrates.  It  is,  indeed,  possible  that  it  has  different  effects  upon 
different  organs,  and  that,  furthermore,  when  the  functions  and  metabolic 
effect  of  the  different  organs  become  disturbed,  they  again  bring  into  play 
secondary  influences  of  the  organs  upon  one  another,  so  that  one  disturb- 
ance causes  a  number  of  complications. 

If  we  summarize  all  that  we  know  positively  concerning  the  cause  of  the 
glucohemia  resulting  from  extirpation  of  the  pancreas,  we  may  say  that 
we  have  to  deal  with  a  disturbance  in  the  regulation  of  the  transforma- 
tion of  sugar,  and  that  evidently  the  pancreatic  gland  gives  up  to  the  blood 
some  substance  which  regulates  the  metabolism  of  carbohydrates.  This 
function  of  the  pancreas,  in  contrast  to  its  other  function  of  forming  and 

1  Z.  physiol.  Chem.  39,  336  (1903);  42,  401  (1904);  43,  547  (1905).  For  objections 
to  Cohnheim's  conclusions,  see  Glaus  andEmbden:  Pankreas  und  Glycolyse,  Hofmeister's 
Beitrage,  6,  214,  343  (1905). 


90  LECTURE  V. 

secreting  the  digestive  ferment,  is  spoken  of  as  that  of  an  internal  secretion. 
An  internal  secretion  is  something  formed  within  a  glandular  organ  and 
given  off  to  the  blood  or  lymph.  The  ordinary  pancreatic  juice  is  called 
an  external  secretion. 

The  discovery  by  Langerhans  1  of  a  peculiar  segregation  of  cells  in  the 
pancreatic  gland  led  to  discussion  as  to  whether  the  gland  possesses  partic- 
ular cells  for  its  various  functions.  These  cell-forms  —  called  islands  of  Lan- 
gerhans —  which  stand  out  very  sharply  from  the  other  cells  in  the  gland 
differ  from  the  latter  not  only  in  outward  appearance,  but,  by  the  fact  that, 
unlike  the  ordinary  secretory  cells,  they  have  no  connection  with  the  exit 
ducts  from  the  gland.  More  recently  Diamare  and  Kuliabko  2  have  taken 
up  anew  the  question  as  to  the  significance  of  these  cells.  They  studied 
the  pancreatic  glands  of  the  Teleostei  because  in  these  animals  the  islands  of 
Langerhans  are  relatively  large,  and  preparations  of  them  may  be  easily 
made  free  from  the  other  cells  of  the  pancreas  tissue.  They  found  that 
only  the  ordinary  cells  of  the  gland  produced  an  amylolytic  ferment, 
while  the  cells  of  the  islands  of  Langerhans  possessed  the  power  of  destroy- 
ing dextrose.  This  sums  up  all  that  we  know  concerning  these  islands  of 
Langerhans,  and  it  remains  undecided  as  to  whether  they  form  an  internal 
secretion  or  not.  We  shall  come  back  to  this  point  in  the  discussion  of 
diabetes. 

Changes  in  the  pancreatic  gland  had  been  observed  before  the  discovery 
of  pancreatic  glucosuria,  namely  in  the  so-called  diabetes  mellitus  of 
man.  Although,  in  discussing  the  phenomena  of  this  pathological  degen- 
eration, we  are  leaving  the  proper  field  of  physiological  chemistry,  we  will, 
nevertheless,  take  it  up  more  or  less  in  detail,  because  in  this  disease  we 
have  in  a  certain  sense  an  experiment  brought  about  by  Nature,  which 
serves  to  give  us  some  insight  into  the  normal  metabolism  of  carbohy- 
drates. We  shall,  however,  discuss  the  disease  only  in  so  far  as  it  is  directly 
or  indirectly  connected  with  the  metabolism  of  carbohydrates,  and  leave 
the  discussion  of  the  remaining  clinical  symptoms  of  this  very  interesting 
disease  to  the  text-books  on  clinical  medicine. 

Diabetes  has  been  known  for  a  long  time.3  The  Indian  and  Arabian 
physician  of  the  Middle  Ages  recognized  the  fact  that  associated  with  the 
disease  was  the  elimination  of  a  sweet  substance  in  the  urine.  It  remained 
for  Thenard,  in  1806,  to  isolate  this  sweet  substance;  Chevreul  crystallized 


1  Beitrage     zur     mikroskopischen     Anatomie    der     Bauchspeicheldriisen,    Berlin. 
Dissert.  1869. 

2  Zentr.  Physiol.  18,  432  (1904). 

3  Cf.  Max  Salomon:  Geschichte  der  Glukosurie  von  Hippokrates  bis  zum  Anfang  des 
19  Jahrhunderts,  Deutsches  Arch.  klin.  Med.  8,  489  (1871),  and  E.  O.  v.  Lippmann: 
Zur  Geschichte  des  diabetischen  Zucker.  Chem.-Ztg.  29,  1197  (1905). 


CARBOHYDRATES.  91 

it  in  1815;  while  Bouchardat l  and  Peligot2  succeeded  in  identifying  it  as 
dextrose,  or  grape-sugar,  in  1838. 

The  cause  of  this  disease  has  for  a  long  time  been  attributed  to  a  marked 
glucohemia.  This  naturally  does  not  account  for  the  whole  nature  of  the 
disease,  but  is  only  one  of  many  symptoms.  It  may  be  caused  in  a  number 
of  different  ways;  and,  according  to  all  we  know  at  present  regarding 
diabetes,  there  is  no  longer  any  doubt  that  diabetes  does  not  represent 
a  single  disease,  but  rather  that  the  glucohemia,  or  rather  the  resulting 
glucosuria,  is  merely  a  symptom  most  readily  recognized,  and  is  produced 
by  the  most  varied  pathological  conditions.  For  this  reason  it  would  be 
out  of  the  question  to  attempt  to  find  a  common  cause  of  glucohemia. 
The  disturbance  in  the  metabolism  of  the  carbohydrates  varies  in  different 
cases. 

We  distinguish  between  a  light  and  severe  form  of  diabetes.  In  some 
cases  sugar  is  eliminated  in  the  urine  only  after  the  patient  has  partaken 
of  starch  or  of  glucose.  In  such  cases  there  is  no  noticeable  glucosuria 
if  the  diet  is  restricted  to  meat  and  fats.  These  mild  forms  show  all 
stages  of  alimentary  glucosuria,  and  make  it  seem  probable  that  the  limit 
of  an  assimilation  for  carbohydrates  has  been  considerably  diminished. 
In  many  cases  sugar  is  found  in  the  urine  only  when  carbohydrates  are 
eaten  on  an  empty  stomach.  Often  muscular  work  suffices  to  arrest  the 
sugar  elimination.  In  other  cases,  the  glucosuria  lasts  only  while  the 
absorption  of  sugar  continues  in  the  intestine.  The  cause  of  this  kind  of 
diabetes  is  generally  attributed  to  a  weakening  of  the  liver  function.  The 
latter  is  obviously  not  able  to  work  over  the  sugar  quickly  enough  into 
glycogen.  It  permits  too  much  sugar  to  get  into  the  circulation.  Thus 
a  glucohemia  results,  which  after  a  time  is  compensated  by  the  elimination 
of  sugar  by  the  kidneys,  only  to  appear  again  from  the  same  cause  as  before. 
Against  this  assumption  the  objection  has  been  raised  that  the  liver  may 
suffer  most  severe  changes,  without  the  appearance  of  sugar  in  the  urine. 
This  is,  however,  not  a  serious  objection,  for  we  know  that  the  liver  has 
quite  a  number  of  different  functions,  of  which  each  is  to  a  certain  extent 
independent  of  the  others,  so  that  one  function  by  itself  may  be  disturbed. 
It  does  not  follow  that  every  disease  of  the  liver  will  attack  that  part  of 
the  cells  which  participates  in  the  regulation  of  carbohydrate  metabolism. 
A  general  weakening  of  the  activity  of  the  liver  cells  can  cause  diabetes ; 
thus  it  is  met  with  in  persons  of  undermined  constitution.  Possibly  the 
fact  established  by  Hofmeister  3  that  dogs,  after  all  forms  of  nourishment 
had  been  withheld  for  a  considerable  time,  eliminated  sugar  in  the  urine, 


1  Compt.  rend.  6,  337  (1838). 

3  Ibid.  7,  106  (1838). 

3   Arch.  exp.  Path   Pharmak.  26,  355  (1890). 


92  LECTURE  V. 

shows  that  many  forms  of  glucosuria  belong  in  this  category.  It  is  not 
impossible,  but  on  the  contrary  extremely  probable  that  many  of  these 
light  forms  of  diabetes  result  from  conditions  similar  to  those  resulting 
from  the  diabetic  puncture,  etc.  The  only  difference  here  is  probably 
that  in  the  case  of  the  operation  we  have  but  a  single  shock  to  the  system, 
whereas  here  there  is  evidently  a  permanent  irritation  of  the  sugar  center. 
This  coincides  with  the  fact  that  many  persons  afflicted  with  the  disease 
are  very  nervous. 

Between  these  light  forms  of  diabetes  and  the  more  severe  types,  there 
are,  as  we  have  said,  all  stages  of  intermediate  types,  and  not  infrequently 
the  former  change  into  the  latter.  In  the  first  case  the  disease  is  not  of 
a  very  bad  character,  and  appears  chiefly  in  elderly  people,  producing 
symptoms  which  are  easily  understood,  but  in  the  more  serious  types  we 
are  astonished  at  the  severity  of  the  disease.  How  great  the  disturb- 
ance in  the  carbohydrate  metabolism  is,  may  be  illustrated  by  the  fact 
that  the  elimination  of  sugar  continues  even  after  carbohydrates  are 
entirely  withheld  from  the  diet,  and  the  patient  eats,  for  example,  only 
meat  and  fat. 

Let  us  now  turn  our  attention  to  the  main  symptom  of  diabetes,  the 
glucohemia.  Why  does  this  exist?  There  are  a  priori  two  possibil- 
ities. On  the  one  hand,  the  amount  of  sugar  formed  may  be  abnormally 
large;  or,  on  the  other  hand,  the  sugar  produced  normally  may  not  be 
consumed  as  it  should  be,  and  thus  lies  unutilized  in  the  tissues  only  to  be 
removed  finally  from  the  organism  as  a  waste-product.  The  last  expla- 
nation is  really  the  more  plausible;  for  although  we  can  easily  conceive 
that  there  mi0ht  be  temporarily  an  increased  formation  of  sugar,  possibly 
from  fat  or  perhaps  from  albumin,  it  is  not  easy  for  us  to  understand 
how  thi  cou'.d  taLe  place  continuously.  Furthermore,  the  whole  behavior 
of  the  patient  does  not  correspond  to  any  such  assumption.  Fats  and 
albumin  agree  with  him.  With  their  help  and  the  removal  of  carbo- 
hydrates from  the  diet,  it  is  possible  greatly  to  diminish  the  elimination  of 
sugar.  On  the  other  hand,  the  glucosuria  immediately  becomes  more 
severe  if  carbohydrates  are  fed  to  the  sick.  In  these  severe  cases  we  cannot 
account  for  the  facts  by  assuming  that  the  liver  has  lost  its  power  of  storing 
up  sugar  in  the  form  of  glycogen.  The  disease  continues  during  a  period 
of  fasting,  long  after  all  carbohydrates  have  left  the  alimentary  canal. 

The  fact  that  the  liver  actually  retains  its  ability  of  storing  up  sugar  in 
the  form  of  glycogen  is  proved  by  the  fact  that  glycogen  has  been  re- 
peatedly found  in  the  livers  of  those  who  have  suffered  from  severe 
diabetes.1  This,  however,  is  not  always  the  case.  Sometimes  the  liver 

1  Cf.  Kiihne:  Virchow's  Arch.  32,  536  (1865).  Jafte:  ibid.  36,  20  (1866).  Kiilz: 
Pfliiger's  Arch.  13,  267  (1876).  J.  v.  Mering:  ibid.  14,  274  (1877).  Abeles:  Zentr. 
med.  Wissensch.  23,  449  (1885).  F.  Th.  Frerichs:  Ueber  den  Diabetes,  Berlin,  1884. 


CARBOHYDRATES.  93 

contains  glycogen,  and  sometimes  it  does  not  contain  a  trace  of  this  poly- 
saccharide.  This  is  not  astonishing  when  we  remember  that  the  name 
diabetes  includes  quite  a  number  of  different  diseases,  all  of  which  show 
the  common  symptom  of  glucohemia. 

We  will  now  attempt  to  answer  the  question  as  to  whether  diabetes  can 
be  explained  entirely  on  the  assumption  that  it  is  due  to  a  diseased  pancreas. 
It  is  certainly  interesting  to  compare  diabetes  with  the  glucosuria  pro- 
duced by  extirpation  of  the  pancreas.  It  has  been  shown  in  many  cases 
that  the  pancreas  of  diabetics  was  diseased,  and  there  is  absolutely  no 
doubt  but  that  there  are  forms  of  diabetes  which  originate  in  a  disturbance 
of  the  functions  of  the  pancreatic  gland.  Recently  changes  have  been 
noticed,  particularly  at  the  islands  of  Langerhans,  and  also  many  degen- 
erations have  been  observed,  e.g.,  hyaline  degeneration.  At  the  present 
time  it  is  impossible  to  decide  whether  the  conclusion  may  be  drawn  that 
there  is  positively  a  connection  between  the  cells  of  the  Langerhans  group 
and  the  metabolism  of  carbohydrates.  At  all  events,  the  fact  that  in  many 
cases  of  diabetes  the  post-mortem  examination  shows  these  cells  to  be 
absolutely  normal,  does  not  necessarily  show  that  any  such  assumption  is 
false,  for  it  is  not  possible  to  trace  all  forms  of  diabetes  back  to  a  common 
cause;  and  furthermore,  the  fact  that  there  is  no  noticeable  histological  sign 
of  a  change  having  taken  place  in  the  tissues,  does  not  prove  that  the  cells 
have  suffered  nothing  as  regards  their  functional  activity.  Perhaps  the 
researches  of  Diamare  and  Kuliabko  *  will  eventually  settle  this  question. 

Let  us  return  to  the  question  as  to  the  sugar  formed  not  being  consumed. 
It  is  possible  that  diabetics  in  general  have  a  limited  capacity  for  oxida- 
tion. On  the  other  hand,  the  fact  that  the  other  forms  of  nourishment  are 
taken  care  of  normally  speaks  a  priori  against  any  such  assumption.  The 
following  experiments  are  a  direct  proof  that  the  organism  of  diabetics 
possesses  its  full  oxidation  capacity.  O.  Schultzen  2  found  that  diabetics 
readily  consume  the  alkali  salts  of  lactic  and  the  vegetable  acids,  also 
inosit  and  mannitol.  M.  Nencki  and  N.  Sieber  3  observed  that  patients 
suffering  from  severe  diabetes  could  take  care  of  the  difficult  ly-oxidiz  able 
benzene  just  as  well  as  the  healthy  organism  could.  Direct  respiration 
experiments  likewise  showed  that  the  respiratory  exchange  in  such  cases 
—  severe  cases  of  diabetes  —  did  not  vary  from  the  proper  physiological 
relations.  It  is  true  that  von  Pettenkofer  and  C.  Voit 4  found  that  there 
was  a  considerable  diminution  in  the  inspired  oxygen  and  expired  carbon 
dioxide,  and  drew  the  conclusion  that  this  was  due  to  a  decreased  capacity 
for  oxidation;  but  this  conclusion  was  later  abandoned  by  Voit5  himself, 


1  Loc.  dt.  2  Ber  klin  Wochschr.  No.  35  (1875). 

3  J.  pr.  Chem.  N.  F.  26,  35  (1882).  4  Z.  Biol.  3,  380  (1867). 

5  Physiol.  allg.  Stoffwechsels  und  der  Ernahrung  (1881),  p.  227,  et  seq. 


94 


LECTURE  V. 


who  found  that  the  limited  absorption  of  oxygen  was  a  result  of  the  dis- 
turbed carbohydrate  metabolism,  rather  than  the  cause  of  it.  The  absorp- 
tion of  oxygen  depends  upon  the  combustion  taking  place  in  the  body. 
Leo,1  as  well  as  Weintraud  and  Laves,2  has  finally  shown  that  the  amount 
of  absorbed  oxygen  is  the  same  with  healthy  people  that  it  is  with  those 
suffering  from  diabetes  of  equal  weight  and  condition  of  nourishment,  and 
finally  that  the  apparent  decrease  in  the  elimination  of  carbonic  acid  is 
caused  by  the  faulty  decomposition  of  carbohydrates. 

Of  especial  importance  as  regards  the  cause  of  the  insufficient  consump- 
tion of  the  sugar  formed  in  the  organism  are  the  experiments  performed  by 
O.  Baumgarten 3  under  the  direction  of  von  Mering.  Baumgarten,  at  von 
Mering's  suggestion,  tried  some  feeding  experiments  upon  diabetics,  and 
upon  dogs  with  removed  pancreas,  employing  substances  which  are  re- 
garded as  decomposition  or  oxidation  products  of  the  sugars.  It  was 
found  that  d-gluconic  acid,  d-saccharic  acid,  mucic  acid,  glucuronic  acid, 
glucosamine-hydrochloride,  succinic  acid,  d-tartaric  acid,  salicylic  alde- 
hyde and  vanillin,  were  consumed  by  diabetics  just  as  readily  as  by 
healthy  individuals.  The  following  summary  illustrates  the  relation 
between  some  of  these  products  and  d-glucose  (also  called  dextrose,  or 
grape-sugar) : 

CHO       'COOH      CHO      COOH     COOH 
H— C— OH   H— C— OH   H— C— OH  H— C— OH  H— C— OH* 

HO— C— H   HO— C— H   HO— C— H  HO— C— H  HO— C— H 

I          I          I         I          I 
H— C— OH   H— C— OH   H— C- OH  H— C— OH  HO— C— H 

I          I          I         I          I 
H— C— OH   H— C— OH   H— C— OH  H— C— OH  H— C— OH 

I                         I  1 

CH2OH            CH2OH            COOH             COOH  COOH 

d-glucose          d-gluconic  d-glucuronic  d-saccharic  d-mucic 

acid                    acid                   acid  acid 

These  experiments  show  that  the  organism  of  diabetics  can  decompose 
in  the  same  way  as  the  healthy  organism,  substances  which  in  their  alde- 
hydic  nature  are  closely  related  to  dextrose,  and  are  to  be  regarded  as 
direct  oxidation  products  of  dextrose;  in  other  words,  a  very  slight 
oxidation  of  the  sugar  molecule  suffices  to  enable  the  organism  of  the 
diabetic  to  attack  it.  In  this  way  the  views  expressed  by  Scheremet- 
jewski,4  Schultzen,5  A.  Cantani,6  and  of  Nencki  and  Sieber  gain  ground; 

1  Z.  klin.  Med.  19  (1890).  2  Z.  physiol.  Chem.  19,  603  (1894);  19,  629  (1894). 

3  Z.  exper.  Path.  u.  Therapie,  2,  53  (1905). 


4  Arbeiten  aus  dem  physiol.  Institut  zu  Leipzig,  1868. 
6  Loc.  cit.  8  Du  Diabetes  mellitus,  Berlin,  1877. 


CARBOHYDRATES.  95 

and,  as  a  matter  of  fact,  it  seems  probable  that  the  principal  cause  of 
glucohemia  and  the  resulting  glucosuria  is  that  the  organism  has  lost  the 
power  of  splitting  the  sugar  molecule.  The  complete  combustion  of  the 
glucose  molecule  is,  according  to  this  view,  always  dependent  upon  a 
previous  hydrolysis,  or  some  attack  which  loosens  up  the  sugar  molecule 
and  disturbs  the  condition  of  equilibrium;  without  some  such  action  the 
combustion  cannot  take  place  in  the  organism.  This  assumption  is  sub- 
stantiated by  the  fact  that  glucose  is  very  readily  consumed  by  the  healthy 
organism,  even  more  readily  than  is  the  case  with  other  foods.  Thus  in 
phosphorus  poisoning,  the  oxidizing  power  is  lost  to  a  considerable  extent 
without  the  appearance  of  glucosuria. 

We  have  again  come  back  to  the  undecided  question  concerning  the 
normal  breaking  down  of  sugar.  The  answer  depends  upon  the  explana- 
tion of  the  inability  of  diabetics  to  break  up  glucose.  It  is  easy  to  con- 
ceive that  the  principal  places  of  sugar  consumption,  the  muscles,  produce 
a  ferment  which  serves  first  of  all  to  loosen  up  the  glucose  molecule  and 
thus  prepare  it  for  oxidation.  That  the  glucose  is  not  itself  directly 
oxidized  is  very  plausible.  In  this  way,  the  sugar  stores  in  the  organism 
are  in  a  measure  protected.  Only  at  the  moment  of  the  expenditure  of 
energy  do  the  muscular  cells  prepare  the  dextrose  molecule  for  consump- 
tion. As  to  why  the  diabetic  has  lost  this  power,  whether  the  ferment 
which  starts  the  process  is  missing,  or  whether  he  has  lost  the  power  of 
activating  this  ferment,  are  questions  which  cannot  be  answered  positively 
at  the  present  time.  An  important  observation  has  been  made  that  when 
cane-sugar  is  taken  into  the  system  often  only  one  half  of  the  molecule 
appears  subsequently  in  the  urine.  This  is  due  to  the  fact  that  many 
diabetics  are  able  to  oxidize  and  assimilate  fructose  without  difficulty.1 
In  fact,  because  the  liver  can  in  such  cases  take  care  of  fructose  and  not  of 
glucose,  it  has  been  proposed  to  feed  diabetics  a  carbohydrate,  such  as 
inulin,  which  on  being  hydrolysed  yields  fructose  rather  than  glucose. 
Unfortunately,  however,  the  above  carbohydrate  is  so  difficultly  digestible, 
that  the  experiment  has  not  met  with  much  success.2  At  all  events,  it  is 
most  remarkable  that  the  liver  should  transfer  fructose  into  glycogen, 
a  process  which  according  to  the  generally  accepted  opinion  involves  the 
intermediate  formation  of  glucose;  and  yet  should  not  be  able  to  use  the 
glucose  which  it  receives  as  such. 


1  E.  Kiilz:  Beitrage  zur  Pathologic  und  Therapie  des  Diabetes  mellitus,  p.  130,  Mar- 
burg, 1874.     Worm-Muller:  Pfliiger's  Arch.  34,  576  (1884);  36,  172  (1885).     F.  Hof- 
meister:  Arch,  exper.  Path.  Pharm.  25,  240  (1889).     J.  Haycraft:  Z.  physiol.  Chem. 
19,  137  (1894).     Minkowski:  Arch,  exper.  Path.  Pharm.  31,  158  (1898).     Sandmeyer: 
Z.  Biol.  31,  12  (31)  (1894).     Fr.  Voit:  Z.  Biol.  29,  147  (1892).     Socin:  Wie  verhalten 
sich  Diabetiker  Lavulose-  und  Milchzuckerfiitterung  gegeniiber?    Dissert.  Strassburg, 
1894. 

2  Sandmeyer:  loc.  cit.  and  Miura:  Z.  Biol.  32,  279  (1895). 


96  LECTURE  V. 

The  assumption  that  in  some  way  or  other  the  muscles  have  lost  the 
power  of  preparing  sugar  for  consumption  does  not  explain  the  cause  of 
diabetes,  for  the  real  beginning  of  the  chain  of  disturbances  which  con- 
stantly brings  into  play  new  effects  is  not,  it  is  certain,  to  be  attributed 
originally  to  a  faulty  combustion  of  sugar;  in  fact,  the  combustion  of 
sugar  is  not  entirely  lost  in  the  organism  of  diabetics.  We  come  back 
here,  as  in  the  case  of  most  disturbances  in  metabolism,  to  the  individual 
cells  themselves  and  their  dependence  upon  the  nervous  system.  Even 
if  we  attribute  the  breaking  down  and  formation  of  glucose  entirely  to 
the  action  of  ferments,  we  fail  even  then  to  get  around  the  responsibility  of 
the  cells,  for  it  is  they  which  form  the  ferment,  and  the  production  of  the 
latter  seems  in  many  cases  to  be  dependent  upon  nervous  influences. 
Now  if,  furthermore,  we  add  to  this  the  fact  that  many  ferments  are 
known  which  are  secreted  by  the  cells  in  an  inactive  condition,  and  are 
only  activated  by  means  of  a  second  ferment  produced  by  other  cells  — 
often  those  of  another  organ  —  then  it  becomes  easy  for  us  to  understand 
how  disturbances  may  originate  at  countless  places  in  the  whole  mechanism. 
These  all  together  may  accomplish  the  final  effect,  namely,  a  glucohemia 
in  consequence  of  the  non-consumption  of  a  part  at  least  of  the  glucose, 
whether  on  account  of  a  disturbance  in  the  nervous  system,  or  the  fact  that 
the  activating  agent  (perhaps  furnished  by  the  pancreas)  is  lacking,  or 
whether  it  may  be  because  the  muscular  cells  themselves  are  diseased. 
In  discussing  these  possibilities,  it  must  be  brought  forward  once  again 
that  in  glucohemia  we  have  merely  a  symptom,  a  consequence  and  not  a 
cause,  which  without  question,  by  means  of  the  resulting  changes  in  the 
composition  of  the  tissue  and  of  the  blood,  may  effect  all  sorts  of  secondary 
disturbances,  and  which  again,  by  a  continuous  circulus  vitiosus,  tends  to 
diminish  the  life  energy  of  the  body  cells  and  aggravate  more  and  more 
the  nature  of  the  disease.  In  investigating  the  causes  of  pathological 
phenomena,  the  endeavor  must  be  more  and  more  to  study  the  purely 
functional  disturbances  on  the  basis  of  biological  experiments,  for  doubt- 
less such  may  be  present  without  there  being  any  indication  of  mor- 
phological changes  discernible  by  present  methods  of  investigation. 

We  have  learned  to  consider  glucosuria  as  an  essential  symptom  of  all 
forms  of  diabetes.  It  can  attain  quite  remarkable  proportions:  —  in  a 
single  day  as  much  as  a  kilogram  (2.2  pounds)  of  sugar  may  be  eliminated. 
Besides  glucose  we  occasionally  meet  with  an  elimination  of  other  kinds 
of  sugar;  for  example,  fructose  and  certain  pentoses.  Furthermore,  in 
the  urine  of  diabetics,  often  higher  molecular  sugars,  such  as  maltose  and 
dextrin-like  compounds,  have  been  detected  without  our  being  able  to 
draw  any  conclusions  from  the  occurrence  of  these  products  of  an  evidently 
incomplete  combustion,  as  to  the  nature  of  the  disturbance  in  the  metab- 
olism of  carbohydrates.  In  severe  cases  of  diabetes  the  urine  has  a 


CARBOHYDRATES.  97 

peculiar,  fruity  odor  which  was  noticed  by  the  older  physicians.  This  is 
due',  as  C.  Gerhardt x  supposed  and  v.  Jaksch2  has  shown,  to  the  presence 
of  acetoacetic  acid  (CH3CO)CH2  .  COOH.  Besides  this  compound  acetone 
CH3  .  CO  .  CH3  and,  as  Minkowski 3  has  shown,  ^-hydroxy-butyric  acid 
CH3CH(OH)CH2  .COOH,  are  also  present  in  many  cases.  All  three  of 
these  compounds,  as  a  glance  at  their  structural  formula?  will  show,  stand 
in  direct  relation  to  one  another.  Acetoacetic  acid  is  evidently  formed 
by  the  oxidation  of  /?-hy droxy-butyric  acid : 

*  CH3.CH(OH)  .  CH2  .  COOH  +  O  =  (CH3  .  CO)  CH2  .  COOH  +  H2O 
/?-hydroxy-butyric  acid  acetoacetic  acid 

From  acetoacetic  acid,  acetone  is  readily  formed  by  loss  of  carbon 
dioxide : 

(CH3  .  CO)CH2  .  COOH  =  CH3  .  CO  .  CH3  +  CO2 
acetoacetic  acid  acetone 

The  fact  that  in  many  cases  /?-hydroxy-butyric  acid  is  not  found  in  the 
urine  when  the  other  two  compounds  are  present,  is  not  remarkable,  for 
we  can  easily  understand  that  in  one  case  the  former  is  oxidized  and  in 
another  case  is  not.  /?-hydroxy-butyric  acid  contains,  as  the  above  formula 
indicates  (*),  an  asymmetric  carbon  atom,  —  i.e.,  it  is  optically  active;  as 
a  matter  of  fact,  the  left-rotating  form  is  always  eliminated. 

It  has  been  attempted  repeatedly  to  establish  the  origin  of  these  com- 
pounds in  the  urine,  and  especially  their  significance  as  regards  disease. 
It  is  above  all  worth  mentioning  that  the  occurrence  of  acetone  in  the 
urine  (acetonurid)  is  not  peculiar  to  diabetes.  To  some  extent  it  has  been 
observed  in  the  urine  of  many  fever  patients.  Acetone  and  acetoacetic 
acid  have  also  been  found  after  long-continued  inanition.4  Acetone  is 
also  eliminated  in  small  amounts  when  healthy  individuals  are  fed  exclu- 
sively with  albumin  and  fat.  All  of  the  acetone  does  not  leave  the  system 
through  the  kidneys,  but  a  part  is  given  off  by  the  lungs.  The  question  as 
to  the  origin  of  these  so-called  acetone  bodies  5  has  been  the  subject  of 
considerable  controversy.  The  simplest  explanation  is  that  they  are  in 
some  way  directly  connected  with  the  disturbance  in  the  metabolism  of 
carbohydrates,6  for  the  observation  that  acetonuria  occurs  after  inanition 


1  Wiener  med.  Presse,  28,  673  (1865).     Cf.  Fetters  Prager  Vierteljahresschrift,  65, 
81  (1857).     Jaksch:  Z.  physiol.  Chem.  7,  485  (1883). 

2  Ber.  15,  1496  (1882). 

3  Zentr.  med.  Wiss.  242  (1884).     Kiilz:  Arch,  exper.  Path.  Pharm.  18,  291  (1884); 
Z.  Biol.  20,  165  (1884);  23,  329  (1887).     O.  Minkowski:  Arch,  exper.  Path.  Pharm. 
31,  183  (1893).     Araki:  Z.  physiol.  Chem.  18,  1  (1894). 

4  von  Jaksch:  Ueber  Azetonurie  und  Diazeturie,  Berlin,  1895.     Fr.  Miiller:  Berlin, 
klin.  Wochschr.  428  (1887). 

5  H.  C.  Geelmuyden:  Z.  physiol.  Chem.  23,  431  (1897). 

6  Cf.  F.  Maignon:  Compt.  rend.  140,  1124  (1905). 


98  LECTURE  V. 

does  not  disagree  with  Hofmeister's  1  experiment  showing  that  glucosuria 
is  produced  in  starving  dogs.  It  has  been  proved,  however,  that  an 
existing  acetonuria  is  diminished  and  even  stopped  by  limiting  the  supply 
of  carbohydrates,  while,  on  the  other  hand,  it  is  a  matter  of  experience 
that  when  carbohydrates  are  entirely  removed  from  the  diet  of  diabetics 
the  direct  consequence  is  often  an  acetonuria.  For  this  reason  it  has  been 
attempted  to  ascribe  the  appearance  of  these  acetone  bodies  to  other 
sources,  to  albumin  especially.  The  appearance  of  the  acetone  bodies  is, 
according  to  one  view,  due  to  the  progressive  decomposition  of  albumin 
taking  place  in  severe  types  of  diabetes.  Now  there  is  no  parallel  between 
the  elimination  of  nitrogen  and  acetone  bodies.  In  starvation  experi- 
ments, for  example,  on  account  of  the  lessened  consumption  of  albumin 
during  the  first  days,  the  amount  of  acetone  eliminated  increases.2  Ac- 
cording to  Weintraud,3  diabetics  can  be  in  equilibrium  as  regards  nitrogen, 
or  may  even  add  to  their  nitrogen  without  the  elimination  of  acetone  being 
affected  in  the  slightest.  The  observation  made  by  Magnus-Levy  4  is  like- 
wise contrary  to  the  assumption  that  the  acetone  bodies  result  from  albumin; 
in  a  case  of  diabetes  there  were  262  grams  of  albumin  decomposed,  and  342 
grams  of  /?-hydroxy-butyric  acid  eliminated.  This  does  not  show  that  ace- 
tone cannot  be  formed  from  albumin,  for  there  may  be  more  than  a  single 
source;  and  then  again  the  discussion  of  this  question  brings  us  once  more 
to  the  possibility  of  one  food-stuff  being  converted  into  another.  Further- 
more, it  must  be  admitted  that  our  present  knowledge  concerning  the 
intermediate  decomposition  of  albumin  is  still  very  limited.  In  no  case 
does  it  follow  necessarily  that  the  amount  of  nitrogen  and  of  sulphur 
eliminated  is  to  be  taken  as  a  measure  for  the  total  decomposition  of  the 
albumin  introduced  into  the  body.  Again  the  point  may  well  be  raised 
that  the  carbon  eliminated  in  the  urine  represents  only  a  part  of  the 
carbon  contained  in  the  albumin,  and  the  remaining  carbon  can  be  retained 
in  the  system  for  a  considerable  time  after  all  of  the  nitrogen  and  sulphur 
have  been  eliminated.5  Again  there  is  much  to  be  said  in  favor  of  fat 
being  the  mother-substance  of  the  eliminated  acetone.  This  agrees  with 
the  fact  that  during  starvation  for  a  time  the  organism  performs  its  tasks 
at  the  expense  of  its  own  fat,  while,  at  the  same  time,  the  elimination  of 
acetone  increases.  The  fact  that  feeding  carbohydrates  lessens  the  ace- 


1  Loc.cit. 

3  Cf.  Giuseppe  Satta:  Hofmeister's  Beitrage,  6,  1  (21),  and  6,  376  (1904). 
8  Arch,  exper.  Path.  Pharm.  34,  169  (1894). 

4  Ibid.  42,  149  (1899),  and  45,  389  (1902). 

8  Acetone  has  been  obtained  in  the  laboratory  to  a  slight  extent  by  the  oxidation  of 
albumin.  These  experiments,  however,  have  no  relation  to  the  formation  of  acetone 
in  the  body.  The  amount  formed  is  far  too  small,  and  the  possible  source  in  fats  or 
carbohydrate  is  not  excluded. 


CARBOHYDRATES.  99 

tonuria  is  explained  by  a  decreased  decomposition  of  fat.  If  large  quan- 
tities of  albumin  are  fed  to  the  organism,  the  elimination  of  the  acetone 
bodies  is  likewise  abated.  Conversely,  if  the  diet  is  made  to  consist  of 
fat  with  exclusion  of  carbohydrates,  more  acetone  is  formed.  Schwarz  l 
observed,  moreover,  that  the  blood  of  diabetics  always  contains  an  exces- 
sive amount  of  fat. 

For  the  present,  we  must  leave  the  question  of  the  source,  or,  perhaps 
more  correctly  speaking,  the  sources,  of  the  acetone  bodies  as  undecided. 
We  know  just  as  little  concerning  their  place  of  formation. 

The  occurrence  of  acetone  bodies  in  the  blood  has  for  a  long  time  been 
considered   to   have   considerable  significance   concerning   the   course  of 
diabetes.     It  has  been  assumed  that  the  presence  of  acids  decreases  the 
alkalinity  of  the  blood,  and  thus  brings  about  severe  disturbances.     This, 
is,  in  general,  not  the  case,  because  the  organism  can  form  ammonia  which 
by  combining  with  acids  keeps  the  reaction  of  the  blood,  and  thereby  that 
of  the  tissues,  within  normal  limits.     The  fact  that  the  interchange  of 
oxygen  is  not  materially  altered  during  the  elimination  of  considerable 
amounts  of  these  aldehyde  bodies,  speaks  in  favor  of  this  assumption. 
Sometimes,    however,    there    takes    place  a   rapid   formation    of    large 
amounts  of  these  acetone  bodies,  resulting  in  considerable  injury  to  the 
whole  organism,  namely  in  coma  diabeticum.     By  this  name  is  meant  a 
complex  of  symptoms  which  very  often  occurs,  in  case  intercurrent  disease, 
has  not  carried  off  the  patient,  at  the  period  near  the  death  of  the  diabetic. 
The  condition  is  characterized  by  progressive  dyspnoea,  somnolence,  and 
sinking  of  the  body-temperature.     In  many  cases  the  patient  recovers, 
the  acetone  bodies  are  again  eliminated  in  the  urine,  and  the  organism  has 
time  to  combat  the  acid  by  the  formation  of  ammonia.     After  some  time 
the  symptoms  reoccur  with  increased  severity,  until  finally  the  patient 
dies  as  a  result  of  such  an  attack.     The  first  explanation  of  this  was  in 
attributing  a  specific   poisonous  action  to  the  acetone  bodies.     This  is, 
however,  as  direct  experiments  with  the  separate  substances  has  shown, 
not  the  case.2     Obviously  we  have  here  a  true  instance  of  acid  poisoning. 
The  blood  and  tissue  react  acid  after  a  diabetic  has  died  in  coma.     There 
takes  place,  together  with  this  change  in  the  reaction  of  the  blood,  a  diminu- 
tion in  the  processes  of  oxidation.     The  /?-hydroxy-butyric  acid  is  no  longer 
oxidized  to  acetoacetic  acid,  or  at  least  only  to  a  slight  extent.     Both  of 
these  acids  unite  with  the  free  alkali  in  the  blood.     This  explains  the  fact 
that  the  amount  of  carbonic  acid  in  the  blood  sinks  during  the  coma.     The 
fact  that  there  is  less  oxidation  in  the  organism  during  this  period  is  proved 
by  the  fact  that  various  products  of  the  hydrolysis  of  albumin  are  now 


1  Deut.  Arch.  klin.  Med.  76  (1903). 

J  F.  T.  Frerichs:   Z.  klin.  Med.    6,   3    (1883).     P.   Albertoni:   Arch,   exper    Path. 
Pharm.  18,  218  (1884).     Stadelmann:  ibid.  17,  419  and  443  (1883). 


100  LECTURE  V. 

found  in  the  urine.1  The  general  symptoms  during  coma  diabeticum,  as 
Walter  2  showed,  have  great  similarity  with  those  observed  during  experi- 
mental acid  poisoning.  He  injected  dilute  hydrochloric  acid  into  the 
stomach  of  rabbits  —  animals  which,  in  contrast  to  all  other  animals  which 
have  been  investigated,  are  not  able  to  combat  acid  by  the  formation  of 
ammonia  —  and  dyspnoea  soon  appeared.  The  carbonic  acid  content  of 
the  blood  was  greatly  lessened,  and  the  ammonia  in  the  urine  considerably 
increased.  By  subcutaneous  introduction  of  bicarbonate  of  soda  the 
symptoms  were  relieved,  and  the  animal  revived. 

The  formation  of  these  acetone  bodies  is  not  restricted  to  diabetes.  It 
takes  place  also  under  certain  conditions  in  all  the  different  kinds  of 
glucosuria.  There  is  always  some  disturbance  in  the  metabolism  of  carbo- 
hydrates, but  there  is  not  necessarily  a  direct  relation  between  the  two 
symptoms.  It  must  not  be  forgotten  that  actually  such  a  deep-seated 
disturbance  of  metabolism  as  exists  both  in  the  mild  and  chronic  forms 
of  glucohemia  can  never  exist  by  itself,  i.e.,  be  limited  in  its  effect  to  one 
class  of  substances.  Since  the  metabolism  of  the  organism  may  be  traced 
back  eventually  -to  the  metabolism  of  its  cells,  it  is  easy  to  see  how  much 
the  whole  metabolism  must  suffer  if  one  group  of  its  most  important 
nourishing  and  building  materials  becomes  afflicted.  It  is  readily 
comprehensible  that  in  the  course  of  time  the  metabolic  disturbance 
becomes  general,  and  the  metabolism  of  the  fats  and  albumins  suffers  as 
well.  It  is  from  this  point  of  view  that  we  must  regard  the  patient  suffer- 
ing from  a  severe  type  of  diabetes,  in  order  to  get  some  idea  of  the  whole 
scope  of  the  disturbance.  It  is  not  alone  the  loss  in  energy  which  goes 
on  during  the  constant  carrying  away  of  large  amounts  of  sugar,  and 
which  indeed  may  be  compensated  to  some  extent  by  other  food-stuffs, 
that  governs  the  whole  disease  and  makes  it  so  serious,  but  the  general 
derangement  of  the  entire  metabolism.  The  abnormal  composition  of 
the  blood  and  of  the  lymph  gives  rise  to  many  secondary  phenomena, 
the  resistance  of  the  tissues  and  cells  to  infection  is  diminished  (the  num- 
erous tissues  furnish  a  favorite  nutriment  for  certain  forms  of  life  — 
furunculi,  colonies  of  aspergilli,  etc.)  and  thus  one  trouble  follows  another, 
eventually  giving  to  the  disease  of  diabetes  its  peculiar  characteristics. 


1  Abderhalden:  Z.  physiol.  Chem.  44,  17  (1905). 

2  Arch,  exper.  Path.  Pharm.  7,  148  (1877). 


LECTURE  VI. 

FATS  —  LECITHIN  —  CHOLESTEROL. 

AMONG  the  foods  of  the  animal  organism,  the  fats  occupy  a  peculiarly 
important  place,  due  to  their  high  calorific  value.  They  also  play  an 
important  role  in  the  plant,  and  especially  in  the  animal  kingdom,  as 
reserve  material.  The  animal  organism  stores  tremendous  reserves  of 
vital  energy  in  the  form  of  fats. 

The  most  important  locations  are  the  intermuscular  connective  tissue, 
the  fatty  tissues  of  the  abdominal  cavity,  and  the  subcutaneous  connective 
tissue.  Small  deposits  occur  in  every  organ  and  cell.  These  fat  reserves 
vary  much  in  size,  depending  on  nutritive  conditions,  so  that  no  definite 
statement  can  be  made  regarding  the  fat  content  of  the  individual  organs. 

In  the  vegetable  kingdom  the  fats  are  also  widely  distributed,  and  act  as 
reserve  stores,  yet  never  to  the  same  extent  as  in  the  animal  organism. 
Fats  are  deposited  in  dormant  parts,  as  in  seeds,  in  which  we  first  find 
the  accumulations  of  carbohydrates,  then  fats;  often  they  occur  together. 
Here  the  fat  does  not  occur  in  the  form  in  which  we  meet  it  in  the  animal 
tissues.  It  is  very  finely  disseminated  throughout  th'e  protoplasm,  only  in 
isolated  cases  occurring  deposited  as  crystalline  aggregates  in  the  nutritive 
cells.  Supplies  of  fat  have  occasionally  been  found  in  stalks  embedded 
in  the  soil;  onions,  tubers,  and  roots,  and  similiarly  the  shoots  and  branches 
of  bushes  in  winter  as  well  as  the  leaves  of  evergreen  have  shown  a  reserve 
supply  of  fat. 

The  fats  are  composed  entirely  of  the  elements  carbon,  hydrogen,  and 
oxygen.  The  natural  fats  belong  to  the  group  of  neutral  fats.  Free  fatty 
acids  are  found  only  in  small  quantities.  The  neutral  fats  are,  in  general, 
to  be  considered  *  as  esters  of  glycerol  and  monobasic  fatty  acids;  i.e.,  in 
the  triatomic  alcohol,  glycerol,  the  hydrogen  atoms  in  all  three  hydroxyl 
groups  are  substituted  by  fatty  acid-radicals  (R) : 

CH20  .  R 
CHO    .R 

CH2O  .  R 

Glycerol  Fatty  acid 
residue     radical 


Cf.  Chevreul:  Chem.  Untersuchungen  iiber  Tierische  Fette.     Paris,  1823. 

101 


102  LECTURE   VI. 

The  three  fatty  acids,  oleic,  Ci8H3402,  stearic,  CigH3602,  and  palmitic, 
CioH3202,  play  the  principal  role  in  the  formation  of  fats.  The  last  two 
belong  to  the  series  of  normal  saturated  fatty  acids,  CnH2nO2,  whose  lower 
members  are  represented  by  formic,  acetic,  and  propionic  acids.  Oleic  acid, 
however,  is  an  unsaturated  fatty  acid:  C8H17.HC  :  CH  (CH2)7.COOH. 
These  fatty  acids  combine  with  the  triatomic  alcohol,  glycerol,  (com- 
monly called  glycerin)  splitting  off  water.  We  speak  of  tripcdmitin,  tris- 
tearin, and  triolein  according  to  the  nature  of  the  fatty  acid  concerned: 

CH2OH        Ci5H31COOH       CH2  .  O  .  CO  .  Ci5H31 

CH  .  OH  +  Ci5H31COOH  =  CH  .  O  .  CO  .  d5H31  +  3  H20 

CH2OH        Ci5H3iCOOH      CH2  .  0  .  CO  .  CI6H3i 

Glycerol         Palmitic  acid       Tripalmitin 

Tripalmitin  and  tristearin  are  solid  at  the  ordinary  temperature,  while 
triolein,  on  the  other  hand,  is  liquid.  As  fats  are  mainly  mixtures  of  the 
triglycerides,  the  solid  or  liquid  condition  of  these  depends  entirely  on  the 
quantity  of  triolein  present.  Besides  these  separate  triglycerides  there 
are  also  mixtures,  for  instance,  dipalmito-olein,  a  fat  whose  glycerol  base 
is  united  to  two  molecules  of  palmitic  and  one  molecule  of  oleic  acid; 
again,  we  have  distearopalmitin.  Aside  from  the  fatty  acids  mentioned, 
there  are  the  volatile  members  of  the  normal  series;  i.e.,  butyric,  caproic 
(hexoic),  caprylic  (octoic),  and  capric  (decoic)  acids.  Thus  in  vegetable  fats 
almost  all  the  different  members  of  the  normal  fatty  acid  series  have  been 
found.  Even  the  higher  fatty  acids,  such  as  lauric  (Ci2H24O2),  myristic 
(Ci4H2802),  and  arachidic  (C2oH40O2),  as  well  as  individual  oxy-fatty 
acids,  have  been  observed.  The  latter  have  been  isolated  with  certainty 
only  in  the  vegetable  kingdom,  while  in  the  animal  body  the  fatty  acids 
may  combine  with  the  higher  alcohols  instead  of  with  glycerin.  Rohmann1 
has  shown  that  in  the  secretions  from  the  oil-bags  of  birds  a  portion  of 
the  fatty  acids  is  combined  with  octadecyl  alcohol,  CH3  .  (CH2)  i6  .  CH2OH. 
The  palmitic  acid  ester  of  cetyl  alcohol,  Ci6H33OH,  from  spermaceti,  or 
cetin,  has  long  been  known  to  occur  in  the  cranium  of  the  sperm  whale. 
The  palmitic  acid  ester  of  myricyl  alcohol  (C3oH61OH)  is  found  in  bees- 
wax. Analogous  combinations  are  widely  distributed  in  nature.  In  only 
a  few  cases,  however,  has  their  identification  been  positive. 

While  triolein  and  the  glycerides  of  the  lower  fatty  acids  constitute  the 
major  part  of  the  vegetable  fats,  tripalmitin  and  tristearin  predominate  in 
animal  fat.  An  exception  occurs  only  in  the  fat  supply  of  cold-blooded 
animals,  which  is  very  rich  in  triolein,  as  a  consequence  of  which  it  remains 
in  a  fluid  state  at  temperatures  which  would  cause  solidification  among 

1  Hofmeister's  Beitrage,  5,  110  (1904). 


FATS  —  LECITHIN  —  CHOLESTEROL.  103 

warm-blooded  animals.  Among  the  latter  there  are  many  differences, 
depending  on  the  species.  For  instance,  human  fat  melts  at  about  25°  C., 
mutton-tallow  at  about  50°  C.,  and  fat  of  the  horse  at  about  65°  C. 

The  fats  decompose  according  to  their  composition,  by  taking  on  water, 
into  fatty  acids  and  glycerol.  This  hydrolysis  can  be  accomplished  by 
various  agents,  for  instance  by  boiling  with  dilute  mineral  acids,  or  with 
alkalies  especially  in  the  presence  of  alcohol,  and,  above  all,  by  the  action 
of  specific  and  widely  distributed  plant  and  animal  ferments  known  in 
this  case  as  lipases.  The  process  of  decomposing  fats  is  called  saponifica- 
tion.1  If  this  be  accomplished  by  the  action  of  free  bases,  we  do  not 
obtain  free  fatty  acids,  but  their  salts.  These  are  called  soaps.  Although 
the  sodium  and  potassium  soaps  are  easily  soluble  in  water,  the  fatty  acid 
salts  of  the  alkaline  earths  (calcium,  barium,  and  magnesium  soaps)  are 
insoluble.  The  neutral  fats  are  perfectly  insoluble  in  water.  If  we  shake 
them  long  and  vigorously  with  water,  we  obtain  an  emulsion,  which,  how- 
ever, soon  disappears,  while  the  fat  separates  again  on  the  surface  of  the 
water.  Absolutely  neutral  fats,  i.e.,  fats  which  do  not  contain  a  trace  of 
free  fatty  acid,  cannot  be  emulsified  even  by  shaking  with  dilute,  alkaline- 
carbonate  solutions.  When  any  free  fatty  acids  are  present,  however,  an 
extremely  fine,  permanent  emulsion  is  obtained. 

With  few  exceptions  fats  are  of  little  influence  in  plant  economy,2  being 
of  far  less  importance  than  the  carbohydrates.  As  a  whole,  they  form 
reserve  material.  In  seeds,  like  Helianthus  and  Curcubita,  we  notice  the 
stored-up  fat  quickly  disappears  on  germination.  Concurrently  we  observe 
an  appearance  of  free  fatty  acid.  A  splitting  of  fat  occurs,  as  was  first 
shown  by  Sigmund,3  by  the  action  of  a  specific  ferment,  lipase,  also  called 
steapsin.  More  recently,  extensive  investigations  have  been  made  on 
tEevery  active  lipase  occurring  in  the  seed  of  the  castor-oil  plant.4  This 
ferment  is  active  in  a  weakly  acid  solution.  The  saponification  of  the  fat 
evidently  changes  it  into  such  a  condition  that  it  can  penetrate  into  the 
protoplasm,  and  through  the  cell- walls.  Small  amounts  of  fatty  acid  in 
the  presence  of  alkali  suffice  to  produce  an  emulsion.  It  has  been  demon- 
strated experimentally  that  these  extremely  minute  globules  are  capable 
of  penetrating  the  cell-membranes,  although  it  has  not  been  decided 
definitely,  how  large  a  quantity  of  the  neutral  fat  is  saponified.  Again, 
nothing  definite  is  known  at  present  concerning  the  further  behavior  of 
the  fatty-acids,  though  Sachs  has  shown  that  their  disappearance  coin- 


1  J.  Gad:  Arch.  Anat.  Physiol.  1878,  179-187. 

3  Cf.  F.  Czapek:  Biochemie  d.  Pflanzen,  vol.  i,  pp.  115-126.     Jena,  1905. 

3  W.  Sigmund:  Sitzungsber.  d.  Wiener  Akad.  99,  407  (1890) ;  100,  328  (1891);  101, 
549  (1892). 

4  W.  Connstein,  E.  Hoyer,  and  H.  Wartenberg:  Ber.  35,  3988  (1902).     Connstein: 
Arch.  Anat.  Physiol.  1905. 


104  LECTURE  VI. 

cides  with  an  increase  in  the  amount  of  carbohydrates.  We  shall  come 
back  to  this  point  later  on. 

Let  us  now  follow  the  course  of  the  fat,  which  is  received  by  the  animal 
organism  in  its  food,  as  it  passes  through  the  alimentary  canal  and  through 
the  paths  of  absorption.  Fat  passes  the  entrance  to  the  alimentary  tract 
(i.e.,  the  mouth)  in  a  perfectly  unaltered  condition.  Saliva  has  no  action 
upon  it,  and,  although  saponification  begins  in  the  stomach,  the  extent  to 
which  this  is  accomplished  is  still  much  in  dispute.1  The  digestion  of  fat 
while  in  the  stomach  is  of  small  moment,  for  the  action  of  the  ferment  is 
soon  lessened,  and  eventually  stops  entirely,  on  account  of  the  acid 
reaction  of  the  stomach  juices.  The  lipase  requires,  moreover,  for  its 
maximum  efficiency  that  the  fats  shall  be  in  an  emulsified  state,  a  con- 
dition which  is  rarely  fulfilled  in  the  stomach.  The  action  of  the  gastric 
juices  is,  however,  of  indirect  importance,  because  the  fat  of  meat  is  set 
free  by  the  digestion  of  the  connective  tissue.  For  these  reasons  there 
is  no  absorption  worth  mentioning  of  the  fats  while  they  remain  in  the 
stomach.  The  real  digestion  of  fat  sets  in  when  it  reaches  the  intestine. 
Here,  first  of  all,  it  undergoes  a  purely  physical  change.  By  the  action 
of  the  free  fatty  acids,  and  on  account  of  the  presence  of  the  alkali  salts 
in  the  intestinal  and  pancreatic  juices  and  the  bile,  the  fat  is  first  of  all 
subdivided.  The  fatty  acids,  which  are  deposited  everywhere  between 
the  tiny  particles  of  fat,  react  with  the  alkaline  carbonates  present.  Soaps 
result  which  now  tear  the  tiny  particles  apart,  making  them  still  finer,  a 
process  which  is  assisted  by  the  carbon  dioxide  set  free  by  the  neutraliza- 
tion. An  emulsion  is  formed.  The  purpose  of  this  process  may  be  two- 
fold. We  can  imagine  that  the  epithelial  cells  of  the  intestine  absorb 
these  fine  globules  directly  in  the  same  manner  as  is  done  by  the  plant 
cells.  Again,  it  is  perfectly  possible  that  the  chief  advantage  of  the 
emulsion  is  to  present  an  enormously  large  surface  to  the  lipase,  thus 
facilitating  its  action. 

We  are  absolutely  certain  that  ingested  fat  is  decomposed  into  fatty 
acids  and  glycerol.  The  fatty  acids  unite  as  much  as  possible  with  the 
alkali  present,  thus  forming  soaps.  A  question  yet  to  be  settled  is  the 
extent  of  saponification;  i.e.,  how  much  of  the  total  fat  in  the  food  is 
entirely  decomposed.  Although  Pfltiger2  assumes  that  the  hydrolysis 
must  be  complete,  i.e.,  that  only  fatty  acids  and  glycerol  are  available  for 
assimilation,  other  investigators  believe  that  only  a  portion  of  the  fat  is 


1  Cash:  Arch.  Anat.  Physiol.  1880,  323.     Ogata:  ibid.  1881,  515.     Volhard:  Miin- 
chen.  med.  Wochschr.  5  and  6  (1900);    Z.  klin.  Med.  42,  414;  Verhandl.  deut.  Naturf. 
Aerzte,  1901,  II,  2d  half  p.  43.      A.  Zinsser:  Hofmeister's  Beitrage,  7,  31  (1905). 
A.  Fromme:  ibid.  7,  51  (1905). 

2  Pfliiger's  Arch.  80,  111  (1900);  ibid.  81,  375  (1900);  ibid.  82,  303  (1900);  ibid. 
85,  1  (1901);  86,  1  (1901);  89,  211  (1902). 


FATS  —  LECITHIN  —  CHOLESTEROL.  105 

saponified,  while  another  portion,  consisting  of  finely  divided  globules,  is 
absorbed  in  this  state.  In  spite  of  numerous  investigations  a  clear  con- 
ception of  fat  digestion  is  not  yet  at  hand.  Radijewski,1  in  investigations 
with  dogs,  showed  that  soap  can  be  assimilated,  and  converted  into  fats. 
To  show  that  a  complete  hydrolysis  of  fat  occurs,  the  work  of  Connstein  * 
has  been  cited.  He  fed  a  dog  with  lanolin.  Tm's  is  not  saponified  by  the 
usual  saponifying  agents,  although  it  forms  an  extremely  fine  emulsion 
when  rubbed  up  with  water.  97 . 5  per  cent  of  the  lanolin  administered 
in  this  form  was  evacuated  unchanged,  in  the  faeces. 

Many  fats  require  complete  decomposition  to  make  them  available  for 
assimilation.  Such  fats  are  the  ones  whose  melting-points  lie  above  the 
body-temperature.  I.  Munk3  has  shown  that  90  per  cent  of  mutton- 
tallow,  melting  at  49°,  was  utilized  by  dogs.  Spermaceti,  melting  at  53°, 
was  also  assimilated.  The  rapidity  and  extent  of  digestion  are  certainly 
influenced  by  the  melting-points  of  the  fats.  The  fats  of  lowest  melting- 
points  are  utilized  soonest  and  in  the  largest  quantities. 

Microscopic  investigations  have  been  made  in  the  attempt  to  estimate 
the  extent  of  the  fat  decomposition  in  the  alimentary  tract,  by  determin- 
ing at  what  place  in  the  epithelial  cells  and  walls  of  the  intestine  the  fat 
is  present  as  such.  In  the  first  place  we  must  state  that  the  walls  of  the 
intestine  are  a  large  factor  in  the  assimilation  of  fats.  In  it  the  fatty  acids 
and  glycerol  molecules  are  reunited  so  that  large  quantities  of  fatty  acids 
and  glycerol  are  prevented  from  entering  the  body.  I.  Munk 4  has  shown 
this  very  clearly.  He  fed  dogs  with  pure  fatty  acids,  and  found  an 
increase  in  the  neutral  fat,  but  no  free  fatty  acid  in  the  lymph  taken  from 
the  thoracic  duct. 

That  the  synthesis  takes  place  in  the  walls  of  the  intestine  is  certain 
from  the  investigations  of  Perewoznikoff.5  He  fed  fatty  acid  and  glycerin 
to  a  fasting  dog,  and  obtained  in  the  epithelial  cells  of  the  intestine  the 
same  microscopic  appearances  as  when  he  administered  fats.  Will 6  and 
C.  A.  Ewald  7  even  observed  a  fat  formation  from  glycerol  and  fatty  acids 
in  a  dissected  intestine.  Microscopical  studies  of  fat  assimilation  have 
not  given  uniform  results.  Some  observers  have  found  the  basal  edges 
of  the  intestinal  epithelial  entirely  homogeneous  and  free  from  fat  globules 
during  the  absorption  of  the  fats,  and  could  indicate  their  presence  only 


1  Virchow's  Arch.   43,  268  (1868). 

2  Connstein:  Arch.  Anat.  Physiol.  1899,  30;  Die  med.  Woche,  No.  15,  1900. 

3  Virchow's  Arch.  95,  407  (1884).     Arnschink:  Z.  Biol.  26,  434  (1890).     O.  Frank, 
Arch.  Anat.  Physiol.  1894,  308.     F.  Miiller:  Z.  klin.  Med.  12,  45  (1887). 

4  Virchow's  Arch.  95,  431  (1884);  ibid.  123,  230  and  484  (1891). 

5  Zentr.  med.  Wissensch.  1874,  851. 
e  Pfliigers  Arch.  20,  255  (1879). 

7  Arch.  Anat.  Physiol.  95,  407  (1884). 


106  LECTURE  VI. 

in  the  second  thir.d  of  the  cells;  other  investigators1  have  noted  globules 
in  the  basal  edge.  The  results  do  not  enable  us  to  arrive  at  any  decision. 
It  has  also  been  stated  that  an  active  ingestion  of  unchanged  fat  globules 
takes  place.2  The  epithelial  cells  are  supposed  to  send  out  protoplasmic 
processes  which  surround  and  absorb  the  fat  globules.  The  leucocytes 
have  also  been  credited  with  a  direct  activity  in  the  assimilation  of  the 
fats.  They  are  believed  to  migrate  in  the  intestinal  lumens  and  saturate 
themselves  with  fat.  Finally,  there  exists  the  possibility  that  other 
methods  may  exist  for  fat  assimilation.  Aside  from  the  fat  absorption  by 
the  cells,  there  remains  the  possibility  of  intercellular  absorption. 

For  the  time  being,  we  can  only  state  with  certainty  that  fat  is  emulsified 
in  the  intestines,  and  that  there  is  always  a  decomposition  of  fat  into 
glycerol  and  fatty  acids.  The  only  question  is  as  regards  the  amount  of 
fat  saponified.  Undoubtedly  the  decomposed  fat  is  recombined  in  the 
walls  of  the  intestine,  so  that  only  neutral  fats  are  introduced  into  the 
organism. 

Many  factors  participate  in  the  process  of  fat  absorption.  One  of  the 
most  important  is  the  pancreas.  It  furnishes,  on  the  one  hand,  the  alka- 
line fluid  which  is  so  necessary  for  the  emulsification  of  the  fats,  and, 
again,  it  supplies  the  fat-splitting  ferment,  which  produces  the  saponifica- 
tion.  If  the  amounts  of  the  pancreatic  juice  be  diminished,  either  by 
extirpation  of  the  gland,  or  through  ligating  the  ducts  of  the  pancreas,  an 
appreciable  reduction  in  fat  absorption  takes  place.  It  is  not  entirely 
abolished,  for  Abelmann  3  has  shown  an  absorption  of  28-53  per  cent  of 
milk-fat  under  these  conditions.  Sandmeyer  has  shown  that,  if  dogs 
whose  pancreatic  glands  have  been  removed  are  fed  with  finely  chopped 
pancreas,  the  amount  of  fat  absorbed  can  be  increased. 

It  is  still  a  question  whether  the  absence  of  lipase,  which  results 
on  the  removal  of  the  pancreatic  juice,  is  the  cause  of  the  diminished 
fat  assimilation.  If  it  be  true  that  a  copious  emulsification  is  sufficient  to 
cause  a  fat  absorption,  we  must  conclude  that  this  can  take  place  without 
the  pancreatic  lipase  being  necessarily  present,  because  fatty  acids  are 
certainly  set  free  in  the  stomach,  and  fats  can  also  be  decomposed  by 
bacterial  action.  The  formation  of  an  emulsion  might,  on  the  other  hand, 
tend  to  prevent  the  diminution  in  amount  of  the  alkaline  pancreatic  juice. 
If  we  saturate  an  emulsion  of  fat  with  an  acid,  we  observe  that  the  emulsion 


1  Cf.  I.  Munk:  Zentr.  Physiol.  14,  6/7,  121,  152,  409  (1900).     Heidenhain:  Pfluger's 
Arch.   43,    Sup.    85    (1888).     Kischensky:  Zentr.  allg.  Path.  u.  path.  Anat.  Heft    1, 
1902;  Beitrage  z.  path.  Anat.  u.  z.  allg.  Path.  32  (1902). 

2  Cf.    Zawarykin:    Pfluger's   Arch.    31,    231  (1883).     Heidenhain:   loc.    cit.     L.  V. 
Thanhoffer:  ibid.  8,  391  (1874).      R.  Wiedersheim :  Festsch.  56  Versam.  deut.   Natur- 
fors.    Aerzte,  1883. 

3  Abelmann:  Inaug.  Diss.  Dorpat,  1890.     Cf.  W.  Sandmeyer:  Z.  Biol.  31,  12  (1894), 


FATS  —  LECITHIN  —  CHOLESTEROL.  107 

gradually  disappears.  Large  oil-drops  are  formed,  which  collect  on  the 
surface  of  the  liquid.  It  is  very  probable  that  the  diminished  fat  absorp- 
tion is  largely  dependent  on  the  reduced  alkalinity  of  the  pancreatic  juice, 
on  account  of  the  acid  contents  of  the  stomach  preventing  the  formation 
of  an  emulsion  in  the  duodenum. 

Although  Teichmann  l  has  shown  that  if  the  pancreatic  duct  of  a  dog 
be  ligated  the  absorption  of  fat  is  not  appreciably  affected,  this  does  not 
invalidate  our  assumption.  The  secretions  in  the  small  intestines  of  the 
herbivora  occur  in  greater  alkalinity  than  is  the  case  with  the  carnivora. 
That  milk-fat  is  even  assimilated  in  the  absence  of  pancreatic  juice  is 
possibly  explained  by  the  following  circumstances.  If  milk  is  coagulated 
by  means  of  rennet,  and  the  coagulum  then  dissolved  in  pepsin-hydro- 
chloric acid,  we  obtain  a  very  stable,  acid  fat-emulsion.  It  is  rather  dif- 
ficult to  obtain  a  clear  conception  of  the  actual  relations  of  fat  assimilation, 
so  long  as  the  conditions  of  fat  digestion  are  so  little  understood.  It  is, 
of  course,  possible  that  the  stomach  lipase  continues  to  act  in  the  duodenum 
even  when  the  alkaline  pancreatic  juice  diminishes,  and  in  this  way  a  part 
of  the  fat  is  decomposed.  We  are  certainly  not  justified  in  concluding, 
from  the  fact  that  fat  assimilation  proceeds  in  the  absence  of  lipase,  that 
neutral  fats  are  directly  absorbed. 

The  bile  especially  is  of  great  importance  in  the  absorption  of  fats. 
Formerly,  a  direct  influence  on  the  intestinal  epithelial  cells  was  assigned 
to  it.  It  was  supposed  to  stimulate  them  to  assimilation.  The  function 
of  the  bile,  however,  has  been  shown  by  Pflliger 2  to  consist  of  the  ability 
to  produce  solutions  of  the  fatty  acids  and  soaps.  Large  quantities  of 
stearic  and  palmitic  acids  were  dissolved  by  a  mixture  of  bile  and  sodium 
carbonate.  The  cholates  of  the  bile  dissolve  even  the  magnesium  and 
lime  soaps  which  are  insoluble  in  water.  That  the  bile  exerts  a  consider- 
able influence  on  the  absorption  of  fat  is  shown  by  the  following  observa- 
tions: Dastre  3  ligated  the  bile  duct  of  a  dog,  and  made  a  fistula  between 
the  gall  bladder  and  the  middle  of  the  small  intestine.  With  a  diet  rich 
in  fat  the  lacteals  showed  a  milky  turbidity  below  this  fistula.  The 
bile  acting  alone  does  not  seem  capable  of  causing  a  fat  assimilation, 
although  it  acts  more  in  conjunction  with  the  pancreatic  juice.  This  can 
be  shown  very  beautifully  by  an  experiment  upon  a  rabbit.  In  this 
animal  the  bile  duct  joins  the  small  intestine  about  ten  centimeters  above 
the  pancreatic  duct.  Between  the  junctions  of  these  two  passages  the 
chyle  vessels  remain  clear  and  transparent,  even  on  a  diet  rich  in  fat. 
It  is  only  below  where  the  pancreatic  juice  enters  that  we  notice  the  turbid 
milky  streams  of  fat-bearing  chyle. 

1  Inaug.  Diss.  Breslau,  1891. 

J  E.  Pfliiger:  Pfliiger's  Arch.  88,  299,  431  (1902);  90,  1  (1902). 

3  A.  Dastre:  Arch.  phys.  norm,  et  path.  V.  22,  315  (1890). 


108  LECTURE  VI. 

Let  us  follow  the  progress  of  the  fat,  that  has  been  absorbed  by  the 
walls  of  the  intestine,  and  which  has  undoubtedly  been  re-formed  to  some 
extent,  in  its  further  passage  through  the  organism.  If  we  examine  the 
viscera  of  a  fasting  or  starving  animal,  we  observe  the  chyle  proceeding 
in  a  transparent  vessel  from  the  intestine  to  the  mesenteric  lymphatics. 
We  obtain  an  entirely  different  appearance  if  we  feed  the  animal  a  diet 
rich  in  fat  just  prior  to  death.  The  lacteals  are  then  plainly  visible.  They 
have  become  milky  and  opaque.  If  we  investigate  their  nature,  we  find 
that  they  are  permeated  with  fat,  even  if  no  fat,  as  such,  but  only  fatty 
acids  have  been  administered.  In  the  latter  case  the  glycerin  was 
necessarily  missing  for  a  fat  synthesis,  which  must  therefore  be  provided 
by  the  organism  in  some  other  manner.  If  we  make  a  fistula  at  the 
entrance  of  the  thoracic  duct  into  the  vena  anonyma  of  a  dog,  we  can  esti- 
mate the  amount  of  chyle  which  escapes  in  a  given  period  of  time.  In 
a  mixed  diet  we  do  not  observe  any  increase  in  the  quantity  of  chyle. 
Its  appearance  only  changes  when  the  food  contains  fat.  Although 
ordinarily  transparent,  it  then  becomes  white  and  opaque.  In  this  process 
of  digestion  the  fats  behave  differently  from  other  food  materials,  all  of 
which  are  poured  directly  into  the  blood-stream,  and  thence  conveyed  to 
the  liver.  The  chyle  itself  retains  the  fat  in  the  form  of  a  finely 
divided  emulsion. 

I.  Munk  and  Rosenstein  *  observed  in  a  girl,  who  was  afflicted  with  a 
fistula  of  the  thoracic  duct,  that  over  60  per  cent  of  the  fat  consumed 
flowed  out  of  the  fistula  in  less  than  twelve  hours.  Only  about  one 
twenty-fifth  of  the  fat  administered  had  been  saponified.  Certainly,  all 
fats  do  not  follow  such  an  indirect  course,  for  on  feeding  a  diet  rich  in  fat 
a  direct  transmission  into  the  blood-stream  occurs.  If  the  thoracic  duct 
is  ligated,  larger  quantities  of  fat  are  carried  into  the  blood.  I.  Munk  and 
Friedenthal 2  found  that  after  a  liberal  consumption  of  cream,  the  fat  con- 
tent of  the  blood  increased  to  six  times  the  normal.  As  much  as  this  had 
passed  into  the  blood,  although  only  32-48  per  cent  of  the  fat  had  been 
assimilated.  Fat  also  appeared  in  the  blood  after  administering  fatty 
acids,  about  four-fifths  of  these  having  been  converted  into  normal  fat. 

The  amount  of  fat  absorbed  depends,  as  previously  indicated,  on  its 
composition.  For  instance,  97.7  per  cent  of  olive  oil  is  utilized,  and 
97.5  per  cent  of  fats,  which  melt  at  temperatures  between  25-34  degrees 
(goose-grease  and  lard).  On  the  other  hand,  90-91.5  per  cent  of  mut- 
ton-tallow, melting  at  49-51  degrees,  and  only  about  15  per  cent  of  sper- 
maceti melting  at  53  degrees,  are  absorbed  by  human  beings. 

Pettenkofer  and  Voit 3  as  well  as  Rubner  4  have  studied  the  absorption 

1  Virchow's  Arch.  123,  230  and  484  (1891);  Arch.  Anat.  Physiol.  1890,  376  and  581. 

2  Zent.  Physiol.  15,  297  (1901). 

8  Z.  Biol.  9,  1  (1873).  4  Ibid.  15,  115  (1879). 


FATS  —  LECITHIN  —  CHOLESTEROL.  109 

of  fats.  The  former  found  that  a  dog,  weighing  35  kilograms,  assimilated 
98  per  cent  of  350  grams  of  fat  administered  in  a  day.  Rubner  main- 
tains that  the  intestine  of  a  human  being  can  absorb  a  like  quantity.  As 
a  rule,  however,  100-120  grams  is  about  as  much  as  the  system  can 
stand. 

The  blood  also  shows  changes  after  the  absorption  of  fat.  Chyle,  charged 
with  fat,  is  continually  poured  into  the  blood-stream  through  the  thoracic 
duct.  The  blood,  and  especially  its  plasma,  quickly  shows  an  increased 
fat-content.  This  is  especially  true  if  the  fat  absorbed  is  large  in  amount, 
and  is  indicated  by  a  milky  turbidity,  of  an  otherwise  clear  plasma. 
Often  a  distinct  separation  of  drops  of  fat  on  the  surface  can  be  obtained 
by  placing  such  plasma  in  the  centrifugal.  Ultimately  the  excess  of  fat 
again  disappears  from  the  blood.  The  process  by  which  this  is  accom- 
plished has  not  yet  been  demonstrated.  The  globules  of  fat  do  not 
migrate  through  the  capillary  walls.  It  is  possible  that  the  leucocytes 
have  some  function  here.  At  one  time  it  was  considered  certain  that  the 
blood  contained  a  lipase.  Why  it  should  be  present,  however,  was  not 
clear,  because,  through  the  syntheses  in  the  intestine,  the  organism  protects 
itself  against  free  fatty  acids.  Why,  then,  should  the  fat  be  decomposed 
again  in  the  blood?  This  hypothesis  has  been  abandoned,  but  on  the  other 
hand  the  investigations  of  Connstein  and  Michaelis  *  have  shown  that  blood 
possesses  the  ability  to  transform  fats  into  unknown  substances,  which 
are  soluble  in  water  and  capable  of  dialysis.  This  process  is  dependent 
upon  the  presence  of  oxygen,  and  seems  to  require  the  interaction  of  the 
red  corpuscles.  A  part  of  the  absorbed  fat  is  taken  directly  to  the  tissue- 
cells  and  consumed. 

The  unused  fat  is  stored  away  as  such.  This  is  evident  from  the 
following  experiments.  Franz  Hofmann  2  allowed  a  dog  to  fast  until  it 
was  devoid  of  fat.  The  beginning  of  this  period  can  be  ascertained  by 
estimating  the  amount  of  excreted  nitrogen.  The  starving  animal  utilizes 
its  stores  of  glycogen  and  then  of  fat,  keeping  its  albumin  intact  as  long 
as  possible.  If  the  fat  supply  is  used  up,  a  rapid  decomposition  of  albumin 
takes  place.  The  nitrogen  elimination  increases  immediately.  This  occurs 
in  from  four  to  six  weeks.  Hofmann  then  fed  the  animal  under  inspection 
with  considerable  bacon  and  little  meat.  The  amounts  of  fat  and  albumin 
given  were  accurately  determined.  It  was  found  that  in  five  days  this 
dog  assimilated  1854  grams  fat,  and  254  grams  albumin;  and  stored  up 
1353  grams  fat.  This  proved  that  fat  in  food  is  utilized  to  increase  the 
fat  supply  in  the  body.  Pettenkofer  and  Voit 3  reached  the  same  conclu- 


1    Sitzungsber.    Akad.   Wissensch.   zu  Berlin,   771,    1896;    Pfluger's  Arch.   65,   473 
(1897) ;  69,  76  (1897).     Cf.  Ergebnisse  d.  Physiologie,  3,  1,  194. 

2  F.  Hofmann:  Z.  Biol.  8,  153  (1872). 

3  Loc.  cit.  Z.  Biol.  9,  1  (1873). 


110  LECTURE  VI. 

sion  by  another  method.  They  determined  the  amounts  of  excreted 
products  from  a  dog,  which  had  been  given  a  liberal  fat  diet,  with  but 
little  meat.  They  found  that  all  the  nitrogen  appeared  again  in  the  excre- 
tions, but  that  all  the  carbon  did  not  do  so.  I.  Munk  1  could  also  obtain 
storage  of  fat  in  a  starved  dog,  by  fats,  or  even  fatty  acids. 

The  proof  that  nutrient  fat  and  stored-up  fat  possess  direct  inter- 
relations, has  also  been  obtained  in  still  another  manner.  For  fourteen 
days  I.  Munk 1  fed  a  dog,  weighing  16  kilograms  after  nineteen  days'  fasting, 
on  fatty  acids  obtained  from  mutton-tallow.  The  weight  of  the  animal, 
which  had  been  reduced  32  per  cent  during  the  previous  fasting  period, 
then  showed  an  increase  of  17  per  cent.  On  dissecting  the  animal,  a  very 
large  fat  addition  was  noted.  On  "  trying  out"  this,  about  1100  grams 
of  fat  were  obtained,  which  was  solid  at  room  temperature,  and  melted  at 
40°  C.  It  is  well  known  that  mutton-tallow  melts  at  this  temperature, 
while  fat  from  a  normal  dog  would  possess  a  far  lower  melting-point 
(about  20°  C.).  I.  Munk  used  rape-seed  oil  in  a  second  experiment.  A  fat 
was  obtained  which  melted  at  23°  C.  while  at  14°  C.  a  granular  crystalline 
deposit  separated.  The  fat  obtained  showed  82 . 4  per  cent  oleic  acid,  and 
12.3  per  cent  fatty  acids.  Normal  dog-fat  contains  only  63.8  per  cent 
oleic  acid,  and  28.8  per  cent  solid  acids.  Rape-seed  oil  contains  erucic 
acid  (C22H42O2).  This  was  isolated  from  the  above  dog-fat. 

It  is  very  remarkable,  that  a  food-stuff,  and  especially  a  vegetable  one, 
should  determine  the  composition  of  an  animal  tissue.  We  shall  see  later, 
that  the  decomposition  of  the  organic  food-stuffs  not  only  makes  it 
possible  for  them  to  be  absorbed,  but  also  enables  the  organism  to  select 
the  material  necessary  for  its  own  development.2  In  fact,  the  fatty  tissues, 
together  with  glycogen,  maintain  a  distinct  individuality  when  compared 
with  the  other  substances  of  the  tissues.  Both  are  reserve-materials 
which  the  organism  stores  up,  in  order  to  utilize  them  when  needed.  We 
do  not,  however,  desire  to  place  glycogen  and  fat  in  the  same  category. 
Glycogen  is  of  far  more  importance  in  metabolism,  than  is  fat  in  the  true 
fatty  tissues.  It  is  continually  being  used  up  in  metabolism,  and  also 
being  constantly  redeposited.  The  fat  supplies  in  the  liver,  and  possibly  in 
other  organs  also,  act  similarly  to  glycogen.  They  likewise  undergo  quick 
changes.  The  fatty-tissue  proper,  however,  is  a  true  tissue  under  ordinary 
circumstances.  Aside  from  its  function  as  a  reserve  material  it  serves  for 
other  purposes,  e.g.,  a  purely  mechanical  one  (like  the  fat  in  the  eye-socket, 
etc.),  and  again  as  a  non-conductor  of  heat.  It  must  not  be  inferred  that 
the  fat  is.  deposited  as  a  dead  mass  entirely  protected  from  metabolism. 


1  Arch.  f.  (Anat.  u.)  Physiol.  1883,   273;  Virchow's   Arch.  95,  407  (1884).     Cf.  G. 
Rosenfeld:  Verb.  d.  17,  Kong.  f.  in.  Med.  503  (1899). 

2  Cf.  E.  Abderhalden:  Zentr.  Stoffwechsel-  Verdauungskrankheiten,  5,  No.  24,  647 
(1904). 


FATS  —  LECITHIN  —  CHOLESTEROL.  1 1 1 

On  the  contrary,  on  leaving  the  blood-stream  in  a  diffusible  condition,  at 
present  not  understood,  it  is  taken  up  by  certain  cells,  and  there  converted 
into  fat.  The  fat-cells  themselves  are  supplied  with  an  efficient  resisting 
membrane.  It  withstands  the  action  of  alcohol  and  ether,  and  is  not 
dissolved  by  acetic  and  dilute  mineral  acids.  The  fat-cells  also  contain  a 
yellow  color  principle.  Like  all  cells  they  contain  protoplasm,  for  which, 
however,  there  is  only  a  limited  space  if  the  fat  supply  be  large.  The 
fatty  tissue  is  closely  interwoven  with  that  of  the  network  of  blood- 
vessels, so  that  this  valuable  material  may  be  quickly  utilized  when 
necessary.  We  do  not  know  how  this  reserve  material  is  liquefied.  It 
has  not  yet  been  determined  in  what  form  the  fat  leaves  the  cell  and  enters 
the  blood-stream.  Nervous  influences  undoubtedly  control  these  large  fat 
supplies,  so  that  the  fat  cells  are  in  this  way  kept  in  unbroken  relations 
with  the  general  metabolism.  It  is  not  improbable  that  the  fat-containing 
cells  of  the  connective  tissue  (i.e.,  the  protoplasm  which  they  contain)  play 
in  the  metabolism  of  the  fats,  a  role  similar  to  that  taken  by  the  cells  of 
the  liver  in  carbohydrate  metabolism.  As  the  latter  build  up  glycogen 
from  grape-sugar  and  so  protect  the  excess  of  carbohydrate  from  oxidation, 
and  in  case  of  need  either  directly  or  indirectly  bring  about  cleavage,  so  the 
fat-cells  withdraw  from  the  blood  the  excess  of  valuable  fat  material, 
retaining  it  for  a  time,  in  order  to  set  it  free  again  for  oxidation  at  the 
required  moment.  The  animal  organism  has  an  efficient  supply  of  reserve- 
material  in  the  fat.  It  possesses  double  the  calorific  value  of  carbohy- 
drates and  of  proteins.  One  gram  of  albumin  gives  4. 1  calories,  one  gram 
carbohydrate  gives  likewise  4 . 1  calories,  while  one  gram  fat,  on  the  other 
hand,  gives  9.3  calories.  In  fasting,  the  fat  supply  is  very  quickly  drawn 
upon.  Ordinarily  the  normal  organism  keeps  this  supply  very  constant. 
Gradually,  equilibrium  is  established  to  a  certain  extent  between  the 
amount  of  the  food  which  is  used  as  fuel  and  that  used  for  the  replace- 
ment of  tissue.  This,  of  course,  applies  only  to  the  mature  organism. 
In  man,  frequently,  this  equilibrium  is  disturbed.  More  fat  is  in  many 
cases  being  added  constantly,  so  that  the  fat  deposits  grow  far  beyond  the 
physiological  requirements,  and  finally  a  condition  results  which  is  vari- 
ously known  under  the  names  of  adiposity,  obesity,  and  polysarchia.  It 
is  impossible  to  distinguish  sharply  between  such  fleshiness  and  a  physi- 
ological reserve  supply  of  fat.  Only  when  difficult  breathing  and  faulty 
heart-action  are  indicated,  does  the  condition  become  a  pathological  one. 
The  causes  of  obesity  are  unknown.  Various  conditions  can  lead  to  this 
same  result.  There  is  unquestionably  a  physiological  obesity,  which  arises 
from  a  rich  diet,  and  a  pathological  obesity,  which  occurs  in  spite  of  all 
precautions.  The  latter  form  belongs  to  the  class  of  metabolic  derange- 
ments, and  can  be  traced  to  an  abnormal  metabolism  of  the  cells.  It  is 
certain,  that,  until  we  are  better  acquainted  with  the  subject  of  physiological 


112  LECTURE  VI. 

fat  assimilation,  we  cannot  get  an  exact  explanation  of  the  causes  of 
obesity.  We  are  confronted  by  a  condition  which  leads  to  many  secondary 
symptoms;  above  all  we  have  to  remember  that  a  very  large  amount  of 
tissue  has  to  be  supplied  with  blood  so  that  unusual  strains  are  placed 
upon  the  heart.  The  condition  of  those  afflicted  with  obesity  undoubtedly 
depends  upon  their  ability  to  satisfy  these  demands. 

The  functions  of  fats  in  the  animal  organism  are  not  restricted  to  the 
part  that  they  play  as  direct  or  indirect  nourishment.  In  the  growing 
individual  the  fat  which  is  in  the  cells,  and  also  otherwise  distributed  in 
the  true  fatty  tissues,  and  the  substances  which  are  closely  related  to  it, 
play  a  part  the  importance  of  which  we  cannot  yet  fully  estimate.  We 
are  acquainted  with  many  materials  which  are  absorbed  in  a  water-soluble 
condition,  and  in  this  form  they  penetrate  the  cells.  On  the  other  hand, 
we  also  know  of  many  substances  which  are  entirely  insoluble  in  water, 
but  which  are,  nevertheless,  easily  taken  up.  The  fats  may  in  these 
instances  act  as  solvents.  Although  a  substance  is  soluble  in  water,  it 
may  be  more  so  in  oils;  and  this  property  may  exert  an  influence  on  cellular 
assimilation,  and  permit  the  cell  to  exercise  a  selection  according  to  its 
constitution  and  condition.  This  suggestion  has  been  made  by  H. 
Meyer  *  and  by  Overton  2  to  explain  the  action  of  certain  narcotics.  It  is 
possible,  and  in  fact,  even  probable,  that  such  relations  are  important  for 
cell-metabolism,  under  ordinary  circumstances. 

Closely  related  to  the  fats,  and  the  functions  which  we  have  just  con- 
sidered, is  the  lecithin  group.  These,  also,  are  combinations  of  glycerol 
with  fatty  acids.  Here  only  two  hydroxyls  are  substituted  by  fatty  acids 
in  the  tri-atomic  glycerol,  while  the  third  is  replaced  by  a  phosphoric  acid 
molecule  which  is  also  combined  with  the  base,  choline.  The  following 
formula  gives  an  idea  of  the  constitution  of  lecithin,  also  called  distearyl- 
lecithin : 3 


CH2— 0— C18H3501 


AH- 


Glycerol  radical 


Choline  radical  |N=  (CH3)3 
XOH 


0— C18H350 


Fatty  acid  radical. 


CH2-0  , 

HO — PO  /   Phosphoric  acid  radical. 


1  Arch.  exp.  Path.  Pharm.  42,  109  (1899). 

2  Studien  u.  d.  Narkose,  etc.,  Jena,  1901.     Cf.  also  H.  J.  Hamburger:  Osmotischer 
Druck  u.  lonenlehre  in  d.  Medicin.  Wiesbaden,  J.  F.  Bergmann,  1904,  vol.  iii,  242. 

3  Cf.  Diakonow:  Zent.  med.  Wissensch.  1868,  438.    F.  Hundeshagen:  J.  pr.  Med.  28, 
219  (1883).     E.  Gilson:  Z.  physiol.  Chem.  12,  585  (1888).     A.  Strecker:  Ann.  148,  77 
(1868). 


FATS  —  LECITHIN  —  CHOLESTEROL.  113 

On  saponification  with  alkalies,  we  obtain  fatty  acids,  glycerol,  phos- 
phoric acid,  and  choline.  Dilute  acids  have  little  action  on  lecithin. 
The  fatty-acid  component  varies.  We  are  acquainted  with  lecithins  con- 
taining stearic,  palmitic,  and  oleic  acids.  Even  two  different  acids  may 
participate  in  the  constitution.  We  have  not  yet  succeeded  in  pre- 
paring lecithin  synthetically.  As  it  is  optically  active,  it  must  contain  an 
asymmetric  carbon  atom.  We  are  justified  in  making  certain  deductions 
regarding  the  method  of  grouping  of  the  glycerol  and  combined  radicals, 
as  indicated  by  R.  Willstadter  and  Karl  Liidecke.1  The  following  formulae 
are  possible  ones: 

CH2— 0— Choline  phosphate  CH2— O— Fatty  acid  A 


*CH 


—O— Fatty  acid  *CH  —O— Choline  phosphate 

CH2— 0— Fatty  acid  CH2— O— Fatty  acid  B 

I  II 

Formula  II  only  contains  an  asymmetric  carbon  atom  when  the  two  fatty 
acids  are  different.  The  investigators  mentioned  decided  in  favor  of 
formula  I,  because  they  succeeded  in  obtaining  an  optically  active  glycero- 
phosphoric  acid  by  hydrolysis.  This  is  only  possible  when  the  molecule 
has  the  following  grouping:  HO  .  CH2— CH  .  OH— CH2  .  O  .  PO3H2. 

* 

The  base  choline  is  of  much  interest.  It  is  a  quaternary- ammonium 
base,  and  has  the  following  constitution: 

/CH3 
CH3 


XOH 

It  is,  therefore,  to  be  considered   as  trimethylhydroxyethylammonium 
hydroxide.      Wurtz  2  proved  this  by  synthesis.      He  combined  ethylene 

/CH3 
oxide,  CoH4O,  trimethylamine  N — CH3  and  water.    Choline  can  also  be 

XCH3 
derived  from  glycol,  as  shown  by  the  following  formula: 

CH2OH 

CH2— N— (CH3)3 


1  R.  Willstatter  and  K.  Liidecke:  Ber.  37,  3753  (1904). 

2  Ann.  Sup.  6,  116  and  197  (1868).     Cf.  M.  Kriiger  and  P.  Bergell:  Ber.  36,  2901 
(1903). 


114  LECTURE  VI. 

In  aqueous  solution  choline  breaks  down  into  glycol  and  trimethyl- 
amine.  It  has  also  been  found  in  a  free  state  in  plants.  It  is  closely 
related  to  another  base,  also  found  in  plants,  and  especially  in  sugar- 
beets,  known  as  betaine,  or  oxyneurine.  Its  formula  is  : 

coov 


It  has  been  obtained  from  choline  by  oxidation.  Other  bases  have  been 
isolated  from  various  plants,  which  in  part  have  been  given  characteristic 
names;  e.g.,  amanitine,  from  toad-stools;  fagine,  from  buchu  seeds,  etc. 
They  are,  however,  all  identical  with  choline.  In  toad-stools  (Amanita 
Muscaria) ,  there  is  found  besides  choline,  another  base  called  muscarine,1 
which  is  evidently  an  oxidation  product  of  choline,  and  can  also  be  obtained 
from  it  by  oxidation.  It  is  commonly  considered  to  be  an  aldehyde, 
although  its  constitution  has  not  yet  been  established  positively: 

CHO 

CH2  .  N  .  (CH3)3 


AH 


Closely  related  to  these  is  neurine,  which  has  been  isolated  from  the 
brain  by  Liebreich.2  Its  composition  is  that  of  trimethylvinylammonium- 
hydroxide  : 

/CH3 
/CH3 
N^-CH3 
XCH  =  CH2 
XOH 

The  second  component  of  lecithin,  the  glycero-phosphoric  acid,  is  easily 
produced  by  uniting  glycerol  and  phosphoric  acid. 

The  lecithins  are  widely  distributed  in  the  plant  and  animal  kingdoms. 
We  could  truly  say  that  every  cell  contains  lecithin.  It  occurs  particu- 
larly in  animal  tissues,  in  the  brain,  nerves,  fish-eggs,  yolk  of  eggs,  and 
in  spermatozoa.  It  is  also  found  in  the  muscles  and  the  blood  (in  the 
plasma  as  well  as  in  the  blood  corpuscles)3  in  the  lymph  and  leucocytes; 
in  fact,  in  every  cell  and  in  every  organ.  We  find  lecithin  very  widely 


1  O.  Schmiedeberg  and  E.  Harnack:  Arch.  exp.  Path.  Pharmak.  6,  101  (1877). 

2  Ann.  134,  29  (1865). 

3  Cf.  E.  Abderhalden:  Z.  physiol.  Chem.  25,  65  (1898). 


FATS  —  LECITHIN  —  CHOLESTEROL.  1 15 

distributed  in  the  vegetable  world,  more  especially  in  seeds.  During 
germination  the  lecithin  content  increases.1 

In  digestion,  lecithin  acts  in  an  analogous  manner  to  the  fats;  in  fact,  it 
resembles  these  very  closely  in  every  respect.  It  forms  an  emulsion  with 
water.  It  partly  resembles  a  colloid.  Lecithin  is  decomposed  by  lipase 
into  glycero-phosphoric  acid,  free  fatty  acids  and  choline;  it  is  not  cer- 
tain that  the  decomposition  of  lecithin  in  the  alimentary  tract  is  complete, 
nor  that  unchanged  lecithin  can  be  directly  absorbed.  It  is  rather  to  be 
assumed  that  Us  components  are  separately  turned  over  to  the  organism 
for  further  use. 

The  wide  distribution  of  lecithin  leads  us  to  conclude  justly  that  it  is 
of  great  importance  to  the  animal  organism.  We,  however,  know  little 
about  its  function  at  present.  From  its  constitution  we  can  indeed 
assume  that  it  acts  as  an  intermediary  body  between  various  groups  of 
compounds.  We  easily  recognize  its  relation  to  the  fats,  from  which  it 
perhaps  derives  two  components,  the  fatty  acids  and  glycerol.  On  the  other 
hand,  lecithin  evidently  acts  as  a  bridge  to  the  very  important  nuclei'ns. 
It  is  possible  that  lecithin  plays  a  leading  part  in  the  internal  metabolism 
of  the  cells.  To  a  certain  extent  it  represents  the  fat  of  the  cells. 
Furthermore,  it  unites  the  inorganic  foods  with  the  organic  ones.  The 
nuclei'ns  possibly  obtain  their  phosphoric  acid  from  lecithin. 

We  do  not  know  anything  at  present  concerning  the  occurrence  of 
lecithin  in  the  organs.  It  may  be  there  in  the  free  state,  or  it  may  enter 
into  numerous  combinations.  .  Many  lecithides  have  .been  described,  but 
as  lecithin  has  the  property  of  readily  enclosing  other  substances,  e.g., 
albumin,  all  such  claims  should,  for  the  moment,  be  regarded  with  con- 
siderable skepticism. 

The  following  experiments  2  may  possibly  give  us  some  conception  of  the 
functions  of  lecithin,  even  if  only  indirectly.  If  we  remove  every  trace  of 
serum  from  the  blood  corpuscles  by  means  of  a  centrifugal  machine,  and 
careful  washing  with  physiological  sodium  chloride  solution,  the  corpuscles 
are  not  dissolved  by  the  cobra  poison  of  the  Naja  snake,  when  suspended 
in  an  isotonic  sodium  chloride  solution.  The  process  of  dissolving  the 
blood  corpuscles  in  such  a  way  is  called  hemolysis,  and  the  poisons 
causing  this  are  hemoli/tic.  If  the  serum  is  not  separated  from  the 
blood  corpuscles  they  immediately  go  into  solution  on  adding  cobra  poison; 
i.e.,  the  hemoglobin  diffuses  from  the  blood  corpuscles  into  the  surround- 
ing medium.  We  can  show  the  influence  of  serum  in  a  better  way 
by  taking  thoroughly-washed  blood  corpuscles,  suspending  them  in  a 


1  Cf.  E.  Schulze  and  A.  Lickiernik:  Z.  physiol.  Chem.  15,  405  (1891). 

2  Cf.  S.  Flexner  and  H.  Noguchi:  J.  Exp.  Med,  6,  No.  3  (1902).     P.  Kyes:  Berl.  klin. 
Wochensch.    38/39  (1902),  Nos.   2-4    (1903);  Z.  physiol.  Chem.    41,  273    (1904).     E 
Abderhalden  and  Le  Count:  Z.  exp.  Path.  Therap.  2,  199  (1905). 


116  LECTURE  VI. 

sodium  chloride  solution,  and  adding  only  one  drop  of  serum  to  this, 
after  having  previously  shown  that  cobra  poison  alone  had  not  caused 
hemolysis.  S.  Flexner  and  H.  Noguchi,  who  first  observed  this  fact,  and 
noticed  it  also  with  other  poisons  (tetanustoxin,  solanin,  saponin,  etc.), 
rightly  concluded  that  some  substance  was  undoubtedly  present  in  serum, 
which  made  it  possible  for  the  cobra  poison  to  act  on  the  hemoglobin  of 
the  corpuscles.  P.  Kyes  then  succeeded  in  showing  that  lecithin  could  be 
substituted  in  place  of  serum.  Minute  traces  are  sufficient  to  cause  hemo- 
lysis. Lecithin  alone,  when  used  in  small  quantities,  does  not  act  hemolyti- 
cally,  but  lecithin  and  the  cobra  poison  together  do  so.  This  is  not  the 
place  to  dwell  upon  this  interesting  biological  phenomenon  and  its  expla- 
nation. We  must  content  ourselves  with  the  knowledge  that  lecithin 
possesses  the  capacity  of  accelerating  the  activity  of  poisons.  Many 
interesting  questions  are  suggested  by  this  fact.  It  is  entirely  possible 
that  lecithin  also  acts  as  an  accelerator  in  the  animal  cells,  and  even  on 
the  intracellular  ferments.  As  a  result  of  recent  investigations  we  are 
forced  to  conclude  that  the  ferments  as  a  whole  are  not  released  from  the 
cells  in  their  active  form,  but  that  they  require  the  influence  of  a  second 
substance  to  develop  their  activity.  With  such  an  hypothesis  we  can 
easily  explain  the  action  of  ferments  in  the  cells. 

To  lecithin  is  ascribed  a  large  influence  in  the  construction  of  the  cell- 
walls,  and  also  in  the  resorption  of  the  cells.  What  was  said  concerning 
the  fat  contents  of  cells  is  also  applicable  to  this  case.  Lecithins  act  as 
solvents. 

There  is  another  substance,  which,  although  not  at  all  related  to  lecithin 
chemically,  is  like  lecithin  indispensable  to  all  cells.  This  is  cholesterol. 
Its  various  modifications  are  widely  distributed  in  the  vegetable  kingdom. 
Vegetable  cholesterins  are  designated  phytosterols.  In  the  animal  organ- 
ism it  is  found  in  all  cells,  in  the  blood,  lymph,  etc.  It  occurs  in  excep- 
tionally large  amounts  in  the  brain  and  nerve  tissues.  In  the  gall  bladder 
it  often  gives  rise  to  the  formation  of  calculi,  although  this  is  almost 
always  a  secondary  effect,  and  a  result  of  disease  of  the  bladder  (catarrh,  etc.) 
It  forms  white,  fatty-feeling  crystals  with  a  pearly  luster.  It  is  absolutely 
insoluble  in  water.  Sometimes  cholesterol  occurs  in  the  free  condition,  as 
in  the  blood  corpuscles;1  then  again  it  forms  ester  combinations.  For 
instance,  it  is  united  with  fatty  acids  2  in  the  blood.  Schulze  isolated  an 
isomer  of  cholesterin  from  wool  fat,  called  isocholesterol.3 

The  way  cholesterol  is  formed  is  still  unknown  to  us.  We  do  not  at 
present  know  its  constitution.  All  that  we  knew  up  to  within  a  short 


1  E.  Abderhalden:  loc.  cit. 

2  K.  Hiirthle:  Z.  physiol.  Chem.  21,  331  (1895-96).     E.  Hepner:  Pfliiger's  Arch. 
1898,  73. 

3  Ber.  5,  1075  (1872),  and  6,  251  (1873). 


FATS  —  LECITHIN  —  CHOLESTEROL.  1 17 

time,  is  that  the  formula  C27H44O,  or  C27H46O,  may  be  assigned  to  it  and 
that  the  molecule  contains  a  double  bond  and  also  an  alcohol  hydroxyl. 
Recent  investigations  l  have  shown  that  cholesterol  belongs  to  a  group  of 
chemical  compounds  widely  distributed  in  the  vegetable  kingdom,  but  not 
hitherto  found  in  the  animal  economy.  Cholesterol  is  evidently  a  terpene. 
The  animal  organism,  therefore,  contains  hydro-aromatic  compounds. 

At  present,  cholesterol  is  considered  to  occupy  an  isolated  position  in 
the  animal  kingdom.  In  the  vegetable  world  we  could  easily  understand 
its  formation  from  the  terpenes  in  a  number  of  ways.  From  its  consti- 
tution, it  hardly  seems  possible  that  cholesterol  originates  in  the  animal 
organism.  Animal  cholesterol  is  undoubtedly  vegetable  cholesterol  which 
has  been  utilized  by  the  animal  organism  for  its  requirements.  We  know 
absolutely  nothing  about  its  decomposition  in  the  animal  body.  Bond- 
zynski  and  Humnickni 2  have  isolated  a  substance  similiar  to  cholesterol 
from  human  faeces,  which  does  not  possess  a  double  bond,  but  has  two  atoms 
of  hydrogen  more  than  cholesterol.  About  one  gram  of  this  compound  is 
excreted  daily.  It  has  been  called  "  dihydro-cholesterol,"  or  coprosterol. 
The  reduction  is  undoubtedly  brought  about  by  the  activity  of  putre- 
factive bacteria. 

We  know  practically  nothing  of  the  significance  of  cholesterol  in  the 
animal  organism.  Its  general  occurrence  leads  us  to  conclude  that  it  is  of 
great  importance  in  cell  metabolism.  We  cannot  possibly  consider  it  as 
a  decomposition  product.  We  only  know  of  one  definite  property  of 
cholesterol.  This  relates  to  the  hemolytic  action  of  lecithin  and  cobra 
poison.  We  have  seen  that  lecithin  accelerates  the  activity  of  cobra 
poison.  Conversely,  cholesterol  retards  the  action  of  lecithin.  We  have 
seen  that  if  we  add  snake  venom  to  blood  corpuscles,  suspended  in  water 
and  freed  from  serum,  no  hemolysis  results;  when,  however,  a  trace  of 
lecithin  is  added,  hemolysis  quickly  follows.  If  we  then  add  a  minute 
quantity  of  cholesterol  suspended  in  methyl  alcohol,  the  lecithin,  which 
previously  had  caused  the  cobra  poison  to  become  active,  is  now  without 
effect.  The  blood  corpuscles  are  not  dissolved.  Lecithin  and  cholesterol 
occur  in  all  cells,  and  especially  in  the  blood  corpuscles.  It  is  probable 
that  they  also  show  their  antagonism  towards  one  another  in  these.  We 
are  acquainted  with  various  kinds  of  blood,  whose  corpuscles  are  dissolved 
by  cobra  poison  alone;  others  require  the  presence  of  lecithin.  It  is 
perfectly  possible,  and  even  probable,  that  lecithin  is  present  in  these 
different  kinds  of  blood  corpuscles  in  different  states  of  combination, 

1  A.  Windaus:  Ber.  36,  3752  (1903);  37,  2027  (1904);  37,  3699  (1904);  37,  4753 
(1904).  O.  Diels  and  E.  Abderhalden:  ibid,  36,  3177  (1903) ;  37,  3092  (1904).  Cf.  also  G. 
Stein:  Inaug.  Diss.  Freiburg,  1905. 

2  St.  Bondzynski  and  V.  Humnicki:  Z.  physiol.  Chem.  22,  396  (1896-97);  Ber.  29, 
476  (1896).  Miiller:  Z.  physiol.  Chem.  29,  129  (1900). 


118  LECTURE  VI. 

or  that  cholesterol  is  present  in  a  different  form,  or  perhaps  to  a  different 
extent  in  one  case  than  in  the  other.  Perhaps  when  the  cholesterol  is  in  a 
combined  state  lecithin  may  act  normally;  and  conversely,  lecithin  may 
be  in  some  such  state  of  combination  that  it  is  less  active,  so  that  in  the 
different  processes  of  the  cell  at  one  time  lecithin  acts  freely,  while  at 
another  it  does  not. 

The  terpenes,  and  especially  the  cyclic  terpenes,  are  very  widely  dis- 
tributed in  the  vegetable  kingdom.  Plant  secretions  are  largely  composed 
of  these.  We  are  acquainted  with  a  large  number  of  the  members  of  this 
class.  Limonene  and  pinene  are  most  widely  distributed.  At  present  we 
cannot  say  anything  1  regarding  their  functions  or  their  origin. 


1  Cf.  F.  Czapek:  Biochemie  der  Pflanzen,  G.  Fischer,  Jena,  1905,  vol.  ii,  p.  658» 


LECTURE  VII. 


ALBUMINS  OR  PROTEINS. 

ELEMENTARY  COMPOSITION.    SIMPLE  SUBSTANCES  OR  MIXTURES. 

CLASSIFICATION. 

THE  albumins,  or  proteins,  occupy  a  distinct  position  among  our  organic 
foods.  They  are  indispensable,  and  cannot  be  replaced  by  either  the 
carbohydrates  or  the  fats.  They  are  large  factors  in  cell-formation,  and 
possess  just  as  important  relations  to  the  animal  organism  as  do  the  carbo- 
hydrates to  the  plants.  We  shall  see  later  that  the  animal  organism 
obtains  all  its  albumin  requirements  from  the  vegetables.  With  the 
herbivora  this  requirement  is  supplied  directly;  with  the  carnivora,  indi- 
rectly. 

The  albumins  present  a  well  characterized  group  of  compounds.  They 
differ  essentially  from  the  carbohydrates  and  the  fats  in  their  elementary 
composition.  Besides  the  elements  C,  H,  and  O,  they  invariably  contain 
nitrogen,  and,  as  far  as  our  present  knowledge  is  concerned,  also  sulphur. 
These  five  elements  are  found  in  proteins l  in  closely  agreeing  amounts. 
The  carbon  varies  from  50-55  per  cent,  hydrogen  from  6.5-7.3  per  cent, 
nitrogen  from  15-17.6  per  cent,  oxygen  from  19-24  per  cent,  and  the 
sulphur  from  0.3-2.4  per  cent.  These  figures,  of  course,  mean  but  little, 
and  give  us  no  conception  of  the  composition  of  the  individual  constituents 
of  proteins.  This  fact  must  be  thoroughly  appreciated,  because  unfortu- 
nately many  far-reaching  conclusions  regarding  the  constitution  and 
identity  of  albuminous  bodies  have  been  made  on  the  basis  of  the  ele- 
mentary analysis. 

Before  we  proceed  to  discuss  the  composition  of  the  proteins,  we  are 
confronted  with  the  question:  Are  we  justified  in  considering  albumin 
itself  as  a  well-defined,  chemical  individual?  We  shall  see  later  that  we 
are  acquainted  with  a  large  number  of  different  proteins,  which  vary 
according  to  their  mode  of  formation,  and,  in  part,  their  place  of  occurrence. 
They  all  possess  the  common  characteristic  of  not  being  able  to  diffuse 

1  The  term  proteid  has  been  used  in  English  as  the  equivalent  for  albuminous 
substances  (German,  Eiweisskorper),  although  Hammarsten,  Neumeister,  and  other 
European  authors  have  designated  as  proteids  what  may  be  called  "compound  proteids." 
It  has  seemed  best,  however,  to  follow  the  German  text  and  to  designate  the  whole 
group  as  that  of  the  proteins. —  TRANSLATORS. 

119 


120  LECTURE  VII. 

through  animal  or  vegetable  membranes.  They  belong  to  that  class  of 
bodies  designated  by  Graham  x  as  "  colloids."  If  the  colloid  be  liquid, 
we  call  it  a  sol;  while  if  it  be  solid,  we  designate  it  as  a  gel.  Liquid  and 
solid  gelatin  represent  these  two  phases.  If  the  colloid  is  distributed 
throughout  water,  in  appearance  practically  dissolved,  we  call  it  in  the 
hydrosol  condition.  We  are  acquainted  with  many  such  colloidal  sub- 
stances among  the  inorganic  compounds.  Silicic  acid  is  a  good  example 
of  this.  If  a  solution  of  sodium  silicate  is  treated  with  an  excess  of 
hydrochloric  acid,  the  silicic  acid  set  free,  remains  apparently  in  solution. 
If  this  is  then  transferred  to  a  dialyzer,  the  excess  of  hydrochloric  acid  and 
the  sodium  chloride  produced  in  the  reaction  diffuses  into  the  liquid  —  in 
this  case  distilled  water  —  which  is  placed  on  the  other  side  of  the  mem- 
brane. The  silicic  acid,  on  the  other  hand,  remains  behind,  in  the  form 
of  a  tough,  viscous  mass,  which  can  be  coagulated  by  introducing  a  few 
bubbles  of  carbon  dioxide  gas.  "  Albumin  solutions  "  act  in  an  analogous 
manner.  If  we  transfer  blood  serum,  which  occurs  as  a  pale  yellow, 
clear  liquid,  to  a  dialyzer,  a  floculent  precipitate  quickly  separates  out. 
This  is  the  globin  of  the  serum,  which  separates,  the  salt  which  had  held 
it  in  "  solution,"  having  been  withdrawn. 

A  question  widely  discussed,  is  this  :  Is  the  colloid  occurring  in  the  sol 
form  to  be  considered  as  an  actual  solution,  or  as  a  suspension?  It  is 
variously  answered.  As  the  albumin  solutions  conduct  the  electric  cur- 
rent, the  products  in  "  solution  "  appear  as  both  anions  and  cations,  it 
has  been  assumed  that  an  actual  solution  exists.2  Nevertheless,  there  is 
no  sharp  dividing  line  between  a  real  and  an  apparent  solution.  We  are 
acquainted  with  all  possible  intermediate  stages.3 

As  the  colloids  lose  many  of  their  characteristic  properties  by  various 
agencies,  so,  also,  the  albumins  are  easily  deprived  of  their  colloidal  nature. 
The  process  is  called  a  "  coagulation."  It  is  irreversible.  As  we  gener- 
ally deal  with  the  coagulated  products  in  our  investigations  of  the 
albumins,  we  shall  devote  a  little  space  to  discussing  the  ordinary 
methods  employed  in  effecting  coagulation.  One  of  the  most  important 
characteristics  of  albumin  solutions  is  that  of  coagulating  on  heating. 
One  of  the  most  important  factors  in  the  phenomenon  of  coagulation 
is  the  amount  of  salt  held  in  solution.  We  can  heat  an  albumin 
solution,  which  has  been  very  carefully  freed  from  salt  by  dialysis,  and  it 
will  not  coagulate.  If  salt  is  then  carefully  added/  albumin  separates 


1  T.  Graham:  Philosophical  Trans.  151,  Part  1,  183,  (1861). 

2  J.  Sjoqvist:  Skand!  Arch.  Physiol.  5,  277  (1895).     S.  Bugarsky  and  L.  Liebermann: 
Pfliiger's  Arch.  72,  51  (1898). 

3  We  have  suspensions,  colloidal  solutions,  and  true  solutions.     It  is  easy  to  dis- 
tinguish between  the  end  members  of  the  series,  but  no  sharp   distinction   is   drawn 
between  these  three  classes.  —  TRANSLATORS. 


ALBUMINS  OR  PROTEINS.  121 

out.  The  reaction  of  the  liquid  is  of  the  greatest  importance.  Complete 
precipitation  of  the  albumin  can  only  occur  when  the  solution  is  faintly 
acid.  Any  excess  of  acid  will  hold  some  albumin  in  solution.  Yet  a 
coagulation  will  take  place  on  heating.  The  coagulated  albumin  has 
combined  with  the  acid.  A  so-called  "  acid-albumin "  results.  The 
presence  of  alkali  will  prevent  the  coagulation  of  albumin  for  the  same 
reason.  "Alkali-albuminates  "  are  formed.  The  coagulated  albumins  are 
insoluble  in  water  and  in  neutral  salt  solutions.  The  readily  soluble  com- 
binations of  albumins  with  alkali  and  acids  can  be  precipitated  by  salts. 

The  coagulating  temperature  of  the  different  albumins  varies.  Efforts 
have  often  been  made  to  utilize  this  fact  in  separating  the  various  albu- 
mins. The  method  is  inefficient.  For  one  thing  the  albumins  in  solution 
have  different  effects  upon  one  another,  and  then,  again,  the  coagulating 
temperature  varies  considerably  with  the  composition  of  the  solvent. 

We  are  also  acquainted  with  other  methods  of  effecting  coagulation 
besides  that  of  heating.  A  number  of  albuminous  bodies,  for  instance, 
globin,  myosin,  and  fibrinogen,  will  go  over  into  the  gel  form  simply  on 
standing.  Many  precipitants,  like  alcohol,  acetone,  metallic-salt  solutions, 
etc.,  will  also  produce  the  same  result.  The  time  required  to  effect  coag- 
ulation varies  considerably.  For  instance,  the  albumins  are  not  immedi- 
ately changed  to  their  insoluble  forms,  on  being  salted-out.  They  can  be 
filtered,  put  into  solution  again,  and  in  this  way  purified,  provided  that 
these  processes  are  carried  out  in  a  short  time.  According  to  Ramsden,1 
coagulation  has  even  been  accomplished  simply  by  shaking. 

The  most  varied  albuminous  bodies  assume  very  analogous  physical, 
and  even  chemical,  properties  after  being  coagulated.  They  all  form  an 
amorphous  powder,  which  is  insoluble  in  water  and  salt  solutions.  We  can 
easily  appreciate  the  fact  that  such  material  when  used  as  a  starting-point 
for  our  investigations  of  the  albumins  gives  little  guarantee  of  purity  or 
homogeneity.  We  know  that  the  colloids  possess  the  property  of  carrying 
down  other  substances  from  solution  when  they  themselves  are  precipitated. 
This  is  also  the  case  with  the  albumins.  They  also  contain  appreciable 
amounts  of  ash.  It  is  not  yet  certain  whether  ash  is  an  essential  constitu- 
ent of  albumin  or  not;  we  do  know  that  the  amount  can  be  decidedly 
diminished  by  dialysis  or  by  other  methods. 

As  a  rule,  when  we  are  investigating  the  composition  of  a  new  sub- 
stance, and  finally  its  constitution,  the  utmost  precautions  are  used 
to  insure  purity.  To  do  this  we  usually  resort  to  crystallization.  By 
re-crystallizing,  and  fractional  crystallization,  adhering  substances  are 
removed.  This  accomplished,  we  analyse  the  substance  in  order  to 
determine  its  composition.  The  size  of  the  molecule  is  obtained  by  a 
molecular  weight  determination;  and  then  by  preparing  a  series  of  deriva- 

1  Arch.  Anat.  Physiol.  1894,  517. 


122  LECTURE  VII. 

tives,  decomposing  the  substance,  and  by  other  means,  we  arrive  at  the 
constitution  of  the  body  in  question.  We  consider  that  the  constitution 
of  a  substance  is  definitely  settled  only  when,  by  synthesis,  we  succeed 
in  reproducing  the  same  substance.  We  must  attempt  to  follow  this 
same  line  of  procedure  in  our  investigations  with  the  albumins.  We  now 
turn  to  the  question  of  crystallizing  the  albuminous  bodies.  Crystals  of 
albumins  have  been  known  for  a  long  time.  T.  Hartig,  in  1850, 1 
noticed  crystalline  substances  in  gluten  meal,  which  are  called  aleuron  grains 
"protein  granules/'  or  "plant  crystalloids."  The  albuminous  nature  of 
these  crystals  was  established  by  Radlkofer.2  They  have  been  observed 
in  many  seeds;  for  instance,  in  pumpkin  seeds,  hemp  seeds,  ricinus 
seeds,  and  especially  in  the  Brazil  nut.  A  beautiful  example  of  this 
kind  of  crystallization  is  presented  by  parasitical  plants  of  the  order 
Orobanchacece,  the  tooth- wort,3  Lathrcea  squamaria.  The  cell  kernels  con- 
tain protein  crystals.  A  vigorous  discussion  has  arisen  as  to  whether  these 
substances  are  real  crystals,  or  whether  they  only  possess  a  crystalline 
appearance.  They  possess  characteristics  which  do  not  correspond  with 
those  of  true  crystals.  In  the  first  place,  these  crystalline-appearing 
substances  swell  up  under  the  influence  of  water,  and  also  of  dilute 
alkali.  The  refractive  index  of  the  crystal  then  diminishes.  The 
crystalline  form  also  changes,  because  it  does  not  expand  uniformly 
along  its  various  axes.  They  are  also  partially  soluble  in  glycerin. 
A  solid  homogeneous  residue  remains,  which  retains  the  form  of  the  original 
crystal.  There  has  been  much  discussion  about  this  phenomenon.  Fr. 
N.  Schulz  4  has  indicated  an  interesting  analogous  example  of  an  inorganic 
crystalline  formation.  If  human  urine  is  allowed  to  stand  for  24-48 
hours  with  dicalcium  phosphate,  and  then  filtered,  a  precipitate  of  crys- 
tals, one-half  mm.  in  size,  appears  when  the  liquid  is  allowed  to  evap- 
orate of  itself.  The  crystals  are  like  honestone  with  ragged  points,  and 
they  are  strongly  refractive  (in  polarized  light,  doubly  refractive).  If 
these  crystals  are  treated  with  dilute  acetic  acid  a  part  is  dissolved. 
A  crystal  remains,  however,  which  has  the  form  of  the  original.  It  is 
now  singly  refractive  towards  polarized  light,  and  has  lost  its  former 
high  refractive  index.  The  dissolved  portion  is  calcium  phosphate;  the 
remainder,  calcium  sulphate.  It  is  possible  that  the  protein  crystals 
mentioned  possess  analogous  characteristics.  There  is,  however,  nothing 
further  known  at  present  to  warrant  these  substances  being  classed 

1  T.  Hartig:  Bot.  Zeit.  50,  881  (1850). 

2  L.  Radlkofer:  Ueber  Kristalle  proteinartiger  Korper  pflanzlichen  und  tierischen 
Ursp rungs,  W.  Engelmann,  Leipzig,  1859. 

3  A.  F.  W.  Schimper:  Diss.  Strassburg,  1878;  Z.  Kristal.  1880.     F.  N.  Schulz:  Die 
Kristallisation  von  Eiweissstoffen  u.  ihre.  Bedeutung  f.  d.  Eiweisschemie,  G.  Fischer, 
Jena,  1901. 

4  Fr.  N.  Schulz:  loc.  cit.,  p.  4. 


ALBUMINS  OR  PROTEINS.  123 

with  normal  crystals.  Such  products  have  also  been  observed  in  animal 
tissues.  Thus,  six-sided  plates  have  been  noticed  in  the  intestinal 
epithelium  of  the  meal-worm,  Tenebrio  molitor.1  R.  List 2  states  that 
he  has  observed  rhombohedrons  and  hexahedrons  in  the  pigment  cells  of 
the  radial  nerves  of  Sphoerechinus  gramdaras,  which  gave  the  albumin 
reactions.  The  small  yolk  plates,  as  well  as  other  rectangular  and  quad- 
rangular plates  obtained  from  the  eggs  of  fishes  and  amphibora,  also  be- 
long to  this  class.  Such  products  have  also  been  observed  in  the  eggs  of 
the  roe3  as  well  as  in  the  epithelium  of  the  testes  in  man.4 

These  discoveries  do  not  lead  to  any  decision  regarding  the  crystalline 
qualities  of  the  albumins.  The  fact  that  some  of  the  products  observed 
gave  albumin  reactions  does  not  prove  that  they  were  albumins.  Small 
impurities  of  albumin  might  have  caused  them.  We  would  be  but  little 
benefited  even  if  the  fact  should  be  established  that  these  crystalline 
substances  were  albumins.  The  only  value  of  crystals  lies  in  possibility 
of  recrystallization  and  purification. 

As  a  matter  of  fact  it  has  been  found  possible  not  only  to  obtain  many 
of  the  albumins  in  crystalline  form  but  many  of  them  have  also  been  re- 
crystallized.  Maschke 5  was  the  first  to  interest  himself  in  this  direction.  By 
evaporating  a  saturated  solution  of  Bertholletia  (Brazil  nuts),  he  ob- 
tained aleuron  crystals  in  six-sided,  tabular  prisms. 

Schmiedeberg  6  continued  this  work.  The  protein  crystals  were  isolated 
from  the  Brazil  nuts  by  washing  them  out  with  petroleum  ether.  They 
were  then  dissolved  in  distilled  water  at  30-35  degrees,  and  precipitated 
by  passing  carbon  dioxide  into  the  solution.  The  precipitate  was  re- 
dissolved  by  treating  it  with  an  excess  of  magnesium  oxide  at  30-35 
degrees.  By  careful  concentrating  the  solution,  small  crystals,  of  the 
size  of  poppy  seeds,  settled  out.  These  contained  1.4  per  cent  MgO. 
Drechsel 7  improved  this  method  considerably.  Instead  of  evaporating  he 
removed  the  water  by  dialysis  with  absolute  alcohol. 

After  grinding  a  large  number  of  seeds  and  removing  the  fat,  octahe- 
dral crystals  have  been  obtained  by  means  of  a  five  per  cent  salt  solution 
at  60  degrees.  They  can  be  redissolved  and  again  precipitated.  Such 
crystals  were  obtained  from  cotton  seed,  hemp  seed,  and  sun-flower 
seeds. 


1  J.  Frentzel:  Arch.  mik.  Anat.  26,  287;  Berl.  entomol.  Zeit.  26,  1882.     W.  Bieder- 
mann:  Pfliiger's  Arch.  72,  105  (1898). 

R.  List:  Anat.  Anzeiger,  7,  185  (1897). 

V.  v.  Ebner:  Sitzungsber.  Akad.  Wissensch.  zu  Wien.  110,  part  3  (1901). 
Lubarsch:  Virchow's  Arch.  145,  317  and  362  (1896). 
O.  Maschke:  J.  prakt.  Chem.  74,  436  (1858). 
O.  Schmiedeberg:  Z.  physiol.  Chem.  1,  205  (1877). 
7  E.  Drechsel:  J.  prakt.  Chem.  19,  331  (1879). 


124  LECTURE  VII. 

It  is  a  matter  of  great  importance  that  albuminous  bodies  have  been 
crystallized  which  do  not  exist  in  the  crystalline  form  in  nature. 
Hofmeister  l  succeeded  in  crystallizing  egg-albumin  by  treating  a  given 
volume  of  egg-white  with  an  equal  volume  of  a  cold,  saturated  solution  of 
ammonium  sulphate.  The  precipitate  consisted  of  globulins,  while  the 
solution  contained  the  albumins.  By  concentrating  the  nitrate  from  the 
globulins  at  the  usual  temperature,  beautiful  microscopic  needles  were 
obtained,  which  could  be  redissolved  in  a  dilute  ammonium  sulphate 
solution,  and  obtained  again  by  evaporation.  The  precipitation  of  these 
crystals  can  be  greatly  accelerated  by  making  the  solution  faintly  acid, 
by  adding  either  dilute  acetic,  sulphuric,  or  hydrochloric  acids.2  Serum 
albumin  has  been  crystallized  in  the  same  manner.3  Albumin  from 
horse-blood  serum  has  also  been  obtained  in  crystalline  form.  We  will 
mention  the  fact  here,  that  other  albuminous  substances  are  said  to 
have  been  crystallized,  such  as  casein,  lactalbumin,  etc.  We  do  not 
need  to  dwell  longer  on  this  subject,  for  the  investigations  are  not  very 
convincing. 

We  are  acquainted  with  a  protein  which  has  itself  not  yet  been  obtained 
in  crystalline  form,  although  one  of  its  compounds  which  occurs  in  nature 
can  be  crystallized  easily.  We  refer  to  the  coloring  matter  of  the  blood, 
which  is  a  compound  of  the  albumin  globin,  and  another  substance, 
hematin,  which  is  not  of  an  albuminous  nature.  Hiinefeld  4  noticed  a 
crystalline  separation  when  blood  was  dried  between  two  glass  plates. 
Reichert, 5  however,  is  credited  with  being  the  true  discoverer  of  oxy- 
hemoglobin  crystals.  He  observed  them  on  the  placenta  of  a  nearly 
mature  guinea-pig  fcetus  and  also  on  the  mucous  membrane  of  the  uterus 
of  the  mother.  Oxyhemoglobin  may  be  prepared  in  various  ways.  The 
most  satisfactory  method  consists  in  centrifugalizing  defibrinated  horse- 
blood,  pouring  off  the  serum,  and  washing  the  paste  of  blood  corpus- 
cles with  isotonic  salt  solution  until  perfectly  freed  from  serum.  The 
blood  corpuscles  are  mixed  with  2-3  times  their  volume  of  water  at 
30-35  degrees  and  the  solution  strained.  In  order  to  remove  the  stro- 
mata  of  blood  corpuscles,  the  solution  is  cooled  to  0  degrees,  shaken  with 
ether  and  one-quarter  of  the  total  volume  of  absolute  alcohol,  also  at 


1  F.  Hofmeister:  Z.  physiol.  Chem.  14,  165  (1889);  16,  187  (1891). 
3  F.  G.  Hopkins  and  S.  N.  Pinkus:   J.  Physiol.  23,  130   (1898).     H.   T.   Krieger: 
Diss.  Strassburg,  1899. 

3  A.    Giirber:  Sitzungsber.  physikal-med.  Gesellsch.  zu  Wiirzburg,   1894,   143.     A. 
Michel:  Verhandl.  d.  physikal-med.  Gesel.  zu  Wiirzburg,  29,28,  No.  3  (1895),  and  Diss, 
Wiirzburg,  1895. 

4  F.  L.  Hiinefeld:  Der  Chemismus  in   der  tierischen   Oxydation,  F.  A.  Brockhaus, 
Leipzig,  1840. 

5  B.  Reichert:  Arch.  Anat.  Physiol.  1849,  p.  197;  1852,  p.  71.     Cf.  Fr.  N.  Schulz: 
loc.  cit.  p.  23. 


ALBUMINS  OR  PROTEINS.  125 

0  degrees.1  The  crystalline  separation  of  oxyhemoglobin  suddenly  occurs 
after  standing  for  some  time  on  ice.  As  the  solubility  of  the  oxyhemo- 
globins  varies  according  to  their  animal  origin,  it  is  necessary  to  use 
varying  quantities  of  water  for  dissolving  them.  Thus,  in  order  to 
obtain  the  oxyhemoglobin  of  the  cat,  it  has  been  found  convenient  to 
use  an  equal  volume  of  water  in  dissolving  the  blood  corpuscles.2 
Crystals  may  also  be  obtained  by  salting  out  with  ammonium  sulphate, 
and  dialysis  with  alcohol.  Hemoglobin  3  and  methemoglobin  4  can  also 
be  obtained  in  crystalline  form. 

Oxyhemoglobin  can  be  redissolved  in  water  at  37-40  degrees,  and 
recrystallized  by  the  addition  of  alcohol  in  the  manner  previously  described. 
When  obtained  from  different  animals  it  crystallizes  in  various  forms: 
thus  the  crystals  obtained  from  the  squirrel  are  hexagonal;  those  from  the 
horse  are  orthorhombic. 

Crystals  from  insect  blood  have  also  been  described.  H.  Landois 5 
has  obtained  crystals  from  the  blood  of  caterpillars,  Pupidce,  beetles,  and 
wasps,  simply  by  evaporation.  It  is  questionable  whether  these  were  albu- 
min crystals.  Crystals  have  also  been  isolated  from  the  red  sea-algae, 
Rhodophycece,  or  Floridece.  The  Cyanophycece  give  a  crystalline  coloring 
matter  called  phycocyan.  More  exact  knowledge  regarding  the  compo- 
nents of  these  albumins  is  not  yet  at  hand.6 

Not  only  are  all  the  external  appearances  of  these  crystals  identical  with 
those  of  real  crystals,  but  crystallographical  investigations  have  shown 
no  differences.  With  the  exception  of  those  albuminous  "plant  crystals  " 
which  belong,  in  part,  to  the  regular  system,  they  are  all  doubly  refractive 
towards  polarized  light.  As  a  whole,  however,  only  a  few  exact  optical 
investigations  of  albumin  crystals  have  been  made. 

We  have  intentionally  devoted  considerable  space  to  the  discussion  of 
these  individual  crystals.  It  is  a  matter  of  the  greatest  importance  to  us 
in  our  investigations  into  the  chemistry  of  albumins.  Are  we  justified, 
or  not,  in  characterizing  a  protein  substance,  as  pure?  Let  us  see  what 
conclusions  we  can  draw  from  the  crystallizability  of  the  proteins.  The 
attempt  has  been  made  to  decide  whether  a  protein  was  homogeneous  by 
means  of  an  elmentary  analysis.  We  have  already  shown  that  it  is  out 
of  the  question  to  decide  the  question  in  this  way.  It  is  a  well-known 

1  Cf.  F.  Hoppe-Seyler:  Med.-chem.  Untersuch.  Vol.  2,  p.  181,  1867.     O.  Zinoffsky:  Z. 
physiol.  Chem.  10,  16  (1885). 

2  E.  Abderhalden:  Z.  physiol.  Chem.  24,  545  (1898).     Cf.  also  Fr.  Kriiger:  Z.  Biol. 
26,  469  (1890),  and  Z.  physiol.  Chem.  25,  256  (1898). 

3  Cf.  G.  Hiifner:  ibid.  4,  382  (1880). 

4  G.   Hiifner  and  J.   Otto:   ibid.   7,   65  (1882);   8,  366   (1884).     A.  Jaderholm:    Z. 
Biol.  20,  419  (1884). 

5  Z.  wiss.  Zool.  14,  55  (1864). 

8  Cf.  H.  Molisch:  Bot.  Zeit.  1894,  177;  1895,  131. 


126  LECTURE  VII. 

fact  that  the  most  varied  albuminous  substances  have  very  similar  elemen- 
tary compositions.  It  is  impossible  to  recognize  the  presence  of  any 
foreign  albumin  in  a  mixture  by  any  such  procedure.  There  is  also  the 
added  objection,  that  the  same  mixture  will  invariably  be  obtained  by 
following  out  a  prescribed  method. 

It  is  very  instructive  in  this  direction  that  oxyhemoglobin  crystals  show- 
ing no  indication  of  any  admixture  under  the  microscope,  may,  neverthe- 
less, be  impregnated  with  foreign  protein.1  This  fact  has  been  established 
through  the  discovery  that  glycocoll  was  present  in  a  globulin  from  serum, 
whereas  oxyhemoglobin  does  not  show  the  least  trace  of  this  amino- 
acid.  It  has  also  been  shown  that  glycocoll  appears  in  the  oxyhemoglobin 
of  horse-blood,  after  one  crystallization.  Another  recrystallization  gives 
us  a  preparation  entirely  free  from  glycocoll.  In  this  connection  we  would 
refer  to  the  various  descriptions  of  albumins  containing  carbohydrates, 
even  when  the  observations  were  made  with  crystalline  preparations.2 

The  crystallization  of  albumins  does  not  correspond  with  the  ordinary 
formation  of  crystals  from  other  sources.  Most  of  the  albumin  crystals 
are  obtained  by  withdrawing  the  solvent.  The  production  of  these 
crystals  does  not  gradually  follow  the  removal  of  the  solvent.  The  crys- 
tallization is,  on  the  contrary,  a  very  sudden  one.  This  can  be  best 
illustrated  by  salting  out  with  ammonium  sulphate.  A  very  slight  excess 
is  sufficient  to  throw  out  large  quantities  of  crystals  from  an  otherwise 
clear  solution.  It  is  certainly  a  matter  of  great  importance  that  no  albu- 
min as  such  has  yet  definitely  been  isolated  in  a  crystalline  state.  A 
possible  exception  would  be  that  of  the  globulins,  generally  called  edes- 
tin,  separated  from  plant  seeds.  They  contain  a  considerable  amount 
of  sodium  chloride.  It  is  impossible  to  remove  this  entirely,  and  still 
retain  the  crystalline  form.  Although  we  are  still  in  the  dark,  regarding 
the  influence  of  sodium  chloride  on  the  crystallization  of  edestin  we  do 
know  that  the  egg-albumin  and  serum-albumin  do  not  themselves  crystal- 
lize, whereas  their  sulphates  do,  as  was  shown  by  K.  A.  H.  Morner.3  The 
crystallization  of  the  globin  in  hemoglobin  depends  on  the  presence  of 
hematin. 

When  we  remember  the  extreme  difficulty  experienced  in  obtaining 
absolutely  pure  crystals  of  substances  of  even  low  molecular  weight,  we 
can  hardly  expect  to  obtain  really  pure  products  through  any  methods 
which  in  themselves  can  give  no  guarantee  of  efficiency.  Although  we 
thoroughly  appreciate  the  advantage  of  possessing  the  albuminous  body 
in  a  crystalline  condition,  we  likewise  find  it  necessary  to  state  that  not 
the  least  confidence  can  be  placed  in  the  method  of  obtaining  the  crystals, 

1  E.  Abderhalden:  Z.  physiol.  Chem.  37,  484  (1903). 

2  E.  Abderhalden,  P.  Bergell  and  T.  Dorpinghans:  Z.  physiol.  Chem.  41,  530  (1904). 
8  K.  A.  H.  Morner:  Z.  physiol.  Chem.  34,  207  (1901). 


ALBUMINS  OR  PROTEINS. 


127 


nor  even  the  system  of  crystallization  itself,  as  a  guarantee  of  the  purity 
of  the  individual  substance.  The  only  advantage  that  crystallization 
possesses  is  that  it  gives  us  a  means  of  separating  one  product  from  the 
mixture,  and  possibly  increasing  its  purity. 

The  fact  that  we  have  so  far  not  succeeded  in  obtaining  a  single  abso- 
lutely pure,  individual,  albuminous  body,  places  the  whole  subject  of 
albumin  investigation  in  a  very  uncertain  light.  At  every  turn  we  meet 
this  same  unfortunate  condition.  We  emphasize  this  point  because  a  very 
large  number  of  investigations  in  the  domain  of  albumin  chemistry  have 
but  little  value  for  this  reason. 

This  is  especially  true  of  the  molecular  weight  determinations  of  albu- 
min.1 These  have  been  carried  out  in  various  ways.  The  elementary 
composition  has  been  investigated  to  see  if  this  would  establish  anything, 
considerable  attention  having  been  given  to  the  sulphur  content.  If 
albumin  considered  as  "  pure/'  contains  one  per  cent  of  sulphur,  then 
the  molecular  weight  of  the  substance  must  be  at  least  3200  times  that  of 
hydrogen.  This  method  gives  us  only  the  minimum  value,  as  we  have  no 
means  of  knowing  that  only  one  atom  of  sulphur  is  present  in  the  molecule. 
The  amount  of  sulphur  in  the  various  albumins  differs  greatly.  The 
following  calculations  have  been  made: 2 


Molecular  Weight:  (with 

Sulphur  in  Per 

the    assumption    that 
each     albumin    mole- 

cule contains  one  atom 

of  sulphur). 

Edestin  (crystallized)     

0.87 

3680 

Oxyhemoglobin  (horse)      

0.43 

7440 

Serum-albumin  (crystallized,  horse)  .    .    . 

1.89 

1700 

Egg-albumin  (crystallized) 

1  3 

2460 

Globulin  

1.38 

2320 

Taking  into  consideration  the  fact  that  the  albumin  may  contain  more 
than  one  atom  of  sulphur,  Fr.  N.  Schulz  3  has  estimated  the  molecular 
weight  of  serum-albumin  to  be  5100,  egg-albumin  4900,  oxyhemoglobin 
14,800,  globulin  4,600,  edestin  7,300. 

The  substituted  albumins,  especially  hemoglobin,  give  us  another  method 
for  estimating  the  molecular  weight.  Oxyhemoglobin  contains,  besides 
the  albumin  globin,  a  substance  containing  iron,  called  hematin.  About 
0 . 4-0 . 5  per  cent  iron  is  present  in  oxyhemoglobin.  Every  hematin  mole- 
cule contains  one  atom  of  iron.  It  is  generally  considered  that  oxy- 

1  Cf.  Fr.  N.  Schulz:  Die  Grosse  d.  Eiweissmolekiils,  G.  Fischer,  Jena,  1903. 

2  Fr.  N.  Schulz:  loc.  tit.  p.  17. 

3  Fr.  N.  Schulz:  loc.  cit.  p.  29. 


128  LECTURE  VII. 

hemoglobin  contains  one  hematin  molecule  and  one  molecule  of  globin, 
an  assumption  for  which  adequate  proof  is  lacking.  A  percentage  of  iron 
of  0.4-0.5  per  cent  indicates  a  molecule  of  14,000-11,200;  a  sulphur  con- 
tent of  0.43-0.67  per  cent  gives  a  molecule  of  14,899-9500;  and  4-5  per 
cent  of  hematin  J  one  of  14,800-11,800. 

Another  method  for  estimating  the  molecular  weight  of  proteins  depends 
on  the  formation  of  metallic  compounds. 

Harnack 2  has  shown  that  many  proteins  can  be  precipitated  from 
solution  by  means  of  copper  sulphate.  We  obtain  a  precipitate  contain- 
ing copper,  called  copper  albuminate.  Harnack  obtained  the  following 
amounts  of  copper  in  the  precipitates  from  egg-albumin:  (I)  1 . 34-1 . 37  per 
cent  Cu,  and  (II)  2 . 48-2 . 73  per  cent  Cu.  Two  different  copper  albumi- 
nates  were  formed  therefore.  We  are  not  acquainted  with  the  conditions 
governing  the  formation  of  one  or  the  other  compound.  Copper  albumin- 
ate  (I)  would  have  a  molecular  weight  of  4700,  while  the  second  compound 
probably  has  the  same  value,  if  the  assumption  of  Harnack  is  correct, 
that  both  albuminates  represent  the  same  protein  substance,  differing 
only  in  the  fact  that  the  first  possesses  one  atom,  while  the  second  has 
two  atoms  of  copper  in  the  molecule. 

Other  metallic  albuminates,  such  as  those  with  silver,  calcium,  etc., 
have  been  prepared.  It  is  difficult  to  state  whether  these  are  salt-like 
compounds,  or  not.  Recent  investigations  on  the  colloids  have  indicated 
the  necessity  of  being  extremely  cautious  in  passing  judgment  on  such 
compounds.  Zsigmondy  3  has  called  attention  to  a  peculiar  property  of 
a  colloidal  gold  solution,  in  the  presence  of  albumin.  A  pure  gold  solution 
is  coagulated  by  an  addition  of  electrolytes;  for  instance,  sodium  chloride. 
If,  however,  albumin  is  present,  the  precipitation  does  not  occur.  The 
albumin  protects  the  colloidal  gold.  Fr.  N.  Schulz  and  Zsigmondy  4  have 
found  it  possible  to  express  the  degree  with  which  each  individual  albu- 
min protects  the  colloidal  gold  numerically.  Thus  globulin,  under  certain 
conditions,  can  protect  twenty  times  its  weight  of  gold.  If  an  albumin 
solution,  mixed  with  a  gold  solution,  is  precipitated,  the  gold  is  dragged 
down.  A  homogeneous  red  precipitate  is  obtained.  If  the  globulin  be 
redissolved,  the  gold  will  likewise  go  into  solution.  It  can  easily  be  seen 
how  such  a  behavior  might  lead  one  to  believe  that  there  is  a  compound 
of  albumin  and  gold,  and  thus  to  erroneous  conclusions.  It  is  of  great 
interest  to  know  that  crystallized  egg-albumin  also  takes  up  gold,  and 
that  the  mixture  can  then  be  recrystallized.  Copper,  iron,  calcium  oxide, 
etc.,  can  also  be  held  in  colloidal  solution  by  means  of  albumin. 


1  Fr.  N.  Schulz:  Z.  physiol.  Chem.  24,  449  (1898). 

2  E.  Harnack:  Z.  physiol.  Chem.  5,  198  (1881). 

3  R.  Zsigmondy:  Z.  anal.  Chem.  40,  597  (1901). 
*  Hofmeister's  Beitrage,  3,  137  (1902). 


ALBUMINS  OR  PROTEINS.  129 

These  statements  are  sufficient  to  show  how  little  value  should  be 
attached  to  the  molecular  weight  determinations  of  such  "  compounds." 
In  individual  cases  we  are  not  able  to  decide  at  present  whether  there  is 
an  actual  chemical  combination,  or  whether  the  metal  is  merely  held  in 
solution.  No  better  results  have  been  obtained  by  using  halogen  substitu- 
tion products  for  the  molecular  weights.  We  are  still  without  the  neces- 
sary knowledge  and  foundation  for  such  work. 

It  might  be  thought  that  the  cleavage-products  could  be  utilized  for 
determining  the  molecular  weights.  Unfortunately,  we  have  not  yet 
sufficiently  perfected  our  methods  to  utilize  any  individual,  character- 
istic, cleavage-product  for  such  a  determination.  We  must  temporarily 
content  ourselves  with  approximations. 

If  we  take  all  the  known  facts  concerning  the  size  of  the  albumin  molecule 
into  consideration,  and  critically  examine  them,  we  must  conclude  that  no 
definite  statement  can  be  made.  It  is,  of  course,  possible  that  the  molecu- 
lar weight  is  as  large  as  has  been  computed;  on  the  other  hand,  it  may  be 
much  smaller.  It  is,  therefore,  practically  useless  to  assign  definite 
formulae  to  individual  proteins  as  long  as  the  methods  of  molecular  weight 
determinations  are  still  so  indirect,  and  based  upon  so  many  unknown 
factors. 

Direct  determinations  of  the  molecular  weights  of  proteins  have  so 
far  been  unsuccessful.  The  raising  of  the  boiling-point  method  is  not 
applicable,  because  most  of  the  albumins  undergo  changes  on  heating. 
Determinations  made  up  to  the  present  by  means  of  the  lowering  of  the 
freezing-point  have  not  taken  sufficiently  into  consideration  the  amount 
of  ash  in  the  proteins.  They  are,  therefore,  practically  worthless. 

Before  discussing  the  decomposition  products  of  the  albumins,  or  con- 
sidering the  question  of  the  constitution  of  the  albumins,  we  will  now 
devote  a  little  attention  to  the  various  kinds  of  proteins  as  far  as  they  can 
be  characterized  by  our  present  methods.  It  is  impossible  now  to  classify 
the  large  number  of  known  proteins  in  accordance  with  purely  chemical 
principles.  We  are  still  forced  to  follow  the  old  grouping.  This  classi- 
fication is,  however,  only  accepted  as  a  matter  of  necessity.  The  farther 
we  proceed  into  the  chemistry  of  the  albumins,  the  more  we  learn  of 
properties  which  can  be  utilized  to  identify  individual  proteins.  We  can 
even  indicate  a  prospective  classification  of  the  proteins  according  to  their 
constituents  in  an  objective  and  satisfactory  manner.  We  shall  presently 
see  that  they  are  essentially  composed  of  amino  acids.  These  are  of -very 
different  kinds.  We  distinguish  between  the  mono-ammo  and  the  di- 
amino  acids.  The  relative  amounts  of  these  two  groups  of  amino  acids 
vary  considerably  in  the  different  proteins.  We  know  of  proteins  like  silk, 
elastin,  etc.,  which  are  mainly  composed  of  mono-amino  acids,  the  di-amino 
acids  being  of  little  importance.  On  the  other  hand,  we  have  the  prot- 


130  LECTURE  VII. 

amines,  which  are  almost  entirely  built  up  of  di-amino  acids.  There  are 
many  intermediate  stages  between  these  two  groups;  thus,  the  histons 
contain  more  di-amino  acids  than  the  above  substances,  which  are  rich 
in  mono-amino  acids,  although  less  than  the  protamines.  The  common 
proteins,  albumin,  globulin,  etc.,  occupy  an  intermediate  position  between 
the  silk,  elastin,  etc.,  group  and  the  histons.  In  this  way  we  may  classify 
the  proteins  as  follows: 

1.  Proteins  with  less  than   10  per  cent  of  di-amino   acids  —  elastin, 
silk,  etc. 

2.  Proteins  with  about  10  to  15  per  cent  of  di-amino  acids  —  serum- 
albumin,  serum-globulin,  casein,  etc. 

3.  Proteins  with  from,  say,  20  to  30  per  cent  of  di-amino  acids  —  histon 
from  the  thymus. 

4.  Proteins  with  larger  amounts  of  di-amino  acids  (sometimes  80  per 
cent  or  more)  (protamines:  salmine,  clupein,  etc.). 

Our  present  knowledge  is  too  inadequate  for  us  to  classify  all  proteins  in 
this  way.  The  boundaries  of  the  different  groups  are  not  sharply  defined, 
and  we  observe  all  sorts  of  intermediate  stages  between  them.  Further- 
more, there  is  no  doubt  but  that  a  member  of  one  group  may  be  trans- 
formed while  in  the  tissues  so  that  it  belongs  to  a  different  group.  F. 
Miescher  J  has  called  our  attention  to  an  interesting  example  of  such  a 
transformation.  It  is  well  known  that,  as  the  spawning  season  approaches, 
the  salmon  journeys  from  the  ocean  into  fresh- water  streams.  During  the 
entire  period  of  several  months  in  which  it  remains  in  the  fresh  water,  the 
fish  eats  nothing.  On  leaving  the  salt  water  it  is  a  powerfully  muscular 
fish.  These  muscles  are  required  for  the  stemming  of  strong  currents. 
Its  sexual  organs  —  testes  and  ovaries  —  are  immaturely  developed. 
Gradually,  however,  the  large  lateral-dorsal  muscle  becomes  smaller, 
while  the  sexual  organs  assume  large  dimensions.  There  can  be  no 
doubt  but  that  the  latter  develop  at  the  expense  of  muscular  tissue.  The 
mature  testis  contains  a  protein  rich  in  di-amino  acids,  known  as  salmine. 
There  is  but  little  of  this  substance  present  in  the  immature  organ.  It 
then  consists  chiefly  of  a  histon-like  substance.  Histons,  as  a  rule,  do  not 
occur  in  any  considerable  amount  in  the  muscles.  It  is  very  probable 
that  the  protein  in  the  muscles  of  the  salmon  loses  di-amino  acids,  thus 
increasing  the  proportion  of  di-amino  acids  in  the  protein,  eventually 
producing  protamine  with  the  intermediate  formation  of  a  histon.  It  is 
highly  interesting  for  the  development  of  our  knowledge  concerning  the 
metabolism  of  proteins  that  we  should  study  such  relations  further. 

There  is  no  question  but  that  we  shall  shortly  be  able  to  classify  the 
proteins  according  to  chemical  principles.  We  must  determine  in  the 

1  Die  histochemischen  und  physiologischen  Arbeiten  von  Friedrich  Miescher. 


ALBUMINS  OR  PROTEINS.  131 

first  place  what  amino  acids  take  part  in  their  formation,  and  then  even- 
tually stereochemical  studies  will  decide  the  question.  We  have  to 
depend  at  present  chiefly  upon  physical  differences.  Although  many 
proteins  may  be  fairly  well  characterized  in  this  way,  by  their  solubility 
in  water,  in  salt  solutions,  etc.,  there  are  many  others  in  which  this  is  not 
the  case. 

The  proteins,  as  a  whole,  may  be  first  of  all  separated  into  two  main 
groups: —  (1)  The  Simple  Proteins,  and  (2)  The  Compound  Proteins,  or 
Proteids.  The  first  group  is  subdivided  into  the  true  albumins  and  the 
so-called  albuminoids.  The  true  proteins  comprise  (a)  the  albumins 
(serum-albumin,  egg-albumin,  and  lactalbumin,  etc.);  (6)  the  globulins 
(serum-globulin,  egg-globulin,  lactoglobulin,  and  cell-globulin);  (c)  the 
plant-globulins  and  plant- vitellins;  (d)  fibrinogen;  (e)  myosin;  (/)  phos- 
phorized  proteins,  or  the  so-called  nucleo-albumins  (casein,  vitellin,  nucleo- 
albumins  of  cell-protoplasm);  (g)  histons;  (h)  protamines.  While  these 
groups  are  fairly  well  distinguishable,  as  we  shall  soon  see,  the  following 
group,  which  likewise  belongs  to  that  of  the  simple  proteins,  is  charac- 
terized more  from  a  morphological  point  of  view.  The  albuminoids 
include  (a)  collagen;  (6)  ceratin  (from  hair,  feathers,  horn,  etc.);  (c) 
elastin;  (d)  fibroin  (from  silk);  (e)  spongin  and  conchiolin;  (/)  amyloid; 
(g)  albumoid  and  perhaps  the  melanins. 

To  the  compound  proteins,  or  proteids,  belong  nucleoproteids,  hemo- 
globin, and  glucoproteids. 

In  the  following  pages  we  shall  merely  devote  space  enough  to  such 
description  of  the  individual  proteins  as  seems  absolutely  necessary  for 
later  discussion.  Those  interested  are  referred  to  the  special  works  on 
the  subject.1 

W^e  will  first  take  up  the  simplest  albuminous  substances,  the  simple 
proteins.  The  albumins  and  globulins  comprise  a  well-characterized  group. 
They  are  generally  found  together;  for  example,  in  blood-serum,  milk,  and 
the  whites  of  eggs.  The  albumins  are  soluble  in  pure  water.  If  blood- 
serum  is  dialyzed  against  distilled  water,  a  precipitate  will  form  on  stand- 
ing. This  is  globulin,  which  had  been  held  in  solution  by  neutral  salts. 
Precipitation  follows  as  the  latter  diffuse.  The  albumins,  on  the  other 
hand,  remain  dissolved.  They  are  also  soluble  in  dilute  salt  solutions,  as 

1  An  exhaustive  description  of  the  individual  proteins  is  found  in  Otto  Cohnheim's 
Chemie  der  Eiweisskorper,  and  in  Gustave  Mann's  The  Chemistry  of  the  Proteids,  which 
is  based  upon  the  former.  We  shall  follow,  as  a  rule,  Cohnheim's  classification.  Even 
to-day  the  chemistry  of  the  amino  acids  might  be  used  as  a  basis  for  a  classification, 
but  in  order  to  prevent  misunderstandings  we  will  here  adhere  to  the  older  method. 

The  following  works  are  instructive:  Viktor  Griessmayer:  Die  Proteide  der  Getreide- 
arten,  etc.  (1897).  Leo  Morochowetz:  Das  Globulin  des  Blutfarbstoffes,  etc.  Le 
Physiologiste  Russe,  41-47  (1903),  and  48-60  (1904).  F.  Hofmeister:  Ueber  Bau  und 
Gruppierung  der  Eiweisskorper,  Ergeb.  Physiol.  (Asher  and  Spiro),  1,  759  (1902). 


132  LECTURE  VII. 

well  as  in  acids  and  alkalies.  Solutions  of  pure  albumins  are  neutral. 
The  albumins  also  differ  from  the  globulins  in  their  behavior  on  "  salting- 
out."  They  are  not  precipitated  when  their  neutral  solution  is  saturated 
with  sodium  chloride.  Even  saturating  the  solution  with  magnesium 
sulphate  solution  does  not  produce  precipitation.  They  are  not  pre- 
cipitated by  a  half-saturated  ammonium  sulphate  solution.  In  acid  solu- 
tions they  are,  however,  precipitated  by  saturating  with  sodium  chloride 
or  magnesium  sulphate.  The  albumins,  as  previously  stated,  have  been 
obtained  in  crystalline  form. 

The  globulins  are  insoluble  in  pure  water  and  in  dilute  acids,  but  are 
dissolved  by  dilute  alkalies  and  neutral  salt  solutions.  They  can  be  pre- 
cipitated from  solution  by  the  addition  of  water  or  acids.  Passing  carbon 
dioxide  through  their  solution  is  sufficient  to  precipitate  them.  The 
globulins  can,  consequently,  be  easily  coagulated.  They  may  be  redis- 
solved,  only  when  freshly  precipitated.  The  globulins  act  like  acids,  and 
turn  blue  litmus  red.  They  are  precipitated  by  a  half-saturated  ammo- 
nium sulphate  solution.  They  are  very  widely  distributed.  The  serum-, 
milk-,  and  egg-globulins  are  best  known.  There  are,  undoubtedly,  other 
groups  of  closely  allied  proteins,  which  are,  at  present,  classified  separately. 
Albuminous  bodies,  very  much  like  the  globulins,  have  been  isolated  from 
various  animal  organs.  Thyreo-globulin 1  is  assigned  to  this  class.  It 
contains  a  large  percentage  of  iodine. 

The  globulin-like  proteins  present  in  plant  seeds  are  grouped  separately. 
They  act  as  reserve  material  for  the  seeds,  often  occurring  in  large  masses, 
and  are  easily  obtainable.2  They  are  occasionally  found  in  crystalline 
form,  as  has  been  mentioned,  and  can  often  be  crystallized.  Edestin, 
the  best  known  of  these,  occurs  in  various  seeds,  and  can  be  dissolved  in  a 
five  per  cent  sodium  chloride  solution  at  sixty  degrees,  and  recrystallized 
therefrom.  These  vegetable  proteins  all  react  acid  and  are  insoluble  in 
water;  they,  however,  all  dissolve  in  salt  solutions,  and  can  be  recovered 
from  these  by  diluting  or  acidifying. 

The  phytovitellins,  also  called  "  vegetable-casein,"  which  have  been 
but  little  investigated,  are  proteins  obtained  from  plants,  and  are  provision- 
ally placed  in  this  class.  Some  of  them  contain  phosphorus,  and  should, 
therefore,  preferably,  be  included  with  the  nucleo-albumins.  It  has  not 
yet  been  decided  definitely  whether  this  phosphorus  is  actually  a  part  of 
the  protein  molecule,  or  only  an  impurity.  The  latter  assumption  seems 
justified,  as  the  method  of  preparation  is  crude,  and  very  little  effort  has 
been  made  to  purify  them.  The  reserve  proteins  stored  in  the  seeds  of 
various  cereals  belong  to  this  class.  These  substances  are  partially 
soluble  in  alcohol.  The  gluten-casein  of  wheat,  legumin  of  the  legumes, 

1  A.  Oswald:  Z.  physiol.  Chem.  27,  14  (1899);  32,  121  (1901). 

2  Cf.  H.  Ritthausen:  Die  Eiweisskorper  der  Getreidearten,  etc.,  Bonn,  1872. 


ALBUMINS  OR  PROTEINS.  133 

conglutin  of  the  lupins,  almonds,  nuts,  etc.,  are  insoluble;  while  gliadin, 
found  in  wheat,  rye,  barley,  and  oats,  is  soluble.  Zein,  a  protein  obtained 
from  corn,  is  soluble  in  alcohol.  This  group  of  alcohol-soluble  albuminous 
bodies  from  plant  seeds  is  also  characterized  by  the  absence  of  lysine,  in 
their  composition,  whereas  almost  all  of  the  other  proteins  yield  this  as 
a  cleavage-product. 

The  group  of  fibrinogens  and  fibrin  is  better  defined.  We  shall  dwell 
more  in  detail  on  these  proteins  *  later  on.  They  have,  in  common  with 
casein  and  myosin,  the  faculty  of  being  clotted,  i.e.,  changed  to  a  solid 
state,  by  a  ferment.  This  curdling  is  not  identical  with  coagulation.  Al- 
though the  curdled  proteins  are  no  longer  soluble  in  water,  they  can  still 
be  coagulated,  i.e.,  completely  denaturized  by  heating  or  by  treating  them 
with  alcohol.  Fibrinogen  is  found  in  the  blood-plasma  of  all  inverte- 
brates. It  is  changed  into  fibrin  by  the  action  of  a  ferment.  The 
coagulation  of  blood,  which  normally  occurs  only  when  the  blood  has  left 
its  containing  vessels,  is  dependent  on  this  action.  We  shall  see  later 
that  this  process  is  an  extremely  complicated  one  which  has  not  yet  been 
explained  entirely. 

Myosin  acts  very  much  like  fibrinogen,  and  is  found  in  the  fibres 
of  striated  muscle  in  a  soluble  form.  Its  curdling  causes  rigor  mortis. 
The  cause  of  the  curdling  of  this  muscle  material  is  not  understood.  A 
ferment  action,  analogous  to  that  of  fibrin  formation,  has  been  offered  in 
explanation,  although  such  a  ferment  has  not  yet  been  proved  definitely 
to  exist.  We  must  also  mention  the  fact  that  besides  myosin  other 
albuminous  substances,  among  these  myogen,2  have  been  described.  It 
is  difficult  to  determine  whether  these  proteins  are  distinctively-charac- 
terized albuminous  substances,  or,  more  probably,  the  same  myosin  in 
different  forms.  We  have  seen  that  many  proteins,  including  mycsin, 
can  be  very  easily  denaturized.  These  products,  therefore,  have  entirely 
different  properties,  and  easily  give  one  the  impression  of  containing  a 
protein  of  a  peculiar  nature.  We  cannot  go  far  astray  if  we  confine  our- 
selves, at  least  for  the  present,  to  calling  them  simply,  "  muscle-albumins." 
We  also  find  these  same  substances  in  the  smooth  muscles.  Analogous 
proteins  must  be  present  in  other  organs,  as  they  also  show  the  same 
rigor  mortis  phenomenon.  This,  however,  gradually  disappears.  No 
satisfactory  explanation  of  this  process  has  as  yet  been  presented. 

We  will  now  discuss  a  group  of  proteins  whose  distinctive  characteristic 
is  the  presence  of  phosphorus.  This  group  of  nucleo-albumins  includes 
a  very  heterogeneous  collection  of  proteins.  They  also  possess  another 
lesser  characteristic  in  being  largely  liquefied  by  pepsin-hydrochloric  acid 
digestion,  the  complex  containing  phosphorus  being  split  off  and  finally 

1  Cf.  the  Lecture  on  Blood. 

2  O.  von  Fiirth:  Ergeb.  Physiol.  (Asher  and  Spiro)  1,  110  (1902). 


134  LECTURE  VII. 

appearing  as  an  insoluble  precipitate.  Later  on  this  goes  into  solution. 
This  complex  has  been  called  paranuclein  by  Kossel,1  and  pseudonuclein 
by  Hammarsten.2  It  is  at  present  entirely  arbitrary  to  include  the  nucleo- 
albumins  among  the  simple  proteins.  Didactic  considerations  were  mainly 
responsible  for  placing  them  in  this  class.  The  nucleo-albumins  have 
often  been  classified  with  the  nucleoproteids  on  account  of  their  com- 
mon phosphorus  content.  The  latter,  however,  are  sharply  distinguishable 
from  the  former  by  the  fact  that  purine  bases,  pyrimidine  derivatives,  and 
pentoses  enter  into  their  composition.  O.  Cohnheim3  proposes  instead 
of  nucleo-albumin  the  name  of  phospho-globulin  to  prevent  such  confusion. 
This  group  includes  casein,  vitellin,  and  a  series  of  cell-neucleo-albumins.  It 
is  possible  that  legumin  and  the  so-called  vegetable-casein  belongs  to  this 
class.  The  nucleo-albumins  are  invariably  distinct  acids.  When  pure 
they  are  insoluble  in  water.  Their  salts,  on  the  other  hand,  are  easily 
soluble  in  alkalies  and  ammonia.  They  are  precipitated  by  acids.  Boiling 
a  solution  of  their  salts  is  not  sufficient  to  coagulate  them. 

We  shall  consider  casein  and  its  digestion  more  in  detail  later.  Here 
its  occurrence  in  milk  will  be  merely  mentioned.  Vitellin  occurs  in  the 
yolk  of  eggs.  It  has  never  been  prepared  in  a  pure  condition.  Nucleo- 
albumins  are  supposed  to  occur  in  all  cells.  With  the  exception  of  casein, 
no  other  member  of  this  group  has  so  far  been  isolated  in  a  pure  condition. 
This  group  already  shows  the  total  inadequacy  of  our  methods  of  prepara- 
tion. As  soon  as  we  are  compelled  to  attempt  the  isolation  of  a  given 
protein  from  a  mixture  of  albuminous  material  by  precipitation  and 
certain  questionable  reactions,  we  meet  with  unsurmountable  difficulties. 
The  names  of  the  various  proteins  are  here  largely  derived  from  their 
morphological  source.  The  physical  properties  of  the  albuminous  sub- 
stances are  naturally  dependent  on  the  medium  in  which  they  are  found. 
That  these  substances  are  largely  influenced  by  extraneous  conditions, 
can  be  easily  shown  by  studying  the  behavior  of  the  same  -protein  when 
dissolved  in  various  solvents.4  The  exceptionally  large  amounts  of 
admixed  salts  necessarily  have  an  effect  on  the  other  physical  properties 
of  any  individually  precipitated  protein.  Although  we  are  undoubtedly 
right  in  considering  the  albumins  and  the  globulins  as  distinct  individuals, 
this  is  not  the  case  with  those  others  just  mentioned.  Many  are  unques- 
tionably mixtures. 

We  shall  now  consider  the  proteins  which  are  relatively  rich  in  di-amino 
acids.  As  a  result  of  their  composition  they  are  of  a  more  or  less  basic 


1  A.  Kossel:  Arch.  Anat.  Physiol.  1891,  181. 

2  O.  Hammarsten:  Z.  physiol.  Chem.  19,  19  (1893). 

3  O.  Cohnheim:  loc.  cit.  p.  190. 

4  Cf.  E.  Abderhalden   and   O.  Rostoski:    Z.   physiol.   Chem.    46,   125    (1905);  E. 
Abderhalden:  Z.  exp.  Path.  Therap.  2,  642,  1905. 


ALBUMINS  OR  PROTEINS.  135 

character.  They  are,  for  this  reason,  precipitated  by  alkalies,  although 
redissolved  by  an  excess.  They  are  readily  soluble  in  acids. 

The  histons  belong  to  this  class.  They  belong  just  as  much  to  the 
simple  proteins  as  to  the  more  complicated  ones.  They  do  not  occur  as 
such  in  nature.  They  are  always  linked  with  some  other  radical,  and  must 
be  separated  from  it  when  prepared  for  study.  The  first  histon,  in  the 
narrower  sense,  was  isolated  by  Kossel l  from  the  blood  corpuscles  of  a 
goose.  The  histon  obtained  from  the  leucocytes  of  the  thymus-glands 
has  been  most  carefully  studied.2  The  histons  are  very  widely  distributed. 
They  are  found  in  the  spermatozoa  of  fishes,  and  can  be  shown  to  occur 
as  antecedents  of  the  protamines;  for  instance,  in  the  immature  testes  of 
the  salmon.3  Many  authors  place  globin,  the  protein  component  of  hemo- 
globin, in  this  class.  It  is  very  basic  in  its  nature,  although  it  otherwise 
behaves  differently  from  the  other  histons.  It  really  occupies  an  inter- 
mediate position  between  the  histons  and  the  simple  proteins. 

The  histons  have  been  very  carefully  examined  by  Ivar  Bang.4  He 
mentions  the  following  as  characteristic  reactions :  —  They  are  precipi- 
tated from  their  water  solutions  by  ammonia,  but  are  redissolved  by  an 
excess.  The  histons  are  only  coagulated  by  boiling  in  the  presence  of 
salts.  They  form  a  precipitate  with  nitric  acid  in  the  cold,  redissolve  on 
heating,  but  again  settle  out  on  cooling.  Neutral  solutions  of  histons 
give  precipitates  with  solutions  of  ovalbumin,  casein,  or  serum-albumin, 
which  contain  but  little  admixed  salts.  This  is  considered  a  very  charac- 
teristic reaction.  These  precipitates  contain  one  part  histon  and  two  of 
casein,  two  of  serum-albumin  or  one  of  ovalbumin.  These  reactions  do 
not  apply  to  all  histons.  The  various  members  of  the  histon  group  differ 
greatly  from  one  another.  Their  chief  characteristic  is  the  large  amount 
of  bases  present. 

The  protamines,  discovered  by  Fr.  Miescher  5  in  the  mature  spermatozoa 
of  the  salmon,  are  closely  related  to  the  histons.  A.  Kossel  6  has  greatly 


1  A.  Kossel:  Z.  physiol.  Chem.  8,  511  (1883-84). 
3  L.  Lilienfeld:  ibid.  18,  473  (1894). 

3  Cf.  F.  Miescher  (O.  Schmiedeberg) :  Arch.  exp.  Path.  Pharmak.  37,  100  (1896). 
One  experiment  showed  only  about  40  per  cent  of  bases  in  a  product  obtained  in  the 
beginning  of  October  from  the  testes  of  the  salmon.     This  was  evidently  a  mixture 
of  histon  and  protamine.     A  second  preparation  showed  about  60  per  cent  of  bases, 
while  the  protamine  obtained  from  mature  testes  showed  as  much  as  80  per  cent  bases. 

4  Ivar  Bang:   Z.   physiol.   Chem.   27,   463    (1897);  30,   508   (1900).     Hofmeister's 
Beitr.ige,  4,  115,  331,  and  362  (1903). 

5  Fr.  Miescher:  Ver.  Naturfors.  Gesellsch.  Basel,  6, 138  (1874).   J.  Piccard:  Ber.  7, 1714 
(1874),  and  Fr.  Miescher's  complete  works,  loc.  cit. 

6  A.  Kossel:  Z.  physiol.  Chem.  22,  176   (1896);  25,  165  (1898);  26,  558  (1899); 
Ber.  34,  3214  (1901);  Z.  physiol.  Chem.  40,  311  (1903-04);   also   A.  Kossel  and  A. 
Mathews:  ibid.  25,  191  (1898).  A.  Kossel  and  F.  Kutscher:  ibid.  31, 165  (1900).  A.  Kossel 
and  H.  D.  Dakin:  ibid.  40,  565  (1903-04). 


136 


LECTURE  VII. 


extended  our  knowledge  of  them;  so  much  so,  that  most  of  their  funda- 
mental constituents  are  already  well  established.  Kossel  and  his  students 
have  also  found  protamines  in  the  spermatozoa  of  other  fishes.  They 
resemble  one  another  very  closely,  although  they  are  not  identical,  as  is 
indicated  by  their  percentages  of  mono-  and  di-amino  acids.  The  pro- 
tamine  group  is  very  well  denned.  They  contain,  above  all,  a  very  large 
amount  of  bases.  Arginine  is  the  main  cleavage-product  of  the  protamines. 
The  amount  varies  between  58-84  per  cent  according  to  the  origin  of  the 
protamine.  They  also  contain  mono-amino,  as  well  as  the  di-amino,  acids, 
as  we  shall  see  later.  To  assign  to  the  protamines  a  particular  position 
among  the  albuminous  substances  would  certainly  be  arbitrary  and  unjusti- 
fiable at  present.  They  are  closely  related  to  all  the  remaining  proteins,  and 
are  formed  from  them.  There  is  also  no  justification  for  considering  them 
as  the  simplest  proteins.  Although  one  of  the  cleavage-products  of  the 
protamines,  arginine,  is  found  in  large  amount,  it  must  not  be  forgotten 
that  other  amino  acids  are  also  present,  and  that  the  constitution  of  the 
protamines  may  be  just  as  complicated  as  that  of  other  proteins. 

The  protamines  can  be  purified,  which  is  of  great  advantage  in  their 
preparation.  The  free  protamines  are  obtained  pure  only  with  difficulty. 
They  are  best  obtained  in  the  form  of  sulphates,  and  then  changed  over 
into  chlorides.  The  latter  can  be  precipitated  from  methyl  alcohol  solution 
by  means  of  platinum  chloride.  M.  Goto  l  has  analyzed  these  platinum 
salts,  and  obtained  the  following  values: 


Variety. 

C 

H 

N 

Pt 

Cl 

0 

Salmine  (from  salmon)  
Clupein  (from  herring)  

22.96 

22.81 

4.32 
4.30 

14.83 
12  59 

24.73 
24  64 

26.56 
26  57 

6.70 
9  09 

Scombrine  (from  mackerel) 

23  49 

4  75 

13  57 

24  09 

25  99 

8  11 

Sturine  (from  sturgeon)    . 

24  32 

4  49 

14  20 

23  10 

25  42 

8  47 

Sulphur  has  not  yet  been  discovered  in  the  protamines,  and  is  probably 
absent.  We  are  not  at  present  aware  of  any  reason  why  a  lower 
molecular  weight  should  be  assigned  to  them  than  to  the  other  proteins. 
The  protamines  are  not  coagulated  by  heat.  While  the  ordinary  proteins 
are  precipitated  by  the  alkaloid  reagents  (for  instance,  phospho-tungstic 
acid)  only  in  acid  solution,  and  the  histons  in  neutral  solution,  the  prot- 
amines will  be  even  thrown  out  in  alkaline  solution.  The  protamines  can  be 
salted-out  by  ammonium  sulphate  and  sodium  chloride. 

The  protamines  have  toxic  properties; 2  15-18  mg.  of  scombrine,  salmine, 


1  M.  Goto:  Z.  physiol.  Chem.  37,  94  (1902). 

3  W.  H.  Thompson:  Z.  physiol.  Chem.  29,  1  (1900). 


ALBUMINS  OR  PROTEINS.  137 

or  clupein,  and  20-25  milligrams  of  sturine,  per  kilo  weight  of  the  animal, 
are  sufficient  to  kill  a  dog.  It  is  still  undecided  whether  this  poisoning  is 
due  to  the  protamines  or  to  some  admixture. 

Besides  the  protamines  mentioned,  cyclopterine  l  from  the  lump-fish, 
(Cydopterus  lumpus],  and  acipenserine,  from  the  testes  of  the  sturgeon 
(Acipenser  stellatus},2  are  also  described  as  protamines.  Two  other  pro- 
tamines may  be  mentioned:  a-  and  /?-cyprinine,3  which  are  obtained  from 
the  sperm  of  the  carp  (Ciprinus  carpio}.  The  sperm  of  the  brook-trout 
(Salmo  fario),  the  white  snapper  (Coregonus  oxyrhynchus} ,  the  sheath- 
fish  (Silurus  glanus),  and  the  pike  (Esox  lucius),4  also  contain  protamines. 
Protamines  have  not  been  isolated  positively  from  any  other  representa- 
tives of  the  animal  kingdom.  The  significance  of  the  protamines  has  not 
yet  been  established. 

Related  to  the  proteins  just  described  is  a  group  of  albuminous  bodies, 
whose  biological  significance  differs  materially  from  that  of  any  so  far 
mentioned.  Their  common  properties  have  united  the  heterogeneous 
substances  into  one  group,  called  the  "  albuminoids."  They  constitute 
the  frame- work  of  the  animal  tissues.  They  are  not  found  in  the  cell  pro- 
toplasm, nor  in  the  tissue  fluids.  We  shall  see  later,  that  their  significance 
also  corresponds  to  their  entire  composition.  They  are  not  to  be  considered 
as  nutrient  materials  in  the  narrower  sense,  and  participate  but  little  in  the 
intermediate  metabolism.  Incidentally  they  are  difficultly  digestible; 
in  fact,  being  somewhat  resistant  to  the  digestive  ferments.  The  albu- 
minoids are  to  the  animal  body  what  the  higher  carbohydrates  (for 
instance,  cellulose)  are  to  the  vegetable.  They  are  all  insoluble  in 
water  and  salt  solutions.  They  are  only  slightly  attacked  by  acids  and 
alkalies.  It  is  practically  useless  to  attempt  to  purify  the  albuminoids. 
They  can  only  be  studied  in  the  manner  in  which  they  occur  in  nature. 
It  is  an  entirely  arbitrary  assumption  that  they  exist  as  a  chemical 
entity. 

Collagen  occupies  a  special  position  among  the  albuminoids.  It  con- 
stitutes the  foundation  of  the  bones  and  cartilages,  and  constructs  the 
fibrils  of  the  connective  tissues.  It  may  be  extracted  from  these  tissues 
by  boiling  with  water.  The  product  which  goes  into  solution  is  called 
glue,  glutin,  or  gelatin.  In  contra-distinction  to  the  other  proteins, 
collagen  is  soluble  in  warm  water,  and  solidifies  on  cooling.  Numerous 
investigations  indicate  that  it  is  not  an  individual  substance,  undoubtedly 
differing  according  to  the  animal,  or  organ,  from  which  it  is  obtained. 
The  nature  of  the  change  underlying  the  formation  of  gelatin  has 

1  N.  Markowin:  Z.  physiol.  Chem.  28,  313  (1899). 

2  D.  Kurajeff :  Z.  physiol.  Chem.  32,  197  (1901). 

3  A.  Kossel  and  H.  D.  Dakin:  ibid.  40,  565  (1903),  loc.  cit. 

4  A.  Kossel:  ibid.  22,  176  (1896),  loc  cit.- 


138  LECTURE   VII. 

been  but  little  studied.      It  may  possibly  be  due  to  a  hydrolytic  decom- 
position. 

Another  group  of  albuminoids  is  included  under  the  name  of  keratins. 
They  comprise  the  so-called  "  horn  substance,"  and  are  found,  as  such, 
in  the  hair,  feathers,  nails,  hoofs,  horns,  etc.  N euro-keratin,  which  forms 
a  part  of  the  sheath  of  the  medullary  nerves,  belongs  to  this  class.  The 
keratins  are  noted  for  their  insolubility  in  water,  dilute  acids  and  alkalies. 
They  have  a  high  percentage  of  sulphur.  Ovokeratin,  in  the  membranes 
surrounding  the  eggs  of  many  animals,  is  closely  related  to  the  keratins. 
Gorgonin,  constituting  the  foundation  of  the  axial  skeleton  of  coral 
(Gorgonia  cavolini),  is  also  included.  It  is  especially  noted  for  its  high 
percentage  of  iodine. 

The  elastin  bodies  form  a  group  by  themselves.  They  predominate  in 
the  formation  of  the  elastic  tissues.  Elastin  is  generally  prepared  from 
the  Ligamentum  nuchce  of  the  ox. 

Fibroin,  obtained  from  the  threads  of  silk-worms,  is  the  best  known 
albuminoid.  It  is  characterized  by  a  very  low  percentage  of  di-amino 
acids.  We  shall  return  to  this  substance  later. 

Spongin,  forming  the  framework  of  sponges,  and  conchiolin,  the  basis 
of  the  skeleton  of  the  mussel,  are  included  among  the  albumoids.  Amy- 
loid, to  whose  content  of  chondroitin-sulphuric  acid  we  recently  referred, 
is  also  assigned  to  this  group.  It  occurs  only  under  pathological  condi- 
tions. It  is  found,  on  the  one  hand,  in  the  form  of  small  kernels  in  the 
brain  (the  so-called  Corpora  amylacea),  and  then,  again,  as  large  deposits 
in  the  parenchyma  of  many  organs.  This  is  called  an  amyloid  degenera- 
tion. The  cause  of  its  formation  is  but  little  known. 

We  must  finally  consider  the  group  of  the  albumoids.  It  includes 
the  most  varied  albuminous  substances,  about  whose  constitution  nothing 
is  at  present  known.  To  this  class  belong  the  Membrance  proprice  of  many 
glands,  sarcolemma,  osseo-albumoid,  chondro-albumoid,  the  albumoid  of 
lentils,  the  elementary  matter  of  Chorda  dorsalis,  ichthylepidin  (occurring 
in  the  scales  of  fishes),  the  horny  layer  in  the  crop  of  birds,  reticulin  (which 
composes  the  reticular  tissues  of  the  intestinal  mucosa),  and  many  other 
analogous  substances. 

It  is  impossible,  at  present,  to  give  any  further  exact  account  of  the 
various  representatives  of  the  albumoids.  The  fact  that  they  are 
obtained  with  difficulty,  and,  more  especially,  that  it  is  almost  impossible 
to  purify  them,  has  made  any  exact  study  of  the  class  up  to  the  present 
time  entirely  futile.  Observers  have  concerned  themselves  chiefly  with 
an  investigation  of  various  physical  properties  of  individual  proteins  of 
this  group,  and  especially  to  the  action  of  ferments  upon  them.  Their 
practical  indigestibility,  has  made  it  possible  to  remove  the  ordinary  pro- 
teins from  them.  The  great  predominance  of  albuminous  substances,  not 


ALBUMINS  OR  PROTEINS.  139 

only  in  the  cells,  but  also  in  all  the  fundamental  and  basic  elements,  dis- 
tinctively separates  the  animal  from  the  vegetable  world.  As  the  plants 
are  capable  of  utilizing  the  very  diverse  carbohydrafes  in  building  up 
the  various  polysaccharides,  so  the  animal  organism  is  able  to  assimilate 
the  simple  proteins  (those  of  milk,  for  example)  for  its  nourishment,  pro- 
ducing the  large  number  of  albuminous  substances  found  in  the  cells  and 
tissues.  The  albuminoid  and  albumoid  groups  are  good  illustrations  of 
how  the  animal  organism  utilizes  the  proteins  for  its  varied  functions,  and 
how  it  adjusts  the  composition  to  the  function. 

We  shall  now  discuss  the  proteids,  or  compound  proteins.  We  can 
do  this  rather  rapidly,  because  the  non-albuminous  component  of  the 
proteids  is  the  more  interesting,  and  will  be  considered  elsewhere.  The 
large  number  of  nucleoproteids  belong  to  this  group.  They  are  com- 
posed of  albumin  and  nucleic  acid.  The  former  may  consist  of  certain 
of  the  protein  groups  previously  mentioned.  We  are  acquainted  with 
compounds  of  nucleic  acids  with  histons,  as  well  as  with  protamines.  It 
is  an 'open  question  as  to  whether  other  proteins  do  not  likewise  partici- 
pate in  the  formation  of  nucleoproteids.  It  must  be  admitted,  how- 
ever, that  the  very  existence  of  the  nucleoproteids  has  been  questioned.1 
Nucleic  acid  has  the  property  of  precipitating  protein  from  solution.  In 
preparing  the  nucleoproteids  we  only  extract  the  various  organs  with, 
for  instance,  water.  On  adding  acid,  generally  acetic  acid,  the  nucleo- 
proteids are  precipitated  from  the  extract.  We  can  imagine  that  the 
nucleic  acid  is  present  in  the  extract  perhaps  in  the  form  of  its  sodium 
salt,  together  with  the  albumin.  As  a  matter  of  fact,  by  acidifying,  the 
nucleic  acid  is  freed,  which  precipitates  the  soluble  albumin.  We  can,  by 
adding  nucleic  acid  to  albuminous  substances,  obtain  precipitates  which 
are  very  much  like  nucleoproteids.  Nucleoproteids  have,  however,  also 
been  obtained  by  "  salting-out."  2  It  is,  therefore,  very  probable  that 
the  nucleoproteids  are  present,  as  such,  in  the  various  organs. 

We  do  not,  at  present,  know  the  manner  of  linking  between  the  nucleic 
acid  and  the  protein.  There  are  apparently  various  kinds  of  combina- 
tion. For  instance,  0.8  per  cent  of  hydrochloric  acid  is  sufficient  to 
separate  histon  from  the  nucleo-histon  obtained  from  the  thymus  gland; 
on  the  other  hand  the  pancreas-proteid  is  decomposed  into  nuclein  and 
albumin,  even  in  neutral  solution  on  boiling.  The  composition  is  not  as 
simple  as  the  name  nucleoproteid  might  indicate.  There  seems  to  be  more 
than  a  mere  combination  of  nucleic  acid  and. protein.  If  a  nucleoproteid 
is  decomposed,  we,  of  course,  obtain  a  protein,  for  instance  histon.  The 

1  I.  Bang:  Z.  physiol.  Chem.  30,  508  (1900).     T.  B.  Osborne  and  I.  F.  Harris:  ibid. 
38,  85  (1902). 

2  F.  Malengreau:  La  Cellule,  17,  339  (1900).     W.  Huiskamp:  Z    physiol.  Chem.  32, 
145  (1901);  39,  55  (1903). 


140  LECTURE  VII. 

other  compound  is  not  a  nucleic  acid,  but  a  combination  of  this  with 
albumin.  This  is  called  nuclein.  On  further  decomposition,  it  breaks 
down  into  albumin  and  nucleic  acid. 

The  nucleoproteids  are  all  soluble  in  water  and  salt  solutions.  They 
are  very  soluble  in  alkalies.  They  are  distinctly  acid  in  their  charac- 
teristics. They  are  precipitated  by  acids,  although  redissolved  by  an 
excess.  The  nucleoproteids  can  be  "  salted-out "  and  coagulated  by 
heat  and  other  means.  When  nucleoproteids  are  digested  with  pepsin- 
hydrochloric  acid,  nuclein  settles  out,  while  the  albuminous  cleavage- 
product  is  dissolved  by  the  ferment  in  the  usual  manner.  Fr.  Miescher,1 
the  discoverer  of  the  nucleins,  noticed  this  characteristic  property.  The 
nucleins  themselves  are  but  little  affected  by  pepsin-hydrochloric  acid, 
although  more  so  by  trypsin.  It  is  very  difficult  to  purify  them;  in  fact,  it 
is  doubtful  whether  they  have  ever  been  isolated  in  a  pure  condition. 

The  nucleoproteids  often  contain  iron,  and  it  is  very  probable  that  the 
main  supply  of  this  element  in  the  system  occurs  in  these,  and  in  hemo- 
globin. They  are  present  in  every  cell,  and  are  found  in  the  nucleus. 
Miescher  first  noticed  them  in  the  little  pus  cells.  They  were  isolated 
shortly  afterwards  also  from  the  blood  corpuscles  of  birds  and  snakes. 
We  must  also  state  that  efforts  have  been  made  to  place  the  ferments 
themselves  in  the  group  of  nucleoproteids.  By  the  discovery  of  nuclein 
and  the  nucleoproteids,  Fr.  Miescher  has  substantially  advanced  our 
knowledge  of  the  constituents  of  the  nuclei.  The  fact  that  all  nuclei  — 
whether  plant  or  animal  —  contain  nucleoproteids  is  another  link  between 
these  two  great  kingdoms.  We  must  not,  however,  forget  that  we  know 
practically  nothing  about  the  biological  significance  of  these  substances. 
They  have  interested  us  greatly,  especially  on  account  of  their  predomi- 
nance in  the  nuclear  material,  and  the  ease  of  obtaining  them.  The 
importance  assigned  to  them  may,  however,  be  entirely  unwarranted. 
Our  knowledge  of  the  other  constituents  of  the  nuclei  is  far  too  meager 
to  tell  us  much  concerning  the  functions  of  the  nucleus. 

Nucleoproteids  have  been  isolated  from  almost  every  organ.  So,  also, 
from  the  spermatozoa-masses.  Those  of  fishes  contain  up  to  96  per  cent 
of  nucleic-acid-protamine,  or  -histon.  Fr.  Miescher  and  Schmiedeberg  give 
the  following  composition  to  salmon  spawn:  60.5  per  cent  nucleic  acid, 
35.56  per  cent  protamine.  A  nucleic-acid-histon  has  been  obtained  from 
the  sea-urchin  (Arbacia  pustulosa)?  The  spermatozoa  of  bulls  also 
contain  a  nucleoproteid,  which,  however,  does  not  contain  protamine 
nor  histon,  but  some  other  kind  of  protein.3  Nucleoproteids  have  also 
been  isolated  from  the  thymus  gland,  from  the  red  corpuscles  of  birds 

1  Fr.  Miescher:  Hoppe-Seyler's  Med.-chem.  Untersuchungen,  p.  441  (1871). 

2  A.  Mathews:  Z.  physiol.  Chem.  23,  399  (1897). 

3  Fr.  Miescher:  Arc.  exp.  Path.    Pharm.  37,  100  (1896). 


ALBUMINS  OR  PROTEINS.  141 

and  reptiles,  from  the  pancreas,  from  the  gastric  juice,  from  the  thyroid 
gland,  from  suprarenal  glands,  and  from  muscles.  Nucleoproteids  have 
also  been  found  in  tumors.  The  nucleoproteid  of  yeast  has  been  much 
studied  on  account  of  the  ease  with  which  its  nucleic  acid  is  obtained. 
We  must  also  call  attention  to  the  presence  of  nucleoproteids  in  the 
vegetable  kingdom. 

Oxy-hemoglobin  likewise  belongs  to  the  group  of  proteids.  It  is 
composed  of  globin  and  hematin.  We  have  met  the  former  while  dis- 
cussing the  histons.  Oxy-hemoglobin  contains,  according  to  the  inves- 
tigations of  Fr.  N.  Schulz,1  about  4-5  per  cent  hematin.  We  do  not,  at 
present,  know  whether  different  kinds  of  animals  possess  different  kinds 
of  hemoglobin;  in  fact,  we  are  not  at  all  certain  that  one  and  the  same 
species  of  animal  has  a  uniform  hemoglobin.  The  crystalline  form  of  the 
hemoglobin  is  of  little  value.  The  investigations  of  the  globin  portion 
have  also  been  of  little  service.  The  hemoglobin  from  the  horse  has  been 
most  thoroughly  studied.  The  decomposition  of  the  hemoglobin  from 
the  dog  gave  corrresponding  amounts  of  amino  acids.  The  second  com- 
ponent, hematin,  seems  to  have  constant  properties,  irrespective  of  the 
animal  from  which  it  is  obtained.  We  shall  devote  more  attention  to 
hematin  when  we  discuss  the  composition  of  blood.  We  shall  also  have 
to  consider  then  the  part  hemoglobin  plays  as  a  carrier  of  oxygen  and 
carbon  dioxide. 

The  glucoproteids  form  the  third  subdivision  of  the  proteid  group. 
They  are  composed  of  a  protein  and  a  carbohydrate  complex.  We  have 
already  met  them  in  our  discussion  of  the  carbohydrates,2  and  have 
seen  that  glucosamine  is  produced  by  the  hydrolysis  of  the  ordinary 
mucins,  while  galactosamine  is  obtained  from  the  mucin  of  frog-spawn. 
These  are  the  only  carbohydrates  that  have  been  positively  isolated  from 
the  glucoproteids.  It  is,  indeed,  very  questionable  whether  the  carbo- 
hydrates mentioned  pre-exist  as  such.  The  whole  group  of  glucoproteids 
is  still  very  indefinite.  While  it  is  comparatively  easy  to  decompose  the 
nucleoproteids  and  hemoglobin  into  their  albuminous  and  non-albumi- 
nous constituents,  this  does  not  hold  with  the  glucoproteids.  The  carbo- 
hydrate group  is  only  split  off  by  boiling  with  mineral  acids  or  by  the 
action  of  alkalies.  It  is,  of  course,  possible  that  the  glucoproteids  are* 
true  albuminous  bodies,  differing  only  from  the  other  proteins,  in  that 
more  carbohydrates  take  part  in  their  formation.  Certain  of  the  ordi- 
nary albumins  may  indeed  really  belong  to  this  group.  If  this  be  true, 
we  would  then  have  all  shades  of  proteins,  some  with  considerable  car- 
bohydrates others  with  less,  and  some  which  do  not  contain  any  carbohy- 
drate at  all  in  the  molecule. 

1  Fr.  N.  Schulz:  Z.  physiol.  Chem.  22,  449  (1898). 

2  Cf.  pp.  20  and  25. 


142  LECTURE  VII. 

It  would  be  much  more  correct  if  we,  for  the  present,  entirely  drop 
the  name  glucoproteid  until  we  were  certain  that  the  carbohydrates 
occupy  the  same  relative  position  to  the  protein  in  the  molecule,  as,  for 
example,  hematin  does  to  hemoglobin.  We  will,  therefore,  classify  the 
glucoproteids  as  true  proteins,  in  the  largest  sense,  and  deal  with  the  car- 
bohydrate cleavage-products  in  the  same  manner  as  with  the  other  pro- 
tein components.  It  is  certainly  a  matter  of  considerable  interest  to  know 
that  amido-carbohydrates  —  that  is,  sugars  which  are  intermediate  be- 
tween the  amines  and  the  true  carbohydrates  —  take  part  in  the  building 
up  of  these  proteins. 

To  this  group  belongs  a  series  of  albuminous  substances  whose  physical 
appearance  is  sufficient  to  identify  them  as  a  class.  They  are  called 
mucins  and  mucoids.  They  may  be  recognized  even  by  their  elementary 
composition.  The  occurrence  of  the  carbohydrate  groups  rich  in  oxygen 
lowers  the  percentages  of  carbon  and  nitrogen.  The  amount  of  carbo- 
hydrate present  is  a  very  variable  one,  ranging  from  3-37  per  cent,  accord- 
ing to  the  substance  in  question.  It  is  very  difficult  to  purify  them  even 
approximately.  They  are  not  coagulated  by  heat,  —  a  property  which  dis- 
tinguishes them  from  the  ordinary  proteins.  They  may,  nevertheless,  be 
easily  denaturized.  They  can  be  "  salted-out."  The  mucins  and  mucoids 
are  distinctively  acid,  and  can  be  precipitated  by  acids.  They  are  readily 
soluble  in  alkalies,  alkaline  carbonates,  and  ammonia. 

The  mucins  are  very  widely  distributed.  They  constitute  the  slimy 
material  of  many  secretions,  and  are  eliminated  by  the  respiratory  1  and 
digestive  tracts,  sometimes,  from  individual  cells  (goblet  cells)  and  again 
from  larger  glands  —  such  as  the  salivary  glands.  There  are  also  mucous- 
producing  cells  in  the  bile  ducts  and  the  urinary  passages.  The  mucins  are 
also  produced  to  a  considerable  extent  by  invertebrates,  e.g.,  slime  of  snails. 
The  mucin  from  the  respiratory  passages  2  and  from  the  submaxillary 
glands,3  has  been  studied  most.  Mucin  from  the  invertebrates  does  not 
seem  to  be  excreted  as  such,  but  is  only  produced  secondarily  from  a  sub- 
stance called  mucinogen. 

Proteins  closely  related  to  the  mucins  have  been  observed  in  ovarian 
cysts,  which  are  peculiar  tumorous  formations  of  the  ovaries.  They  are 
called  para-  and  pseudo-mucin.*  The  latter  differs  from  the  ordinary 
mucins  in  that  it  is  not  precipitated  from  its  solutions  by  acetic  or  nitric 
acids.  Paramucin  is  occasionally  found  in  gelatinous  masses  in  cysts.  It 
resembles  mucin  in  being  precipitated  by  acids. 

The   mucoids   are  closely  related  to  the  mucins.     They  are  found  to 

1  F.  Miiller:  Z.  Biol.  42,  468  (1901). 

3  O.  Hammarsten:  Z.  physiol.  Chem.  12,  163  (1887). 

3  O.  Hammarsten:  Pfluger's  Arch.  36,  373  (1883). 

4  O.  Hammarsten:  Z.  physiol.  Chem.  6,  194  (1882). 


ALBUMINS  OR  PROTEINS.  143 

some  extent  dissolved,  and  to  some  extent  they  participate  in  the  con- 
struction of  tissue.  Their  classification  is  based  upon  principles  morpho- 
logical rather  than  chemical-physical.  They  are  sometimes  included  with 
the  mucins,  and  sometimes  classed  as  an  independent  group.  We  shall 
mention  only  the  most  important  of  them.  Deserving  of  mention  are  the 
mucoids  prepared  from  tendons,  bones,  and  cartilages.  The  last  named 
has  been  thoroughly  investigated.  Chondro-mucoid  in  conjunction  with 
collagen  constitutes  the  elementary  material  of  cartilage.  It  contains 
considerable  sulphur  and  a  reducing  sugar.  When  hydrolyzed  we  obtain 
a  protein  and  a  carbohydrate-ethereal  sulphuric  acid,  the  so-called  chon- 
droitin-sulphuric acid.1  This  is  a  colloidal  substance,  and  has  been  investi- 
gated by  Schmiedeberg,2  and  later  by  A.  Orgler  and  C.  Newberg.3  By 
boiling  with  acids  for  a  short  time  it  decomposes  into  sulphuric  acid  and 
a  residue,  chondroitin,  free  from  sulphuric  acid.  Further  treatment  with 
acid  produces  an  amido-polysaccharide,  whose  exact  nature  has  not  yet 
been  determined.  Chondroitin-sulphuric  acid  is  found  not  only  in  carti- 
lages, but  also  in  bones  in  ligamentum  nuchce,  and  in  the  mucous  mem- 
brane of  the  pig.  It  occurs  especially  in  amyloid,  a  protein  which  is 
found  in  the  tissues  under  certain  pathological  conditions.  Morner 4 
found  chondroitin-sulphuric  acid  repeatedly  in  the  urine  to  the  extent  of 
0.05  per  cent. 

The  proteins  found  in  the  vitreous  humor,  in  the  cornea,  and  in  the  um- 
bilical cord,  also  belong  to  the  group  of  mucoids,  as  does  the  ovomucoid 
obtained  from  the  white  of  an  egg.  The  latter  may  be  isolated  by  coagu- 
lating the  globulin  and  albumin,  and  adding  alcohol  to  the  filtrate.  A 
reducing  substance,  gluocsamine,  can  be  split  off  from  it.  Steudel 5  ob- 
tained 29.4  grams  glucosamine  from  100  grams  ovomucoid.  Blood  serum 
also  contains  a  mucoid  body.  Morner  describes  another  substance  be- 
longing to  this  group,  which  he  obtained  from  the  urine.  An  analogous 
product  also  occurs  in  the  ascitic  fluid. 

We  must  admit  that  a  large  amount  of  uncertainty  attaches  to  this 
group  of  albuminous  substances.  Secure  foundations  are  lacking.  It  is 
practically  impossible  to  purify  these  products,  beyond  getting  rid  of 
gross  impurities.  The  properties  of  the  various  members  of  this  group 
are  such,  that  it  is  very  difficult  to  work  with  them.  It  is  difficult  to  ob- 
tain them  in  large  quantities.  We  must,  therefore,  look  with  skepti- 
cism upon  all  new  mucins  and  mucoids,  and  should  await  the  time  when 
purely  chemical  investigations  will  have  sufficiently  classified  the  mem- 


C.  T.  Morner:  Skand.  Arch.  f.  Physiol.  1,  210  (1889).     Cf.  Lecture  III,  p.  49. 
O.  Schmiedeberg:  Arch.  exp.  Path.  Pharm.  28,  355  (1891). 
A.  Orgler  and  C.  Neuberg:  Z.  physiol.  Chem.  37,  399  (1903). 
K.  A.  H.  Morner:  Skand.  Arch.  Physiol.  6,  332  (1895). 
H.  Steudel:  Z.  physiol.  Chem.  34,  353  (1901-02). 


144  LECTURE  VII. 

bers  of  this  group,  at  least  to  the  extent  of  recognizing  the  nature  of  the 
individual  decomposition  products. 

Hammarsten  *  has  isolated  a  peculiar  substance  from  the  albuminous 
gland  of  the  Roman  snail  (Helix  pomatia),  which  is  possibly  a  protein, 
difficult  to  classify,  or,  more  probably,  a  proteid.  It  contains  a  Isevo- 
rotary  carbohydrate,  which  yields  a  dextro-rotary  substance  on  boiling 
with  acids.  This  material  also  contains  phosphorus.  It  does  not  belong 
to  the  nucleo-proteids,  because  it  possesses  no  xanthin  bases.  To  this 
group,  called  "  phospho-glucoproteids,"  is  assigned  the  substance  ichtulin, 
which  has  been  obtained  from  fish  eggs. 

The  proteins  and  proteids  already  mentioned  do  not,  by  any  means, 
exhaust  the  list.  We  have  mentioned  only  those  which  have  been  fairly 
well  characterized,  and  which  are  starting  points  for  further  investiga- 
tion. The  albuminous  substances,  and  especially  some  of  the  albumin- 
oids, isolated  from  plant  seeds  and  the  animal  fluids,  are  undoubtedly  best 
known.  We  frankly  admit  that  our  knowledge  is  very  vague  concern- 
ing the  albumins  which  participate  in  the  construction  of  the  various 
organs.  It  is  very  probable  that  the  number  of  proteins  and  proteids 
occurring  in  the  tissues  is  extremely  large  as  is  indicated  by  the  descrip- 
tion of  the  various  tissue-albumins.  On  the  other  hand,  we  must  remem- 
ber that  when  proteins  are  attacked  but  slightly  their  properties  are 
changed  completely  so  that  they  may  be  mistaken  for  new  kinds  of  pro- 
tein. It  is  also  probable  that  the  tissues,  and  especially  the  cell  proteins, 
are  continually  undergoing  changes.  It  is  still  undecided  whether  the 
albuminous  constituents  of  the  tissues  are  to  be  considered  as  stable  sub- 
stances, to  a  certain  degree,  or  as  undergoing  continual  decomposition 
and  reconstruction.  From  this  question  arises  the  extremely  important 
problem  of  the  whole  subject  of  protein  metabolism,  about  which  we  are 
still  in  the  dark. 

We  have,  so  far,  neglected  to  mention  a  group  of  nitrogenous  com- 
pounds, which  are  closely  related  to  the  proteins.  These  are  the 
melanins,  which  are  very  widely  distributed  in  the  animal  kingdom. 
They  are  found  in  the  very  large  number  of  pigments  occurring  in  the 
hair,  feathers,  choroidea  of  the  eyes,  skin,  etc.  Their  presence  in  tumors 
is  very  interesting;  and  their  unusually  large  occurrence  in  the  melano- 
sarkoma  of  horses  —  especially  of  white  horses  —  has  drawn  much  atten- 
tion to  them.  In  the  muscles  of  these  animals  (for  instance,  the  glutsei), 
there  are  often  embedded  very  large  tumors,  which  appear,  according  to 
age,  as  very  black,  firm  masses,  or  like  a  cyst,  containing  an  inky,  finely 
granulated  fluid.  It  is  certainly  significant  that  these  masses  of  pigment 
are  obtained  in  animals  whose  hair  has  no  pigments.  The  pure  white 


O.  Hammarsten:  loc.  cit.  Pfliiger's  Ann.  36,  373  (1883). 


ALBUMINS  OR  PROTEINS.  145 

horse  produces,  therefore,  a  pigment,  but  it  is  not  utilized.  This  pigment, 
called  hippomelanin,  has  been  very  exhaustively  investigated.1  It  occurs 
as  a  very  finely  divided,  brownish-black  powder.  No  individual  constit- 
uent of  melanin  has  so  far  been  definitely  isolated.  The  constituents  of 
the  other  melanins,  prepared  from  the  hair,  choroidea,  etc.,  has  also  never 
been  cleared  up.  The  melanins  are,  undoubtedly,  not  simple  substances. 
It  is  difficult  to  obtain  any  exact  knowledge  about  these  substances, 
because  they  are  not  readily  purified.  They  are  extremely  resistant  to 
acids  and  alkalies,  and  to  oxidation  and  reduction  processes.  Some  will 
dissolve  in  alkali;  others  will  not.  Some  contain  iron;  in  others,  this  ele- 
ment is  lacking.  It  has  been  suggested  that,  because  some  of  the  melanins 
contain  iron,  they  are  related  to  the  coloring  matter  of  the  blood.  It 
is  possible  that  some  of  these  pigments  may  trace  their  origin  back  to 
hematin,  although  no  proof  has  been  presented  to  substantiate  this 
hypothesis.  The  melanins  are  characterized  by  a  high  carbon  and  a  low 
hydrogen  content.  Many  of  them  have  considerable  sulphur  in  their 
composition. 

By  the  hydrolysis  of  almost  all  the  albuminous  bodies  with  acids, 
products  are  obtained  which  very  much  resemble  the  naturally-occurring 
melanins.  These  black  products  are  called  humin  substances.  They  are 
supposed  to  be  related  to  the  natural  melanins,  and  the  suggestion  has 
been  made  that  glucosamine,  tryptophane,  tyrosine,  and  lysine  participate 
in  the  formation  of  pigment.  We  know  nothing  definite 2  about  the 
constituents  of  these  humin  substances,  and  are  unable  to  decide  whether 
there  is  any  distinct  relationship  between  these  and  the  melanins.  We 
will  particularly  emphasize  the  fact  that  the  hypothesis  just  mentioned 
to  the  effect  that  the  humin  substances  are  built  up  of  the  fundamental 
constituents  of  the  albumins,  is  entirely  without  empirical  justification. 

We  have  nowr  mentioned  the  most  important  classes  of  the  remarkably 
diversified  group  of  the  proteins,  or  albuminous  substances.  The  unsatis- 
factoriness  of  the  whole  system  of  classification  is  evident  from  our  pre- 
sentation of  the  subject.  It  only  serves  as  a  temporary  basis  for  further 
orientation.  It  is  highly  important  that  we  should  sharply  and  distinctly 
emphasize  how  slight  the  proofs  are  in  the  case  of  most  of  these  substances 
that  we  are  dealing  with  simple  substances  rather  than  with  mixtures, 
and  how  extraordinarily  cautious  we  must  be  for  this  reason  in  passing 
judgment  upon  the  results,  which  must  eventually  be  referred  to  more 
physico-chemical  investigations. 

1  J.  Berdez  and  M.  Nencki:  Arch.  exp.  Path.  Pharm.  20,  346  (1885).     M.  Nencki 
and  N.  Sieber:  ibid.  24,  17  (1887). 

2  Cf.  also  Fr.  Samuely:  Hofmeister's  Beit.  2,  355  (1902) 


LECTURE  VIII. 

ALBUMINS  OR  PROTEINS. 
II. 

THE  COMPONENTS  OF  PROTEIN. 

ALTHOUGH  the  number  and  distribution  of  the  proteins  in  Nature  are 
very  great,  still  they  show  great  similarity  in  the  way  they  are  constructed. 
Various  methods  have  been  tried  for  effecting  the  cleavage  of  proteins. 
Up  to  the  present  time,  hydrolysis,  whether  brought  about  by  the  action 
of  acids,  of  alkalies,  or  of  ferments,  has  alone  been  productive  of  results. 
Experiments  performed  in  the  attempt  to  obtain  known  products  by 
oxidation  have  thus  far  been  unfruitful.1  It  is,  moreover,  hardly  to  be 
expected  that  in  the  case  of  such  a  complicated  substance  as  albumin  we 
shall  obtain  much  idea  of  its  chemical  constitution  by  means  of  oxidation 
or  reduction  processes.  We  shall  limit  ourselves  here,  therefore,  to  a 
consideration  of  those  investigations  which  have  been  of  service  in  the 
further  development  of  the  entire  chemistry  of  the  proteins.  We  shall 
first  of  all  take  up  those  substances  which  are  formed  by  the  hydrolysis 
brought  about  by  the  action  of  acids  or  alkalies.  If  a  protein  is  boiled 
for  some  time  with  fuming  hydrochloric  acid,  or  with  twenty-five  per 
cent  sulphuric  acid,  its  character  is  completely  changed.  It  is  broken 
down  into  numerous,  simpler  cleavage-products.  These  are  of  various 
kinds.  They  possess,  however,  certain  common  characteristics.  As  far 
as  we  know,  they  nearly  all  crystallize  well,  and  contain  nitrogen,  hydro- 
gen, and  oxygen.  These  cleavage-products  are  known  in  general  as  amino 
acids.  They  can  be  easily  identified  and  prepared  in  a  pure  condition. 
Besides  these  amino  acids  we  find  varying  amounts  of  ammonia,  and  fre- 
quently humin  substances.  We  shall  presently  see  that  we  are  acquainted, 
with  a  large  number  of  the  cleavage-products  of  the  proteins,  although  an 
appreciable  part  of  the  molecule  is  still  unexplained.  We  shall  also 
soon  learn  that  all  proteins,  as  far  as  our  present  knowledge  goes,  contain 
these  same  amino  acids.  Occasionally  one  or  another  amino  acid  is 
missing,  although,  as  a  whole,  there  is  a  very  general  agreement  in  the 
qualitative  composition.  The  following  amino  acids  have  been  isolated 
up  to  the  present  time: 


1  Cf.  Otto  von  Furth:  Hofmeister's  Beitrage,  6,  296  (1905).     The  older  literature  is 
carefully  compiled  in  this  article. 

146 


ALBUMINS  OR  PROTEINS.  147 


I.    ALIPHATIC    SERIES. 


1 .  Mono-amino-mono-carboxylic  acids . 


Glycocoll. 

Alanine. 

Amino-isovaleric  acid. 


Leucine. 
Isoleucine. 

2.  Mono-amino-hydroxy-mono-carboxylic  acids:  Serine. 

3.  Mono-amino-di-carboxylic  acids  .  .    f  Aspartic  acid. 

I  Glutamic  acid. 


4.  Di-amino-carboxylic  acids  .....  J 

[  Argmme 

5.  Di-amino-hydroxy-mono-carboxylic  acids.    Di-amino-tri-hydroxy-dodecylic  acid. 

6.  Amino  acids  containing  Sulphur:  Cysteine  and  Cystine. 

n.    AROMATIC    SERIES. 

Mono-amino-mono-carboxylic  acids  :  Phenylalanine. 
Mono-amino-hydroxy-mono-carboxylic  acids:  Tyrosine. 

III.    HETERO-CYCLIC    COMPOUNDS. 

Mono-a-amino-mono-carboxylic  acids  .  \  Pyrolidine^arboxylic  acid. 

(  Tryptophane. 

Hydroxy-mono-amino-mono-carboxylic  acids:  pyrrolidine-carboxylic  acid. 

Histidine. 

The  carbohydrate  group  should  also  be  included.  These  occupy  a  pecu- 
liar position,  because  they  are  absent  from  a  large  number  of  the  proteins; 
in  others  their  occurrence  is  questioned;  while  in  still  another  group  of 
proteins  they  appear  in  larger  amount,  but  only  in  part  as  a  direct  constitu- 
ent of  the  albumin  molecule.  Many  authors  classify  all  these  proteins  con- 
taining carbohydrates  as  compound  albumins.  As  previously  indicated, 
we  do  not  consider  this  as  justifiable.  We  shall  subsequently  return  to 
this  carbohydrate  group. 

Let  us  turn  to  the  individual  amino  acids.  We  shall  consider  their 
distribution  when  we  return  to  the  composition  of  the  individual  proteins. 
For  the  moment  we  will  only  classify  them  according  to  their  constitution, 
as  this  is  necessary  in  order  to  understand  their  biological  significance. 

The  mono-amino-mono-carboxylic  acids  can  be  derived  from  the  normal 
fatty  acid  series:  CnH2nO2.  The  simplest  member  of  this  series  is  glyco- 
coll,  also  called  glycine  or  amino-acetic  acid: 


OOH 


1  We  shall  use  this  formula,  but  the  following  is  also  possible: 

COO 


CH.-NH, 


148  LECTURE  VIII. 

Glycocoll  was  one  of  the  first-known  cleavage-products  of  proteins.  As 
early  as  1820  Braconnot  l  obtained  it,  in  conjunction  with  leucine,  on  boiling 
glue  with  dilute  acid  or  alkali.  It  is  also  obtained,  as  such,  from  the 
muscles  of  the  scallop,  Pecten  irradians. 

Alanine  is  the  next  homologue  of  glycocoll.     It  is  an  a-amino-propionic 

acid:  CH3  .  CH(NH2).  COOH.     It  contains  an  asymmetric  carbon  atom, 
* 

*,  and  is  consequently  optically  active,  as  are  most  of  the  other  acid 
cleavage-products  of  albumin,  which  itself  rotates  the  plane  of  polarized 
light.  Alanine,  as  it  occurs  in  nature,  is  dextro-rotary. 

An  ammo-butyric  acid  has  been  described  as  a  cleavage-product  from 
proteins.  Later  investigations,  however,  have  not  shown  its  presence  in 
the  protein  molecule.  On  the  other  hand,  its  next  homologue,  amino- 
valeric  acid,  has  been  obtained  very  often.  The  amino-valeric  acid  so  far 
isolated  from  the  proteins  does  not  have  a  normal  chain,  but  a  branch- 

PTT 

ing  one.     It  is  an  a-amino-isovaleric  acid:  nTT3>CH  .  CH(NH2)COOH. 

^*l3  -X- 

It  is  dextro-rotary. 

Leucine  also  has  a  branching  chain,  and  is  an  a-amino-isobutyl-acetic  acid: 

>CH  .  GH2  .  CH(NH2)COOH.     The  leucine,  usually  obtained  by  the 
•& 

cleavage  of  proteins,  is  Z-leucine.  In  this  form  it  occurs  in  many  plants 
and  in  invertebrates.  Penicillium  glaucum  produces  d-leucine  from  the 
inactive  leucine.  The  constitution  of  leucine  has  been  proved  by  E. 
Schulze  and  A.  Lickiernik.2 

Felix  Ehrlich  3  has  recently  separated  an  isomer  of  leucine  from  molasses 
sludge,  and,  soon  after,  also  showed  its  presence  in  many  plant,  and 
animal  proteins.  It  is  an  a-amino-methyl-ethyl-propionic  acid: 

r?  w3  >CH  .  CHNH2  .  COOH. 
^2*15  # 

Its  constitution  has  been  proved  by  its  synthesis,  and  also  that  it  is 
decomposed  by  pure-culture  yeast  into  d-amyl-  alcohol.  The  relations 
of  iso-leucine  to  d-amyl-alcohol  are  shown  as  follows.  We  will  com- 


3 


1  H.  Braconnot:  Ann.  Chim.  Phys.  13,  113  (1820). 

2  Ber.  24,  669  (1891),  and  Z.  physiol.  Chem.  17,  513  (1893). 

3  Felix   Ehrlich :    Ber.    37,    1809    (1904)  ;    Z.   Ver.    Zuckerind,    1904,    975 ;    55, 
592   (1905).      We  shall   dwell  upon  the  syntheses  and  decomposition  of  the  amino 
acids,   only   as   much    as   is   necessary   in   order  to   understand  biological  processes. 
We  may  also   add,  that  this  form  of  synthesis  has  often  been  utilized  in  the  reac- 
tions between  ammonia  and  the  halogen  fatty  acids.     Cf.  E.  Fischer:  Ber.  39,  530 
(1906). 


ALBUMINS  OR  PROTEINS. 


149 


pare  at  the  same  time  the  formation  of  ordinary  leucine  from  iso-amyl- 
alcohol: 

^3>CH.CH2.CH2OH 

•      iso-amyl-alcohol 

+  O 
1      -  H20 


™3>CH.CH2.CHO 

i      iso-valeraldehyde 
+  HCN  +  NH3 


— u 

i      d-amyl-alcohol 
+  0 

™~    XAf 


>0 


•  d-valeraldehyde 
+  HCN  +  NH3 

*  -  H2O 


.  CH2  .  CHNH2  .  CN 

iso-valero-amino-nitril 

+  2H2O 

-NH3 


C23>CH.CHNH2.CN 
^2ri5 

I      d-valero-amino-nitril 

+  2H2O 
*      -  NH3 


>CH .  CH2 .  CHNH2  .  COOH 
a-amino-isobutyl-acetic  acid 

=  leucine 


[3>CH.CHNH2.COOH 

a-amino-methyl-ethyl-propionic 
acid 
isoleucine 


Serine  is  closely  related  to  alanine.     It  was  isolated  in  1865,  by  Cramer,1 
from    silk    glue    (or    sericin).      It    is    an  a-amino-/3-oxypropionic    acid: 

CH2(OH).  CH(NH2).  COOH.(2).     Serine  as  it  occurs  in  nature  is  laevo- 
•* 

rotary.3 

Of  the  di-basic  amino  acids  only  two  are  known:    a-aspartic  acid  and 
glutamic  acid.     The  former  is  an  a-amino-succinic  acid. 

COOH 
*CH(NH2) 
CH2 
COOH. 


1  E.  Cramer:  J.  prakt.  Chem.  96,  76  (1865). 

2  For  the  synthesis  from  ammonia,  hydrocyanic  acid,  glycolaldehyde,  cf.  E.  Fischer 
and  H.  Leuchs:  Sitzber.  Akad.  Wiss.  Berlin,  1902,  and  Ber.  35,  3787  (1902). 

3  Emil  Fischer:  Ber.  40,  1501  (1907). 


150 


LECTURE  VIII. 


The  latter  is  the  next  higher  homologue,  a-amino-glutaric  acid: 

COOH 
*CH(NH2) 
CH2 
CH2 
COOH. 

Although  the  amino  acids  previously  mentioned  which  possess  both  car- 
boxyl  and  amino  groups  are  not  distinct  acids  nor  bases,  but  possess  their 
combined  characteristics,  these  dicarboxylic  acids  have  a  distinctively  acid 
character.  The  natural  aspartic  acid  is  the  laevo-rotary.  Glutamic  acid 
rotates  polarized  light  to  the  right.  Both  dicarboxylic  acids  occur  widely 
distributed  in  the  vegetable  kingdom  as  amides.  Thus  asparagine  is  an 
amide  of  amino-succinic  acid: 

CONH2 


HNH2 
CH2 

COOH 

Asparagine. 

It  was  first  found  in  asparagus  sprouts.  Soon  afterwards  it  was  found 
that  the  asparagine  collects  in  the  embryo,  which  are  kept  in  the  dark. 
Asparagine  seems  to  play  an  important  part  during  germination.  E. 
Schulze,1  whom  we  have  to  thank  for  very  exhaustive  investigations 
on  the  accumulation  of  asparagine  in  embryo,  gives  the  following  values: 


Age  of  embryo  in  days    .    . 
%  asparagine  of  the  dry  sub- 
stance of  the  embryo  .    . 

4 
3.3 

7 
11.2 

10 
17.3 

12 
22.3 

15 
25.0 

16 
25.7 

%    asparagine    of    the    dry 

substance  of  the  seeds    . 

3.12 

9.78 

15.24 

18.22 

19.43 

As  regards  the  distribution  of  asparagine  in  various  portions  of  the 
embryo,  it  is  worthy  of  note  that  Schulze  found  31 .81  per  cent  of  aspara- 
gine in  the  dry  substance  of  the  axillary  organs  of  lupines,  while  the 
cotyedons  gave  only  7. 62  percent.  Asparagine  occurs  in  plants  in.  the 
dextro-  and  Isevo-rotating  varieties.  The  latter  occurs  more  abundantly. 


E.  Schulze:  Landwirtsch.  Jahrb.  1878,  411. 


ALBUMINS  OR  PROTEINS.  151 

The  two  varieties  can  be  easily  recognized  by  their  crystalline  structure. 
One  is  left-handed  hemihedral,  and  the  other  right-handed.  The  d-variety 
tastes  sweet,  while  the  other  is  insipid. 

Glutamine,  the  amide  of  amino-glutaric  acid,  has  been  found  in  germi- 
nating pumpkin  seeds,  by  Schulze  and  Barbieri.1  Its  occurrence  is  simi- 
lar to  that  of  asparagine. 

As  far  as  we  know,  these  two  amides  do  not  occur  in  the  animal  organism. 
We  shall  later  on  consider  their  value  as  a  food  material. 

Before  discussing  the  properties  of  the  di-amino  acids,  we  shall  devote 
a  little  attention  to  the  remaining  mono-amino  acids.  Phenylalanine,  first 
discovered  by  Schulze  and  Barbieri 2  in  the  embryo  of  lupines,  has  recently 
been  recognized  as  an  invariable  constituent  of  all  the  albumins  so  far 
investigated.  Its  constitution  is  that  of  phenyl-amino-propionic  acid: 

C6H5 .  CH  .  CHNH2COOH.     It  occurs  in  nature  as  the  /-variety. 

•x- 

Another  aromatic  amino  acid,  which  has  been  known  for  a  long  time 
as  a  constituent  of  albumin,  is  tyrosine,  which  can  be  easily  isolated  on 
account  of  its  difficult  solubility  in  water.  It  is  p-hydroxy-phenyl- 
amino-propionic  acid:  C6H4OH  .  CH2 .  CH(NH2)  .  COOH.  It  occurs  in 

nature  in  both  modifications,  although  mainly  in  the  laevo  form. 

Tyrosine  gives  several  color  reactions,  of  which  that  of  Hoffmann  is  the 
most  important.  It  is  known  under  the  name  of  Milton's  reaction.  If 
tyrosine  is  boiled  with  a  nitric  acid  solution  of  mercuric  oxide,  containing 
a  little  nitrous  acid,  the  liquid  becomes  colored,  and  the  resulting  precipi- 
tate is  rose-colored  or  a  dark  brownish  red.  This  reaction  is  not  confined 
to  tyrosine.  It  is  given  by  all  benzene  derivatives,  in  which  a  hydrogen 
atom  has  been  substituted  by  a  hydroxyl  group.  This  reaction  has 
become  of  great  importance  on  account  of  the  fact  that  all  proteins 
which  contain  tyrosine  will  give  it.  Millon's  reaction  is,  therefore,  a  test 
for  proteins. 

We  now  come  to  the  heterocyclic  compounds.  Two  representatives  of 
this  class  have  been  discovered  by  Emil  Fischer:8  a-pyrrolidine-carboxylic 
acid,  also  called  proline,  and  hydroxy-pyrrolidine-carboxylic  acid;  the  latter 
being  probably  an  hydroxy-a-pyrrolidine-carboxylic  acid: 

CH2 CH2 

and        C5H9N03 . 
%      CH2       *CH .  COOH 
\        / 
NH 
Proline  Hydroxy-proline 


1  E.  Schulze  and  J.  Barbieri:  Ber.  10,  199  (1877). 
*  Ibid.  14,  1785  (1881);  Z.  f.  physiol.  Chem.  12,  405  (1888). 

3  E.  Fischer:  Z.  physiol.  Chem.  33,  151  (1901);  Ber.  36,  2660  (1902).     Cf.  H.  Leuchs: 
Ibid.  38,  1937  (1905). 


152  LECTURE  VIII. 

Both  proline  and  oxy-proline  have  been  found  in  the  decomposition 
products  of  most  albumins.  The  first  is  invariably  present.  It  is,  of 
course,  a  question  whether  we  are  dealing  with  primary  products.  It  is 
possible  that  they  are  produced  secondarily  from  another  substance  by 
ring  formation.  Sorensen  l  has  suggested  that  the  primary  substance  in 
the  production  of  proline  may  be  a-amino-d-hydroxyvaleric  acid.  We 
have  not  yet  succeeded  in  isolating  the  amino-hydroxy valeric  acid,  and 
it  must  be  remembered  that  a-proline  is  obtained  by  alkali  hydrolysis, 
as  well  as  by  acid.2  A  small  amount  of  proline  has  also  been  obtained 
by  peptic 3  and  tryptic 4  digestion.  We  have  nothing  at  hand  at  present 
to  warrant  us  in  excluding  a-proline  and  oxy-proline  as  primary  albumin 
decomposition  products. 

Tryptophane  also  belongs  to  this  class  of  amino  acids.  It  had  been 
known  for  a  long  time,  that  especially  in  tryptic  digestion  mixtures  5  some 
substance  was  present  which  was  characterized  by  certain  color  reactions. 

In  an  acetic  acid  solution  it  gives  with  chlorine  or  bromine  water  a  violet 
color.  Also,  if  we  insert  a  pine  splinter,  which  has  been  previously  dipped 
into  hydrochloric  acid  and  then  rinsed  off,  into  a  concentrated  tryptophane 
solution,  the  stick  will  turn  purple  on  drying.  This  is  the  so-called  pyrrole 
reaction.  It  was  soon  shown  that  many  of  the  reactions  characteristic  of 
the  albumins  were  due  to  the  presence  of  tryptophane.  If  we  add  a  little 
glyoxylic  acid,  and  then  concentrated  sulphuric  acid,  to  a  water  solution 
of  albumin,  a  beautiful  blue- violet  coloration  appears.  O.  Neubauer  and 
Rohde fl  have  indicated  recently  a  new  reaction  for  tryptophane  in  albumin. 
If  we  add  to  a  water  solution,  or  suspension,  of  albumin,  5  to  10  drops  of  a 
5  per  cent  solution  of  p-dimethyl-amino-benzaldehyde  containing  10  per 
cent  of  sulphuric  acid,  and  then,  while  shaking,  cautiously  pour  into  the 
solution  a  little  concentrated  sulphuric  acid,  a  reddish-violet  coloration 
appears,  which  soon  takes  on  a  beautiful  reddish  violet  shade.  The 
absorption  spectrum  shows  a  wide,  faint  band  in  the  orange  (X  615-670), 
and  a  second,  obscure,  band  in  the  green  (A.  555-540). 

F.  G.  Hopkins  and  Cole 7  were  the  first  to  prepare  tryptophane  in  a  pure 

1  S.  P.  L.  Sorensen:  Compt.  rend.  trav.  Lab.  Carlsberg,  6,  137  (1905);  Z.  physiol. 
Chem.  44,  448  (1905). 

2  E.  Fischer:  Z.  physiol.  Chem.  35,  227  (1902). 

3  Commercial  pepsin  was  used  in  these  experiments.      The  possibility,  therefore, 
remains  that  other  tissue  ferments  might  have  acted  in  conjunction  with  the  pepsin, 
for  the  reason  that  the  commercial  preparation  is  obtained  by  extracting  the  mucous 
lining  of  the  stomach. 

4  E.  Fischer  and  E.  Abderhalden:  Z.  physiol.  Chem.  40,  215  (1903). 

6  Cf.  E.  Stadelmann:  Z.  Biol.  26,  491  (1890).     R.  Neumeister:  ibid.  26,  324  (1890). 
M.  Nencki:  Ber.  28,  560  (1895) 

8  E.  Rohde:  Z.  physiol.  Chem.  44,  161  (1905). 

7  F.  G.  Hopkins  and  S.  W.  Cole:  J.  Physiol.  27,  418  (1901) ;  29,  451  (1903). 


ALBUMINS  OR  PROTEINS  153 

state.  They  permitted  bacteria  to  act  on  tryptophane,  and  obtained  indole, 
skatole,  skatole-carboxylic  acid,  and  skatole-acetic  acid.  The  bacillus  of 
anthrax,  and  Bacterium  coli,  in  a  strong  anaerobic  solution,  produce  skatole- 
acetic  acid,  while  putrefactive  bacteria,  on  the  other  hand,  give  skatole- 
carboxylic  acid  in  conjunction  with  indole  and  skatole.  The  constitution 
of  tryptophane  has  been  recently  established  by  the  synthesis  of  Ellinger 
and  Flamand.1  It  is  mdole-a-aminopropionic  acid. 

H 
C 

/    ^ 
HC       C—  C  .  CH2  .  CH  (NH2)  .  COOH 


H!! 


\     //  \  / 

C       N 
H       H 

Tryptophane 

The  common  form  is  dextrorotary  both  in  alkaline  and  acid  solutions. 

It  may  be  mentioned  that  tryptophane  is  related  to  a  peculiar  metabolic 
product  of  the  dog,  namely,  kynurenic  acid,  which  is  a  y-hy  droxy-  /?- 
quinolin-carboxylic  acid  of  the  following  constitution:  2 

H 


/          \ 

C  C.COOH 

/     ^         // 
HC         C—  € 


II          I     OH 

:c       G] 


HC          CH 

\     // 

C 

H 

Kynurenic  acid 

The  transformation  of  tryptophane  into  this  acid  is  not  yet  understood. 
Possibly  some  idea  of  the  process  may  be  obtained  from  the  fact  that  a 
compound  rich  in  oxygen  which  can  be  converted  into  quinolin  is  found 
together  with  tryptophane.  At  present,  however,  we  do  not  know 
whether  this  oxy-tn/ptophane  corresponds  to  a  primary  decomposition 
product  from  protein,  or  whether  it  is  formed  secondarily  from  trypto- 
phane. 

To  the  group  of  heterocyclic  building  material  of  protein  histidine  also 


1  A.  Ellinger  and  C.  Flamand,  Ber.  40,  3029  (1907). 

2  E.  Abderhalden  and  M.  Kempe;  Z.  physiol.  Chem.  52,  207  (1907). 


154  LECTURE  VIII. 

belongs.  We  are  indebted  to  A.  Kossel J  for  its  discovery  among  the 
cleavage-products  of  the  protamine,  sturine.  It  was  for  a  long  time 
assigned  to  the  di-amino  acids,  also  called  hexon  bases.  Pauly 2  has 
recently  succeeded  in  throwing  some  light  on  its  constitution.  He  gives 
it  the  formula  of  a-amino-/9-imidazol-propionic  acid: 

CH— NH 


CH2 
*CH .  NH2 

COOH 

Histidine 

F.  Knoop  and  A.  Windaus,3  through  further  investigations,  have  shown 
this  constitution  to  be  correct.  The  compound  is  lavorotary  and  has  an 
alkaline  reaction. 

Only  three  di-amino  acids  are,  as  yet,  known.  These  are  lysine,  arginine, 
and  di-amino-tri-hydroxydodecoic  acid.  The  constitution  of  the  latter  is  not 
yet  determined.  It  was  separated  from  casein  by  Emil  Fischer  and  Emil 
Abderhalden.4  There  are  many  indications  that  it,  or  other  closely  allied 
substances,  occurs  in  other  proteins. 

Drechsel 5  first  isolated  lysine.  He  noticed  in  the  decomposition  of 
casein  by  hydrochloric  acid  that  other  substances  besides  ammonia  and 
mono-amino  acids  were  formed,  which  possessed  a  strong  basic  character. 
Among  these  lysine  was  found.  Drechsel  concluded  that  it  was  probably 
a  di-amino-caproic  acid.  Ellinger6  proved  that  this  supposition  was 
correct.  He  allowed  putrefactive  bacteria  to  act  on  lysine,  and  after  a 
while  obtained  pentamethylenediamine  (cadaverine).  Ladenburg  has 
shown7  that  cadaverine  has  the  following  constitution: 

CH2  .  CH2  -  CIi2  .  OH2  .   CH2 

NH2  NH2 

Cadaverine 


A.  Kossel:  Z.  physiol.  Chem.  22,  177  (1896-97);  Sitzber.  Akad.  Wiss.  Berlin,  1896. 
H.  Pauly:  Z.  physiol.  Chem.  42,  508  (1904). 

F.  Knoop  and  A.  Windaus:  Hofmeister's  Beitr.  7,  144  (1905);  8,  407  (1906). 
Fischer  and  Abderhalden:  Z.  physiol.  Chem.  42,  540  (1904). 

E.  Drechsel:  Ber.  21,  117  (1889);  Arch.  Anat.  Physiol.  1891,  254.     E.  Schulze  and 
E.  Winterstein:  Ergebnisse  Physiol.  (Asher  and  Spiro),  1,  32  (1902). 

6  A.  Ellinger:  Z.  physiol.  Chem.  29,  334  (1902).     Cf.  Ber.  31,  3183  (1899);  32,  3542 
(1900). 

7  Ladenburg:  ibid.  19,  780  (1886). 


ALBUMINS  OR  PROTEINS.  155 

We  can  assume  that  cadaverine  is  formed  by  splitting  off  carbon  dioxide 
from  lysine,  which  has  the  empirical  formula  C6H14N2O2  : 

CH2  .  CH2  .  CH2  .  CH2  .  CH  .  COOH 

NH2  NH2 

Lysine 

=  CH2 .  CH2  .  CH2  .  CH2  .  CH2  +  CO2 

NH2  NH2 

Cadaverine 

By  synthesizing  the  inactive  lysine,  Emil  Fischer  and  Fritz  Weigert 1  have 
shown  that  lysine  is,  as  the  above  formula  indicates,  an  a-,  e-,  diamino- 
caproic  acid. 

E.  Schulze  2  has  also  found  lysine  in  germinating  plants.  It  is  widely 
distributed  among  the  proteins  and  is  rarely  absent  from  them.  It  reacts 
strongly  alkaline.  As  yet  it  has  not  been  obtained  in  crystalline  form. 
It  rotates  polarized  light  towards  the  right. 

Arginine  was  discovered  by  E.  Schulze  and  Steiger  s  in  the  cotyledons  of 
lupine  seeds,  and  in  the  etiols  of  germinating  pumpkin  seeds.  It  rotates 
towards  the  right,  and  likewise  reacts  alkaline.  It  was  soon  shown  that 
arginine  could  not  be  considered  an  individual  compound  in  the  same  sense 
as  the  other  amino  acids  mentioned.  E.  Schulze  and  E.  Winterstein  4 
then  showed  that  arginine  yields  urea  and  a  base,  on  treatment  with  baryta 
water.  Schulze  and  Winterstein  isolated  this  base  by  forming  its  benzoyl 
derivative.  This  had  the  same  composition  and  properties  as  a  di-benzoyl 
compound  isolated  by  Jaffe5  from  the  excreta  of  hens,  which  had  been 
fed  benzoic  acid.  It  proved  to  be  a  benzoyl  compound  of  ornithine, 
and  was  called  by  Jaffe,  omithuric  acid.  Jaffe  recognized  ornithine  as 
diaminovaleric  acid.  Ellinger 6  corroborated  this  view  in  the  same  manner 
as  was  done  with  lysine,  by  acting  on  ornithine  with  putrefactive  bacteria 
and  obtaining  tetramethylenediamine  (putrescine) .  By  this  conversion 
it  was  shown  that  the  two  amino  groups  occupy  the  a  and  d  positions. 
The  splitting  of  ornithine  occurs  in  the  following  manner: 

CH2  .  CH2  .  CH2  .  CH  .  COOH  =  CH2  .  CH2  .  CH2  .  CH2  +  CO2 
NH2  NH2  NH2  NH2 


1  E.  Fischer  andF.  Weigert:  Sitzber.  Akad.  Wiss.  Berlin,  1902;  Ber.  36,  3772  (1902). 

2  E.  Schulze:  Z.  physiol.  Chem.  24,  18  (1898);  30,  276  (1900);  28,  465  (1899). 

3  E.  Schulze  and  E.  Steiger:  ibid.  11,  43  (1887);  Ber.  30,  2879  (1898). 

4  E.  Schulze  and  E.  Winterstein :  Z.  physiol.  Chem.  26,  1  (1898) ;  Ber.  30,  2879  (1898). 
*•  M.  Jaffe:  ibid.  10,  1925  (1877);  11,  401  (1878). 

a  A.  Ellinger:  loc.  dt. 


156  LECTURE  VIII. 

The  position  of  the  carboxyl  group  had  not  been  determined.  Emil 
Fischer  1  finally  cleared  up  the  constitution  of  ornithine  by  its  synthesis. 
By  this  it  was  definitely  determined  that  ornithine  was  an  a-,  d-,  diamino- 
valeric  acid. 

Thus  one  of  the  decomposition  products  of  arginine,  the  ornithine,  was 
identified.  It  was  next  to  be  decided  in  what  form  the  urea  which  was 
obtained  from  arginine  occurred  in  it.  E.  Schulze  and  E.  Winterstein 
suggested  that  a  guanidine  derivative  was  united  to  the  ornithine.  The 
separation  of  urea  and  ornithine  from  such  a  compound  would  proceed  in 
the  following  manner: 

NH2  NH2 

NH  =  C— NH— CH2— CH2— CH2— CH— COOH  +  H2O  = 

•3f 

Arginine 
NH2       NH2  NH2 

C=O      +    CH2— CH2— CH2— CH— COOH 


Urea  Ornithine 

Schulze  and  Winterstein  finally  succeeded  in  synthesizing  arginine  from 
ornithine  and  cyanamide,  thereby  establishing  the  constitution  of  arginine. 

NH2  NH2 

I  I 

CH2—  CH2—  CHz—  CH—  COOH  +   CN—  NH2  = 


Ornithine  Cyanamide 

NH2  NH2 

I  I 

NH  =  C—  NH  .  CH2  .  CH2  .  CH2  .  CH  .  COOH 

^-  -  -y  f 

Arginine 

B.  Benech  and  F.  Kutscher  3  succeeded  in  obtaining  guanidine  from 
arginine,  by  oxidation  with  barium  permanganate. 

We  have  only  one  group  of  the  remaining  protein  decomposition 
products  to  consider;  that  is,  those  containing  sulphur.  We  have  pre- 
viously mentioned  that  sulphur  is  one  of  the  essential  constituents  of 
albumin.  It  is  only  absent  from  the  protamines.  The  occurrence  of 
sulphur  in  proteins  was  recognized  at  an  early  date.  It  had  been  noted 
that  on  boiling  albuminous  material  with  alkalies  considerable  amounts 


1  E.  Fischer:  Sitzber.  Akad.  Wiss.  Berlin,  1900;  Ber.  34,  454  (1901). 
*  E.  Schulze  and  E.  Winterstein:  Z.  physiol.  Chem.  34,  128  (1901). 
8  E.  Benech  and  Fr.  Kutscher:  ibid.  32,  278  (1901). 


ALBUMINS  OR  PROTEINS.  157 

of  alkaline  sulphides  were  split  off.1  Fleitmann  2  was  the  first  to  observe 
that  only  a  part  of  the  sulphur  was  split  off  by  the  action  of  alkalies,  while 
another  portion  remained  unacted  upon.  From  these  observations  he 
differentiated  between  oxidized  and  un-oxidized  sulphur  in  albumin. 
The  latter,  only,  was  susceptible  of  being  split  off.  This  distinction  later 
on  caused  much  misunderstanding  among  investigators  of  the  sulphur 
components  of  albumin.  A.  Kriiger  3  is  entitled  to  much  credit  for  having 
shown  the  futility  of  this  classification.  He  makes  a  distinction  between 
"  loosely-  "  and  "  firmly-  "  combined  sulphur.  Fr.  N.  Schulz  4  proved 
that  such  a  distinction  was  more  justifiable,  by  showing  that  one  of  the 
sulphur  cleavage-products  of  albumin,  cystine,  only  gave  off  part  of  its 
sulphur  on  boiling  with  alkali;  in  fact,  little  more  than  half.  Various 
albuminous  substances,  such  as  keratin  (from  the  horn  of  cattle,  and 
human  hair),  serum-albumin,  and  serum-globulin,  acted  in  the  same 
manner  as  cystine.  Morner  5  then  succeeded  in  obtaining  large  quantities 
of  cystine  from  the  above-mentioned  proteins,  and  showed  that  this  amino 
acid  is  probably  the  only  sulphur  compound  present.  Other  proteins  cer- 
tainly contain  other  sulphur  compounds  besides  cystine. 

Among  the  decomposition  products  containing  sulphur,  cystine  is  the 
only  one  that  has  been  positively  identified.  Wollaston,6  in  1810,  first 
isolated  this  from  a  renal  calculus.  Since  then  it  has  been  separated 
also  from  organs.  Kiilz 7  first  isolated  it  from  digestive  solutions  of  fibrin, 
and  Emmerling  8  found  it  in  horn.  The  wide  distribution  of  cystine  as  a 
decomposition  product  of  albumin  is  now  generally  acknowledged. 

The  constitution  of  cystine  has  only  recently  been  established;  it  is  an 
a-diamino-/?-dithio-dilactylic  acid : 

CIl2 O o CIl2 

*CH.(NH2)    *CH(NH2) 

COOH  COOH 

Cystine 


1  The  sulphur  content  of  the  proteins  was  at  one  time  a  factor  of  great  importance 
in  the  views  prevailing  concerning  their  constitution.  Cf.  E.  Friedmann:  Ergeb. 
Physiol.  (Asher  and  Spiro)  1,  15  (1902).  E.  Abderhalden:  Biochem.  Zentr.  2,  257 
(1904). 

T.  Fleitmann:  Ann.  61,  121  (1847);  66,  380  (1848). 

A.  Kruger:  Pfliiger's  Arch.  43,  244  (1888). 

Fr.  N.  Schulz:  Z.  physiol.  Chem.  25,  16  (1898). 

K.  A.  H.  Morner:  ibid.  28,  595  (1899);  34,  207  (1901-02). 

Wollaston:  Phil.  Trans.  1810,  220. 

E.  Kiilz:  Z.  Biol.  27,  415  (1890). 
8  O.  Emmerling:  Verh.  Ges.  Naturforsch  Aerzte.  2,  391  (1894). 


158  LECTURE  VIII. 

By  reduction,  we  obtain  cysteine  from  it,  which  is  an  a-amino-/2-thio- 
propionic  acid: 

CH2 .  SH 

(NH2) 


V-/-I-J-2  • 

in. 
i 


OOH 

Cysteine 

Cysteine,  therefore,  is  closely  related  to  alanine  and  serine.  Friedmann  l 
oxidized  cysteine  and  obtained  cysteic  acid: 

CH2  .  SO2  .  OH 
CH(NH2) 

COOH 

Cysteic  acid 

from  which,  by  splitting  off  carbonic  acid,  we  obtain  taurine: 

CH2  .  S02  .  OH 

CH2(NH2) 

Taurine 

This  indicated  an  important  relationship  between  a  product  related  to 
taurocholic  acid  and  cystine.  The  correctness  of  the  formula  of  cystine 
as  presented  by  E.  Friedmann,  and  soon  after  by  C.  Neuberg,2  has  recently 
been  strengthened  by  the  synthesis  of  cystine  by  Erlenmeyer.3 

Observations  by  Baumann  and  Preusse  4  do  not  harmonize  with  the 
above  formula.  They  found  that  when  brombenzene  was  fed  to  a  dog, 
the  excreted  urine  contained  a  compound  containing  bromine,  nitrogen, 
and  sulphur  in  its  composition.  Its  composition  was  CnHi2BrNSO3. 
Baumann  and  Preusse  designated  this  compound:  Bromphenyl  mer- 
capturic  acid.  From  this,  acetic  acid  and  a  compound,  C9H10BrNSO2, 
are  obtained  by  hydrolysis.  The  latter  formula  corresponds  to  the 
empirical  formula  of  cysteine,  if  the  bromphenyl  residue  is  replaced  by 
a  hydrogen  atom.  The  compound  formed  together  with  acetic  acid  was 
therefore  considered  as  bromphenyl  cysteine.  From  the  resulting  cleavage- 


1  E.  Friedmann:  Hofmeister's  Beitr.  3,  1  (1902). 

2  C.  Neuberg:  Ber.  35,  3161  (1902).     Cf.  K.  A.  H.  Morner:  Z.  physiol.  Chem.  42, 
349  (1904). 

3  Erlenmeyer:  Jr.  Ber.  36,  2720  (1903). 

4  E.  Baumann  and  C.  Preusse:  ibid.  12,  806  (1879);  Z.  physiol.  Chem.  5,  309  (1881). 


ALBUMINS  OR  PROTEINS.  159 

products,   Baumann    and    Preusse    proposed   the    following   formula  of 
mercapturic  acid: 

CH3 

CH3CO—  NH  .  C—  S  .  C6H4Br 
COOH 

If  this  formula  be  correct,  then  it  must  correspond  to  a  differently 
constituted  cysteine  than  the  above  one.  We  might  expect  that  cystine 
could  occur  in  various  modifications.  E.  Friedmann,1  proceeding  from  this 
hypothesis,  undertook  to  prove  the  constitution  of  mercapturic  acid,  and 
showed  that  such  an  assumption  was  unnecessary,  for  he  found  that  mer- 
capturic acid  and  cysteine  have  their  amino  and  thio  groups  analogously 
situated: 


NH  .  CO  .  CH3 


CH  .  NH2  CH  . 


COOH  COOH 

Albumin-cysteine  Mercapturic  acid 

Recent  investigations  have  also  shown  that  probably  only  one  cysteine 
exists.2  Patten  3  has  shown  that  only  cystine  and  not  cysteine  occurs  in  the 
original  albumin  molecule. 

It  is  necessary  to  mention  at  this  point  that  all  the  compounds  so  far 
discussed,  with  the  exception  of  phenylalanine,  can  also  be  obtained  by 
the  hydrolytic  action  of  ferments  upon  the  albumins.  Phenylalanine,  as 
already  indicated,  is  found  as  such  in  plant  seeds.  As  fermentation 
hydrolysis  undoubtedly  furnishes  the  mildest  possible  form  of  decom- 
position, we  are  justified  in  concluding  that  the  cleavage-products  of 
protein  which  have  been  just  mentioned  exist  as  such  in  the  albumin 
molecule. 

While  discussing  the  proteids,  we  mentioned  the  so-called  "  gluco- 
proteids  "  of  the  albumins,  which  are  characterized  by  a  high  percentage 
of  glucosamine,  and,  possibly,  other  carbohydrates.  On  account  of  the 
firmness  with  which  these  groups  are  attached  to  the  albumin  molecule. 
it  is  at  present  considered  more  correct  to  place  them  with  the  simpler 
proteins  rather  than  with  the  complex  varieties.  We  can  easily  imagine 
that  glucosamine  is  held  in  combination  in  a  manner  analogous  to  that 
which  unites  the  amino  acids  to  one  another.  We  can  also  easily  indicate 


1  E.  Friedmann:  Hofmeister's  Beitr.  4,  486  (1903). 

3  E.  Fischer  and  U.  Suzuki:  Z.  physiol.  Chem.  45,  405  (1905). 

8  A.  J.  Patten:  ibid.  39  350  (1903). 


160  LECTURE  VIII. 

the  close  relationship  of  glucosamine  to  the  amino  acids  as  well  as  to  the 
carbohydrates.     This  is  very  evident  from  the  following  comparison: 

CH2 .  OH  CH2  .  OH  CH2  .  NH2 

CH  .OH  CH .  OH  CH2 

CH.OH  CH.OH  CH2 

CH  .OH  CH .  OH  CH2 

CH.OH  CH.NH2  CH.NH2 

CH  :  O  CH  :  O  COOH 

Glucose  Glucosamine  Lysine 

It  is  not  right  to  consider  as  exceptional  the  albumins  containing  carbo- 
hydrate groups.  It  is  more  correct,  according  to  our  present  knowledge, 
to  speak  of  albuminous  bodies  characterized  by  a  high  content  of  gluco- 
samine, just  as  we  know  of  proteins  which  have  considerable  glycocoll. 
Just  as  there  are  proteins  which  contain  only  small  amounts  of  glycocoll, 
and  some  with  none  at  all,  so  we  also  recognize  proteins  which  possess 
small  quantities  of  glucosamine,  as  well  as  those  which  have  none  of  this 
hexose  base.  The  fact  that  other  amino  sugars  probably  participate  in 
the  constitution  of  proteins  does  not  affect  this  conception.  It  is  doubtful 
whether  nitrogen-free  sugars  occur  in  albumin.  It  must  also  not  be 
forgotten  that  the  presence  of  glucosamine,  as  a  primary  cleavage-product, 
is  doubted.  A  complex  carbohydrate  has  been  assumed  to  be  the  ante- 
cedent of  the  glucosamine.  The  results  at  present  are  not  sufficiently 
exact  to  settle  the  question.1  The  conception  that  the  "  carbohydrate- 
group  "  is  a  constituent  of  the  albumin  molecule  in  the  same  sense  as  the 
amino  acids,  is  rendered  somewhat  improbable  by  the  fact  that  various 
observers  have  obtained  entirely  different  carbohydrate  values  in  the 
analysis  of  one  and  the  same  substance.  It  has  even  been  suggested  that 
specific  proteins,  e.g.,  serum-albumin,  unite  with  the  sugars,  conduct 
them  to  the  tissues,  and  finally  give  them  up  to  the  latter.  Such  an 
assumption  would  be  comprehensible  if  it  were  known  that  the  carbo- 
hydrate groups  were  loosely  bound  to  the  albumin  molecule.  This, 
however,  is  not  the  case.  A  more  satisfactory  explanation  would  be 
that  the  varying  carbohydrate  content  of  the  proteins  was  due  to  the 
albumins  investigated  not  being  identical. 

As  yet  we  know  but  little  about  the  quantities  of  glucosamine  present 
in  the  mucins,  —  the  proteins  richest  in  carbohydrates.  It  is  only  known 

1  L.  Langstein:  Ergebnisse  der  Physiologie  (Asher  and  Spiro),  1,  63  (1902);  3,  453 
(1904). 


ALBUMINS  OR  PROTEINS.  161 

that  the  mucins  and  their  related  substances  can  contain  as  much  as  30  per 
cent  glucosamine.  It  is  not  at  all  unreasonable  to  expect  varying  results 
from  the  same  mucin,  because  it  is  absolutely  impossible  to  purify  these 
compounds  thoroughly.  It  is  more  striking  that  egg-albumin,  which 
is  so  easily  crystallized,  does  not  give  concordant  results  on  the  amount 
of  glucosamine.  It  must  also  be  remembered  that  egg-albumin  contains, 
besides  albumin  and  globulin,  ovi-mucoid,  which  contains  about  30 
per  cent  glucosamine.  By  the  recent  investigations  of  Fr.  N.  Schulz 
and  Zsigmondy,1  it  was  shown  how  extremely  difficult  it  is  to  free 
egg-albumin  from  colloidal  substances,  even  after  sixfold  crystalliz- 
ation. In  recrystallized  egg-albumin,  values  varying  from  16  to  less  than 
one  per  cent  of  glucosamine  were  found.2  We  do  not  err,  in  assigning  the 
fluctuations  of  the  carbohydrate  content,  which  far  exceed  the  analytical 
error,  to  this  cause  of  varying  purity  of  the  substance  under  investiga- 
tion. It  is,  therefore,  not  yet  determined  whether  egg-albumin  is  entitled 
to  a  "  carbohydrate  group."  The  same  holds  true  regarding  serum 
albumin.  This,  also,  invariably  incloses  some  serum-mucoid,3  which  is 
relatively  rich  in  glucosamine.  In  fact,  serum-globulin  is  distinctly 
different,  in  that,  aside  from  a  trace  of  glucosamine,  it  also  splits  off 
grape-sugar.  Now  serum-globulin  is  obtained  by  precipitation  with 
ammonium  sulphate  solution.  To  purify  this,  to  the  extent  possible 
with  the  crystallizable  proteins,  is  entirely  impossible.  Besides  grape- 
sugar,  serum  also  contains  small  quantities  of  other  carbohydrates  of 
unknown  constitution.  It  is  very  probable  that  the  precipitated  serum- 
globulin  contains  such  a  carbohydrate  mixed  with  it.  Up  to  the  present 
time,  we  have  had  no  investigation  which  would  warrant  us  in  assigning 
any  nitrogen-free  carbohydrates  to  the  albumin  molecule. 

If  we  sum  up  what  we  know  about  the  "  carbohydrate  groups " 
of  the  proteins,  we  will  conclude  that  the  mucins  and  mucoids  contain 
such  groups;  while  although  the  remaining  proteins  may  contain  carbo- 
hydrates, their  presence  has  not  been  proved  positively. 

It  is  very  important  that  absolute  clearness  should  prevail  in  regard  to 
this  question.  We  shall  see  later,  that  many  facts  make  it  seem  probable 
that  carbohydrates  are  formed  from  albumin.  The  assumption  that, 
according  to  our  present  knowledge,  the  "  carbohydrate  group  "  of  the 

1  Fr.  N.  Schulz  and  Zsigmondy:  loc.  cit. 

2  E.  Abderhalden,  P.  Bergell,  and  T.  Dorpinghaus:  Z.  physiol.  Chem.  41,  530  (1904). 
Direct  experiment  showed  that   repeated   recrystallization   reduced  the  quantity  of 
glucosamine  present  in  albumin.     Albumin  crystallized  once  gave  7  per  cent,  three 
times  gave  4  per  cent,  while  the  seventh  time  showed  only  2.5  per  cent  glucosamine. 
That  the  values  in  this  case  are  higher  than  in  the  work  just  mentioned,  is  due  to  the 
fact  that  the  crude  osazone  was  weighed,  while  in  the  former  the  analytically  pure 
osazone  was  used  as  a  basis  for  the  calculation. 

3  C.  N.  Zanetti:  Ann.  Chim.  Farmac.  12,  1897. 


162  LECTURE  VIII. 

proteins  is  the  source  of  the  sugar  formation  from  albumin,  is  without 
justification,  as  we  have  just  said.  If  sugars  are  formed  from  albumin, 
then  undoubtedly  the  amino  acids  are  to  be  considered  as  their  immediate 
antecedents.  It  may  be  mentioned  in  addition  that  glucosamine  espe- 
cially is  apparently  not  utilized  at  all  by  the  organism  for  the  production 
of  glycogen. 

It  is  certainly  not  without  significance  that  the  mucins  and  mucoids, 
proteins  which  are  also  widely  distributed  among  the  invertebrates, 
should  contain  glucosamine  —  an  amino-hexose  —  which  is  known  to  be 
the  basis  for  the  formation  of  chitin. 

The  presence  of  carbohydrates  in  the  albumins  is  indicated  by  certain 
color  reactions.  If  we  add  a  few  drops  of  an  alcoholic  solution  of  a-naphthol 
to  a  solution  of  albumin,  and  allow  a  layer  of  concentrated  sulphuric  acid 
to  flow  beneath  this,  a  violet  ring  appears  at  the  junction  of  the  two 
fluids.  On  shaking,  the  whole  solution  takes  on  a  violet  tinge.  On 
adding  alcohol,  ether,  or  caustic  potash  to  this,  the  coloration  becomes 
yellow.  If  we  use  thymol  instead  of  the  a-naphthol,  the  coloration 
produced  is  carmine-red.  It  turns  green  on  dilution.  These  reactions  — 
called  the  "  Molisch  sugar  tests  "  *  —  depend  on  the  formation  of  furfurol 
from  the  carbohydrates  present,  by  the  action  of  sulphuric  acid. 

Another  test  which  has  been  supposed  to  indicate  the  presence  of  a 
carbohydrate  group  in  proteins  is  the  violet  to  deep  blue  color  obtained 
by  boiling  with  fuming  hydrochloric  acid,  when  they  have  previously 
been  hydrolyzed.  This  is  known  as  "  Liebermann's  reaction,"  but  it  is 
not  certain  that  this  albumin  reaction  is  due  to  carbohydrates. 

In  this  connection  we  must  call  attention  to  two  other  albumin  reactions. 
If  we  add  strong  nitric  acid  to  an  aqueous  solution  of  albumin,  a  yellow 
coloration  appears,  very  often  in  the  cold,  although  generally  only  on 
boiling.  If  we  add  an  excess  of  caustic  soda  to  this,  the  solution  becomes 
reddish  brown;  while  if  ammonia  be  used,  an  orange  color  results.  This 
is  called  the  "  xantho-proteic  reaction,"  and  depends  on  the  formation  of 
nitre-derivatives,  and,  according  to  Salkowski,2  requires  the  presence  of 
aromatic  groups. 

All  the  reactions  which  have  now  been  mentioned  for  albumin,  require 
the  presence  of  specific  groups,  and  only  apply  to  such  proteins  as  contain 
them.  The  blackening,  which  results  when  a  protein  is  heated  with 
caustic  alkali  and  a  lead  salt,  is  characteristic  of  a  group  containing  sul- 
phur. It  depends  on  the  formation  of  lead  sulphide.  Millon's  reagent 
indicates  the  tyrosine  group;  the  glyoxylic  acid  characterizes  the  trypto- 
phane  combination.  The  carbohydrate  group  is  detected  by  the  Molisch 
reaction,  and  also,  possibly,  by  the  Liebermann  reaction.  The  xantho- 

1  Molisch:  Monatsh.  7,  198  (1888). 

2  E.  Salkowski:  Z.  physiol.  Chem.  12,  211  (1887). 


ALBUMINS  OR  PROTEINS.  163 

proteic  reaction  indicates  the  presence  of  aromatic  groups.  We  are  also 
acquainted  with  another  important  color  reaction,  which  does  not  properly 
characterize  any  group  as  such.  This  is  the  so-called  "  Biuret-reaction." 
If  we  freely  add  caustic  soda  or  potash  to  an  albumin  solution,  and 
then  carefully,  drop  by  drop,  a  dilute  solution  of  copper  sulphate,  a 
blue  to  rose-violet  coloration  appears,  which  goes  over  into  a  blue  on  the 
addition  of  more  copper  sulphate.  The  higher  decomposition  products 
of  albumin,  the  peptones,  give  a  red  coloration. 

The  cleavage-products  of  protein  just  mentioned,  have  been  obtained 
by  the  hydrolytic  action  of  acids  and  of  alkalies.  We  can  easily  imagine 
that  in  these  cases  secondary  decompositions  take  place.  A  number  of 
scientists  doubted  the  occurrence  of  so  many  amino  acids,  and  preferred 
to  assume  that  the  proteins  contained  groups  which  gave  rise  to  the  forma- 
tion of  these  various  amino  acids  during  the  hydrolysis  brought  about  by 
the  reagents.1  It  were  conceivable  that  ornithine,  proline,  and  amino- 
valeric  acid  originate  from  the  same  atomic  grouping;  also  lysine  and 
leucine,  on  the  one  hand,  and  tyrosine  and  phenylalanine  on  the  other. 
Such  a  conclusion  does  not  harmonize  with  our  present  knowledge  of  the 
actions  of  acids  and  alkalies,  because  they  invariably  yield  the  indi- 
vidual amino  acids  in  the  same  quantities.  That  these  amino  acids  occur 
in  the  proteins  is  very  evident  from  their  appearance,  as  such,  in  sprouting 
plants,  and  even  in  the  animal  organism  under  specific  conditions.  The 
most  important  proof  of  their  original  occurrence  is  indicated  by  their 
appearance  during  digestion.  The  albumins  are  broken  down  by  the 
hydrolytic  action  of  ferments,  especially  by  trypsin,  into  amino  acids. 
The  decomposition  by  fermentation  is  the  mildest  imaginable.  It  takes 
place  at  37°  C.  All  the  known  amino  acids  have  been  obtained  from  diges- 
tion mixtures  except  phenylalanine  and  diamino-trihydroxy-dodecylie 
acid.  The  latter  has  never  been  looked  for,  while  the  former  does  not 
appear  in  a  state  of  combination  which  is  accessible  to  the  proteolytic 
ferments. 

The  albumin  as  it  reaches  the  digestive  organs  of  an  animal  is  subjected 
to  the  action  of  two  proteolytic  ferments,  pepsin  and  trypsin.  Later  on 
we  shall  go  more  into  detail  regarding  the  behavior  of  the  albumins  during 
the  process  of  natural  digestion.  We  shall,  at  present,  devote  our  atten- 
tion to  the  subject  of  artificial  digestion,  i.e.,  the  digestion  of  the  protein 
outside  of  the  alimentary  tract.  We  must  say  that  the  results  obtained 
in  these  investigations  do  not  harmonize  in  matters  of  detail.  This  is 
mainly  due  to  the  different  methods  employed  in  using  these  ferments. 
Until  recently,  the  physiological  chemist  utilized  extracts  of  organs  whether 
of  the  stomach  or  of  the  pancreatic  gland,  and  the  extirpated  organs 

1  O.  Loew:  Hofmeister's  Beitr.  1,  567  (1900). 


164  LECTURE  VIII. 

themselves.  We  are,  however,  aware  that  many  ferments  occur  in  the 
tissues,  which  are  far  more  energetic  in  metabolic  processes,  and  act 
in  another  direction,  than  the  digestive  ferments.  Many  of  the 
results  obtained  are  undoubtedly  due  to  the  interaction  of  these  tissue- 
ferments.  We  are  now  able  to  obtain  the  digestive  fluids  in  purest  form, 
thanks  to  the  excellent  methods  originated  by  Pawlow  l  and  his  students. 
It  is  possible,  on  the  one  hand,  to  prepare  a  small  special  stomach,  that  is, 
a  pouch  obtained  by  tying  up  a  part  of  the  walls  of  the  stomach  so  as  to 
form  a  blind-sack,  from  which  the  pure  gastric  juice  may  be  obtained  with- 
out the  least  admixture  of  any  food  residues.  On  the  other  hand,  we  can 
obtain  absolutely  pure  pancreatic  juice,  clear  as  water,  by  making  a 
pancreatic  fistula,  i.e.,  by  grafting  into  the  abdominal  wall  that  part  of  the 
mucous  membrane  of  the  duodenum  at  which  the  pancreatic  duct  enters. 
As  we  shall  see  later,  this  fluid  is  inactive  when  the  piece  of  intestinal 
mucous  membrane  carrying  the  papilla  is  cut  away.  It  must  first  be 
made  active  preferably  by  the  addition  of  intestinal  juice.  It  is  only 
possible  to  obtain  absolutely  correct  results  by  utilizing  such  ferment 
solutions. 

Amino  acids  do  not  immediately  appear  when  the  proteins  —  edestin, 
for  example  —  are  undergoing  digestion.  We  observe  first  of  all  that  the 
albumin  is  dissolved.2  We  notice  at  the  same  time  that  the  digestion 
mixture  contains  dialyzable  substances  which  are  not  amino  acids. 
The  digesting  mixture  may  even  be  boiled  without  causing  coagulation. 
It  has  been  held  that  the  protein  molecule  by  hydrolytic  cleavage  is 
decomposed  into  products  with  lower  molecular  weights;  the  higher  of 
these  are  known  as  albumoses,  from  which  in  turn  peptones  are  formed. 
There  is  no  sharp  distinction  between  these  two  classes.  Strictly  speak- 
ing, the  conception  of  albumoses  and  peptones  is  not  a  chemical,  but  a 
biological  one,  and  we  shall  treat  of  them  here  as  forming  one  class,  and 
drop  the  term  "albumose."  It  represents,  instead  of  certain  chemical 
individuals,  a  group  of  compounds  which  exist  temporarily  in  a  similar 
condition.  For  the  present,  these  names  do  not  signify  much  to  us. 
Not  content  with  this  distinction  of  the  two  groups  of  substances, 
scientists  have  classified  them  according  to  their  solubility  relations,  - 
according  to  the  extent  to  which  they  may  be  precipitated,  etc.,  —  thereby 
designating  them  with  new  names.  It  has  also  been  found  that  the 
peptones  obtained  from  different  proteins  are  not  identical,  so  that  they 
have  been  named  according  to  the  protein  from  which  they  are  formed. 


1  J.  P.  Pawlow:  Ergebnisse  d.  Physiol.  (Asher  and  Spiro)  1,  246  (1902). 

*  The  earliest  observations  on  tryptic  digestion  were  made  by  Corvisart:  Gaz.  Heb- 
dom.  Nos.  15,  16,  19  (1857).  W.  Kiihne:  Virchow's  Arch.  39,  130  (1867).  Cf.  also 
E.  Abderhalden:  Z.  physiol.  Chem.  44,  17  (1905). 


ALBUMINS  OR  PROTEINS.  165 

Thus  we  speak  of  globuloses,  vitelloses,  etc.  Undoubtedly,  we  shall  even- 
tually find  that  a  great  deal  of  this  difference  in  behavior  is  due  to  the 
different  amino  acids,  which  are  contained  in  the  different  proteins,  and 
their  arrangement  in  the  molecule,  so  that  before  long  we  shall  be  able  to 
replace  this  purely  biological  conception  by  a  chemical  one.  For  the  present 
the  investigations  have  gone  beyond  our  actual  knowledge,  and  have  led  to 
certain  results,  which  do  not  yet  rest  upon  a  firm  foundation.  For  this 
reason  we  shall  not  attempt  to  describe  any  of  the  numerous  special  albu- 
moses  and  peptones,  but  simply  content  ourselves  with  the  conception 
itself.  The  albumoses  are  in  general  characterized  by  the  fact  that  they 
are  precipitated  when  their  solutions  are  saturated  with  ammonium  sul- 
phate, while  the  peptones  then  remain  in  solution.  By  means  of  the 
behavior  of  a  digesting  mixture  towards  ammonium  sulphate,  we  can 
determine  how  far  the  digestion  has  already  gone.1 

Up  to  this  point  the  changes  produced  upon  the  protein  molecule  by 
the  pepsin-hydrochloric  acid  of  the  stomach  and  the  trypsin  of  the  pan- 
creas are  apparently  quite  similar.  In  both  cases  albumoses  and  pep- 
tones are  formed.  Of  course  the  action  of  pepsin  may  nevertheless  be 
entirely  different  from  that  of  trypsin  in  spite  of  this  external  similarity. 
It  may  be  that  a  different  place  in  the  protein  molecule  is  attacked. 
Unquestionably  -  even'  in  gastric  digestion  a  large  quantity  of  products 
are  obtained  which  represent  lower  products  than  the  peptones,  and 
some  of  these  do  not  even  give  the  biuret  reaction.  Simple  amino  acids, 
however,  with  the  exception  of  traces  of  tyrosine,  have  not  been  found 
here.2 

Tryptic  digestion  goes  much  farther.  We  quickly  observe  crystalline 
depositions  on  the  walls  of  the  vessel  in  which  the  digestive  mixture  is 
placed.  This  is  tyrosine,  which  separates  on  account  of  its  difficult  solu- 
bility. It  is  very  quickly  split  off  from  the  albumin  molecule.  In  48 
hours,  and  even  in  less  time,  the  entire  tyrosine  content  of  the  albumin  can 
be  isolated  as  such.3  In  the  digestion  of  edestin  from  cotton-seeds,  for 
example,  the  following  observations  were  made: 4 


PERCENTAGE  OF  TYROSINE  OF  THE  TOTAL  AMOUNT  OCCURRING 

IN  EDESTIN. 


Time 

of  digestion     

1  day 

2  days 

3  days 

8  days 

78.4 

97.6 

97.6 

100 

1  See  page  188. 

2  Emil  Abderhalden  and  Otto  Rostoski:  Z.  physiol.  Chem.  44,  265  (1905). 
8  E.  Abderhalden  and  B.  Reinbold:  Z.  physiol.  Chem.  44,  284  (1905). 

4  Ibid.  46,  159  (1905). 


166  LECTURE  VIII. 

Tryptophane,  as  well  as  cystine,  can  be  obtained  just  as  quickly  as 
tyrosine;  the  former  being  easily  recognized  by  the  violet  color  which  is 
formed  when  bromine  water  and  acetic  acid  are  added  to  the  digesting 
liquid.  The  remaining  amino  acids  are  obtained  later  on.  This  has  been 
successfully  proved  in  the  case  of  glutamic  acid.  The  following  per- 
centages of  the  total  amount  of  this  amino  acid  occurring  in  edestin,  were 
obtained: 


Time  of  digestion   

1  day. 

2  days. 

3  days. 

8  days. 

16  days 

4.3 

7.4 

10.9 

31.1 

60.2 

Alanine,  leucine,  amino-valeric  acid,  and  aspartic  acid,  acted  in  the 
same  manner;  while  a-proline  and  phenylalanine  could,  in  no  case,  be 
separated  from  a  digesting  fluid. 

The  following  observations  have  given  us  an  explanation  of  this  peculiar 
behavior:  l  If  we  digest  casein,  edestin,  serum-globulin,  egg-albumin, 
hemoglobin,  or  fibrin  with  pancreatin,2  or  even  with  pancreatic  juice,  we 
obtain  all  the  mono-amino  and  di-amino  acids  in  the  digesting  mixture, 
with  the  exception  of  proline  and  phenylalanine.  These  amino  acids  do 
not  occur,  or,  if  so,  only  in  minute  quantities,  even  when  tryptic  digestion 
precedes  that  of  the  pepsin-hydrochloric  acid.3  Now  we  can  precipitate 
even  from  a  greatly  diluted  digesting  mixture,  by  means  of  phospho- 
tungstic  acid,  a  product  which  apparently  is  a  mixture  of  highly  compli- 
cated compounds.  It  sometimes  gives  the  biuret  reaction;  then  again, 
no  result  is  obtained  —  according  to  the  time  of  digestion.  No  free  amino 
acids  can  be  isolated  from  this  product,  although  we  can  obtain  such  by 
hydrolysis  with  fuming  hydrochloric  or  25  per  cent  sulphuric  acid.  In  the 
presence  of  small  amounts  of  alanine,  leucine,  aspartic  acid,  and  glutamic 
acid,  we  obtain  large  amounts  of  a-proline  and  phenylalanine;  and,  in 
those  proteins  containing  glycocoll,  even  this  amino  acid,  in  amounts 
approximating  those  contained  in  the  protein  in  question.  The  proteins 
evidently  contain  groups  which  resist  the  action  of  ferments.  Of 
especial  interest  is  the  fact  that  here  also  the  rate  at  which  the  individual 
amino  acids  are  separated  varies. 

From  these  investigations  it  is  clear  that  fermentative  decomposition  is  a 
progressive  one.  An  immediate  disruption  of  the  protein  does  not  occur. 


1  E.  Fischer  and  E.  Abderhalden:  Z.  physiol.  Chem.  39,  81  (1903). 

3  A  commercial  preparation  of  pepsin  was  used  in  this  experiment,  consequently 
impure.  It  is  very  probable  that  the  latter  disintegrated  albumin  more  than  the  gastric 
Juice  alone  would  do. 

8  E.  Fischer  and^.  Abderhalden:  Z.  physiol.  Chem.  40,  215  (1903). 


ALBUMINS  OR  PROTEINS. 


167 


The  following  diagram  will  give  an  idea  of  the  hydrolysis  brought  about 
by  means  of  the  pancreatic  ferment,  trypsin: 

Protein 

i 

'Peptones- 


A  mixture  of  complicated  compounds 
composed  of  various  amino  acids. 
"  Polypeptides." 


^4 

Tyrosine,  tryptophane,  cystine,  alan- 
ine,  aminovaleric  acid,  leucine, 
aspartic  acid,  glutamic  acid,  histi- 
dine,  lysine,  and  arginine. 


The  product  consisting  of  amino  acids  still  combined  with  one  another, 
and  which  may  for  the  present  be  designated  as  "  polypeptides,"  is  dif- 
ferent in  the  case  of  different  proteins.  In  the  case  of  edestin  the  amount 
is  smaller  than  in  the  case  of  casein,  and  that  obtained  from  the  latter 
is  less  than  from  serum-globulin. 

From  the  investigations  of  Abderhalden  and  Reinbold,1  it  has  been 
clearly  shown  that,  even  the  peptones,  which  still  give  the  characteristic 
red  biuret  reaction,  do  not  immediately  break  down  into  amino  acids. 
There  are  certainly  intermediate  products  between  the  peptones  and  the 
amino  acids.  Here,  again,  the  progressive  decomposition  is  clearly 
evident.  Doubtless  the  simpler  peptides,  which  we  will  shortly  discuss, 
also  appear  as  intermediate  products.  We  shall  return  to  this  shortly. 

The  most  important  result  obtained  from  these  investigations  is,  that 
the  amino  acids,  which  split  off  from  albumin  by  the  action  of  alkalies  and 
acids,  are  already  formed  in  the  albumin  molecule  and  are  not  formed  by 
a  secondary  process;  and,  further,  that  in  spite  of  the  early  appearance  of 
crystalline  cleavage-products,  the  fermentative  decomposition  need  not 
necessarily  be  far  advanced.  All  the  tyrosine  occurring  in  a  digesting 
mixture  can  be  detected,  even  if,  for  instance,  only  seven  per  cent  of  the 
amount  of  glutamic  acid  occurring  in  the  albumin  has  been  set  free. 

Besides  pepsin  and  trypsin,  we  have  to  consider  erepsin,  which  occurs  in 
the  alimentary  tract  as  an  albumin-splitting  ferment,  and  has  been  isolated 
by  O.  Cohnheim.2  It  does  not  act  on  the  -proteins  themselves,  but  only 
on  their  decomposition  products,  the  peptones.  The  only  exceptions 
to  this  rule  are  casein,  protamines,  and  histons;  these  are  attacked 


1  Loc.  dt. 

2  O.  Cohnheim:   Z.  physiol.  Chem.  33,451   (1901);   36,     134  (1902). 
Salaskin:  ibid.  35,  419  (1902). 


Cf.  also  S. 


168  LECTURE  VIII. 

by  erepsin.  The  decomposition  products  are  the  same  as  those  produced 
by  trypsin.  At  present  it  is  difficult  to  pass  judgment  on  the  actual 
existence  of  this  ferment.  According  to  the  investigations  of  Vernon,1 
it  occurs  widely  distributed  in  the  animal  kingdom,  and  is  to  be  found  in 
all  tissues.  It  is  very  difficult  to  decide  whether  the  proteolytic  ferments 
should  be  considered  as  homogeneous  or  as  mixtures  of  ferments  of  differ- 
ent individual  functions.  It  is  not  unreasonable  2  to  assume  that  for  each 
protein,  or  for  a  class  of  these  substances,  a  special  series  of  ferments  exists. 
On  the  other  hand,  we  could  easily  imagine  that  one  ferment  follows 
another,  step  by  step,  in  the  decomposition,  in  the  same  manner  as  is 
true  with  the  carbohydrates,  in  which  case  diastase  decomposes  them 
only  to  the  maltose  stage,  leaving  the  latter  to  be  further  acted  upon  by 
maltase.3 

As  a  matter  of  course,  proteolytic  ferments  must  also  be  active  in  the 
tissues  and  cells,  and  many  observations  indicate  that  the  action  is  anal- 
ogous to  that  of  trypsin.  This  applies  not  only  to  the  animal  cells,  but 
also  to  those  of  plants.  Especially  noteworthy  is  the  ferment  papayotin 
occurring  in  the  milk  of  the  melon,  Carica  papaya.  It  quickly  dissolves 
albumin.  Its  action  appears  to  be  similar  to  that  of  trypsin.4  Other 
active  ferments  have  also  been  isolated  from  various  plants,  as,  for  instance, 
from  the  sap  of  the  fig-tree,  Ficus  carica,  and  macrocarpa.  Other  plants, 
like  the  banana,  are  credited  with  possessing  a  ferment  analogous  to 
pepsin. 

Especial  interest  attaches  to  those  plants  which  also  secrete  ferments 
externally  which  correspond  to  the  digestive  fluids  characteristic  of  the 
animal  organism.  They  constitute  the  large  group  of  carnivorous  plants. 
We  will  mention  merely  the  Drosera  and  Pinguicula,  growing  in  peat 
bogs;  and  the  varieties  of  Utricularia  inhabiting  brooks  and  stagnant 
pools.  The  Nepente  species,  Dioncea  muscipula,  act  on  a  larger  scale.  It 
is  still  a  question  whether  the  action  of  the  ferment  produced  is  analogous 
to  that  of  pepsin  or  to  that  of  trypsin.  It  has  even  been  suggested  that  the 
fermentative  action  of  Nepente  is  due  to  bacteria. 

In  the  cryptogams  the  proteolytic  ferments  are  also  widely  distributed, 
and  in  many  cases  have  been  detected. 

Before  discussing  the  manner  in  which  the  fundamental  constituents  of 
the  albumins  are  combined,  we  must  devote  a  little  attention  to  several 
other  substances  which  occur  among  the  cleavage-products  of  the  proteins, 


1  H.  M.  Vernon:  J.  Physiol.  32,  33  (1904);  33,  81  (1905). 

2  Cf.  Lecture  on  Ferments. 

3  Cf.  W.  M.  Bayliss  and  E.  H.  Starling:  J.  Physiol.  29,  174  (1903).     K.  Mays:  Z. 
physiol.  Chem.  38,  428  (1903).     L.  Pollak:  Hofmeister's  Beitr.  6, 95  (1904).     K.  Kiesel: 
Pfliiger's  Arch.  108,  334  (1905). 

4  O.  Emmerling:  Ber.  35,  695  (1902). 


ALBUMINS  OR  PROTEINS.  169 

but  which,  nevertheless,  probably  do  not  occur  as  a  constituent  of  the 
original  molecule. 

Amongst  these  is  leucinimide.  It  is  an  anhydride  of  leucine,  and  is  3-6, 
di-isobutyl,  2-5,  di-acipiperazine: 

C4H9  .  CH  .  NH  .  CO 

CO  .  NH  .  CH  .  C4H9 

Ritthausen 1  first  observed  this  in  an  acid  hydrolysis.  Cohn 2  also 
described  it.  Salaskin  and  Kowalewsky  3  recently  even  separated  it, 
although  only  in  minute  quantity,  from  peptic  and  tryptic  digestion.4  It 
has  not  yet  been  decided  whether  leucinimide  occurs  as  such  in  the 
albumin  molecule.  It  is  possible  that  it  is  formed  by  a  secondary  process, 
perhaps  from  a  leucyl-leucine. 

Pyroracemic  acid,  CH3 .  CO .  COOH,  discovered  by  Morner,5  is  un- 
questionably formed  by  a  secondary  reaction.  It  is  probably  produced 
from  alanine,  serine,  or  cystine.  The  origin  of  a-thiolactic  acid,  discovered 
by  Suter,6  is  problematical.  It  may  possibly  be  derived  from  cystine, 
although  this  has  the  thio  group  in  the  ft  position.  Ornithine,  which  is 
certainly  a  secondary  decomposition  product,  is  derived  from  arginine. 

The  albumins  quickly  undergo  putrefaction.7  They  are  also  decomposed 
by  bacteria  in  the  intestines.  It  is  necessary  to  become  acquainted  with 
the  compounds  formed  in  this  manner.  They  are  all  related  to  the  amino 
acids  already  mentioned.  The  bacteria  decompose  the  albumin  in  the 
same  manner  as  do  the  proteolytic  ferments,  especially  trypsin.  Peptones, 
and  finally  amino  acids,  are  produced. 

1  Ritthausen:  Die  Eiweisskorper  der  Getreidearten,  Bonn,  1872. 
a  R.  Cohn:  Z.  physiol.  Chem.  22,  153  (1896-97);  29,  283  (1900). 

3  S.  Salaskin  and  K.  Kowalewsky:  ibid.  38,  567  (1903). 

4  The  author  has  himself  also  tried  to  isolate  leucinimide  from  peptic  and  tryptic 
digestion  products,  but  in  vain.     Something  went  into  solution  in  the  acetic  ether.     Its 
easy  solubility  in  dilute  hydrochloric  acid  showed  that  it  was  not  leucinimide.     He, 
however,  succeeded   in  obtaining  about  one  per  cent  of   leucinimide  by  hydrolyzing 
casein  with  25  per  cent  sulphuric  acid. 

5  K.  A.  H.  Morner:  Z.  physiol.  Chem.  42,  121  (1904). 

8  Suter:  ibid.  20,  564  and  577  (1895);  Hofmeister's  Beitr.  3,  184  (1902).  K.  A.  H. 
Morner:  Z.  physiol.  Chem.  42,  365  (1904). 

7  E.  and  H.  Salkowski:  Z.  physiol.  Chem.  8,  417  (1884);  ibid.  9,  8  (1884);  9,  491 
(1885) ;  27,  302  (1899).  N.  Nencki:  Ber.  7,  1593  (1874) ;  8,  336  (1875) ;  10,  1032  (1877) ; 
J.  pr.  Chem.  26,  47  (1882);  Z.  physiol.  Chem.  4,  371  (1880);  Z.  med.  Wiss.  1878,  47. 
Nencki:  Opera  omnia,  vol.  i,  pp.  92,  113,  144,  244,  246,  674,  537,  354,  418,  etc. 
E.  Baumann:  Ber.  12,  1450  (1879);  Z.  physiol.  Chem.  4,  304  (1880);  6,  183  (1882);  7, 
282  and  553  (1895).  E.  Baumann  and  L.  Brieger:  ibid.  3,  149  and  284  (1879).  L. 
Brieger:  J.  pr.  Chem.  17,  124  (1877);  Ber.  10,  1027  (1877);  12,  1986  (1879);  Z. 
physiol.  Chem.  2,  241  (1878);  3,  134  (1879);  4,  414  (1880);  5,  366  (1881).  Cf.  also  L. 
Brieger:  Die  Ptomaine,  Berlin,  1886. 


170  LECTURE  VIII. 

The  decomposition,  however,  does  not  end  here.  The  bacteria  break 
these  down  in  two  directions.  On  one  hand  they  split  off  the  amino 
acids.  Simple  acids  remain:  acetic  acid  is  produced  from  glycocoll;  pro- 
pionic  acid  from  alanine;  valeric  acid  from  ammo-valeric  acid;  etc.  The 
<5-amino-valeric  acid,  found  in  putrefying  mixtures,  may  be  produced 
from  ornithine,  or  by  splitting  off  the  pyrrole  ring  from  a-pyrrolidine- 
carboxylic  acid.  Tartaric  acid,  phenyl-propionic  acid,  p-hydroxyphenyl- 
propionic  acid,  and  skatble-acetic  acid  are  also  found.  On  the  other  hand, 
carbon  dioxide  is  split  off  from  the  amino  acids  by  bacterial  action.  This 
process  gives  us  pentamethylenediamine  (cadaverine)  from  lysine;  while 
tetramethylenediamine  (putrescine)  results  from  arginine  and  ornithine. 

From  phenylalanine  we  obtain  phenylethylamine  CoH5 .  CH2 .  CH2NH2, 
with  evolution  of  carbon  dioxide;  and  from  tyrosine,  oxyphenylethyl- 
amine.  As  a  rule  the  decomposition  does  not  stop  at  these  products. 
They  are  oxidized.  We  can  indicate  the  further  destruction  of  tyrosine 
(p-hydroxyphenyl-amino-propionic  acid)  as  follows: 

p-hydroxyphenyl-amino-propionic  acid  CeH4  .  OH  .  CH2.  CH.NH2.COOH 
p-hydroxyphenyl-propionic  acid  C6H4.  OH.  CH2.  CH2.COOH 

p-hydroxyphenyl-acetic  acid  C6H4 .  OH  .  CH2.  COOH 

p-hydroxymandelic  acid  C6H4  .  OH  .  CH(OH)  .  COOH 

p-cresol  C6H4 .  OH  .  CH3 

phenol  C6H5 .  OH 

In  an  analogous  manner  phenylalanine  (phenyl-amino-propionic  acid) 
breaks  down  through  phenyl-propionic  acid  and  phenyl-acetic  acid. 
Tryptophane  (skatole-amino-acetic  acid)  gives  skatole-acetic  acid,  skatole- 
carbonic  acid,  skatole  and  indole.  We  shall  meet  with  phenol,  skatole, 
and  indole  in  the  animal  organism.  They  are  produced  in  intestinal 
putrefaction,  and  appear  in  the  urine  combined  with  sulphuric  acid. 
Sulphureted  hydrogen  is  liberated  from  cystine. 


LECTURE   IX. 

ALBUMINS   OR   PROTEINS. 

III. 
COMPOSITION  OF  INDIVIDUAL  PROTEINS.     CONSTITUTION. 

IN  the  formation  of  proteins,  the  amino  acids  alone  participate,  as  far 
as  we  know,  with  the  single  exception  of  the  amino-hexose,  glucosamine, 
which  occurs  in  many  varieties  of  albumin.  The  number  of  these  amino 
acids  already  discovered  is  very  large.  It  includes  the  following :  glycocoll, 
alanine,  amino-valeric  acid,  leucine,  isoleucine,  a-pyrrolidine-carboxylic 
acid  (proline),  oxypyrrolidine-carboxylic  acid  (oxyproline),  serine,  phenyl- 
alanine,  glutamic  acid,  aspartic  acid,  tyrosine,  cystine,  tryptophane,  lysine, 
histidine,  arginine,  and  diaminotrihydroxydodecoic  acid.  It  is  of  chief 
interest  to  learn  whether  the  proteins,  at  present  known,  contain  the  same 
fundamental  substances,  or  whether  specific  groups  of  proteins  are  char- 
acterized by  their  content  of  individual  amino  acids.  Another  matter  of 
considerable  importance  is  the  relative  quantity  of  the  different  amino 
acids,  occurring  in  the  proteins.  It  is  possible  that  the  differences  between 
the  various  proteins  are  due  to  varying  relations  of  the  quantities  of 
individual  amino  acids  present.  On  the  other  hand,  it  is  a  matter  of  the 
greatest  importance  to  know  the  quantitative  amounts  of  these  con- 
stituents of  the  albumins  for  use  in  furthe?  work  on  this  subject.  We 
should  like  to  know  how  great  a  portion  of  the  whole  albumin  molecule 
is  already  understood.  Unfortunately,  we  have  no  quantitative  method 
for  estimating  the  amino  acids.  True,  we  can  estimate  very  exactly  some 
of  the  cleavage-products,  like  tyrosine  and  glutamic  acid,  but  for  the 
remainder  of  the  amino  acids  we  can  only  estimate  the  approximate 
amounts.  Our  knowledge  concerning  protein  formation  was,  until  re- 
cently, very  limited. 

Although  various  amino  acids  had  been  isolated,  and  the  quantitative 
relations  of  lysine,  arginine,  and  histidine  in  different  albumin  molecules 
had  been  established,  through  the  researches  of  A.  Kossel,  investigators  as 
a  rule  attempted  only  to  prepare  the  proteins  in  as  pure  a  form  as  possible, 
and  to  classify  them  according  to  their  elementary  composition.  A  turn- 
ing-point in  the  whole  chemistry  of  the  albumins  was  reached  when  E.- 
Fischer  l  introduced  a  new  method  for  isolating  the  amino  acids.  Briefly, 
the  process  consists  in  forming  the  esters  of  the  mono-amino  acids,  and 

1  E.  Fischer:  Z.  physiol.  Chem.  33,  151  (1901). 

171 


172 


LECTURE   IX. 


separating  them  by  fractional  distillation.  The  amino  acids  are  then  re- 
covered by  saponifying  the  amino  acid  esters.  On  account  of  considerable 
differences  in  the  boiling-points  of  these  esters,  it  is  possible  to  obtain  by 
mere  distillation  a  fairly  satisfactory  complete  separation  of  the  amino 
acids.  With  the  help  of  this  method  a  considerable  number  of  protein 
substances  have  been  carefully  examined.  We  will  give  in  the  follow- 
ing summary  the  results  thus  arranged  according  to  the  classification 
previously  given.  It  may  be  said  that  the  amounts  of  amino  acids 
indicated,  represent  the  minimum  values.  As  the  various  proteins  were 
all  analyzed  under  the  same  conditions,  it  is,  therefore,  possible  to  com- 
pare the  individual  proteins  according  to  their  percentages  of  mono- 
amino  acids.  The  values  given  are  all  based  on  100  grams  of  ash-free 
material,  dried  at  100  degrees. 

1.   THE  ALBUMIN   GROUP. 


Serum  - 
albumin.1 

Egg- 
albumin.2 

Glycocoll 

o 

0 

Alanine                       .                   .                       ... 

2  7 

8  1 

Leucine                           .           »    . 

20  0 

7  1 

a  -Proline            .        

1.0 

2  25 

Phenylalanine    

3.1 

4.4 

Glutamic  acid        

7.7 

8.0 

Aspartic  acid 

3  1 

1  5 

Cystinc 

2  3 

0  2 

Serine 

0  6 

Tyrosine                                                  

2  1 

1.1 

Tryptophane  

present 

present 

1  E.  Abderhalden:  ibid.  37,  495  (1903). 

2  E.  Abderhalden  and  F.  Pregyl:  ibid.  46,  24  (1905). 

2.  THE  GLOBULIN  GROUP. 


Serum  - 
globulin.1 

Edestin 
from 
hemp-seed.3 

Edestin 
from 
cotton  -seed.4 

Edestin  from 
sunflower 
seed.5 

Glycocoll                  .       

3  5 

3.8 

1.2 

2.5 

Alanine          

2.2 

3.6 

4.5 

4.5 

Aminovaleric  acid  

present 

present 

present 

0.6 

Leucine 

18  7 

20  9 

15.5 

12.9 

at  -Proline 

2  8 

1  7 

2.3 

2.8 

Phenylalanine 

3  8 

2.4 

3.9 

4.0 

Glutamic  acid 

8  52 

6.3 

17.2 

13.0 

Aspartic  acid           .    .       .... 

2  5 

4.5 

2.0 

3.2 

Cystine      ...       

0.7 

0.25 

Serine     

0.33 

0.4 

0.2 

Tyrosine    

2.5 

2.1 

2.3 

2.0 

Tryptophane 

present 

present 

present 

present 

Oxyproline 

2.0 

•Lysine                              .... 

1.0 

Arginine                        

1.7 

Histidine  

11.1 

1  E.  Abderhalden 
3  E.  Abderhalden 

3  E.  Abderhalden 

4  E.  Abderhalden 
8  E.  Abderhalden 


:  Z.  physiol.  Chem.  44,  17  (1905). 
and  F.  Samuely:  ibid.  46,  193  (1905). 
:  ibid.  37,  499  (1903);  40,  249  (1903). 
and  O.  Rostoski:  ibid.  44,  265  (1905). 
and  B.  Reinhold:  ibid.  44,  284  (1905). 


ALBUMINS  OR  PROTEINS.  173 

3.  GROUP  OF  THE  PLANT-CASEINS,  PHYTOVITELLINS,  LEGUMINS,  ETC. 


Proteins  soluble 
in  alcohol. 

Conglutin 
from 
Lupinus  seeds.5 

Legumin.7 

Albumin 
from 
Pine  seeds.8 

Gliadin  1 
from 
wheat  flour. 

Zein.2 

Glycocoll  .  .  .  . 
Alanine 

0.9 
2.7 
0.33 
6.0 
2.4 
2.6 
37.5 
1.3 
0.12 
2.4 
about  1.0 

o.     ] 

3.4    Y 

1.7     • 

not 
determined 
0.5 
present 
11.2 
1.5 
7.0 
11.8 
1.0 

io.'i3 
6'.'    ) 

1.82     • 
0.81    J 

0.8 
2.5 
1.1 
6.75 
2.6 
3.1 
19.5 
3.0 
present 
2.1 
present 
2.1      1 
6.6       " 
0.65    J 

1.0 
2.8 
1.0 
8.2 
2.3 
2.0 
16.3 
4.0 

2.8 

5.5      I 
4.6       ' 
1.1      J 

0.6 
1.8 
present 
6.2 
2.8 
1.2 
7.8 
1.8 
present 
1.7 
present 
0.25   } 
10.9       * 
0.62   j 

Aminovaleric  acid 
Leucine  .  . 

a-Proline  .... 
Phenylalanine  .  . 
Glutamic  acid  .  . 
Aspartic  acid  .  . 
Serine 

Tyrosine 

Tryptophane  .  .  . 

Lvsine  .  . 

Arginine  .  . 

Histidine  .... 

E.  Abderhalden  and  F.  Samuely:  Z.  physiol.  Chem.  44,  276  (1905) 
L.  Langstein:  ibid.  37,  508  (1903). 

F.  Kutscher:  ibid.  38,  111  (1903). 

A.  Kossel  and  F.  Kutscher:  ibid.  35,  165  (1900). 
E.  Abderhalden  and  J.  B.  Herrick:  ibid.  45,  479  (1905). 
E.  Schulze  and  E.  Winterstein:  ibid.  33,  547  (1901). 
E.  Abderhalden  and  B.  Babkin:  ibid.  47  (1906). 
Abderhalden  and  Teruiichi:  ibid.  45,  473  (1905). 


4.   GROUP  OF  FIBRINOGENS  AND  FIBRINS.1 


Glycocoll 3.0 

Alanine 3.6 

Aminovaleric  acid 1.0 

Leucine      15.0 

a-Proline 3.6 

Phenylalanine 2.5 

Glutamic  acid      10.4 

Aspartic  acid       2.0 

Serine 0.8 

Tyrosine 3.5 

Tryptophane present 


1  Abderhalden  and  Voitinovici  :    Z.   physiol.   Chem.   52,   368   (1907).     Cf.  also  A. 
Bruner  :  Diss.  Berlin,  1905. 


174 


LECTURE  IX. 
5.   GROUP  OF  NUCLEO-ALBUMINS. 


Casein 
from 
cow's  milk.1 

Casein 
from 
goat's  milk.6 

Glycocoll                    .       

o 

o 

Alanine               .    . 

0.9 

1  5 

Aminovaleric  acid    

1.0 

Leucine    

10.5 

7  4 

a-Proline     

3.1 

4  6 

Phenylalanine   

3.2 

2  75 

Glutamic  acid    

11.0 

12  0 

1.2 

1  2 

0  065  2 

0  23s 

Tyrosine              

4  5 

4  95 

Tryptophane 

1  5 

present 

Diaminotrihydroxydod6coic  acid 

0  75  4 

present 

Hydroxyproline 

0  25  3 

Lysine      

5  801 

Arginine      

4  84[5 

Histidiii6                                

2  59J 

Cf.  also  E.  Abderhalden:  loc.  tit.  and  E.  Fischer:  Z.  physiol.  Chem.  33,  151  (1901). 

K.  A.  H.  Morner:  ibid.  34,  207  (1901-02). 

E.  Fischer:  ibid.  39,  155  (1903). 

E.  Fischer  and  E.  Abderhalden:  ibid.  42,  540  (1904). 

E.  Hart:  ibid.  23,  347  (1901). 

E.  Abderhalden  and  A.  Schittenhelm :  ibid.  47,  1906. 

6.   GROUP  OF  THE  HISTONS. 


Histon 
from  the  thy- 
moid  gland.1 

Globin 
from  Oxy- 
hemoglobin  of 
the  horse.2 

Glycocoll                    

0  5 

0 

3  5 

4  2 

11.8 

29.0 

ft-Proline 

1  5 

2  3 

Phenylalanine                                                  ...        . 

2  2 

4  2 

0.5 

1.7 

Aspartic  acid                            

not  found 

4  4 

0  3 

Serine                                  .       

0  6 

present 

5  2 

1.5 

1.5 

6  9 

4.3 

15  5 

5.4 

1.5 

11.0 

1  E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  41,  278  (1904). 
8  E.  Abderhalden:  ibid.  37,  484  (1903).     Cf.  also  E.  Fischer  and  E.  Abderhalden; 
ibid.  36,  268  (1902). 


ALBUMINS  OR  PROTEINS. 


175 


7.  GROUP  OF  THE  PROTAMINES. 

The  protamines,  as  we  have  already  mentioned,  have  been  very  carefully 
studied  by  A.  Kossel  and  his  students.  They  are  mainly  composed  of 
di-amino  acids.  It  is  only  recently  that  mono-amino  acids  have  been 
detected  in  the  protamines.  A.  Kossel l  states  that  the  protamines  con- 
tain only  small  quantities  of  specific  mono-amino  acids.  An  observa- 
tion somewhat  at  variance  with  this,  was  made2  in  a  very  carefully 
purified  sample  of  salmine,  but  this  may  be  explained  perhaps  by  an 
immature  condition  of  the  testes  from  which  the  preparation  was  obtained. 
We  have  already  mentioned  that  as  a  matter  of  fact  the  amounts  of 
di-amino  acids  isolated  from  the  proteins  in  the  testes  of  the  salmon 
depend  on  the  maturity  of  the  latter.  It  is  very  probable  that  the 
protamines,  which  evidently  can  be  traced  back  to  the  proteins  of 
the  muscles,  are  formed  from  histons,  which  are  to  be  considered  as  the 
transition  stage  in  the  transformation  from  the  proteins  of  the  muscles 
to  the  protamines.  The  salmine  investigated  contained  alanine,  leucine, 
and  a-proline,  while  phenylalanine  and  aspartic  acid  were  also,  undoubt- 
edly, present. 

Kossel  and  his  students  give  the  following  amino  acids  as  the  constituents 
of  the  protamines: 


In  100  grams  of  Albumin  are  present 

Arginine. 

Lysine. 

Histidine. 

Alanine. 

Salmine         

gms. 
87.4 
82.2 
62.5 
+ 
58.2 
4.9 
+ 

gms. 
0. 
0. 
0. 
0. 
12.0 
28.8 
+ 

gms. 
0. 
0. 
? 
0. 
12.9 
0. 

•o. 

-f 

Clupeine    

Cyclopterine    

Scombrine 

Sturine                  .    . 

Cyprinine  

Cyprinine  II     

In  100  grams  of  Albumin  are  present 

Amino- 
valeric 
acid. 

a-Proline. 

Tyrosine. 

Trypto- 
phane. 

Serine. 

Salmine                 .    . 

4.3  gms. 

+ 

+ 

11.0  gms. 

8.0  gms. 
traces 

4- 

7.8 

+ 

Clupeine    

Cyclopterine     

Scombrine     

Sturine       .    .    . 

Cyprinine  

Cyprinine  II     

1  Cf.  A.  Kossel:  Z.  physiol.  Chem.  40,  311  (1903).     A.  Kossel  and  H.  D.  Dakin:  ibid. 
40,  565  (1904);  41,  407  (1904). 

2  E.  Abderhalden:  ibid.  41,  55  (1904). 


176 


LECTURE  IX. 


8.   GROUP  OF  ALBUMINOIDS. 


Silk 
fibroin.1 

Edestin.4 

Keratin 
from 
horn.7 

Keratin 
from  horse- 
hair.9 

Keratin 
from 
goose- 
feathers.10 

Glycocoll  

36  0 

25  75 

0  34 

4  7 

2  6 

Alanine  

21.0 

6  6 

1  2 

1  5 

1  8 

Aminovaleric  acid  .  . 
a-Proline  
Leucine  
Phenylalanine  .  .  . 
Glutamic  acid  .... 
Aspartic  acid  .... 

Cystine  
Serine  

0. 
present 
1.5 
1.5 
0. 
present 

1.63 

2 

1.0 

1.7 
21.4 
3.9 
0.8 
probably 
present 

5.7 
3.6 
18.3 
3.0 
3.0 
2.5 

very  much  8 
0.7 

0.9 
3.4 
7.1 
0.0 
3.7 
0.3 

over  10  per 
cent  8 
0.6 

0.5 
3.5 
8.0 
0.0 
2.3 
1.1 

0.4 

Tyrosine  

10.5 

0.34  5 

4.6 

3.2 

3.6 

Lysine  

in  small 

Arginine  .  . 

amounts 
1  0 

.  3 

0  3  6 

2  25 

Histidine  .  .... 

in  small 

_ 

_• 

amounts 

Gelatin.11 

Silk 
Gelatin.12 

Glycocoll 

16  5 

01—02 

Alanine                              .                          .    . 

0  8 

5 

Aminovaleric  acid 

1  0 

Leucine           .    .                  .           .       

2.1 

_ 

a-Proline     

5.2 

_ 

Phenylalanine   

0.4 

_ 

Glutamic  acid 

0  88 

Aspartic  acid                                      , 

0  56 

Cystine 

Serine 

0  413 

6  6 

Tyrosine                                                        

0 

5.0 

Tryptophane  .    .                                      

0 

Lysine  

2.75  ) 

_ 

Arginine  

7.62  >  14 

+ 

Histidine 

0  40  ) 

4 

Hydroxyproline                                                                         .    . 

3  O15 

1  E.  Fischer  and  A.  Skita:  Z.  physiol.  Chem.  33,  177  (1901). 

2  E.  Fischer:  ibid.  39,  155  (1903). 

3  Fischer  and  Skita:  ibid.  35,  221  (1902). 

4  E.  Abderhalden  and  A.  Schittenhelm :  ibid.  41,  293  (1904). 

5  H.  Schwarz:  ibid.  18,  487  (1894). 

6  A.  Kossel  and  F.  Kutscher:  ibid.  25,  551  (1898). 

7  E.  Fischer  and  T.  Dorpinghaus:  ibid.  36,  462  (1902). 

8  K.  A.  H.  Morner:  28,  595  (1899);  34,  207  (1901-02). 

9  E.  Abderhalden  and  H.  G.  Wells:  ibid.  46,  31  (1905). 

10  E.  Abderhalden  and  E.  R.  LeCount:  ibid.  46,  40  (1905). 

u  E.  Fischer,  P.  A.  Levene,  and  R.  H.  Aders:  ibid.  35,  70  (1902). 

12  E.  Fischer:  ibid.  35,  221  (1902). 

18  E.  Fischer  and  E.  Abderhalden:  Z.  physiol.  Chem.  42,  540  (1904). 

14  E.  Hart:  ibid.  23,  347  (1901). 

18  E.  Fischer:  ibid.  35,  221  (1902). 


ALBUMINS  OR  PROTEINS.  177 

A  glance  at  the  composition  of  the  different  kinds  of  proteins  shows  that 
they  all,  with  the  exception  of  the  protamines,  contain  the  same  funda- 
mental constituents.  Occasionally  one  or  another  amino  acid  is  absent; 
thus,  glycocoll  does  not  occur  in  egg-  or  serum-albumin;  lysine  is  absent 
in  the  plant  albumins  which  are  soluble  in  alcohol;  tyrosine  and  trypto- 
phane  in  gelatin.  If  we  compare  the  relative  amounts  of  the  various 
amino  acids  occurring  in  the  individual  proteins,  we  notice  appreciable 
differences.  This  is  especially  striking  if  we  compare  the  individual 
groups.  In  the  first  place  we  notice  the  varying  proportions  of  the 
mono-  and  di-amino  acids  that  go  to  make  up  the  individual  proteins. 
The  latter  are  very  strongly  represented  in  the  protamines,  and  least  so 
among  the  albuminoids.  Between  these  two  extremes  we  find  the  com- 
mon albumins  and  the  histons.  Very  noticeable  is  the  predominance  of 
special  mono-amino  acids,  e.g.,  glutamic  acid  and  leucine  in  the  albumins 
present  in  the  seeds  of  plants.  It  constitutes  one-third  of  gliadin. 
If  we  compare  the  individual  groups  of  proteins  among  themselves,  we 
find  in  many  cases  a  very  general  similarity.  Thus,  glycocoll  is  absent 
in  egg-albumin  and  serum-albumin,  whereas  the  globulins  invariably  con- 
tain it.  We  are,  therefore,  in  a  position  to  classify  chemically  at  least  a 
portion  of  the  different  proteins.  The  fact  that  they  all  contain  the  same 
fundamental  constituents  makes  it  easier  for  us  to  understand  their  trans- 
formations in  the  animal  organism. 

Although  the  complete  hydrolysis  of  itself  serves  to  give  us  a  fairly 
comprehensive  knowledge  of  the  amino  acids  participating  in  the  con- 
struction of  the  albumins,  it,  on  the  other  hand,  does  not  give  us  any  idea 
of  the  manner  in  which  these  substances  are  united.  Until  recently  it  had 
not  been  possible  to  split  off  complexes  from  the  proteins,  and  to  identify 
positively  individual  compounds  containing  only  a  part  of  the  total  amino 
acids.  We  are  certainly  justified  in  concluding  that  the  albumoses  have  a 
lower  molecular  weight  than  the  original  proteins,  and  that  the  peptones 
are,  without  doubt,  to  be  considered  as  still  lower  cleavage-products.  Up 
to  the  present  time  the  albumoses  and  peptones  have  been  grouped  almost 
entirely  according  to  their  limits  of  precipitation  and  solubility.  Only  in 
specific  cases  have  they  been  characterized  by  the  absence  of  a  definite 
amino  acid,  or  by  an  excess  of  such.  Recently  M.  Siegfried  and  his 
students  have  tried  to  obtain  products  by  cautious  hydrolysis  of  some 
of  the  albuminous  substances  which  would  contain  only  a  part  of  the 
amino  acids  occurring  in  the  original  protein.  Siegfried1  has  described 
several  such  products.  He  calls  them  kyrines.  It  is  at  present  impossible 

1  Siegfried:  Ber.  math-physikal.  Kl.  klg.  sachsischen  Gesel.  Wiss.  Leipzig,  Sitzung  II. 
III.  p.  63,  1903;  Z.  physiol.  Chem.  38,  259  (1903);  43,  46  (1904);  43,  44  (1904).  Cf. 
also  C.  Bockel:  ibid.  38,  289  (1903).  T.  R.  Kriiger:  ibid.  38,  320  (1903).  W.  Scheer- 
messer:  ibid.  41,  68  (1904).  Z.  H.  Skraup  and  R.  Zwerger:  Monatsh.  26,  1403  (1905). 


178  LECTURE  IX. 

to  say  whether  they  are  individual  substances  or  mixtures.  Thus  far  their 
study  has  not  helped  our  knowledge  regarding  the  construction  of  the  albu- 
min molecule.  There  is  no  doubt  that  the  product  obtained  by  Emil 
Fischer  and  Emil  Abderhalden  by  means  of  tryptic  digestion,  which  did 
not  give  the  biuret  reaction  and  was  designated  as  "  polypeptide,"  repre- 
sents a  cleavage  product  of  a  lower  order  of  magnitude  than  the  peptones. 
It  is  very  probably  a  mixture  of  various  decomposition  products.  The 
reason  why  we  have  not  yet  succeeded  in  getting  an  idea  of  the  structure 
of  albumin  by  means  of  partial  decomposition,  is  due  to  the  fact  that  with 
the  large  number  of  amino  acids  we  should  necessarily  expect  to  find  a 
great  many  different  decomposition  products.  For  instance,  in  a  digest- 
ing mixture  we  find,  besides  peptones  and  free  amino  acids,  other  cleavage- 
products  which  do  not  give  the  biuret  reaction.  As  it  is  almost  impossible 
to  separate  the  amino  acids  already  known  from  such  a  mixture,  it  is,  there- 
fore, natural  to  expect,  considering  our  unfamiliarity  with  the  higher  com- 
plexes, that  we  can  hardly  hope  to  isolate  them  in  a  satisfactory  manner. 

Recognizing  this  fact,  Emil  Fischer  l  recently  began  to  investigate  the 
constitution  of  the  albumins  from  an  entirely  different  standpoint.  He 
chose  the  synthetic  method.  By  linking  the  amino  acids  together,  com- 
pounds must  necessarily  result  which  bear  some  relation  to  the  albumins. 
After  obtaining  a  knowledge  of  the  characteristics  of  these  synthetic  sub- 
stances, it  should  be  possible  to  devise  ways  and  means  to  produce  analo- 
gous compounds  from  the  albumins.  We  may  say,  at  the  start,  that  Emil 
Fischer's  early  expectations  have  already  been  partially  realized.  While 
the  constitution  of  albumin  was,  until  recently,  very  much  in  darkness,  we 
can  now  thank  Emil  Fischer  and  his  students  for  their  extensive  researches 
toward  solving  this  problem.  Emil  Fischer's  work  will,  undoubtedly, 
constitute  the  foundations  of  both  the  chemistry  and  the  biology  of 
the  albumins.  We  must  return  to  it  in  all  phases  of  the  question,  and 
shall,  therefore,  only  briefly  outline  its  fundamental  characteristics  here. 

Emil  Fischer  started  with  the  assumption  that  the  amino  acids  in  the 
albumins  were  combined  in  the  form  of  an  amide-linking.  He  has  shown 
that  the  amino  acids  possess  the  ability  of  easily  combining  among  them- 
selves, thereby  splitting  off  water,  the  amino  group  of  one  amino  acid 
reacting  with  the  carboxyl  group  of  another.  The  simplest  representative 
of  this  class  of  compounds,  glycyl-glycine,  is  produced  in  the  following 
manner : 

NH2.CH2.COOH    +    HNH.CH2.COOH    — H20 

V , /  V -y ' 

Glycocoll  Glycocoll 

=  NH2  .  CH2  .  CO  .  NH  .  CH2  .  COOH 

v  -\- — — — — ' 

Glycyl-glycine 


1  Cf.  E.  Fischer:  Ber.  39,  530  (1906). 


ALBUMINS  OR  PROTEINS.  179 

In  the  same  way  we  can  conceive  a  combination  of  two  alanine  mole- 
cules forming  alanyl-alanine;  from  two  leu  cine  molecules  we  obtain  leucyl- 
leucine,  etc.  Emil  Fischer  has  called  this  whole  class  of  compounds 
"  peptides."  Just  as  the  carbohydrates  are  divided  into  mono-,  di-,  tri-, 
or  polysaccharides,  so  Emil  Fischer  has  classified  the  peptides  according  to 
the  number  of  amino  acids  participating  in  the  composition  of  the  mole- 
cule as  mono-,  di-,  tri-,  tetra-,  penta-,  hexa-,  etc.  and  poly-peptides.  He 
characterizes  them  according  to  the  amino  acids  entering  into  their  com- 
position. We  can  just  as  successfully  unite  two  or  more  different  amino 
acids  as  we  can  two  similar  ones  in  producing  peptides.  Emil  Fischer 
and  his  students  have  already  produced  a  very  large  number  of  such 
chains.  As  examples  of  these  we  mention  —  Dipeptides:  glycyl-alanine, 
alanyl-glycine,  alanyl-leucine,  leucyl-alanine,  leucyl-glycine,  glycyW 
tyrosine,  glycyl-phenyl-alanin,  leucyl-proline,  prolyl-leucine,  seryl-serine, 
lysyl-lysine,  arginyl-arginine,  histidyl-histidine;  Tripeptides:  leucyl-glycyl- 
glycine,  leucyl-alanyl-alanin  ;  Tetrapeptides  :  dileucyl-glycyl-glycine,  tetra- 
glycine,  dialanyl-cystine,  dileucyl-cystine;  Penta-peptides:  penta-glycine, 
leucyl-tetraglycine,  etc.  The  number  of  combinations  possible  by  link- 
ing these  amino  acids  together  is  necessarily  very  great.  If  we  also  take 
into  consideration  the  fact  that  all  of  the  amino  acids,  excepting  glycocoll, 
contain  an  asymmetric  carbon  atom  (isoleucine  has  two  of  them),  the 
possible  number  of  isomeric  combinations  is  still  further  increased.  The 
number  of  individual  optical  isomers,  according  to  van  't  Kofi's  formula, 
is  represented  by  2  n,  in  which  n  indicates  the  number  of  asymmetric 
carbon  atoms  which  in  this  case  —  if  we  neglect  glycine  and  isoglycine  — 
is  equal  to  the  number  of  component  amino  acids. 

In  order  to  give  a  more  satisfactory  idea  of  the  syntheses  of  peptides,  an 
example  of  each  important  method  will  be  briefly  given. 

If  glycocoll  is  converted  into  its  ester,  CH2  .  NH2  .  CO  .  0  .  C2H5,  the 
latter  goes  over  into  glycine  anhydride,  a  diketopiperazine  : 

XCH2.CO  N 


CO    .CH2 

according  to  the  following  equation:  ^ 

O-H-2  .  CO 

2  NH2  .  CH2  .  CO  .  O  .  C2H5  =  2  C2H5OH  +  NH( 

Ethyl  alcohol  CO    -  CH2 

From  this  substance  Emil  Fischer  l  succeeded  in  producing  the  first  and 
simplest  of  the  peptides,  by  the  action  of  dilute  alkali  : 

CH2.COV 

NH  (  ;  NH  +  HoO  =  NH2  .  CH2  .  CO  .  NH  .CH2  COOH. 

^CO  .CH 


Glycine  anhydride  Glycyl-glycine 


Cf.  literature  E.  Fischer:  Ber.  39,  530  (1906). 


180  LECTURE  IX. 

In  the  same  manner,  although  with  more  difficulty,  alanine  hydride 
gives  us  alanyl-alanine;  while  from  leucinimide  we  get  leucyl-leucine. 

A  second  method  of  coupling  the  amino  acids  consists  in  uniting  them 
with  an  acid  radical  containing  halogen,  and  then  replacing  the  halogen 
by  an  NH2  group.  The  following  may  act  as  an  example  of  this  form  of 
polypeptide  synthesis: 

In  order,  for  instance,  to  produce  glycyl-glycine,  glycocoll  is  caused  to 
unite  with  chloroacetyl  chloride.  Chloroacetyl-glycine  results: 

Cl  .  CH2  .  CO  .  01  +  NH2  .  CH2  .  COOH  =  Cl  .  CH2  .  CO  .  NH  .  CH2COOH 

~V  HC1. 

Chloroacetyl  Glycocoll  Chloroacetyl-glycine 

chloride 

If  ammonia  is  allowed  to  act  on  chloroacetyl-glycine,  we  immediately 
obtain  glycyl-glycine: 

CICH2  .  CO  .  NH  .  CH2COOH  +  2  NH3  =  NH4C1  + 

Chloroacetyl-glycine 

NH2  .  CH2  .  CO  .  NH  .  CH2COOH. 


Glycyl-glycine 

We  can  then  take  this  dipeptide,  glycyl-glycine,  treat  it  again  with 
chloroacetyl  chloride,  thus  adding  another  glycyl  radical  to  it.  Treating 
the  substance  thus  formed  with  ammonia  gives  us  digly cyl-glycine : 

NH2  .  CH2  .  CO  .  NH  .  CH2  .  CO  .  NH  .  CH2  .  COOH. 

Naturally,  by  following  out  this  same  method,  we  can  use  other  acid 
radicals,  thus  introducing  other  amino  acids.  Should  we,  for  instance, 
desire  to  produce  alanyl-glycine,  we  start  with  glycocoll  and  bromo- 
propionyl  chloride,  forming  a-brom-iso-capronyl  chloride,  which  corre- 
sponds to  leucine. 

It  will  be  noticed  that,  by  following  the  above  method,  it  is  only  possible 
to  extend  the  chain  in  one  direction,  —  towards  the  amine  group.  It 
was,  of  course,  also  desirable  to  add  new  amino  acids  to  the  carboxy  side. 
This  was  accomplished  by  chlorinating  the  amino  acids.  If  phosphorus 
pentachloride  be  added  to  an  amino  acid  under  definite  conditions,  the 
carboxyl  group  is  changed  into  the  COC1  group.  The  free  amino  acid  also 
combines  at  the  same  time  with  a  molecule  of  hydrochloric  acid.  The 
hydrochloride  of  the  amino- acid-chloride  results: 

R  .  CH  .  COC1 


iH2  .  HC1. 

The  peptides   can,  naturally,  be  chlorinated,   and  the  grouping  further 
extended.     By  this  means  we  quickly  obtain  long  chains. 


ALBUMINS  OR  PROTEINS.  181 

As  an  example  of  the  formation  of  a  polypeptide  by  lengthening  the 
chain  at  the  carboxyl  end,  we  may  cite  the  synthesis  of  leucyl-glycyl- 
glycine  from  brom-iso-capronyl-glycine-chloride  and  glycine-ethyl-ester. 
The  resulting  brom-iso-capronyl-glycyl-gly cine-ester  is  saponified;  and  the 
tripeptide,  leucyl-glycyl-glycine,  results  on  treating  this  with  ammonia. 
This,  itself,  can  then  be  chlorinated,  and  again  united  with  a  peptide- 
ester,  or  even  with  a  peptide  itself. 

We  have  gone  into  the  subject  of  the  synthesis  of  the  peptides  some- 
what in  detail,  owing  to  the  importance  of  the  problem.  Synthesis  has 
always  been  a  great  factor  in  biological-chemical  knowledge.  By  this 
means  the  constitutions  of  many  substances  have  been  determined,  and 
many  debatable  questions  settled.  Synthesis,  as  we  have  seen,  plays  an 
even  more  important  part  in  the  chemistry  of  the  albumins.  With  its 
assistance  we  hope  to  determine  the  constitution  of  the  albumin  molecule, 
and  with  it,  also,  we  expect  to  clear  up  the  questions  relating  to  the  first 
decomposition  products,  —  the  peptones. 

Most  of  these  syntheses  have  been  carried  out  with  inactive  amino  acids. 
The  structure  of  these  peptides  is  definitely  known,  depending  on  the 
method  of  procedure.  The  subject  is  not  so  simple  when  we  consider 
its  stereo-chemical  side.  We  have  already  mentioned  that  all  the  amino 
acids,  excepting  glycocoll,  contain  an  asymmetric  carbon  atom.  The  num- 
ber of  asymmetric  carbons  in  the  polypeptides,  therefore,  corresponds  to 
the  number  of  amino  acids  combined  in  the  molecule  —  with  the  exception 
of  glycocoll.  If,  for  instance,  we  have  a  dipeptide  of  the  following  general 
formula, 

NH2  .  CHR  .  O  .  CO  .  NH  .  CHR  .  COOH, 

*  * 

it  is  necessary  to  have,  according  to  van  't  Hoff's  formula,  on  account  of 
the  two  asymmetric  carbon  atoms,  indicated  by  asterisks,  four  different 
active  varieties.  If  we  designate  the  optical  antipodes  by  d  and  I,  the 
following  forms  will  be  possible:  dd,  II,  dl,  Id.  Two  can  produce  a 
racemic  compound  (dd-ll)  (dl-ld) .  If  we  start  with  the  racemic  amino 
acids,  as  has  been  very  generally  done,  we  necessarily  expect  to  obtain 
two  isomeric  inactive  compounds.  This,  in  fact,  is  actually  the  case 
in  practice.  Other  complications  also  arise,  as,  for  instance,  when  we 
combine  a  racemic  amino  acid  with  an  active  one;  for  example,  in  pre- 
paring leucyW-tyrosine.  Here  we  have,  on  the  one  hand,  d/-leucine, 
and  on  the  other  Z-tyrosine.  In  this  case  we  expect  two  compounds: 
a  dl-  and  a  ^/-variety.  The  relations  are,  of  course,  much  simpler,  if  we 
employ  only  active  components  in  the  synthesis.  In  such  a  case,  we 
obtain  only  active  peptides  ;  and  if  we  proceed  from  those  optically 
active  forms  of  amino  acids,  which  occur  in  nature,  we  must  obtain  amino 
acid  chains,  which  correspond  to  those  occurring  in  the  albumin  molecule. 
For  our  requirements  the  optically  active  polypeptides  are  naturally 


182  LECTURE  IX. 

of  much  more  importance  than  the  racemic  bodies  above  mentioned. 
We  have,  therefore,  referred  to  them  here,  only  because  it  will  be  necessary 
to  dwell  on  them  more  in  detail  later,  when  we  consider  more  fully  l 
the  subject  of  fermentation.  It  is  clear,  that  we  can  never  tell,  a  priori, 
whether  the  polypeptides  constructed  from  racemic  amino  acids,  comprise 
the  modifications  existing  in  the  albumin,  or  not.  It  is,  therefore,  of  the 
greatest  importance  for  the  whole  future  investigation,  that  Emil  Fischer, 
supported  by  his  satisfactory  method  of  chlorinating  the  amino  acids,  is 
producing  polypeptides  from  active  materials  exclusively,  which  he  obtains 
by  splitting  the  racemic  compounds  into  their  optically  active  components. 

We  must  not  forget  to  mention  that  the  peptide  chains,  produced  from 
di-amino  acids,  and  especially  the  di-carboxylic  acids,  aspartic  and  glu- 
tamic  acids,  give  much  greater  opportunities  for  variation.  In  the 
latter  cases  the  amino  acids  can  attach  themselves  first  to  the  amino 
groups,  and  then,  again,  at  the  two  carboxyls,  thus  producing  branching 
chains,  as  can  be  shown  by  the  following  formula?: 

COOH  COOH 

I  I  /CH3 

CH  .  NH  .  CO  .  CH2  .  NH2   CH  .  NH  .  CO  .(NH2)CH  .  CH2CH' 
|  |  XCH3 

CH2  CH2 

COOH  COOH 

Glycyl-aspartic  acid  Leucyl-aspartic  acid 

COOH  CO  .  NH  .  CH2  .  COOH 

CH  .  NH2  or  CH  .  NH2 

CH2  CH2 

CO  .  NH  .  CH2  .  COOH  COOH 

Aspargyl-mono-glycine 
CO.NH.  (CH3)CH.COOH 


CH  .  NH2 
Ho 


v-» 

i 

Jo 


.NH.  (CH3)CH.COOH 

Aspargyl-dialanine 

These  illustrations  may  suffice  to  indicate  the  many  possible  combina- 
tions which  may  arise  by  introducing  these  dibasic  amino  acids  into  the 
peptide  chains.  We  will  refer  here  again  to  a  discovery  which  we  have 
already  touched  upon.  If  we  hydrolyze  albumin,  that  is,  alter  the  substance 
by  addition  of  water,  either  by  acids,  alkalies,  or  ferments,  ammonia  will 

1  Cf .  Lecture  on  Ferments. 


ALBUMINS  OR  PROTEINS.  183 

be  set  free.  This  is  especially  true  in  many  of  the  varieties  of  albumin 
from  plants.  Owing  to  the  vigorous  action  of  the  acid  or  alkali,  secondary 
products,  the  humin  substances  are  produced.  We  might  imagine  that  the 
liberated  ammonia  stood  in  some  relation  to  the  formation  of  these  sub- 
stances. This  assumption  is,  however,  doubtful,  because,  on  the  one  hand, 
the  quantity  of  ammonia  set  free  bears  little  relation  to  the  amount  of 
humin  substance  formed;  and  then  again,  ammonia  is  produced  in  especially 
large  amounts  in  the  hydrolysis  by  ferments.  It  would  be  more  nearly 
correct  to  assume  that  acid-amides  are  present  in  the  albumins,  and,  pos- 
sibly, in  the  following  form :  * 

COOH  COOH 


CH3 

:.CH 


NH2.CH2.CO.NH.CH  >CH.CH2.CH.(NH2).CO.NH.CH 

|  CH3  | 

CH2  CH2 

CONH2  CONH2 

Glycyl-asparagine  Leucyl-asparagine 

These  compounds  are  of  especial  interest  to  us  on  account  of  the  fact 
that  the  reserve  albumin,  which  is  stored  in  plant  seeds,  is  broken  down 
by  fermentation  when  these  seeds  begin  to  germinate,  while  large  quan- 
tities of.asparagineandglutamine  appear  in  its  place.  We  can,  of  course, 
also  conceive  that  these  acid-amides  pre-exist  in  the  albumin.  As  it  is, 
these  problems  are  still  very  much  in  doubt. 

As  Emil  Fischer  has  pointed  out,  the  simple  amide  structure  is  not  the 
only  possible  conception  of  the  grouping  of  the  amino  acids  in  the  protein 
molecule.  There  is  no  reason  why  piperazine  rings  should  not  be  present 
in  albumin.  The  hydroxyacids,  like  tyrosine  and  serine,  present  another 
possibility  of  combination.  They  can  go  over  into  esters  or  ether-groups 
by  intramolecular  anhydride  formation. 

A  question  of  utmost  importance  to  us  is:  What  justification  have  we 
for  assuming  an  anhydride  system  of  linkage  for  the  amino  acids  in  the 
albumin  molecule?  There  are  various  reactions  among  the  members  of 
the  polypeptide  group  confirming  this  conception.  Many  of  them  give  the 
biuret  reaction.  It  is  naturally  of  some  interest  that  glycyl-glycine  and 
triglycine  do  not  give  the  biuret  reaction,  while  tetraglycine  does  so  in  a 
very  marked  degree.  It  has  been  known  for  a  long  time  that  the  so- 
called  "  biuret-base,"  which  has  recently  been  shown  to  be  the  ester  of 
triglycyl-glycine,  gives  a  very  strong  biuret  reaction.  It  is  very  easily 
produced  when  glycine-ester  is  simply  allowed  to  stand  carefully  protected 
against  moisture.  Dialanyl-cystine  shows  a  very  beautiful  biuret  reaction. 
The  higher  polypeptides,  containing  seven  or  more  amino  acids,  as  leucyl- 
pentaglycine,  give  a  distinctively  red  biuret  test,  whose  shade  exactly 

1  E.  Konigs:  Diss.  Berlin,  1903. 


184  LECTURE  IX. 

corresponds  with  that  of  the  peptones  from  silk.  Many  polypeptides  are 
precipitated  from  dilute  solution  by  phospho-tungstic  acid.  It  is  also 
interesting  to  note  that  difficultly  soluble  amino  acids  produce  polypeptides 
which  are  easily  soluble,  and  that  difficultly  soluble  polypeptides  often 
instantaneously  become  soluble  on  the  introduction  of  another  amino  acid. 
Tetraglycine  is  difficultly  soluble.  Leucyl-tetraglycine  is  easily  soluble. 
As  is  well  known,  the  peptones  are  all  easily  soluble  in  water,  although 
it  is  necessary  to  remember  that  we  are  here  dealing  with  mixtures  whose 
components  may  be  capable  of  keeping  each  other  in  solution.  The  changes 
which  occur  in  the  taste  of  these  substances  is  also  very  interesting:  for 
instance,  when  sweet-tasting  amino  acids  are  linked  together  the  resulting 
product  has  often  a  bitter  taste.  The  peptones  also,  as  a  rule,  taste 
distinctly  bitter. 

We  must  admit  that  many  analogies  exist  between  the  synthetic  polypep- 
tides and  the  peptones.  We  can  make  no  sharp  distinction  in  this  direction. 
We  must  not  lose  sight  of  the  fact  that  we  are  comparing  a  sharply  defined 
chemical  compound  with  a  mixture.  The  name  "  peptone  "  does  not 
indicate  any  definite  compound;  in  fact,  may  not  even  represent  distinctly 
analogous  cleavage-products  of  protein.  It  is  much  better  to  assume  that 
the  peptones  represent  all  stages  of  decomposition  between  that  of  albu- 
moses  and  the  amino  acids. 

Although  we  do  not  expect  at  present  to  obtain  positive  results  by 
direct  comparison  in  this  way,  excellent  progress  has  been  made  by  biological 
experiments.  It  was  of  the  greatest  significance  that  certain  polypeptides 
were  decomposed  by  the  pancreatic  ferment1  in  the  identical  manner  as  the 
peptones  themselves.  Thus  glycyl-Z-tyrosine  quickly  breaks  down  into  its 
components,  glycocoll  and  Z-tyrosine.  It  is  also  especially  interesting  to 
note  that  the  racemic  polypeptides  are  broken  down  asymmetrically;  that 
is,  only  half  of  the  racemic  substance  is  attacked.2  The  following  example 
is  given  to  illustrate  this  clearly.  If  we  prepare  the  polypeptide,  alanyl- 
leucine,.from  racemic  alanine  and  leucine,  we  necessarily  expect  to  obtain, 
according  to  the  theoretical  conceptions  previously  considered,  four  com- 
binations, which  contain  the  four  active  amino  acids,  I-  and  d-alanine  and 
I-  and  d-leucine.  One  racemic  compound  contains  d-alanine  and  d-leucine 
and  Z-alanine  and  Z-leucine  (d-alanine-d-leucine  +  Z-alanine-£-leucine) . 
The  second  is  constructed  in  the  following  manner:  d-alanine-Meucine 
+  Z-alanine-d-leucine.  The  pancreatic  ferment,  however,  splits  only 
one  of  these  two  racemic  combinations.  Experience  has  already  taught 
us  that  optically  active  amino  acids  in  the  albumins  are  split  off;  hence, 
we  are  justified  in  concluding,  that  of  the  two  racemic  compounds  men- 

1  E.  Fischer  and  P.  Bergell:  Ber.  36,  2592  (1903);  37,  2103  (1904).     E.  Fischer  and 
E.  Abderhalden:  Sitzungsber.  Akad.  Wiss.  Berl.  1905;  Z.  physiol.  Chem.  46,  52  (1905). 

2  For  further  details,  see  Lecture  on  Ferments. 


ALBUMINS  OR  PROTEINS.  185 

tioned,  the  ferment  will  attack  only  that  specific  combination  which  con- 
tains the  corresponding  optically  active  amino  acid  in  the  albumin.  As 
d-alanine  and  /-leucine  are  formed  by  the  hydrolysis  of  albumin,  the  racemic 
compound  necessarily  contains  the  combination,  d-alanyl-/-leucine.  There- 
fore the  partially  hydrolysed  racemic  body,  obtained  by  fermentation  is 
d-alanyl-Z-leucine  +  Z-alanyl-d-leucine.  The  unchanged  portion  must  be 
d-alanyl-d-leucine  +  /-alanyl-Weucine. 

We  have  intentionally  taken  this  example  in  order  to  show  the  selective 
action  of  trypsin  on  the  large  number  of  polypeptides,  on  the  one  hand, 
and,  on  the  other,  to  illustrate  the  fact  that  the  different  behavior  of  the  fer- 
ments towards  various  racemic  compounds  can  be  utilized  in  determining 
the  configuration  of  the  substance  in  question. 

The  results  obtained  by  fermentation  only  become  conclusive  after  all 
of  the  different  racemic  compounds  have  been  subjected  to  the  treatment. 
We  can  only  then  decide  whether  or  not  a  definite  compound  is  attacked 
by  trypsin.  The  relations  become  much  more  simple  when  the  active 
peptides  are  subjected  to  investigation.  Even  then,  however,  if  a  certain 
combination  of  amino  acids  is  not  hydrolyzed  by  trypsin,  it  does  not  by  any 
means  follow  necessarily  that  such  a  combination  is  not  present  in  albumin. 
We  have  already  seen  that  in  the  breaking  down  of  the  different  proteins  by 
trypsin,  different  amounts  of  residues  remain  which  resist  digestion  strongly. 
The  albumin  molecule  evidently  contains  chains  which  are  not  broken 
by  trypsin. 

We  already  know,  and  shall  later  discuss  the  subject  more  in  detail,1 
that  the  ferments,  as  a  rule,  work  in  a  specific  manner,  and  are  very  strongly 
influenced  by  differences  of  configuration.  The  fact  that  trypsin  splits 
the  synthetic  polypeptides  is  a  strong  indication  for  the  assumption  that 
such  anhydride-linked  amino  acid  chains  are  present  in  albumin. 

Another  important  proof,  that  completely  agrees  with  Emil  Fischer's 
assumptions,  is  obtained  by  a  study  of  the  behavior  of  the  polypeptides  in 
the  animal  organism.  They  are  decomposed  in  the  same  manner  as  pro- 
teins, even  when  injected  subcutaneously.  Glycyl-glycine  is  hydrolyzed. 
A  small  part  of  it  appears  in  the  urine  as  glycocoll.2  Dialanyl-cystine  and 
clileucyl-cystine  are  similarly  acted  upon,  and  the  cystine  is  consumed  in  the 
same  manner  as  if  it  were  introduced  as  such  into  the  animal  organism. 
Glycyl-Z-tyrosin  is  likewise  completely  consumed.3  Finally,  it  has  been 
definitely  proved  for  glycyl-glycine,  tri-glycine,  and  alanyl-alanine,4  that 
the  decomposition  of  these  peptides  proceeds  in  the  same  manner  as  if  the 
individual  components  alone  had  been  introduced. 


1  E.  Abderhalden  and  P.  Bergell:  Z.  physiol.  Chem.  39,  9  (1903). 

2  E.  Abderhalden  and  F.  Samuely:  ibid.  46,  187  (1905). 

3  E.  Abderhalden  and  P.  Rona:  ibid.  46,  176  (1905). 

4  E.  Abderhalden  and  Y.  Teruuchi:  ibid.  47,  159  (1906). 


186  LECTURE  IX. 

Glycine  anhydride  and  alanine  anhydride  are  likewise  utilized.  They  may 
possibly  be  decomposed  in  the  intestine,  and  converted  first  of  all  into 
polypep tides.  Leucyl-leucine  is  utilized  in  the  same  manner  as  leucine.1 

The  keystone  of  the  whole  proof  must  be  regarded  as  certainly  reached 
if  we  can  obtain  from  albumin  itself  products  analogous  to  the  polypeptides. 
This  has  been  accomplished.  Its  accomplishment  was  due  entirely  to 
applying  the  knowledge  gained  concerning  the  synthetic  polypeptides  to  the 
study  of  the  decomposition  of  proteins.  It  was  found  possible  to  act  upon 
proteins  in  such  a  way  lhat  they  did  not  break  down  entirely  into  their 
simplest  components,  —  the  amino  acids,  —  and,  on  the  other  hand,  to 
carry  the  decomposition  beyond  the  point  of  the  most  complicated  cleavage- 
products.  Such  a  partial  decomposition  could  be  most  easily  accom- 
plished by  acting  on  those  albumins  on  which  the  usual  reagents,  acids 
and  alkalies,  and,  above  all,  the  proteolytic  ferments,  have  least  effect.  We 
have  succeeded  in  obtaining  from  silk-fibroin,  by  a  preliminary  action  of 
acid  in  the  cold  and  a  subsequent  digestion  by  pancreatic  juice,  apolypep- 
tide  in  the  form  of  its  anhydride.2  All  its  characteristics,  and  especially  its 
cleavage  into  d-alanine  and  glycocoll,  as  well  as  its  conversion  into  the 
polypeptide,  proved  that  a  compound  was  present  which  corresponded  to 
the  polypeptide  composed  of  d-alanine  and  glycine.  We  do  not  err  in 
designating  it  as  glycyl-d-alanine.  The  compound  was  isolated  as  a 
polypeptide-ester  and  converted  into  its  anhydride  by  the  action  of  alco- 
holic ammonia.  By  splitting  the  glycyl- alanine  anhydride  we  naturally 
obtain  two  products  depending  on  the  portion  of  the  piperazine  ring 
attacked;  thus,  glycyl-d-alanine  or  d-alanyl-glycine  result,  as  is  indicated  by 
the  following  formula: 

II 

CH2-CO\NH 
NH  (  /^H 

IXCO— CH-CH3 

If  the  ring  is  ruptured  at  I,  we  obtain,  by  the  addition  of  water:  glycyl- 
alanine,  NH2  .  CH2  .  CO  .  NH  .  CH  .  CH3  .  COOH.  If  at  II,  we  get  alanyl- 
glycine,  NH  .  CH  .  CH3  .  CO  .  NH  .  CH2  .  COOH. 

The  anhydride  itself  does  not,  therefore,  give  us  the  answer  regarding 
the  form  of  polypeptide  from  which  it  was  produced.  We  do.  however, 
know  that  alanyl-glycine  is  easily  separated  into  its  constituents  by  trypsin, 
whereas  glycyl-alanine  is  not  acted  upon.  We  may,  therefore,  conclude 
that  the  compound  isolated  was  glycyl-d-alanine.  Then,  again,  this  same 
cleavage-product  is  formed  by  acid  action  —  whether  by  concentrated 
hydrochloric,  or  70  per  cent  sulphuric  acid.  Under  these  conditions,  i.e. 


1  E.  Abderhalden  and  F.  Samuely:  Z.  physiol.  Chem.  47  (1906). 

2  E.  Fischer  and  E.  Abderhalden:  Ber.  39,  752  (1906). 


ALBUMINS  OR  PROTEINS.  187 

in  the  absence  of  proteolytic  action,  a  second  polypeptide  could  be  obtained 
in  the  form  of  its  anhydride;  namely,  glycyl-/-tyrosine  and  Z-tyrosyl- 
glycine.  Finally  it  has  been  found  possible  to  isolate  from  elastin, 
glycyl-Z-leucine  anhydride1  and  d-alanyl-leucine  anhydride;2  furthermore, 
glycyl-d-alanine  has  been  isolated  directly  from  silk,2  and  /-leucyl-d- 
glutamic  acid  prepared  from  gliadin.2  The  most  important  discovery  in 
this  field  is  undoubtedly  the  fact  that  the  tetrapeptide 2  obtained  from 
silk-fibroin,  consisting  of  two  glycine  molecules,  one  of  alanine,  and  one  of 
tyrosine,  shows  properties  with  which  many  albumoses  correspond.  This 
proves  that  the  albumoses  are  not  closely  related  to  the  proteins;  i.e., 
they  are  not  very  complicated  compounds.  In  fact,  the  properties  of  the 
so-called  albumoses  result  from  the  nature  of  the  amino  acids  of  which 
they  are  composed.  In  the  above  case  the  properties  of  Z-tyrosine  are 
evident.  It  will  be  well,  in  the  future,  to  drop  the  name  albumose,  and 
for  the  present  speak  only  of  peptones  which  are  precipitated  by 
ammonium  sulphate  and  of  those  which  are  not.  The  more  complicated 
cleavage-products  are  not  precipitated  by  ammonium  sulphate,  while 
the  ]  simpler  ones,  |  e.g.  tyrosine  '  or  cystine,  are  salted  out  by  this 
reagent. 

There  is  no  doubt  that  other  dipeptides,  and  especially  those  with  longer 
amino  acid  chains,  will  shortly  be  discovered  in  the  same  manner.  The 
train  of  thought  suggested  by  Emil  Fischer's  difficult  researches  concern- 
ing the  constitution  of  the  albumins  has  thereby  received  complete  jus- 
tification. Where  formerly  all  was  darkness,  a  bright  light  has  suddenly 
appeared.  It  is  no  longer  difficult  to  picture  the  whole  subject  of  albumin 
decomposition.  A  whole  array  of  new  problems  is  immediately  suggested 
by  Fischer's  investigations.  While  his  successes  in  developing  the  chem- 
istry of  carbohydrates  and  purines  were  of  tremendous  value  in  advancing 
both  fields  from  a  biological  standpoint,  it  is  doubtless  true  that  his  new 
efforts,  which  are  of  far  greater  biological  importance,  will  result  in  great 
changes  concerning  our  conceptions  of  the  entire  biology  of  the  proteins. 
Much  darkness,  however,  still  surrounds  many  questions. 

We  are  still  incapable  of  interpreting  the  significance  of  the  albumins  as 
food  .for  the  animal  organism.  We  anxiously  await  the  moment  when 
the  fetters  will  be  loosened,  which  for  decades  have  restricted  the  progress 
of  the  whole  subject  of  biology.  We  are  deeply  interested  in  all  problems 
in  connection  with  albumin.  Here  stands  a  large  group  of  ferments  — 
conceptions  with  no  tangible  support.  The  same  applies  to  the  tremen- 
dous number  of  toxins,  anti-toxins,  and  allied  substances.  All  investiga- 
tors of  these  various  subjects  are  anxiously  awaiting  the  solution  of  the 


1  E.  Abderhalden  and  F.  Samuely:  Z.  physiol.  Chem.  47  (1906). 

2  E.  Fischer  and  E.  Abderhalden:  Ber.  39,  752  (1906). 


188  LECTURE  IX. 

problem  of  the  constitution  of  albumin!  They  all  anticipate  new  impulses 
therefrom  —  new  developments;  and,  above  all,  new  methods.  Although 
many  dreams  will  not  come  true  and  many  hopes  may  be  unfulfilled,  the 
biology  of  the  albumins  will,  undoubtedly,  especially  in  the  narrower  sense, 
open  new  fields  of  effort,  and,  when  placed  upon  a  satisfactory  foundation, 
will  show  great  progress. 

Let  us  see  now  what  assumptions  concerning  decomposition  of  the 
albumins  by  ferments  can  be  based  upon  the  above  observations.  We 
have  seen  that  the  first  cleavage-products  of  albumin  are  the  peptones. 
We  can  easily  imagine  that  the  albumin  molecule  breaks  down  in  the 
first  place  into  a  series  of  long  chains  of  amino  acids.  Even  these  may 
be  much  differentiated  among  themselves.  It  is  not  necessary  that  each 
of  these  chains  should  contain  all  the  amino  acids  present  in  the  albumin. 
These  chains  then  break  down  into  cleavage-products  containing  a  smaller 
number  of  amino  acids.  We  can  imagine  hereby  that  a  complicated 
cleavage-product  breaks  down  into  several  simpler  ones,  each  containing 
more  than  one  amino  acid.  Many  observations  indicate,  however,  that 
the  amino  acids  themselves  appear  at  an  early  stage. 

It  is  of  interest  that  practically  simultaneously  with  the  appearance  of 
tyrosine,  cystine,  tryptophane,  etc.,  in  the  digesting  liquid,  those  products 
called  albumoses  diminish  in  amount,  and  finally  disappear.  This  cor- 
responds to  the  observations  made  in  the  breaking  down  of  tetrapeptides. 
As  soon  as  the  tyrosine  is  removed  by  trypsin,  the  albumose  character 
disappears.  Tyrosine  can  be  detected  within  a  few  hours  after  the 
beginning  of  digestion.  Subsequent  decomposition  takes  place  with  the 
constant  production  of  more  amino  acid.  Smaller  chains  are  produced  from 
the  peptones  with  larger  amounts  of  amino  acids,  until  finally  the  greater 
part  of  the  amino  acid  chains  are  decomposed  into  their  constituents.  The 
peptones  are  therefore  to  be  considered  as  a  large  mixture  of  various  kinds 
of  polypeptides.  The  best  distinction  that  we  can  make  is  that  only  those 
polypeptides  belong  to  the  peptone  class  which  will  give  the  biuret  reaction. 
Unquestionably,  the  term  peptone  will  gradually  disappear,  and  we  shall 
eventually  deal  only  with  chemical  individuals. 

We  shall  here  refer,  as  we  now  do  in  the  synthetic  chemistry  of  albumins, 
to  di-,  tri-,  tetra-,  and  polypeptides.  The  biuret  reaction  is  only  used  as  a 
convenience  in  indicating  the  limit  of  the  branching  compounds  to  be 
included  in  the  peptone  class.  The  polypeptides  which  give  this  reaction 
gradually  pass  over  into  those  which  no  longer  do  so.  Between  the 
peptones  of  the  longest  chains  and  the  simple  amino  acids  there  are  con- 
tinuous transitory  stages. 

The  decomposition  of  the  proteids  by  means  of  trypsin  can  be  illustrated 
in  the  following  manner: 


ALBUMINS  OR  PROTEINS, 
etc. — Albumin — etc. 


189 


Polypeptides  of  high  molecular  weight  which  for  the  most  part  still 
contain  all  the  amino  acids 

/\  /\  /\ 

Amino     Poly-  Amino      Poly-   Amino      Poly- 
acid    peptides  acids    peptides    acids  peptides 


Amino  acids 


Decapeptides 


Amino  acids 


Amino  acids 


Decapeptides 

Amino  acids 


Pentapeptide 

|     ^  Amino 
Tetrapeptidev     acid 


Peptone 


\ 


Amino 


Tripeptidev      acid 
I         Amino 


Pentapeptide 

/\ 
Tripeptide       Dipeptide 

/\  /\ 

Amino    Dipeptide   Amino    Amino  acid 
acid  /\         acid 

Amino  acid       Amino  acid 


Dipeptide^     acid 

i        Amino 
acid 

This  is,  of  course,  only  a  scheme,  and  we  are  frank  in  stating  that 
future  investigations  alone  can  establish  its  validity.  Many  other  com- 
binations are  possible.  We  can  easily  imagine  that  the  amino  acid  chains 
also  break  down  in  such  a  manner  that  the  amino  acids  are  not  produced 
immediately,  but  that  chains  are  formed,  containing  only  a  part  of  the 
original  amino  acids  occurring  in  the  polypeptide.  In  this  connection  we 
are  reminded  of  dialanylaspartic  acid.  If  we  assume  that  the  chain  is 
lengthened  from  the  alanine  group,  one  of  the  chains  could  very  easily  be 
split  off,  leaving  an  "  aspartic-acid-mono-polypeptide."  We  must  also 
remember  that  there  are  polypeptides  which  are  evidently  not  affected  by 
the  digestive  ferments.  We  can  very  easily  imagine  such  combination  as 
a  result  of  our  investigations  concerning  the  behavior  of  the  synthetical 
polypeptides  to  the  pancreatic  ferments.  It  is  not  without  interest,  that 
the  mixture  of  polypeptides  observed  in  the  tryptic  digestion  of  albumin 
contained  large  amounts  of  phenylalanine  and  proline,  the  very  acids  from 
which  synthetic  peptides  were  formed  that  resisted  the  action  of  ferments. 

If,  departing  from  the  plan  of  our  lectures,  we  attempt  here  to  unravel 
a  problem  which,  according  to  the  experimental  knowledge  at  hand,  is  not 
yet  fully  ripe  for  discussion,  this  is  done  partly  because  many  discoveries 
give  important  support  to  these  views,  and  largely  because  only  upon  such 
a  foundation  are  we  able  to  obtain  a  clearer  understanding  of  the  breaking 


190  LECTURE  IX. 

down  and  building  up  of  albumin  in  the  animal  organism.  By  means  of 
such  a  progressive  decomposition  the  cell  is  able  to  transform  and  build 
up  anew  the  albuminous  material  that  reaches  it,  so  that  it  is  suited  for  all 
the  requirements  of  the  cell-content.  It  is  not  difficult  to  understand  how 
from  a  definite  compound-albumin  all  sorts  of  different  proteins  may  be 
prepared  containing  the  various  amino  acids  in  proportions  quite  different 
from  those  in  the  original  mother  substance.  It  is  not  necessary  that 
such  a  transformation  should  involve  a  complete  reduction  of  the  original 
protein  to  its  fundamental  constituents;  a  partial  decomposition  may 
answer  all  requirements.  Although  the  details  of  fermentation  are 
not  yet  definitely  known,  we  can,  however,  consider  the  fundamentals  of 
protein  decomposition  as  fairly  well  established.  We  can  also  point  out 
the  very  close  analogy  to  the  disintegration  of  the  polysaccharides.  We 
know  that  starch,  before  it  is  converted  into  dextrose,  undergoes  many 
intermediate  transformations,  concerning  the  exact  nature  of  which  we  are, 
up  to  the  present  time,  as  much  in  darkness  as  we  are  in  regard  to  the  albu- 
moses  and  peptones.  We  are  only  able  to  recognize  the  former  as  mixtures, 
calling  them  dextrins.  The  first  definite  chemical  cleavage-product  is  the 
disaccharide  maltose.  The  dextrins,  which  we  still  consider  as  com- 
plicated polysaccharides,  correspond  to  the  peptones.  The  dextrins  and 
related  compounds  may  very  easily  be  considered  as  mixtures  of  long 
chains  of  dextrose  molecules.  The  maltose  would  then  correspond  to  a 
dipeptide.  The  conditions  in  the  carbohydrates  are  comparatively  simple, 
because  starch  is  considered  as  composed  of  a  series  of  only  one  kind  of 
molecular  combination,  i.e.,  dextrose,  —  whereas,  with  the  albumins,  there 
are  many  different  fundamental  substances.  On  the  other  hand,  we  are 
also  acquainted  with  proteins  —  like  the  protamine,  salmin  —  which  are  of 
simple  construction,  being  mainly  composed  of  arginine,  while  we  also  know 
of  polysaccharides  in  the  vegetable  world  which  are  not  far  behind  the 
proteins  as  regards  complexity.  As  an  example  of  a  "  mixed  "  disaccharide, 
we  have  cane-sugar,  which  breaks  down  into  one  molecule  of  dextrose  and 
one  of  laevulose,  and  also  to  mannorhamnose,  which  splits  into  one 
molecule  of  mannose  and  one  of  rhamnose. 

We  are  also  acquainted  with  mixed  trisaccharides.  On  hydrolyzing 
rhamninose,  a  glucoside  occurring  in  the  fruit  of  Rhamnus  infectoria,  two 
molecules  of  rhamnose  and  one  of  d-glucose  are  obtained.  Gentianose, 
from  varieties  of  Gentiana,  contains  two  molecules  of  glucose  and 
one  molecule  of  fructose.  We  know  of  a  large  number  of  poly- 
saccharides, in  whose  constitution  many  sugar  varieties  participate:  pen- 
toses,  methylpentoses,  hexoses,  etc.  We  only  mention  these  examples 
to  illustrate  the  analogy  between  the  polysaccharides  and  the  proteins. 
A  very  large  number  of  combinations  are  possible  by  using  many  different 
constituents.  The  ^proteins  predominate  in  the  animal  organism.  They 


ALBUMINS  OR  PROTEINS.  191 

are  characteristic  of  the  individual  tissues.  The  secret  of  the  individuality 
of  the  various  cells  undoubtedly  depends  on  their  configuration.  Every 
species,  every  variety, —  in  fact,  every  individual, —  has  its  own  "  albu- 
min." According  to  this  conception,  the  carbohydrates  are  of  less  sig- 
nificance to  the  animal  organism.  They  are  essentially  food  materials, 
and  are  necessarily  but  a  small  factor  in  the  production  of  animal  tissues. 
It  is  entirely  different  when  we  consider  the  vegetable  kingdom.  The 
carbohydrates  predominate  here.  They  construct  the  plant  tissues,  and 
all  the  numerous  living  processes  are  dependent  on  their  presence.  Hence 
their  variety,  and  their  production  from  the  heterogeneous  elements. 
Carbohydrates,  as  regards  their  entire  physiological  significance  and  their 
composition,  are  to  the  vegetable  world  what  the  protein  substances  are  to 
the  animal  organism. 

The  greater  the  number  of  amino  acids  participating  in  the  composition 
of  a  protein,  the  wider  the  uses  to  which  that  protein  can  be  put.  On 
the  other  hand,  the  simpler  the  function  of  the  protein,  the  more  dominant 
becomes  one  or  the  other  of  the  amino  acids.  Fibroin  from  silk,  for 
instance,  contains  36  per  cent  glycocoll,  and  over  20  per  cent  alanine; 
elastin  gives  us  26  per  cent  glycocoll,  and  over  10  per  cent  leucine;  gliadin, 
a  "  reserve  albumin  "  of  plants,  contains  over  30  per  cent  glutamic  acid; 
while  in  the  protamines  we  often  find  over  80  per  cent  arginine.  It  would, 
of  course,  be  wrong  to  compare  these  albuminous  bodies  with  others,  and 
say  that  they  were  simple  in  composition.  They  are  simply  more  homo- 
geneous. Whether  the  amino  acids  grouped  together  are  all  of  a  kind  or 
much  diversified,  has  but  little  bearing  on  the  question  of  their  constitu- 
tion or  configuration. 

The  observation  that  the  pancreatic  ferment  does  not  attack  some  of 
the  synthetic  polypeptides,  and  the  discovery  that  during  the  digestion  of 
proteins  many  complicated  cleavage-products  remain,  which  still  contain 
large  percentages  of  glycocoll,  phenylalanine,  and  /-proline,  leads  us  to  con- 
clude that  the  animal  organism  utilizes  such  groups,  or  similar  ones,  as  a 
foundation,  or  back-bone,  for  building  up  new  albuminous  substances.  It 
is  certainly  of  some  significance  that  elastin  contains  so  much  glycocoll  and 
leucine.  The  combination  leucyl-glycine,  on  the  other  hand,  is  obviously 
unacted  upon  by  trypsin.  Silk  also  contains  such  compounds,  as  is  shown 
by  the  discovery  of  glycyl-d-alanine  in  it.  The  cell  can  protect  itself  by 
forming  just  such  combinations.  The  fact  that  most  vigorous  fermenta- 
tion processes  are  continually  taking  place  in  the  cell,  and  that  in  spite  of 
this  the  cell  retains  its  own  constituents  —  its  amour  —  intact,  becomes 
much  more  comprehensible  to  us  from  such  considerations. 

The  significance  of  Emil  Fischer's  synthetic  polypeptides  lies,  moreover, 
in  still  another  direction.  Up  to  the  present  time  it  has  not  been  possible 
to  test  the  proteolytic  ferments  as  to  their  homogeneity.  We  have  to 


192  LECTURE  IX. 

content  ourselves  with  a  knowledge  of  their  methods  of  action.  There  is  no 
doubt  that  with  the  assistance  of  these  synthetic  polypep tides,  new  questions 
will  arise  in  this  connection  and  will  probably  be  solved.  We  shall  be 
able  to  determine  whether  the  various  kinds  of  animals  possess  the  same 
kinds  of  proteolytic  ferments,  or  those  which  act  differently.  We  are 
inclined  to  the  latter  belief,  at  least  in  special  cases.  We  know  that  the 
feathers  of  birds  and  the  hair  of  the  Mammalia  are  subjected  to  the 
inroads  of  parasites,  being  eaten  up  by  them.  These  minute  animals  must 
possess  much  more  vigorous  proteolytic  ferments  than  have  been  vouch- 
safed to  us,  because  the  keratins  are,  so  far  as  we  know,  entirely  indi- 
gestible by  vertebrates.  We  also  hope  to  obtain  a  complete  explanation 
of  the  differences  between  the  action  of  trypsin  and  of  pepsin  by  studying 
the  relations  of  these  proteolytic  ferments  toward  the  polypeptides.1  Up 
to  the  present  time  none  of  the  synthetic  peptides  have  been  acted  upon 
by  pepsin.2  It  is  possible  that  the  amino  acid  chains  utilized  were  not 
long  enough.  In  fact,  pepsin-hydrochloric  acid  seems  to  decompose  albu- 
min in  a  manner  entirely  different  from  that  characteristic  of  trypsin.3 
Evidently  peptones,  and  other  cleavage-products  which  do  not  give  the 
biuret  reaction,  are  produced.  There  are,  however,  no  amino  acids 
formed.1  The  significance  of  gastric  digestion  is  still  quite  obscure. 
It  may  possibly  be  that  it  causes  a  preparatory  cleavage  of  the  albumins, 
so  that  the  trypsin  has  more  opportunity  to  act.  It  can  also  be  shown 
experimentally  that  tryptic  digestion  is  hastened  and  proceeds  much 
farther,  if  a  pepsin-hydrochloric  acid  one  precedes  it. 

With  the  assistance  of  the  polypeptides  we  also  hope  to  get  an  insight 
into  cell  metabolism.  It  has  already  been  demonstrated  that  the  tissues, 
especially  the  liver,  contain  proteolytic  ferments,  which  are  capable  of 
dissolving  bonds  between  amino  acids  that  are  unattacked  by  trypsin. 
Thus,  an  extract  from  the  liver  will  split  glycyl-glycine  completely  into 
its  components.4  By  extending  these  investigations  to  include  the  various 
organs,  we  will  ultimately  succeed  in  finding  those  which  are  the  most  import- 
ant factors  in  the  decomposition  of  the  albumins.5  The  polypeptides  will 
also  be  of  great  service  to  us  for  comparative  purposes.  It  will  be  of  the 
greatest  interest  to  learn  whether  the  representatives  of  the  various  ani- 
mal classes  will  disintegrate  the  individual  polypeptides  in  the  same  manner, 
or  whether  there  will  be  differences  in  the  decomposition  products. 

From  all  these  problems  it  is  at  once  obvious  how  important  is  the 
synthetic  linking  together  of  the  amino  acids  into  the  polypeptides  for  all 
branches  of  biological  science. 

1  E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  47  (1906). 

2  E.  Fischer  and  E.  Abderhalden:  ibid.  46,  52  (1905). 

3  E..  Fischer  and  E.  Abderhalden:  ibid.  40,  215  (1903).     F.  Obermeyer  and  E.  P. 
Pick:  Hofmeister's  Beitr.  7,  331  (1905). 

4  E.  Abderhalden  and  O.  Rostoski:  ibid.  44,  265  (1905). 

5  E.  Abderhalden  and  Y.  Teruuchi:  Z.  physiol.  Chem.  47,  1906. 


LECTURE   X. 

ALBUMINS    OR   PROTEINS. 
IV. 

DEGRADATION   AND   FORMATION   OF    PROTEIN   IN   THE    ANIMAL    AND 
VEGETABLE   ORGANISMS. 

IT  will  be  necessary  to  learn  something  about  the  origin  of  the  proteins 
in  our  food,  before  proceeding  to  discuss  the  behavior  of  such  substances 
when  taken  into  the  animal  organism,  their  decomposition  in  the  alimen- 
tary tract,  their  absorption  and  assimilation,  and  the  end-products  result- 
ing from  their  combustion.  The  animal  organism,  as  we  shall  see  later, 
is  only  capable  of  synthesizing  its  albumins  from  the  same  material,  or 
from  its  immediate  decomposition  products.  It  is  incapable  of  utilizing 
inorganic  nitrogenous  compounds  to  produce  its  albumins,  and  similarly 
the  animal  cells  cannot  synthesize  the  albumins  from  organic  nitrogen- 
ous substances,  unless  these  are  related  directly  to  the  albumins  them- 
selves. The  animal  organism  is  entirely  dependent  on  the  vegetable 
kingdom  for  its  albumin  requirements.  The  plants  prepare  the  proteins 
for  it. 

When  living  material,  whether  it  be  vegetable  or  animal,  decays,  its 
organic  constituents  undergo  putrefaction.  Ammonia,  in  large  amount, 
is  finally  produced  from  nitrogenous  compounds.  This  is  changed  into 
nitric  acid  in  the  soil,  nitrates  resulting.  The  formation  of  saltpeter  in 
the  soil  is  a  process  which  has  been  known  for  a  long  time.  Even  H. 
Davy  l  was  aware  of  the  production  of  nitrates  at  the  expense  of  ammonia 
and  atmospheric  oxygen.  It  was  eventually  discovered  that  the  process 
of  forming  saltpeter,  also  called  "  nitrification,"  was  due  to  the  vital 
activity  of  microbes.  The  pure  culture  of  these  organisms  followed  much 
later.2  This  was  due  to  the  fact  that  the  bacteria  possess  the  peculiar 
ability  of  thriving  on  an  exclusively  inorganic  nutrient  medium,  as  was 
shown  by  Hueppe  3  and  Heraeus.4 

They  satisfy  their  nitrogen  and  carbon  requirements  from  ammonium 


1  Elements  of  Agricultural  Chemistry,  1814. 

2  S.  Winogradsky:  Compt.  rend.  110,  1013  (1890). 

3  Tageblatt  Naturforscher-Versammlung  Wiesbaden,  1887. 

4  Zentr.  Bakt.  3,  Nr.  13  (1887). 

193 


194  LECTURE  X. 

carbonate.1  Nitrification  is  not  a  simple  process.  It  requires  the  simul- 
taneous activity  of  several  varieties  of  bacteria.  One  oxidizes  the  ammonia 
to  nitrite,  and  another  converts  the  nitrite  into  nitrate.  The  nitrifying 
bacteria  are  found  everywhere.  They  play  an  extremely  important  part 
in  the  economy  of  nature.  They  effect  the  nitrogen  cycle. 

Even  the  nitrogen  which  the  animal  organism  utilizes  for  its  nutrition, 
is  finally  returned  to  the  ground  again  as  ammonia.  We  shall  see  later 
that  the  largest  part  of  albuminous  nitrogen  reappears  in  the  form  of  urea 
in  the  urine  of  mammals.  Under  the  action  of  specific  bacteria  this  is 
broken  down  into  ammonia,  which  is  then  converted  into  nitrates.  The 
plants  utilize  this  anew  for  the  synthesis  of  albumins,  and  the  nitrogen 
completes  its  cycle  of  usefulness,  first,  in  the  form  of  inorganic,  and  then  as 
organic  compounds.  This  process  is  not  as  simple  in  practice  as  the 
statement  indicates.  A  large  amount  of  free  nitrogen  is  produced  simul- 
taneously with  the  combined  nitrogen.  When  nitrogenous  organic  mate- 
rial undergoes  combustion,  free  nitrogen  is  obtained  as  well  as  ammonia. 
The  amount  of  the  former  may  be  very  considerable  under  favorable 
conditions.  This  is  the  case  when  the  combustion  is  carried  put  at  a  high 
temperature  with  a  liberal  supply  of  air.  Nitrogen  is  also  liberated  in 
large  quantity  by  the  explosion  of  gunpowder.  It  is  liberated  not  only  by 
artificial  processes,  but  also  through  the  intermediacy  of  organisms  occur- 
ring in  nature.  To  be  sure  the  assumption  that  free  nitrogen  is  liberated 
in  the  metabolism  of  higher  plants  has  been  disproved  by  exact  investi- 
gations, just  as  the  oft-repeated  question  as  to  whether  nitrogen  is  elim- 
inated as  such,  from  albuminous  material  in  the  animal  organism,  has 
been  answered  in  the  negative.  We  are  acquainted  on  the  other  hand 
with  a  large  number  of  organisms  of  common  occurrence  which  are  incapable 
of  liberating  nitrogen  from  organic  compounds,  but  can  do  so  from  nitrates. 
This  process,  also  called  denitrification,  has  been  known  for  a  long  time. 


1  It  may  be  interesting  to  note  that  there  are  also  other  organisms  capable  of  utilizing 
inorganic  instead  of  organic  materials.  The  group  of  sulphur  bacteria  is  best  known. 
Kernels  of  sulphur  are  found  in  their  cell-bodies.  They  thrive  in  sulphur  springs  and 
produce  therein  a  characteristic  flora.  They  constitute  the  group  of  Beggiatoa,  and  are 
aerobic.  The  Beggiatoa  are  capable  of  oxidizing  sulphuretted  hydrogen,  when  in  the 
presence  of  oxygen,  to  sulphur.  The  stored-up  sulphur  is  then  further  utilized  in  the 
cells,  sulphuric  acid  being  formed,  which  seems  to  be  their  characteristic  product. 
They  need  only  small  amounts  of  organic  material.  During  the  oxidation  of  a  gram- 
molecule  sulphuretted  hydrogen  to  sulphuric  acid,  62.4  cal.  of  heat  energy  are  obtained 
by  the  bacteria. 

Many  thread-bacteria,  especially  Leptothrix  ochracea,  form  other  examples.  They 
oxidize  ferrous  carbonate  into  a  ferric  salt,  which  is  decomposed  with  the  formation  of 
ferric  hydroxide.  Winogradsky,  to  whom  we  owe  our  knowledge  of  these  sulphur  and 
iron  bacteria,  suggests  the  possibility  of  the  latter  participating  in  the  formation  of 
bog-ore  deposits. 


ALBUMINS  OR  PROTEINS.  195 

Davy  l  called  attention  to  the  fact  that  gaseous  nitrogen  was  set  free 
from  decomposing  organic  material  in  the  soil.  Gayon  and  Dupetit 2 
were,  however,  the  first  to  announce  that  the  nitrogen  originated  from 
the  nitrates.  Since  that  time  a  large  number  of  bacteria  have  been  isolated 
which  produced  nitrogen  from  nitrates.  Gayon  and  Dupetit  cultivated 
two  varieties  of  anaerobic  bacteria  from  the  soil,  which  they  called  bacterium 
denitrificans,  a  and  /?.  Denitrifying  bacteria  can  live  without  oxygen. 
They  utilize  the  nitrates  as  a  source  of  energy.  They  work,  in  a  sense,  in 
constant  opposition  to  the  nitrifying  bacteria.  With  a  liberal  supply  of 
oxygen  the  latter  will  predominate,  while  if  the  oxygen  supply  be  dimin- 
ished, the  reverse  will  be  true.  There  is  no  doubt  but  that  appreciable 
amounts  of  nitrogen  are  being  continually  set  free.  Nitrogen  would  be 
constantly  withdrawn  in  this  way  from  the  organized  world  were  it  not 
for  the  fact  that  other  processes  are  at  work  to  recombine  it.  We  also 
know  that  atmospheric  nitrogen  and  oxygen  are  combined  under  the  influ- 
ence of  electrical  discharges,  producing  nitric  acid.  The  amount  of  nitrogen 
combined  in  this  manner  must  necessarily  be  small.  It  is  certainly  insig- 
nificant in  comparison  with  the  production  of  nitrogen  from  other  sources. 
During  recent  years  various  bacteria  have  been  isolated  which  possess  the 
faculty  of  assimilating,  or  "  fixing,"  the  atmospheric  nitrogen.  Berthellot 3 
first  called  attention  to  this  process.  He  found  an  enrichment  of  soils 
which  were  free  from  higher  plants,  and  whose  only  source  of  nitrogen 
was  the  atmosphere.  Winogradsky  4  was  the  first  to  succeed  in  isolating 
a  bacterium  which  was  capable  of  fixing  nitrogen  directly  from  the  air. 
This  was  the  anaerob  Clostridium  Pasteurianum.  Winogradsky  showed 
that  a  culture  of  this  bacillus,  shut  off  from  every  other  source  of  nitrogen 
except  the  air,  was  capable  of  assimilating  24 . 7-28 . 9  grams  nitrogen  in 
15-20  days.  It  is  interesting  to  note  that  this  Clostridium  is  not  found 
alone,  but  is  accompanied  by  two  aerobic  bacteria.  Evidently  this  is  a 
case  of  symbiosis.  The  aerobic  bacteria  remove  the  oxygen  which  is 
deleterious  to  the  development  of  the  Clostridium.  They  undoubtedly 
receive  nitrogenous  material  from  the  latter  in  return.  Since  this  dis- 
covery other  bacteria  have  been  isolated,  which  possessed  the  ability  of 
assimilating  free  nitrogen.  Kr tiger  and  Schneidewind  5  describe  a  bacte- 
rium, a  culture  of  which  in  62  days  converted  4 . 6-8 . 5  grams  atmospheric 
nitrogen  into  albuminous  nitrogen.  It  is  noteworthy  that  the  Clostridium 
has  been  found  in  the  slime  of  ocean  bottoms,  and  in  the  plankton  of  salt 


1  Elements  of  Agricultural  Chemistry. 
3  Compt.  rend.  95,  644  (1882). 

3  Ibid.  101,  775  (1885);  104,  205  and  625  (1887);  106,  569,  1049,  1214  (1888);  107, 
372  (1888) ;  108,  700  (1889) ;  109,  277  and  417  (1889) ;  115,  569  (1892) ;  116,  842  (1893). 

4  Compt.  rend.  116,  1385  (1893);  118,  353  (1894). 
6  Landwirtsch.  Jahrb.  29,  801  (1900). 


196  LECTURE  X. 

and  fresh  water.  The  following  observations  of  Ktihn  l  are  mentioned  to 
give  an  idea  of  the  significance  of  the  activity  of  these  nitrifying  bacteria. 
A  field,  which  for  twenty  years  had  not  had  any  nitrogenous  fertilizer 
added  to  it,  gave  an  average  return  of  1976  kilograms  of  grain  per  hectare. 
Not  only  was  there  no  decrease  in  the  annual  yield  due  to  the  gradual 
removal  of  the  nitrogen  of  the  soil,  but  it  actually  showed  an  increase  of 
11.6  per  cent  in  grain  produced.  There  was  annually  withdrawn  from  a 
hectare  of  land  in  crops  of  rye,  from  25-30  kilograms  of  nitrogen.  This 
amount  of  nitrogen  must  have  been  taken  from  the  air  and  transferred  to 
the  soil.  Even  the  fallen  leaves  in  forests  assimilate  nitrogen  by  the  activity 
of  the  bacteria  contained  within  themselves.  It  is  not  at  all  impossible 
that  these  bacteria  are  the  pioneers  in  converting  decomposed  rock  into 
arable  land. 

It  is  a  well-known  fact  that  some  plants,  for  instance  the  legumes, 
enrich  the  soil  with  nitrogen,  while  others  only  deplete  it.  The  practical 
farmer  utilizes  this  fact  by  not  planting  cereals  year  after  year  on  the  same 
soil,  but  rotates  the  legumes  and  the  grains.  Hellriegel 2  and  Willfarth  3 
have  satisfactorily  explained  the  whole  subject  as  a  result  of  their  experi- 
ments. They  proved  that  the  legumes  assimilated  the  nitrogen,  and 
showed  that  this  formation  was  intimately  connected  with  the  enlarge- 
ments of  the  so-called  "  root-nodules  or  tubercles  "  of  these  plants.  It  was 
also  shown  that  the  legumes  could  be  made  to  grow  nodules  on  sterilized 
soil  if  infusion  of  ordinary  soil  be  sprinkled  over  it.  There  must  evidently 
be  micro-organisms  present  in  the  soil  which  cause  the  formation  of  these 
nodules.  The  infusion  obtained  from  the  soil  loses  its  activity  on  being 
heated.  The  gramince  act  entirely  different.  They  are  not  influenced  in 
their  consumption  of  nitrogen  by  any  infusion  from  the  soil.  Their  nitrogen 
assimilation  is  dependent  on  the  nitrates  already  present  in  the  soil.  Free 
nitrogen  is  of  no  service  to  them.  The  legumes,  on  the  other  hand,  are 
entirely  independent  of  'any  increase  of  nitrates.  If  the  legumes  are 
grown  in  sterilized  soil,  they  behave  like  the  graminse.  They  lose  the 
faculty  of  fixing  the  free  nitrogen,  and  rely  entirely  upon  the  nitrates  in  the 
soil.  The  following  experiments  are  referred  to  as  illustrating  the  assim- 
ilation of  nitrogen  through  the  nodules  of  the  legumes.  Schloesing  and 
Laurent 4  cultivated  legumes  in  sterilized  soil  and  in  sterilized  glass  cyl- 
inders. The  amounts  of  carbon  dioxide,  oxygen  and  nitrogen  in  the  air 

1  Fruhlings  landw.  Ztg.  p.  2,  1901;  quoted  by  F.  Czapek:  Biochemie  der  Pflanzen: 
G.  Fischer,  p.  131,  1905. 

2  Tageblatt  Naturforscher-Vers.  Berlin,  1886,  p.  290. 

3  Tageblatt  Naturforscher-Vers.  Berlin,  Wiesbaden,  1887,  p.  362 ;  Zeit.  Ver.     Riiben- 
zuckerind.  Beilageheft,  1888,  p.  234,  and  Ber.  botan.  Ges.  7,  138  (1889).     For  further 
literature  see  J.  Vogel:  Zent.  Bakt.  u.  Parasitenkunde  15,  11,  33,  1905. 

4  Compt.  rend.  Ill,  750  (1890);  113,  776(1891);  115,  881,  1017  (1892) ;  Ann.  Inst. 
Pasteur.  6,  65  and  824  (1892). 


ALBUMINS  OR  PROTEINS. 


197 


present  were  exactly  known.  Sterilized  water  was  added  in  one  experi- 
ment, while  the  others  were  watered  with  infusions  of  powdered  nodules. 
Three  months  later  the  air  was  removed  from  the  cylinders  and  the  amounts 
of  nitrogen  present  estimated.  It  was  found  that  it  was  diminished  only 
in  those  cases  where  nodule  extractions  had  been  added.  Two  of  these 
experiments  in  which  root  nodule  infusions  were  used  gave  the  following 
values: 


I 

II 

Nitrogen  present  in 
periment 

air  at  beginning  of  ex- 

2681.2  cm.3 

2483.3  cm.3 

Nitrogen  present  in 
Nitrogen  pbsorbed 

air  at  end  of  experiment  . 

2652.1  cm. 
{  _  29.1  cm. 

2457.4cm. 
(  _      25.9cm. 

}       36.5mg. 

(          32.5mg. 

The  nitrogen  absorption  can  be  shown  even  better  by  the  following 
table.  In  experiment  III  there  were  no  root  nodules  present,  whereas 
I  and  II  contained  these: 


I 

II 

III 

Nitrogen  in  the  soil  and  in  the  leguminous 
seeds  (peas)  at  the  start  
Nitrogen  in  the  soil  at  the  end  
Nitrogen  taken  up  by  the  plants  . 

32.6  mg. 
73.2  mg. 
40  6  mg 

32.5  mg. 
66.6  mg. 
34  1  me 

32.5  m?. 
33.1  mg. 
0  6  mg 

These  root  nodules  contain  bacteria,  as  has  been  proved  by  Beijerinck.i 
They  live  in  symbiosis  with  the  cells  of  the  nodules.  Beijerinck  names  the 
bacillus  B.  radicicola.  It  is  widely  distributed  in  land  and  water.  Recent 
investigations  indicate  that  this  nitrifying  organism  is  not  a  separate 
individual.  It  seems  as  if  various  bacilli  are  assigned  to  the  different 
varieties  of  Papillionacce.  Successful  inoculations  of  the  nodules  have  only 
been  possible  with  closely  related  members  of  this  family.  For  instance, 
we  have  not  succeeded  in  forming  nodules  on  the  robinia  roots  by  means 
of  the  bacteria  from  peas.  It  is  also  very  interesting  to  note  that  Soja 
Hispida  very  often  fails  to  produce  nodules  in  European  gardens,  but  will 
do  so  when  impregnated  with  Japanese  earth.  To  indicate  the  impor- 
tance of  these  discoveries  we  may  add  that  the  nodule  bacteria  have  become 
an  article  of  commerce. 

It  is  problematical  whether  these  nodule  bacteria  are  restricted  to  the 
Papillionacce.  There  are  indications  that  they  are  also  found  in  other 
plant  species.  They  are  believed  to  be  present  in  the  Rhinantacce,  Elceag- 


1  Bot.  Zeit.  (1888)  p.  725. 


198  LECTURE  X. 

nac(E,  Cycadece,  Coniferce,  etc.  The  assumption  has  also  been  made  that 
the  hypomycetes,  which  often  exist  symbiotically  with  the  roots  of  higher 
plants,  have  a  similar  function  to  that  of  the  nodules.  These  experiments 
have  not  yet  been  completed.  Many  observations  on  the  wild  plants 
seem  to  indicate  a  wider  distribution  of  such  symbioses.  We  know  of 
many  plants  which,  year  by  year,  always  grow  in  the  same  spot  with  the 
usual  profusion,  while  many  others  suddenly  spring  up  and  after  a  short 
"  period  of  blossoming  "  gradually  fade  away.  In  this  way  the  dominant 
species  in  a  meadow,  and  especially  in  a  dump-heap,  may  follow  one  another 
in  rapid  succession,  probably  because  these  short-lived  plants  rely  exclu- 
sively on  the  nitrates  of  the  soil. 

It  is  of  great  importance  to  us  in  considering  this  subject  to  realize 
that  nature  possesses  ways  and  means  of  assimilating  the  free  nitrogen 
of  the  air.  On  the  one  hand,  nitrogen  is  set  free;  and  on  the  other,  it  is 
recombined.  We  are  not  prepared  to  state  the  relations  existing  between 
these  two  processes,  —  whether  they  maintain  an  equilibrium,  or  whether 
the  liberation  of  nitrogen  far  exceeds  that  of  recombination.  It  would 
be  very  interesting  to  know  the  compounds  into  which  these  organisms 
convert  the  nitrogen.1  At  present  we  have  no  knowledge  concerning  this. 
We  assume  that  the  final  substance  produced  is  albumin,  which  is  then,  in 
part,  assimilated  by  the  plants  with  the  help  of  fermentation. 

The  discovery  that  ordinary  nitrogen  can  be  directly  assimilated  closes 
the  chain  of  the  nitrogen  cycle,  which  had  apparently  been  broken  open  by 
the  discovery  of  the  denitrifying  organisms.  We  have  forgotten  to  men- 
tion one  point.  We  shall  see  later,  when  considering  the  inorganic  nutrient 
materials,  that  the  earth  possesses  the  power  of  "  fixing  "  certain  constitu- 
ents. This  applies,  for  instance,  to  the  important  elements,  phosphorus, 
potassium,  ammonia,  etc.,  which  are  so  necessary  for  the  develop- 
ment of  the  plants.  As  soon  as  their  solutions  come  in  contact  with  cer- 
tain constituents  of  the  earth  they  are  changed  into  insoluble  compounds, 
and  are  thus  protected  from  being  washed  away  by  rain-water.  The  salts 
of  nitric  acid,  the  nitrates,  behave  quite  differently.  They  are  not  absorbed 
by  the  earth.  They  are  readily  soluble  in  water,  and  are  continually  being 
washed  away,  carried  to  brooks  and  streams,  and  finally  appear  in  the  ocean. 
The  amount  of  nitrogen  abstracted  yearly  from  the  soil  in  this  manner 
is  really  enormous.  K.  Brandt2  estimates  it  at  40,000,000  kilograms 
per  year.  We  are  confronted  with  the  question  of  how  this  large  amount 
of  nitrogen  is  returned  to  the  general  nitrogen  cycle.  That  this  must  take 


1  Recently  it  has  been  found  possible  to  convert  technically  large  amounts  of  atmos- 
pheric nitrogen  into  its  compounds. 

2  Wissenschaftlichen  Untersuchungen.     Report  of  the  Kommission  zur  Untersuchung 
der  deutschen  Meere,  1899  and  1901.     Cf.  also,  E.  Schulze:  Schweizer.  landwirtschaftl. 
Zentralblatt.  1902. 


ALBUMINS  OR  PROTEINS.  199 

place  is  evident  from  the  fact  that  the  vegetation  which  has  grown  for 
thousands  of  years  still  continues  doing  so  in  the  customary  manner,  in 
spite  of  the  leaching  of  the  mainland  which  has  taken  place.  There  is 
practically  no  difference  in  the  behavior  of  the  plants  and  animals  of  the 
ocean  and  those  of  the  mainland.  Marine  plants  assimilate  carbon  dioxide; 
this  process  also  requires  the  assistance  of  the  sun's  energy,  which  accounts 
for  the  absence  of  plant  life  at  great  depths  to  which  the  sun's  rays  cannot 
penetrate.  Marine  plants  also  require  nitrates  for  the  formation  of  their 
albuminous  constituents.  The  fishes  in  the  ocean  also  obtain  their  albu- 
min ultimately  from  the  vegetable  world.  Marine  vegetation  is  incapable 
of  utilizing  all  of  the  immense  amounts  of  nitrogen  presented  to  it.  Nitro- 
genous compounds  are  set  free  from  dead  plants  and  animals  through 
putrefactive  processes.  These  are  changed  into  ammonia,  which  then  goes 
over  into  nitrites  and  nitrates  in  the  same  manner  as  on  the  mainland. 
The  ocean  occasionally  casts  large  masses  of  sea-weed  on  the  shores.  The 
amount  of  nitrogen  from  this  source  is  infinitesimal  in  comparison  with  that 
leached  from  the  soil.  It  is,  therefore,  of  great  interest  to  learn  that  the 
ocean  also  possesses  denitrifying  bacteria,  which  are  continually  setting 
nitrogen  free.  They  complete  the  cycle  of  the  nitrogen  washed  into  the 
ocean  as  nitrogen  compounds. 

The  significance  of  the  great  value  of  the  denitrification  process  now 
becomes  apparent,  in  contradistinction  to  its  undesired  appearance  in  the 
soil.  The  great  part  which  the  nitrogen-assimilating  bacteria  play  in 
nature,  is  now  explained.  The  living  requirements  of  the  whole  world  of 
organisms  guarantee  an  interchange  of  material!  These  smallest  living 
beings  furnish  us  with  the  fundamental  requirements  of  our  existence. 
The  discovery  of  the  denitrifying  bacteria  has  also  solved  an  apparent 
contradiction.  It  is  well  known  that  the  concentration  of  plant  and 
animal  life  on  the  mainland  diminishes  from  the  equator  towards  the 
poles.  This  is  not  the  case  in  the  ocean.  This  circumstance  is  very  strik- 
ing, as  one  would  be  led  to  expect  much  better  development  of  conditions 
in  the  tropical  seas,  owing  to  the  great  preponderance  of  light,  in  com- 
parison with  the  dark  arctic  regions.  It  is  probable  that  this  state  of 
affairs  may  be  traced  to  the  denitrifying  bacteria  in  some  manner.  A 
tropical  environment  is  ideal  for  them  and  their  activities.  They  develop 
to  best  advantage  at  a  temperature  of  25°-30°C.  They  would,  there- 
fore, abstract  more  nitrogen  from  marine  plants  in  tropical  seas,  than  in 
the  seas  of  the  arctic  zone.  We  will  at  once  state  that  this  is  merely  offered 
as  an  explanation.  We  know  that  the  growth  of  all  organisms  is  governed 
by  the  Law  of  the  Minimum,  i.e.,  of  all  the  substances  which  are  accessible 
to  the  organism,  the  amount  utilized  is  governed  by  the  amount  of  that 
substance  present  to  the  smallest  extent.  While  the  marine  plants  may 
have  a  large  quantity  of  available  nitrogen  in  the  form  of  nitrates,  it  may 


200  LECTURE  X. 

be  that  the  supply  of,  say,  phosphorus,  for  example,  is  unusually  small. 
The  plants  would  then  only  be  capable  of  utilizing  the  nitrates  in  propor- 
tion to  the  amount  of  phosphorus  present.  It  is  perhaps  possible  that 
the  conditions  of  nourishment  are  different  in  different  zones. 

In  any  case,  the  free  nitrogen  in  organic  nature  plays  an  exceedingly 
important  part  in  the  nitrogen  cycle.  The  amounts  of  nitrogen  produced 
artificially,  whether  by  the  combustion  of  organic  substances  or  by  the 
explosion  of  gunpowder,  although  large,  to  be  sure,  have  little  effect  upon 
the  equilibrium  of  the  nitrogen  cycle.  Such  amounts  are  in  time  recom- 
bined  and  again  take  part  in  the  natural  cycle. 

Albumin  contains,  besides  nitrogen,  also  carbon,  hydrogen,  and  sulphur. 
We  have  already  pointed  out  the  central  position  that  the  carbohydrates 
in  the  plant  organism  play  in  the  assimilation  of  carbon  dioxide,  and  called 
attention  to  the  fact  that  it  evidently  forms  the  starting  point  of  the  syn- 
thesis of  albumin.  In  another  place  we  shall  go  into  this  matter  more  in 
detail.  Here  we  shall  merely  suggest  that  certain  relations  are  known 
to  exist  between  the  simple  carbohydrates  and  individual  amino  acids,  so 
that  we  can  easily  understand  the  formation  of  the  latter  from  the  former. 
Thus  carbon  and  hydrogen  for  the  synthesis  of  albumin  originate  in  the 
air  and  water.  In  this  form  the  animal  organism  gives  back  these  elements 
to  the  vegetable  kingdom  again. 

The  plants  obtain  their  sulphur  from  the  soil,  in  which  this  element  is 
present  as  sulphates  of  the  alkalies  and  alkaline  earths.  Plants  utilize 
sulphur  almost  exclusively  for  the  formation  of  albumin,  and  it  also  reaches 
the  animal  organism  in  this  form.  In  the  animal,  this  sulphur  is  largely 
converted  into  sulphuric  acid,  and  given  back  to  the  general  cycle  in  the 
form  of  its  alkali  salts. 

It  is  difficult  to  estimate  the  value  of  albuminous  substances  to  the  vege- 
table kingdom,  from  the  experiments  at  hand.  Our  knowledge  of  the 
metabolism  of  albumin  in  plants  is  remarkably  slight.  We  are  certain 
that  it  by  no  means  plays  the  same  part  in  the  plant  that  it  does  in  the 
animal  organism.  We  should  like  above  all  to  know  whether  the  plants 
consume  albumin  at  all,  i.e.,  oxidize  it.  Oxidation  processes,  as  we  have 
seen  in  considering  the  assimilation  of  carbonic  acid,  play  a  subordinate 
role  in  plants  to  processes  of  reduction.  They  undoubtedly  take  place  to 
some  extent.  We  do  know  that  the  albumin  in  the  animal  organism  is 
almost  entirely  decomposed,  partly  into  urea,  or  partly  into  uric  acid.  Such 
substances  have  been  looked  for  in  vain  in  the  vegetable  kingdom.1  It  is 
interesting,  however,  to  learn  that  many  plants  produce  substances  closely 
allied  to  the  uric  acid  group,  namely,  methylated-xanthine  derivatives, 
such  as  theo-bromine  and  caffeine,  both  of  which  are  important  con- 

1  A  discovery  of  urea  has  been  reported  among  the  varieties  of  Ly coper dacece.  Cf. 
Max  Bamberger  and  Anton  Landsiedl:  Monatsh.  24,  218  (1903). 


ALBUMINS  OR  PROTEINS.  201 

stituents  of  table  accessories.  Concerning  the  relations  which  the  purine 
bases,  and  their  accompanying  intermediate  products,  bear  to  the 
metabolism  of  albumin,  nothing  can  be  affirmed.  It  is,  of  course, 
possible  that  they  are  derived  from  the  nucleins.  The  alkaloids  have 
often  been  assigned  a  relationship  to  albumin.  We  know  little  about 
their  origin.  It  is  possible  that  the  dyestuff,  indigo,  is  related  to  albumin 
metabolism.  In  discussing  the  decomposition  products  of  proteins  we 
met  with  tryptophane,  skatole-amino-acetic  acid,  and  have  seen  that 
putrefaction  decomposes  this  into  indole,  skatole,  skatole-acetic  acid,  and 
skatole-carboxylic  acid.  Skatole  is  rarely  found  in  plants.  The  Japanese 
wood,  Ulmacace,  Celtis  reticulosa  Miq.,  contains  approximately  1  per  cent 
of  skatole.  Recent  investigations  also  indicate  the  occasional  appearance  of 
indoxyl  among  plants.  We  know  nothing  definite  about  the  relations  of  the 
indoxyl  derivatives  to  the  albumin  decompositions  in  the  plant  organism. 

We  are  not  much  better  informed  concerning  the  processes  participating 
in  albumin  syntheses.  The  nitrates  which  the  plant  takes  up  must  be 
reduced.  It  is  now  usually  assumed  that  the  leaves  are  mainly  instru- 
mental in  effecting  the  albumin  syntheses;  the  idea  being  that  amino  acids 
are  first  formed,  which  by  recombining  among  themselves  produce  higher 
complexes,  and  finally  albumin  itself.  Although  the  leaves  themselves  are 
incapable  of  utilizing  the  nitrogen  of  the  air,  as  such,  observations  have 
been  made  indicating  that  they  can  absorb  small  amounts  of  ammonia. 
It  seems  that  light  has  also  an  effect  upon  the  production  of  albumin. 
Albumin  is,  to  be  sure,  formed  in  the  dark,  but  the  synthesis  proceeds  much 
more  rapidly  in  the  sunlight.  We  are  still  entirely  in  doubt  as  to  how 
the  amino  acids  are  formed.  We  can  assume,  as  previously  indicated, 
that  they  are  derived  from  simple  carbohydrates,  —  for  instance,  from  gly- 
cerose;  or  we  can  just  as  easily  imagine  that  the  formation  of  the  amino 
acids  is  a  more  direct  assimilation  process.  The  manner  in  which  the 
nitrates  are  utilized  presents  a  difficult  problem.  It  is  certain  that  they 
must  be  reduced.  The  nitrite  formation  has  also  been  followed  directly.  We 
have  assumed  that  HNO3  goes  over  into  HNO2,  and  this  into  HN :  O. 
The  addition  of  water  would  produce  hydroxylamine,  NH2 .  OH,  which, 
in  conjunction  with  formaldehyde,  obtained  by  the  reduction  of  carbonic 
acid,  produces  formamide,  HCO  .  NH^.1  The  formation  of  hydrocyanic 
acid  and  the  reduction  of  a  nitrate  to  ammonia  have  also  been  suggested. 
It  is  almost  impossible  at  present  to  draw  any  positive  conclusions.  The 
synthesis  of  albumin  in  the  organism  of  plants,  or,  perhaps  better  stated, 
the  formation  of  the  amino  acids,  as  yet  remains  entirely  unexplained. 

We  have  a  better  conception  of  albumin  metabolism  in  germinating 
seeds.  Ripe  seeds  contain  large  stores  of  albumin.  They,  therefore,  act 


1  A.  Bach:  Compt.  rend.  122,  1499  (1896). 


202  LECTURE  X. 

as  sources  for  the  production  of  plant  proteins.  We  note  great  changes 
as  soon  as  germination  begins;  in  fact,  the  entire  cell  contents  are  drawn 
upon.  We  have  already  considered  the  conversion  of  the  carbohydrates 
into  fats,  and  vice  versa.  Besides  such  processes  hydrolysis  undoubtedly 
causes  other  metabolic  changes  to  take  place.  The  proteins  are  disin- 
tegrated into  their  components  by  the  activity  of  proteolytic  ferments. 
Complicated  products.  "  peptones/' *  are  first  formed,  and  finally  amino 
acids,  which,  at  least  in  part,  are  then  decomposed  further.  We  may 
compare  the  beginning  of  germination  with  the  intestinal  processes.  The 
purpose  is  in  many  respects  the  same.  The  germinating  cell  disintegrates, 
in  order  to  utilize  the  various  elementary  components  for  the  construction 
of  a  new  cell  body.  We  are  still  undecided  whether  the  protein  molecule  is 
completely,  or  only  partially,  disintegrated  by  hydrolysis.  Asparagine 
has  been  detected  in  germinating  legumes,  while  glutamine  has  been 
observed  in  other  cases.  The  amount  of  asparagine  may  be  increased  by 
germinating  in  the  dark.  We  are  still  unaware  of  the  significance  of  the 
formation  of  asparagine.  It  is  possible  that  it  does  not  participate  further 
in  the  construction  of  albumin,  but  that  it  acts  as  an  intermediate  step 
to  other- nitrogenous  substances;  or,  even,  that  it  has  nothing  further  to  do 
with  such  substances,  but  now  enters  into  relations  with  the  carbohydrates 
and  fats. 

That  asparagine  does  not  directly  participate  in  the  synthesis  of  albumin, 
which  immediately  follows  its  breaking  down,  is  evident  from  the  fact 
that  it  does  not  dimmish  to  the  same  extent  that  the  albumin  formation 
progresses. 

We  will  add  here  that  the  seedlings  at  the  beginning  of  their  existence 
also  disintegrate  their  other  constituents,  the  nucleins,  fats,  etc.,  into  the 
components.  It  reconstructs  everything  anew.2  We  may  compare  the 
metabolism  of  this  germinating  seedling  with  that  of  the  animal. 

When  we  take  everything  that  we  know  about  the  formation  of  the 
proteins  in  the  vegetable  kingdom  and  their  albumin  metabolism  into 
consideration,  we  find  it  very  difficult  to  formulate  any  distinct  conception 
of  what  actually  occurs,  based  on  experimental  results.  We  have  felt 
that  we  ought  to  consider  briefly  this  subject  here,  because,  as  we  have  re- 
peatedly said,  we  can  expect  to  have  a  complete  understanding  of  biological 
processes  only  when  we  have  as  broad  a  foundation  as  possible.  There  is 
no  sharp  dividing  line  between  the  plant  and  animal  kingdoms.  It  would 
be  a  gross  error  to  try  to  separate  the  biological  investigations  in  these  two 
fields.  The  absolute  dependence  of  the  animal  organism  on  the  products 
of  the  vegetable  kingdom  forces  us  to  consider  in  detail  the  biological 
chemistry  of  plants. 

1  W.  R.  Mark:  Z.  physiol.  Chem.  42,  259  (1904). 

2  Cf.  among  others,  J.  R.  Green  and  H.  Jackson:  Pr.  Roy.  Soc.  77  (B),  69  (1905). 


ALBUMINS  OR  PROTEINS.  203 

Let  us  now  return  to  the  relations  of  the  animal  organism  to  the  albu- 
mins it  obtains  in  its  food.  They  are  not  at  all  attacked  by  saliva,  with 
which  they  first  come  into  contact.  This  secretion  does  not  contain  any 
ferment  which  can  act  upon  the  proteins. 

The  albumins  are  next  subjected  to  the  action  of  pepsin  in  the  stomach. 
Spallanzani l  was  the  first  to  give  a  clear  demonstration  of  the  digestive 
action  of  the  gastric  juice.  Normal  gastric  juice  reacts  acid.  It  contains 
free  hydrochloric  acid.  This  was  definitely  established  by  Bidder  and 
Karl  Schmidt.2  They  estimated  quantitatively  the  total  chloride  present 
in  the  stomach,  and  also  all  the  bases,  —  potash,  soda,  lime,  magnesia, 
iron  oxide  and  ammonia,  —  and  found  after  computing  the  amount  of 
hydrochloric  acid  required  to  combine  with  these,  that  some  remained 
uncombined.  We  shall  discuss  the  composition  of  gastric  juice  and  its 
secretions  more  in  detail  later,  confining  ourselves  at  present  to  the  state- 
ment that  the  proteolytic  ferment  mentioned,  i.e.  pepsin,  is  only  active 
when  in  acid  solution.  It  was  first  believed  that  the  pepsin  was  united 
with  the  hydrochloric  acid  and  exercised  its  functions  as  pepsin-hydro- 
chloric acid.  It  was,  however,  soon  shown  that  the  hydrochloric  acid 
could,  on  the  one  hand,  be  substituted  by  other  acids,  for  instance,  lactic 
acid,  while,  on  the  other  hand,  other  acids  did  not  replace  the  hydrochloric 
acid  in  equivalent  amounts.  The  amount  of  hydrochloric  acid  in  the  gas- 
tric juice  is  very  appreciable.  The  gastric  juice  of  dogs  contains  0.5-0. G 
per  cent  hydrochloric  acid;  that  of  cats  0.5  per  cent;  while  for  human  beings 
from  0.2-0.3  per  cent  is  reported.  The  attempt  has  been  made  to  assign 
to  the  hydrochloric  acid  content  of  the  stomach  an  antiseptic  action  as 
its  greatest  function.  Although  there  is  undoubtedly  such  an  action,  the 
fact  also  remains  that  hydrochloric  acid  participates  in  the  digestion  of 
albuminous  substances.  The  mechanism  of  its  activity  has,  however,  not 
been  thoroughly  explained.  It  may  be  summed  up  as  follows:  If  we  add 
hydrochloric  acid,  or  even  gastric  juice,  to  albumin,  a  peculiar  change 
takes  place.  The  albumin  swells  up  and  fills  the  entire  vessel  as  a  gel- 
atinous mass.  Large  amounts  of  hydrochloric  acid  are  simultaneously 
combined.  The  quantity  of  free  hydrochloric  acid  diminishes.  We  can 
imagine  that  the  hydrochloric  acid  enters  into  combination  with  the  albu- 
min, producing  soluble  albumins,  the  so-called  "  acid- albumins."  It  is 
possible  that  the  hydrochloric  acid  loosens  up  the  albumin  molecule,  i.e., 
changes  it  in  some  way,  preparing  it  for  the  action  of  pepsin.  There  are, 

1  Versuche   iiber  das   Verdauungsgeschaft.     German   by    Michaelis.    Leipsic,   1785. 
Eberle:  Physiolog.  Verdauung  auf  natiirlichem  und  k'instlichem  Wege  Wurzburg,  1834. 
Cf.  also  Gamgee-   Physiologische  Chemie  der  Verdauung:   Leipsic   and  Vienna,   1897. 
W.  Beaumont:  Neue  Versuche  und  Beobachtungen  iiber  den  Magensaft  und  die  Physi- 
ologic der  Verdauung.     German  by  B.  Luden.     Leipsic,  1834. 

2  Bidder  and  Schmidt:  Die  Verdauungssafte  u.  d.  Stoffwechsel,  Mitau  u.  Leipsic, 
1852. 


204  LECTURE  X. 

for  instance,  many  albuminoids  nearly  immune  to  the  action  of  the  gastric 
juice,  which,  under  the  influence  of  mineral  acids  in  the  cold,  are  so 
changed  that  they  are  then  appreciably  disintegrated  by  pepsin.  It 
seems,  however,  that  the  hydrochloric  acid,  besides  exercising  this  effect 
on  the  albumin,  also,  in  some  manner,  directly  influences  the  pepsin. 
This  is  evident  from  the  fact,  that,  when  all  the  hydrochloric  acid  has 
combined  with  the  albumin  and  its  cleavage-products  in  an  artificial  digest- 
ing mixture,  the  pepsin  digestion  then  ceases,  and  can  only  be  brought  to 
renewed  activity  by  the  addition  of  fresh  hydrochloric  acid.  We  are 
justified  in  believing  that  the  albumin  combines  with  more  hydrochloric 
acid,  in  proportion  to  the  greater  number  of  cleavage-products  formed. 
Direct  observation  has  also  shown  that  the  hydrochloric  acid  disappears 
in  proportion  to  the  time  of  digestion. 

The  breaking  down  of  the  proteins  by  the  action  of  the  gastric  juice  is 
not  at  all  extensive.  Complicated  peptones  are  mainly  formed,  accom- 
panied, of  course,  by  some  of  the  lower  cleavage-products,  evidently  of 
the  group  of  simple  polypeptids.  Amino  acids,  under  normal  condi- 
tions, are  not  to  be  detected.1  The  digestion  of  albuminous  substances 
in  the  stomach  evidently  serves  to  prepare  them  for  the  action  of 
trypsin,  with  which  they  next  come  in  contact.  Test-tube  experiments 
have  shown  that  tryptic  digestion  is  quicker  and  more  intense  when 
preceded  by  a  pepsin-hydrochloric  acid  digestion.2-  Certain  difficultly 
digestible  albuminous  substances,  as  for  instance  serum-globulin,  show 
this  property  very  plainly.  It  is  evident  that  the  preliminary  digestion 
in  the  stomach  of  the  different  albuminous  substances  is  of  varying 
importance.  It  is  of  little  significance  for  those  easily  digested.  The 
advantage  of  such  a  preliminary  decomposition  becomes  especially  clear 
when  we  consider  how  rapidly  the  absorption  of  the  albumin  cleavage- 
products  follows  in  the  duodenum  and  the  remaining  small  intestine. 
In  spite  of  an  extremely  liberal  diet  of  meat,  we  find  only  small  amounts 
of  digesting  material  in  the  duodenum.  Accordingly  as  the  stomach 
is  emptied  through  the  pylorus,  trypsin  digestion  and  the  absorption  of 
cleavage-products  take  place  in  rapid  succession.  A  much  larger  field 
of  action  is  presented  to  the  trypsin  ferment  at  one  time.  Instead  of 
acting  upon  an  albumin  molecule,  it  can  immediately  attack  a  large 
number  of  cleavage-products,  and  quickly  disintegrate  them  into  more 
simple  components. 

The  proteids,  when  in  the  stomach,  are  disintegrated  first  of  all  into 
their  constituents.  Hematin  is  split  off  from  hemoglobin,  and  the  globin 
is  digested  by  itself.  The  nucleoproteids  give  off  nuclein,  which,  being 


1  Emil  Abderhalden:  Z.  physiol.  Chem.  44,  17  (1905). 

2  Emil  Fischer  and  Emil  Abderhalden:  ibid.  40,  215  (1903). 


ALBUMINS  OR  PROTEINS.  205 

only  slightly  attacked  by  the  pepsin,  remains  undissolved  for  the  most 
part,  and  for  this  reason  was  first  discovered. 

The  pepsin  of  the  gastric  juice  also  possesses  another  action  besides 
that  of  direct  disintegration.  It  causes  milk  to  curdle.  This  striking 
property,  not  yet  entirely  explained,  is  due  to  a  specific  ferment,  known 
as  rennin,1  or  chymosin.  We  will  state  at  once  that  the  assumption  of  a 
separate  ferment  has  been  questioned.  Pawlow  and  Parastschuk  2  con- 
clude, from  their  experiments,  that  the  two  actions  attributed  usually 
to  pepsin  and  rennin  are  due  to  the  same  ferment.  They  arrive  at  this 
conclusion  from  the  fact  that  the  proteolytic-  and  milk-coagulating  effect! 
of  the  gastric  juice  take  place  parallel  to  one  another.  Both  actions  are 
accelerated  and  retarded  by  the  same  influences,  not  only  qualitatively, 
but  also  quantitatively.  We  know  that  neither  the  pepsin  nor  the  rennin 
is  secreted  as  such  in  the  walls  of  the  stomach.  Both  are  found  in  the 
inactive  form  as  zymogen.  It  is  only  by  the  action  of  acid  that  this  zymogen 
is  converted  into  active  ferment.  Activating  these  ferments  of  the  gastric 
juice  is  another  important  function  of  its  acid  contents.  The  ferments  are 
only  present  in  their  inactive  state,  and  are  incapable  of  doing  their  work 
when  the  free  acid  of  the  gastric  juice  is  missing.  Pepsin  and  rennin  are 
both  rendered  active  by  the  same  agent;  in  fact,  to  the  same  extent. 
This  parallelism  has  caused  the  Russian  authors  above  mentioned  to 
stop  speaking  of  two  ferments,  but  of  two  different  actions  of  one  and 
the  same  ferment.  We  cannot,  at  this  time,  accept  Pawlow's  decision. 
The  more  we  study  the  action  of  ferments,  the  clearer  it  becomes  that  they 
are  delicately  adjusted  for  definite  compounds,  and  are  influenced  by 
very  slight  differences  of  configuration.  In  fact,  such  differences  in  the 
configuration  of  molecules  are  oftentimes  first  indicated  by  the  fact  that 
a  ferment  does  or  does  not  act  upon  a  certain  substance,  whereas  its- 
ordinary  chemical  behavior  has  not  led  us  to  suspect  such  a  difference. 
This  of  itself  is  sufficient  to  make  it  seem  improbable  that  a  ferment 
could  have  two  such  different  actions.  An  important  objection  immedi- 
ately arises.  We  do  not  exactly  know  how  to  interpret  the  activity  of 
rennin.  It  is,  of  course,  possible  that  this  activity  may  produce  the  same 
result  as  does  pepsin,  namely,  an  hydrolysis.  We  know  that  the  essential 
function  of  rennin  consists,  not,  as  formerly  believed,  in  the  curdling  of  the 
casein,  but  in  the  conversion  of  casein  into  another  albuminous  body, 
possessing  entirely  different  characteristics.  If  the  assumption  be  correct 
that  this  is  merely  a  hydrolysis,  then  the  analogy  to  that  of  pepsin  would 
be  complete.  We  would  only  have  to  assume  that  the  nature  of  the 

1  Cf.  O.  Hammarsten:  Sitzber.  kgl.  Gesellsch.  Wissensch.  Upsala,  1877. 

2  Z.  physiol.  Chem.  42,  415  (1904),  and  Die  Identitat  des  Pepsins  und  Chymosins. 
Verhandl.  Sektion  Anat.,  Physiol.  mediz.  Chem.  Vers.  nordischer  Naturforscher  u.  Aerzte 
in  Helsingfors.  7,  12,  July,  1902,  p.  28. 


206  LECTURE  X. 

cleavage-products  was  due  to  the  peculiar  nature  of  casein,  which  we  will 
soon  consider.  In  this  case  it  would  be  more  correct  not  to  speak  of  a 
milk-coagulating  function,  but  of  that  of  the  proteolytic  ferment,  pepsin. 
We  are  inclined  to  look  upon  the  pepsin  and  rennin  ferment  as  probably 
identical,  not  from  the  fact  that  these  have  never  been  isolated  in  a  satis- 
factorily pure  condition,  but  more  especially  because  of  the  interesting 
observations  of  Pawlow  and  Parastschuk.  They  found  that  the  secretions 
of  the  pancreatic  gland  act  towards  casein  in  exactly  the  same  manner  as 
does  the  gastric  juice,  with  this  modification,  that  the  proteolytic  ferment 
of  the  pancreatic  juice,  trypsin,  acts  only  in  alkaline,  neutral,  or  weakly 
acid  solutions.  The  establishment  of  this  fact  has  settled  one  thing.  We 
must  either  assume  that  different  ferments  exist  which  will  coagulate  milk, 
i.e.,  one  which  acts  in  distinctly  acid  reaction,  and  another  which  is  efficient 
in  neutral  or  alkaline  solution  (the  rennin  of  the  stomach  and  the  trypsin 
from  the  pancreas  are  activated  by  entirely  different  agents) ;  or,  as  is  far 
simpler,  we  must  assume  that  only  one  process  takes  place,  namely,  a 
hydrolysis.  Coagulation  occurs  as  a  secondary  effect  in  the  general 
decomposition  of  casein.  It  is  caused  by  the  precipitation  of  the  early 
cleavage-products.  It  is  possible  that  this  stage  of  decomposition,  which 
probably  takes  place  before  the  formation  of  peptones,  is  common  to 
all  proteins.  On  the  other  hand,  it  is  also  possible  that  casein  occupies 
a  unique  position,  and  that  perhaps,  corresponding  to  its  functions,  it 
represents  a  particularly  complicated  protein.  We  should  like  to  place 
stress  upon  the  above  observations  of  Pawlow  rather  than  upon  the 
established  similar  behavior  of  the  two  ferments,  and  will  state  once  more 
that  we  do  not  wish  to  speak  of  two  different  actions  of  one  ferment. 
Until  we  have  an  accurate  knowledge  of  these  relations  we  will  retain 
the  conception  of  two  separate  ferments,  pepsin  and  rennin,  in  our  pre- 
sentation of  the  subject. 

Rennin  is  very  widely  distributed  in  the  whole  animal  kingdom,  and 
ferments  acting  in  an  analogous  manner  are  undoubtedly  found  in  the 
vegetable  world.  It  has  been  found  in  animals  which  chew  their  cud, 
and  especially  in  the  fourth,  so-called  rennet-stomach  of  the  calf.  Its 
main  function  has  generally  been  considered  to  be  the  curdling  of  milk. 
It  has  been  found,  however,  that  this  precipitation  of  casein  is  not  the 
primary  process.  The  nature  of  casein  is  changed  first  of  all  by  the  action 
of  the  rennin.  Another  protein  with  different  properties  is  produced. 
Curdling  depends  on  the  formation  of  insoluble  calcium  salts,  arising  from 
the  casein,  which  has  been  changed  by  the  rennin.  That  this  conception 
is  correct  is  evident  from  the  fact  that  casein  will  not  be  curdled  by  rennin 
if  the  solution  is  free  from  calcium  salts,  but  it  will,  nevertheless,  undergo 
a  change.  If  the  casein,  treated  in  the  above  manner,  is  then  boiled,  — 
thus  destroying  the  rennin,  —  it  will  curdle  on  the  addition  of  calcium 


ALBUMINS  OR  PROTEINS.  207 

salts.  The  latter  property  is  therefore  dependent  on  the  presence  of  cal- 
cium salts,  and  has  no  direct  relation  with  the  rennin  as  such.  The  albu- 
min formed,  para-casein,  differs  essentially  from  casein,  inasmuch  as  it  is 
precipitated  by  calcium  salts.  The  precipitate  contains  large  amounts 
of  calcium  phosphate.  We  do  not  know  what  relation  this  salt  has  to 
the  curdling. 

According  to  the  general  conception,  the  pepsin  action  follows  the 
precipitation  of  the  para-casein,  disintegrating  it  in  the  same  manner  as 
it  does  the  remaining  proteins.  The  phosphoric  acid  portion,  the  so- 
called  pseudonuclein  (a  compound  as  yet  insufficiently  investigated),  is 
thrown  out  at  this  stage.  It  does  not  possess  any  of  the  ordinary  com- 
ponents of  the  nucleins.  The  purpose  of  the  rennin  action  is  not  at  all 
clear.  It  is  certainly  significant  that  we  always  find  evidence  of  the 
activity  of  rennin  wherever  there  are  proteolytic  ferments.  Rennin  is  found 
in  the  intestine  and  in  the  organs.  It  cannot  be  denied  that  the  concep- 
tion that  the  activity  of  rennin  is  to  be  regarded  as  being  an  hydrolytic 
attack,  and  the  precipitation  by  the  calcium  salts  as  only  an  intermediate 
effect,  depending  on  the  specific  characteristics  of  the  first  cleavage-products 
of  casein,  these  being  then  subjected  to  the  further  disintegrating  action  of 
the  pepsin,  is  certainly  a  very  attractive  one.  The  behavior  of  casein 
during  digestion  is  thus  removed  from  its  special  position,  while  the 
assumption  of  Pawlow  and  Parastschuk  that  rennin  and  pepsin  are  iden- 
tical is  given  a  further  support,  to  be  sure  in  the  sense  that  it  is  a  case  of 
one  and  the  same  kind  of  fermentation,  and  not  that  of  two  different 
actions.  These  processes  are  still  very  obscure. 

The  opinion  has  often  been  expressed  that  pepsin  and  rennin  are  not 
simple,  individual  ferments.  The  various  species  of  animals  are  supposed 
to  possess  different  kinds  of  ferments.  The  rennins  from  human  beings 
and  from  swine  are  supposed  to  be  different  from  that  obtained  from 
the  calf.  Bang  1  has  isolated  a  rennin,  parachymosin,  from  the  stomach 
of  the  calf,  whose  properties  are  essentially  different  from  those  obtained 
from  other  sources.  Not  even  the  pepsins  from  different  animals  are 
alike.  Differences  undoubtedly  exist,  which  may  possibly  be  due  to  the 
nature  of  the  different  nutrient  albumins  supplied  to  the  animals.  As 
long  as  we  are  not  acquainted  with  the  ferments  as  such,  and  are  unable 
to  study  their  activity  in  uniform  materials,  it  will  be  difficult  to  pass  judg- 
ment on  the  results  obtained  with  different  ferments.  It  is  to  be  hoped 
that  the  transference  of  such  investigations  to  the  complicated  polypep- 
tides  of  known  structure  and  configuration  will  throw  light  upon  this 
subject. 

We  must  refer  to  another  peculiar  phenomenon  as  yet  entirely  unex- 


1  Pfliiger's  Arch.  79,  425  (1900). 


208  LECTURE  X. 

plained.  If  some  rennin  is  added  to  a  clear  solution  of  the  so-called  albu- 
moses  and  peptones,  a  flocculent  precipitate  is  formed.  This  is  called 
plastein,  and  is  supposed  to  occur  only  in  the  presence  of  albumoses. 
Its  amount  has  been  variously  estimated,  from  3  to  27  per  cent.  It  is 
suggested  that  the  closer  the  cleavage-products  stand  in  relation  to  albu- 
min, the  more  readily  will  they  be  precipitated  by  rennin.  The  forma- 
tion of  plastein  is  still  unexplained.  It  has  been  looked  upon  as  a 
synthetic  process,  although  this  assumption  has  not  been  substantiated  by 
any  experimental  proof.1 

The  albumin,  already  partly  disintegrated,  passes  from  the  stomach 
into  the  duodenum,  being  there  subjected  to  the  influence  of  the  pancreatic 
juice,  and  especially  to  the  trypsin  contained  therein.  This  also  is  not 
delivered  to  the  intestines,  as  such.  It  is  secreted  in  the  zymogen  form, 
and  only  becomes  active  in  the  intestine.  There  is  a  substance,  called 
"  enterokinase,"  in  the  intestinal  juice,  which  converts  the  trypsin- 
zymogen  into  the  active  ferment.  We  shall  return  to  this  particular 
process  later.  We  were  a  long  time  uncertain  regarding  the  extent  of 
the  decomposition  of  the  albumins  reaching  the  duodenuni  in  the  form  of 
a  mixture  of  peptones  of  different  degrees  of  complexity.  We  assumed, 
until  recently,  that,  as  a  rule,  only  the  so-called  albumoses  and  peptones 
were  formed,  and  that  these  were  absorbed  directly.  Such  a  conception  is 
particularly  plausible,  if,  as  has  been  generally  done,  digestion  is  only 
regarded  as  a  means  of  preparing  the  nutrient  material  for  absorption. 
This  assumption  was  still  believed,  even  when  free  amino  acids,  especially 
leucine  and  tyrosine,  were  repeatedly  found  in  the  alimentary  canal.  This 
view  obtained  added  support  from  the  experiment  of  Hofmeister.2  He  put 
a  piece  of  the  stomach  or  intestinal  wall  of  a  recently  killed  animal  in  a 
moist  chamber  for  a  time  at  40°  C.,  and  showed  that  its  peptone  content 
had  diminished  when  compared  with  a  piece  of  the  same  size,  whose 
peptone  content  had  been  immediately  estimated.  In  fact,  after  two 
to  three  hours,  all  the  peptones  had  disappeared.  Salvioli 3  also  showed 
that  peptones  quickly  disappeared  when  introduced  into  a  ligated  intes- 
tine. There  seems  to  be  no  doubt  that  peptones  are  absorbed;  in  fact, 
it  has  even  been  asserted  that  albumin  itself  is  directly  taken  up.  It 
was  shown  by  the  researches  of  Kutscher  and  Seeman,4  and  of  O. 


1  Cf.  A.  Danilewsky  and  Okunew:  Inaug.  Diss.  St.  Petersburg,  1895.     M.  Lawrow: 
Inaug.  Diss.  St.  Petersburg,  1897.     Sawjalow:  Diss.  Jurjew.  1899,  an>d  Pfliiger's  Arch. 
85,  171  (1901).     H.  Bayer:  Hofmeister's  Beitrage,  4,  554  (1903).     M.  Lawrow  and  S. 
Salaskin:  Z.  physiol.  Chem.  36,  277  (1902).     Kurajeff:  Hofmeister's  Beitrage,  1,  121 
(1901);  2,  141  (1902). 

2  Pfliiger's  Arch.  19,  8  (1885). 

3  Arch.  Anat.  Physiol.  Sup.  1880,  p.  95. 

4  Z.  physiol.  Chem.  34,  528  (1901  and  1902);  35,  432  (1902). 


ALBUMINS  OR  PROTEINS.  209 

Cohnheim,1  that  the  breaking  down  of  the  proteins  in  the  intestine  was 
more  extensive  than  was  originally  thought.  The  former  succeeded  in 
isolating  crystalline  cleavage-products  from  the  intestinal  contents  of  dogs 
which  had  been  fed  on  a  diet  rich  in  albumin,  the  animals  being  killed 
at  varying  times,  —  for  instance,  at  intervals  of  six  hours. 

The  discovery  of  O.  Cohnheim,  that  the  mucous  membrane  of  the 
intestine  contains  a  ferment,  erepsin,  which  further  disintegrates  the  pep- 
tones, casts  doubt  upon  the  conclusions  drawn  from  the  above-men- 
tioned experiments  of  F.  Hofmeister  and  Salvioli. 

Recent  investigations,  from  various  standpoints,  indicate  a  considerable 
disintegration  of  the  albumin  molecule.  It  has  been  shown  for  one  thing 
that  intestinal  digestion  is  very  similar  to  that  artificially  produced  by  tryp- 
sin.  Amino  acids,  e.g.,  tyrosine,  leucine,  alanine,  glutamic  acid,  aspartic 
acid,  lysine,  arginine,  and  histidine,  are  formed  in  the  intestinal  canal  and 
even  the  polypeptides  which  are  observed  in  artificial  digestion  with 
trypsin,  and  are  attacked  with  difficulty,  if  at  all,  by  ferments.  It  is  at 
present  uncertain  as  to  how  far  the  disintegration  goes  in  individual  cases, 
as  to  whether  polypeptides  with  a  small  number  of  amino  acids  result,  or 
that  the  digestion  stops  while  the  chains  are  more  complicated.  We 
have  already  shown  that  we  can  draw  no  conclusion  as  to  the  extent 
of  the  decomposition  simply  on  account  of  the  appearance  of  free 
amino  acids.  More  complex  substances  may  be  present  at  the  same 
time. 

We  have  reached  a  like  conclusion  concerning  the  decomposition  of  the 
proteins  in  the  intestinal  tract  from  another  standpoint.2  The  significance 
of  the  function  of  digestion  is  not  merely  to  prepare  the  food  for  absorption. 
It  goes  far  beyond  this  point.  The  separate  components  of  the  food  are 
not  in  a  condition  suitable  for  the  economy  of  individual  beings.  Every 
species  of  animal  —  in  fact,  every  individual  —  has  its  own  specifically 
constituted  tissues  and  cells.  If  the  diet  were  always  the  same,  the  for- 
mation of  the  tissues  might  bear  some  close  relation  to  the  components 
of  the  food.  The  diet  varies,  however,  and,  especially  in  the  case  of 
human  beings  and  the  omnivora,  is  exceedingly  diverse  in  nature.  In 
order  to  maintain  the  individuality  of  the  animal,  and  to  make  its 
organism  independent  of  the  outer  world  in  the  matter  of  food  taken,  it 
disintegrates  the  nutrient  it  receives,  and  utilizes  those  components  which 
may  be  of  service  to  it  in  building  up  new  complexes.  This  conception 
of  the  process  of  digestion,  as  a  whole,  will  become  especially  clear  when 
we  consider  the  most  important  food  of  growing  mammals,  i.e.,  milk. 


1  Ibid.  33,  451  (1901). 

2  Emil   Abderhalden:  Z.'physiol.  Chem.  44,   17  (1905);  Zent.  Stoffwechs.-Verdau- 
ungs-Krank.  6,  647    (1904);  Med-  Klinik.  1,  Nr.  1  and  2  (1905);  1,  Nr.  46   and  47 
(1905). 


210 


LECTURE  X. 


All  of  the  tissues  are  formed  from  this.  The  only  proteins  contained  in 
milk  are  lactoalbumin,  lactoglobulin,  and  casein.  From  these,  and  also  in 
the  case  of  animals  in  which  the  albumin  content  of  the  milk  is  less  prom- 
inent than  is  true  of  human  milk,  all  sorts  of  different  proteins  with 
their  varying  functions  must  be  formed.  We  need  only  refer  to  the  albu- 
minous substances  of  the  blood,  to  serum-globulin,  serum-albumin,  hemo- 
globin, then  to  the  numerous  albuminous  constituents  of  the  tissues,  and 
all  of  the  other  proteins.  A  glance  at  the  following  table  will  give  a  good 
conception  of  the  great  changes  which  one  protein  must  undergo  to  produce 
all  the  others. 


Casein. 

Serum- 
albumin. 

Serum- 
globulin. 

Globin  from 
hemoglobin. 

Glycocoll                       .    . 

3.5 

Alanine            .        

0.9 

2.7 

2.2 

4.2 

Aminovaleric  acid    

1.0 

present 

present 

Leucine    

10.5 

20.0 

18.7 

29.0 

Proline  

3.1 

1.0 

2.8 

2.3 

Phenylalanine    

3.2 

3.1 

3.8 

4.2 

Glutarnic  acid 

11  9 

7  7 

8  5 

1  7 

Aspartic  acid     

1.2 

3.1 

2.5 

4.4 

Cystine    

0.065 

2.3 

0.7 

0.3 

Serine 

0  23 

0  6 

0.6 

Tyrosine 

4  5 

2.1 

2.5 

1.5 

Lysine 

5  8 

4.3 

Arginine          ....       .... 

4.8 

_ 

_ 

5.4 

Histidine     

2.6 

_ 



11.0 

Fibrin. 

Histon  from 
thymus 
gland. 

Elastin. 

Keratin. 

Glycocoll        

3.0 
3.6 
1.0 
15.0 
2.5 
2.0 
8.0 
2.0 

present 
3.5 

0.5 
3.5 

11.8 
1.5 
2.2 
0.5 

5.2 
6.9 
15.5 
1.5 

25.75 
6.6 
1.0 
21.4 
1.7 
3.9 
0.8 

0.34 
0.3 

4.7 
1.5 
0.9 
7.1 
3.4 

3.7 
10.0 
0.6 

'3.2 

Alanine        

Aminovaleric  acid    

Proline 

Phenylalanine              .    . 

Glutamic  acid 

Aspartic  acid                 .    .    . 

Cystine 

Arffinine 

Histidine                           •    .    . 

ALBUMINS  OR  PROTEINS.  211 

Even  if  all  the  proteins  so  far  investigated  are  not  all  derived  from  the 
same  animal,  and  the  methods  of  analysis  are  not  so  employed  as  to  give 
exact  results,  it  is,  nevertheless,  clear  that  casein  must  undergo  great 
changes  in  order  to  make  possible  the  transformation  into  these  very 
different  products.  We  have  disregarded,  to  be  sure,  the  other  albuminous 
components  of  milk,  albumin  and  globulin.  It  is  possible  that  certain  of 
the  proteins  in  the  body  are  more  closely  related  to  these  than  to  casein,  — 
at  least,  as  far  as  their  composition  is  concerned.  Such  a  discovery  would 
not  alter  our  conception,  as  there  can  be  absolutely  no  doubt  but  that 
the  casein  plays  a  large  part  in  the  economy  of  the  nursling.  This  is 
evident  from  the  large  amount  present  in  milk.  It  might,  of  course,  be 
objected  that  casein  is  mainly  utilized  as  a  combustible  material,  and 
does  not  participate  to  any  great  extent  in  the  building  up  of  the  body. 
While  such  an  assumption  is  not  yet  supported  by  any  proof,  still  on  the 
other  hand,  we  can  reply  that  our  knowledge  of  the  composition  of  the 
lactoalbumin  and  lactoglobulin  is  such  as  to  warrant  the  belief  that  they 
can  only  participate  to  a  limited  extent  in  the  formation  of  the  albuminous 
components  of  the  body.  They  would  also  have  to  undergo  great  changes 
in  order  to  make  them  available  for  the  requirements  of  the  cells  of  the 
body. 

It  is  not  difficult  to  imagine  the  formation  of  all  of  the  varied  albuminous 
substances  from  one  primitive  body,  if  we  take  into  consideration  the 
fact  that  a  very  extensive  decomposition  occurs  even  in  the  alimentary 
tract.  From  the  complicated  albumin,  the  intestine  receives  the  individual 
constituents  either  as  such  or  in  long  or  short  chains.  The  intestine  is 
able  to  unite  these  in  varying  proportions,  forming  definite  products  to 
meet  its  requirements.  The  same  process  can  take  place  in  every  cell. 

We  might  expect  to  obtain  an  insight  into  the  digestion  of  the  albumins 
by  studying  the  blood.  It  were  conceivable  that  the  cleavage-products 
are  only  recombined  in  the  various  organs.  Such  a  conception  has  much 
to  commend  it.  We  must  not,  however,  forget  that  the  organism  strives 
to  maintain  a  constant  composition  for  its  blood-stream.  The  blood  has 
important  functions  to  fulfill,  and  any  disturbance  is  accompanied  by 
far-reaching  results.  It  were,  in  fact,  not  a  matter  of  indifference  to  have 
the  various  decomposition  products  introduced  into  the  blood.  The  cells 
would  require  that  all  the  elementary  components  be  brought  to  them  and 
in  definite  proportions,  in  order  that  they  might  build  up  their  own  albu- 
mins, a  condition  of  affairs  hardly  probable  with  a  large  part  of  these 
components. 

We  have  not  yet  succeeded  in  definitely  isolating  any  peptones  or 
other  protein  cleavage-products  from  the  blood/  The  serum  of  the  blood 

1  E.  Abderhalden  and  C.  Oppenheimer:  Z.  physiol.  Chem.  42,  155  (1904).  Cf.  also 
P.  Morawitz  and  R.  Dietschy:  Arch.  exp.  Path.  Pharm.  54,  88  (1905). 


212 


LECTURE  X. 


undoubtedly  carries  mainly  albumin,  which  occupies  the  same  relation 
to  the  albumin  metabolism  that  grape-sugar  does  to  the  transport  of  the 
carbohydrates.  As  the  sugar  content  of  the  blood  is  very  constant,  so, 
also,  the  sum  total  of  the  albumins  in  the  blood-serum  is  subject  to  but 
little  variation.  The  serum-albuminous  bodies  are  mainly  composed  of 
albumin  and  globulin.  Their  relative  amounts  vary.  During  starvation 
the  former  gradually  diminishes,  while  the  latter  increases.  We  could 
imagine  that  the  composition  of  the  serum-albuminous  bodies  were  depend- 
ent on  that  of  the  albumin  in  the  food.  This  ought  to  be  subject  to  proof 
by  direct  experiment.1  Six  liters  of  blood  were  taken  by  venesection 
from  a  horse,  which  had  been  fed  mainly  on  hay  and  oats,  and  the  amounts 
of  tyrosine  and  glutamic  acid  present  in  the  serum  were  estimated.  The 
animal  was  then  made  to  fast  a  whole  week  in  order  to  guarantee  that  the 
intestines  were  entirely  emptied  of  their  contents.  Another  sample  of 
blood  (six  liters)  was  taken,  and  the  amounts  of  tyrosine  and  glutamic 
acid  present  in  the  serum  again  determined.  The  animal  was  now  fed  an 
albuminous  substance  which  possessed  36.5  per  cent  glutamic  acid 
and  2.37  per  cent  tyrosine.  The  serum-globulin  of  the  horse  contains, 
under  normal  conditions,  about  the  same  amount  of  tyrosine,  but  only 
8 . 5  per  cent  glutamic  acid.  Serum-albumin  contains  7 . 7  per  cent  glu- 
tamic acid.  The  animal  under  investigation,  therefore,  was  fed  an  albu- 
min, gliadin,  which  possessed  five  times  as  much  glutamic  acid.  The 
following  table  gives  a  summary  of  the  results : 

EXPERIMENT  I. 


Normal. 

After  8  days' 
fasting. 

After  feed- 
ing 1500  g. 
gliadin. 

After  feed- 
ing 1500  g. 
gliadin. 

Tyrosine  

Per  cent. 
2  43 

Per  cent. 
2  60 

Per  cent. 
2  24 

Per  cent. 
2  52 

Glutamic  acid    

8  85 

8  20 

7.88 

8.25 

EXPERIMENT  II. 


Normal. 

After  7  days' 
fasting. 

After  feed- 
ing 2500  g. 
gliadin. 

Tyrosine  .           

Per  cent. 
2.50 

Per  cent. 
2.55 

Per  cent. 

2.48 

Glutamic  acid     

9.52 

8.52 

8.00 

E.  Abderhalden  and  F.  Samuely:  Z.  physiol.  Chem.  46,  193  (1905). 


ALBUMINS  OR  PROTEINS.  213 

These  experiments  show  clearly  that  the  composition  of  the  serum- 
albuminous  bodies  remains  unchanged  and  is  independent  of  the  nature 
of  the  albumin  administered.  The  amounts  of  glutamic  acid  remained 
very  constant,  in  spite  of  the  fact  that  the  horse  had  to  renew  a  supply  of 
serum-albumin,  due  to  a  large  loss  of  blood.  The  albumin  in  the  food 
must  certainly  have  undergone  a  complete  change  before  it  entered  into 
the  general  circulation.  The  blood  was  taken  from  the  Vena  jugularis  in 
these  experiments.  As  the  albuminous  substances  do  not  seem  to  enter 
the  general  circulation  through  the  lymph-stream,  but  only  through  the 
blood,  it  was  conceivable  that  the  transformation  of  the  nutrient  albumin, 
that  is,  the  synthesis  of  the  cleavage-products,  was  carried  out  in  the 
liver.  We  have,  as  yet,  no  exact  proof  of  this.  Our  present  knowledge 
indicates  that  a  synthesis  of  the  albuminous  cleavage-products  takes 
place  in  the  walls  of  the  intestine.  From  the  various  different  albumins 
in  the  food,  the  serum-albumins  are  formed  first.  From  the  latter,  each 
cell  constructs  the  protein  that  it  requires.  The  cell,  therefore,  obtains 
the  same  nourishment  entirely  independent  of  external  conditions.  The 
functions  of  the  intestine  and  of  the  digestive  ferments  are,  according  to 
this  conception,  to  be  regarded  in  a  quite  particular  light.  First  of  all, 
they  guarantee  collectively  the  correct  course  of  the  general  metabolism. 
The  digestive  ferments  act  before  the  intestine  does.  They  furnish  the 
intestine  with  the  building  materials  from  which  it  forms  homogeneous 
products  for  the  cell-metabolism.  It  now  becomes  apparent  why  any 
derangement  of  the  alimentary  tract  should  have  such  a  far-reaching  effect 
upon  all  processes  of  metabolism.  It  is  not  the  deranged  absorption  which 
is  so  important.  It  is  the  deranged  assimilation.  The  intestine  itself  is 
one  of  the  most  important  organs.  Many  important  syntheses  and  changes 
are  carried  on  within  its  walls. 

That  syntheses  play  necessarily  in  albumin-metabolism  a  part  as  impor- 
tant as  in  the  case  of  fats  and  carbohydrates,  is  evident  from  the  fact  that 
animals  which  are  supplied  with  greatly  disintegrated  albuminous  material, 
can  be  easily  maintained  in  nitrogen  equilibrium,  as  the  experiment  on 
the  next  page  shows.1 

The  casein  decomposed  by  tryptic  digestion  consisted  of  80-85  per  cent 
of  simple  cleavage-products,  the  amino  acids  constituting,  by  far,  the 
larger  portion,  while  the  smaller  part  was  composed  of  substances  akin  to 
polypeptides.  At  most,  15-20  per  cent  of  the  total  material  administered 
consisted  of  complicated  polypeptides,  which,  however,  no  longer  gave  the 
biuret  reaction.  Whether  the  organism  is  capable  of  producing  albumins 
from  the  amino  acids  alone  remains  undecided,  and  at  present  is  not  sus- 


1  E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  42,  528  (1904);  44,  108  (1905). 
Cf.  O.  Loewi:  Arc.  exp.  Path.  Pharm.  48,  303  (1902). 


214 


LECTURE  X. 


ceptible  to  direct  proof;  because,  in  the  first  place,  we  are  not  acquainted 
with  all  the  albumin  cleavage-products,  and,  on  the  other  hand,  many  of 
the  amino  acids  are  evidently  destroyed  during  the  complete  hydrolysis  by 
acids  and  alkalies. 


Total 

Date. 

N. 

Urine. 

Dried  Faeces. 

N. 

N. 

in 

Bal- 

Weight 

Observations. 

Food. 

ance. 

1£05. 

Amt. 

N. 

Amt. 

N. 

Outgo. 

Jan.  12 

















fasting. 

13 

— 

— 

— 

— 

— 

— 

— 

— 

(i 

14 

2  g. 

120 

2.30] 

0.27 

2.57 

-0.57 

2  .  740 

fed  per  day: 

15 

i 

115 

2.00J. 

14.7 

0.27 

2.27 

-0.27 

2.750 

33.  3  g.  sliced  meat. 

16 

130 

1.981 

0.27 

2.25 

-0.25 

2.785 

25.0  g.  fat. 

17 

118 

1.46 

7.3 

0.38 

.84 

+  0.06 

2.790 

50.0  g.  starch. 

18 
19 
20 
21 

2g- 

105 
110 
100 
95 

1.85i 
1.50J 
1.72, 
1.66J 

10.0 
16.6 

0.14 
0.14 
0.23 
0.23 

.99 
.64 
.95 

.78 

+  0.01 
+  0.36 
+  0.05 
+  0.22 

2.800 
2.820 
2  .  825i 
2.830 

10.0  g.  cane-sugar. 
5.  Og.  grape-sugar. 

22 

110 

1.38 

20.1 

0.47 

.85 

+  0.15 

2.840 

fed  per  day: 

23 
24 

115 
110 

1.35, 
1.39/ 

20.4 

0.36 
0.36 

.71 
.75 

+  0.29 
+  0.25 

2.870 
2.880 

23  .  5     g.     digested 
casein. 

25 
26 

120 
105 

1.50, 
1.31J 

23.6 

0.37 
0.37 

.87 
.68 

+  0.13 
+  0.32 

2.900 
2.945 

25.0  g.  fat. 
50.0  g.  starch. 

27 

28 

100 
120 

1.29-. 
1.34J 

15.3 

0.34 
0.34 

.63 
.68 

+  0.37 
+  0.32 

2.960 
2.970 

10.0  g.  cane-sugar. 
5.  Og.  grape-sugar. 

29 

105 

1.39 

15.9 

0.35 

.74 

+  0.26 

2.985 

30 

100 

1.64 

12.6 

0.19 

1.83 

+  0.17 

3.010 

31 

90 

1.36i 

0.52 

1.88 

+  0.12 

3.030 

Feb.    1 

100 

1.86J 

28.8 

0.52 

1.87 

+  0.13 

3.045 

2 

105 

1.5h 

on   A 

0.38 

1.89 

+0.11 

3.030 

3 

95 

1.681 

&\j  .  4 

0.38 

1.91 

+  0.09 

3.040 

4 

110 

1.58 

16.1 

0.45 

2.03 

-0.03 

3.010J 

Total 

32  g. 

— 

23.19 

— 

5.86 

29.05 

+  3.01 



Average 

2g- 

1.45 

0.36 

1.85 

+  0.19 

~ 

Closely  related  to  this  question,  is  the  problem  whether  the  organism  is 
capable  of  getting  along  with  albuminous  substances  which  are  deficient 
in  specific  groups.  Under  normal  conditions  we  constantly  consume  a 
mixture  of  proteins.  Based  on  the  above  conception,  regarding  the  degra- 
dation and  reconstruction  of  the  albumins,  we  can  imagine  that  it  is  imma- 
terial whether  one  or  the  other  protein,  or  this  or  that  elementary 
constituent,  is  absent.  The  fact  that  they  are  all  finally  present  in  the 
digesting  mixture  is  the  important  consideration.  We  can  also  imagine 
that  the  animal  organism  possesses  the  ability  of  producing  certain  amino 
acids  from  others;  for  instance,  glycocoll.  That  an  organism  can  get 
along  with  an  albuminous  substance  in  which  glycocoll  is  entirely  absent, 
is  evident  from  the  feeding  experiment  mentioned,  in  which  the  cleavage- 
products  of  casein  were  used. 


ALBUMINS    OR   PROTEINS.  215 

The  reason  that  many  albuminous  substances,  like  the  keratins,  are  not 
looked  upon  as  food  material,  is  due  to  the  fact  that  their  amino  acid  con- 
stituents are  in  such  combinations  that  they  are  attacked  with  difficulty, 
or  not  at  all,  by  trypsin.  Among  the  albuminous  substances  so  far  con- 
sidered, we  mentioned  one  which  was  characterized  by  the  absence  of 
almost  all  of  the  members  of  the  aromatic  series.  This  is  gelatin.  Tyrosine 
and  tryptophane  are  entirely  absent,  while  phenylalanine  is  present  in  only 
very  small  amount.  We  are  justified  in  concluding,  from  the  idea  pre- 
viously suggested,  that  gelatin  is  not  a  satisfactory  substitute  for  albumin 
in  the  ordinary  sense.  The  animal  organism  seems  unable  to  synthesize 
tyrosine  and  tryptophane.  It  would  have  to  produce  aromatic  compounds 
from  substances  of  the  fatty  acid  series.  It  is,  in  fact,  impossible  to  main- 
tain the  nitrogen  balance  by  feeding  gelatin  exclusively.  It  is,  of  course, 
possible  to  substitute  gelatin  for  a  part  of  the  nutrient  albumin,  in  the 
same  manner  as  when  we  do  this  with  a  large  supply  of  carbohydrates  or 
fats.  Taking  the  above-described  metabolic  processes  into  consideration, 
we  may  conclude  that  gelatin  is  a  much  better  "albumin-sparer"  than 
the  nitrogen-free  foodstuffs  mentioned,  for  the  reason  that  it  delivers  to 
the  organism  a  whole  series  of  albumin  constituents  which  it  is  capable  of 
uniting  with  the  other  albumin  degradation  products  to  form  its  serum- 
albumins.  We  must  expect  that  it  can  act  as  a  substitute  for  more  nutrient 
albumin,  in  proportion  to  the  richness  of  the  latter  in  aromatic  groups. 
Experiments  to  confirm  this  have  not  yet  been  undertaken,  although 
efforts  have  been  made  to  increase  the  "  nutritive  index  "  of  gelatin  by 
the  addition  of  the  missing  ingredients,  tyrosine  and  tryptophane.  It  has 
in  fact  been  found  possible  to  increase  greatly  the  amount  of  gelatin  used 
as  substitute  by  adding  simultaneously  these  amino  acids.1  Cystine  was 
used  in  these  experiments.  The  reason  that  we  have  so  far  been  unable 
to  replace  completely  albumin  with  gelatin,  and  the  addition  of  the  missing 
amino  acids,  may  be  due  to  the  fact  that  we  are  not  yet  acquainted  with 
all  of  the  albumin  components.  It  seems  far  more  probable,  however, 
that  gelatin  contains  numerous  combinations,  which  are  very  resistant  to 
the  action  of  the  proteolytic  ferments,  and,  possibly,  it  also  restricts  the 
rapid  decomposition  and  reconstruction  in  cell-metabolism. 

Effort  has  also  been  made  to  obtain  values,  as  albumin-sparers  of  sub- 
stances closely  related  to  albumin,  especially  of  asparagine,  which  occurs 
so  abundantly  in  germinating  seeds.2  The  interesting  discovery  was 

1  M.  Kauffmann:  Pfliiger's  Arch.  109,  1  (1905).     Cf.  also  the  earlier  investigations 
of  Eschle:  Vierteljahresschrift  naturforsch.  Ges.  Zurich,  1876,  36.     K.  H.  Lehmann: 
Sitzber.  Miinchener  morphol.-physiol.  Ges.  March  10,  1885. 

2  O.  Kellner:  Z.  Biol.  39,  313  (1900).     Politis:  ibid.  28,  492  (1891).     S.  Gabriel:  ibid. 
29,  115  (1892).      C.  Voit:  ibid.  29,  125  (1892).      Mauthner:  ibid.  28,  507  (1891).     I. 
Munk:   Virchow's  Arch.  94,  441    (1883).     Weiske:   Z.  Biol.  17,  415  (1881);  ibid.  30, 
254  (1894).     W.  Voltz:  Pfliiger's  Arch.  107,  360  (1905);  107,  415  (1905). 


216  LECTURE  X. 

made  that  this  substance  acted  differently  in  the  organisms  of  the  car- 
nivora  than  in  that  of  the  herbivora.  With  the  former  and  with  the 
omnivora,  asparagine  cannot  be  utilized  as  a  substitute  for  albumin;  but 
this  substance  does  act  as  an  albumin-sparer  with  the  herbivora.  It  is 
not  easy  to  interpret  this  result.  We  cannot  exactly  realize  how  asparagine 
can  act  as  a  substitute  for  albumin.  It  is,  of  course,  possible,  in  fact 
very  probable,  that  the  animal  organism  is  capable  of  forming  one  amino 
acid  at  the  expense  of  another;  we  cannot,  however,  believe  it  possible 
to  produce  albumin  from  asparagine  alone.  Such  an  assumption  is  entirely 
out  of.  the  question.  It  seems  more  probable  that  it  is  active  in  another 
direction.  It  has  been  thought  that  the  asparagine  in  the  intestines  pro- 
tects the  albuminous  material  of  the  food,  before  disintegration,  against 
the  attacks  of  micro-organisms;  in  fact,  it  has  even  been  suggested  that 
the  bacteria  in  the  intestines  synthesize  albumin  from  asparagine,  which 
is  then  absorbed  by  the  organism.  It  is  interesting  to  note  that  ammo- 
nium acetate  l  and  succinamide 2  are  credited  with  having  the  same  effect 
as  that  of  asparagine.  .We  cannot  consider  this  question  as  solved,  from 
the  investigations  at  hand;  only  this  much  is  certain,  that  asparagine  can- 
not be  looked  upon  as  a  substitute  for  albumin  in  the  sense  that  gelatin 
is.  Its  action  is  an  indirect  one. 

In  this  connection  we  may  state  that  the  lower  forms  of  life,  like  the 
molds,  can  utilize  an  individual  amino  acid  as  a  starting-point  in  the 
synthesis  of  albumin.  This  is  not  so  remarkable,  for,  if  the  nitrate- 
nitrogen  is  available,  then  the  amino  acid-nitrogen  ought  also  to  be  of 
value.  Experiments  with  Aspergillus  niger  3  indicate  that,  within  certain 
limits,  the  production  of  albumin  is  entirely  independent  of  the  source  of 
the  nitrogen.  This  mold  synthesized  its  albumin  just  as  efficiently  in 
a  potassium  nitrate  medium  as  when  it  was  supplied  with  glycocoll  or 
glutaminic  acid  as  its  sole  source  of  nitrogen.  Furthermore,  the  exam- 
ination of  the  albumin  in  the  mold  showed  it  to  be  composed  of  apparently 
the  same  relative  amounts  of  individual  amino  acids  in  all  three  experi- 
ments. Glycocoll,  alanine,  leucine,  glutamic  acid,  and  aspartic  acid  were 
all  obtained  from  the  mold.  This  phenomenon  might  be  explained  by 
assuming  that  this  mold  evidently  decomposes  the  amino  acids  presented 
as  nutriment,  i.e.,  possibly  splits  off  the  amino  group,  and  starting  from 
ammonia  begins  the  synthesis  anew.  In  the  same  manner  it  probably 
produces  the  same  substances  from  the  nitrates,  and  eventually  forms 
most  complicated  compounds.  Czapek 4  and  O.  Emmerling 5  have  already 


1  O.  Kellner:  Z.  Biol.  39,  339  (1900). 

2  Weiske:  Z.  Biol.  20,  279  (1884). 

8  E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  46,  179  (1905). 

4  F.  Czapek:  Hofmeister's  Beit.  1,  542  (1902). 

5  O.  Emmerling:  Ber.  35,  2289  (1902). 


ALBUMINS  OR  PROTEINS.  217 

shown  that  the  amino  acids  act  very  efficiently  as  sources  of  nitrogen. 
The  latter  also  called  attention  to  the  interesting  fact  that  the  molds  will 
only  attack  the  a-amino  acids,  while  other  acids,  with  the  amino  groups 
differently  situated,  are  unacted  upon.  We  may  add  that  Aspergillus 
niger  will  also  act  on  the  polypeptides  produced  from  the  a-amino  acids, 
as  well  as  on  the  polypeptides  which  are  not  decomposed  by  trypsin;  for 
instance,  glycyl-glycin  and  dileucyl-glycyl-glycin.  This  is  not  very  unu- 
sual, for  we  know  that  the  animal  organism  possesses  ferments  in  the  cells 
which  are  capable  of  breaking  down  compounds  unattacked  by  trypsin. 
That  this  assumption  is  correct,  is  evident  from  the  previous  description 
of  the  behavior  of  individual  polypeptides  in  the  animal  organism.1 

Ammonium  oxalate 2  has  been  observed  as  a  metabolic  end  product  in 
mold  activity,  but  only  during  growth  with  a  supply  of  certain  amino 
acids;  for  instance,  glycocoll,  alanine,  serine,  aspartic  acid,  glutamic  acid, 
and  proline.  On  the  other  hand,  no  oxalic  acid  is  produced  from  leucine, 
phenylalanine,  lysine,  arginine,  and  histidine.  Ammonia  is  very  often 
one  of  the  end-products  of  mold  and  bacterial  metabolism.  We  would 
refer,  for  example,  to  the  cleavage  of  urea  by  bacterial  action  with  the 
formation  of  ammonium  carbonate.  The  different  varieties  of  mold  and 
bacteria,  moreover,  produce  unequal  amounts  of  ammonia.  Bacillus 
mycoides,  for  instance,  converts  as  much  as  forty-six  per  cent  of  the 
nitrogen  in  albumin  into  ammonia.3 

We  might  expect  that  carnivorous  plants,  unlike  the  Aspergillus  niger 
which  we  have  just  considered,  would  be  able  to  assimilate  directly  the 
amino  acids  and  higher  albuminous  cleavage-products,  synthesizing  them 
into  albumin  in  the  same  manner  as  does  the  animal  organism,  i.e.  without 
preliminary  decomposition.  The  metabolism  of  such  plants  has,  unfortu- 
nately, been  studied  but  little,  and  we  do  not  even  know  how  they  digest 
albumin.  That  there  are  organisms  in  the  vegetable  world  which  are 
only  capable  of  forming  albumin  from  its  cleavage-products,  is  evident 
from  the  researches  of  Beijerinck,4  from  which  it  appears  that  the  conidial- 
alga,  Cystococcus  humicola,  the  alga  of  the  lichen,  Physica  parietina,  with 
which  it  lives  in  symbiosis,  prepares  peptones  for  the  nourishment  of  the 
latter.  It  would  be  interesting  to  study  the  true  parasites  and  the  sapro- 
phytes from  this  point  of  view. 

Let  us  return  to  the  behavior  of  the  albuminous  substances  in  the 
intestine.  Not  all  the  cleavage-products  of  the  proteins  are  absorbed. 
A  part  is  decomposed  in  another  manner,  and  is  lost  for  the  further  syn- 
thesis of  albumin  in  the  animal  body.  Bacteria  are  present  in  the  intes- 


1  Cf.  p.  203. 

2  O.  Emmerling:  Zentr.  Bakt.  u.  Parasitienkunde,  II,  10,  273  (1903). 

3  E.  Marchal:  Zentr.  Bakt.  II,  1,  1753  (1895). 

4  Beijerinck:  Bot.  Zeit.  1890,  No.  45,  Zentr.   Bakt.  13,  368  (1893). 


218  LECTURE  X. 

tines,  living  at  the  expense  of  our  food  materials  and  especially  the  albu- 
minous substances.  They  are  found  in  the  small  as  well  as  in  the  large 
intestine,  and  occur  there  as  aerobes  and  anaerobes.1  The  intestinal 
"  flora,"  that  is,  the  bacterial  content  of  the  intestines,  is  very  dependent 
upon  the  nature  of  the  nourishment,  and  varies  with  it.  The  anaerobic 
bacteria,  and  especially  the  Bacillus  putrificus,  are  largely  responsible  for 
the  putrefaction  of  albumin.  The  activity  of  this  bacillus  is  accelerated 
by  the  presence  of  aerobic  bacteria,  especially  Bacterium  coli  and  lactis 
aerogenes.  They  predominate  when  a  large  amount  of  oxygen  is  present ; 
the  activity  of  the  anaerobes  then  becomes  restricted,  as  a  result  of  which 
the  albumin  putrefaction  is  also  diminished.  When,  on  the  other  hand, 
there  is  a  small  amount  of  oxygen  present,  the  anaerobic  bacteria  become 
active.  That  the  anaerobic  and  aerobic  species  of  bacteria  act  together 
is  due  to  the  fact  that  the  latter  consume  the  oxygen  which  restricts  the 
living  processes  of  the  former;  while  the  anaerobes,  on  the  other  hand,  form 
products  by  their  activity  which  serve  as  sources  of  nutriment  for  the 
aerobes.  Naturally,  the  action  of  anaerobic  bacteria  alone  on  albumin  will 
not  give  the  same  products  as  when  the  two  kinds  of  bacteria  act  together. 
The  bacteria  themselves  are  introduced  into  the  intestines  with  the  food. 
The  intestines  of  the  new-born  are  sterile.2  No  bacteria  can  be  found  in 
their  meconium,  the  first  excretory  product  from  the  intestine.  When  a 
definite  bacterial  flora  has  settled  itself  in  the  intestines,  the  amount 
present  is  but  slightly  dependent  upon  any  further  addition  from  the  food- 
supply.  The  fate  of  the  bacteria  is,  then,  determined  by  the  food  presented 
to  them,  their  nutrient  medium.  There  is,  furthermore,  a  vigorous 
struggle  for  existence  in  the  intestines.  Those  bacteria  whose  nutrient 
requirements  are  satisfied  most  favorably  triumph  over  the  others.  On  the 
other  hand,  a  form  of  symbiosis  develops  by  which  one  variety  of  bacteria 
will  consume  the  products  of  another,  thus  giving  rise  to  quite  a  variety 
of  bacteria.  Their  development  is  kept  within  certain  limits  in  a  number 
of  ways,  so  that  the  putrefactive  processes  do  not  play  any  great  part 
in  the  intestines,  and  only  a  small  portion  of  our  food  is  sacrificed  to 
them. 

Great  importance  has  been  attached  to  the  hydrochloric  acid  in  the 
stomach  for  restraining  bacterial  activity;  in  fact,  for  a  long  time  it  was 
believed  that  this  was  its  most  important  function.  The  amount  of 
hydrochloric  acid  in  the  gastric  juice  varies  in  different  animals,  as  already 
mentioned.  It  is  sufficient,  however,  to  restrict  the  activity  of  the  putre- 

1  Cf.  also  Escherich:  Die  Darmbakterien  des   Sauglings,  Stuttgart,  1886.     A.  Mac- 
fayden,  M.  Nenki,  and  N.  Sieber:  Arch.  exp.  Path.  Pharmak.  28,  311  (1891).     D.  Ger- 
hardt:  Ueber  Darmfaulniss.  Ergebnisse  der  Physiologic  (Asher  and  Spiro),  3,  1,  107 
(1904). 

2  Bienstock:  Arch.  Hyg.  36,  335  (1899);  ibid.  39,  301  (1901). 


ALBUMINS  OR  PROTEINS.  219 

factive  bacteria,  as  has  been  shown  by  N.  Sieber.1  Even  Spallanzani 2 
was  acquainted  with  this  property.  He  showed  that  a  lizard  which  had 
been  swallowed  by  a  snake  did  not  show  any  indication  of  putrefactive 
changes  during  sixteen  days  in  which  the  digestion  of  the  animal  in  ques- 
tion was  carried  out,  He  also  found  that  when  he  inserted  decaying  meat 
into  an  animal's  stomach  that  the  putrefactive  changes  were  diminished 
and  that  the  putrefactive  odor  disappeared.  It  is,  therefore,  certain  that 
the  free  hydrochloric  acid  of  the  stomach  is  of  service  in  this  direction. 
It  is,  however,  questionable  whether,  as  some  observers  maintain,  the  putre- 
factive changes  in  the  intestines  are  prevented  to  any  extent  by  the  hydro- 
chloric acid  from  the  stomach.  At  any  rate,  no  increase  in  putrefaction 
has  been  observed,  even  after  the  stomach  was  completely  removed. 
Hydrochloric  acid  is  often  absent  in  human  beings  under  certain  path- 
ological conditions,  while,  in  other  cases,  it  is  often  secreted  in  excess.  No 
definite  influence  on  putrefactive  changes  is  discernible  under  such 
conditions.  On  the  other  hand,  we  should  like  to  call  attention  to  an 
indirect  significance  of  the  hydrochloric  acid  of  the  stomach  in  this  con- 
nection. We  have  already  mentioned  that  the  hydrochloric  acid  un- 
doubtedly plays  an  important  part  in  the  preliminary  preparation  of  the 
albuminous  bodies  for  their  disintegration.  This  splitting  up  of  the  pro- 
teins into  numerous  larger  and  smaller  cleavage-products  in  the  stomach 
has  for  its  main  object,  according  to  our  present  conception,  the  presen- 
tation of  the  largest  possible  surface  of  attack  to  the  trypsin,  which  facili- 
tates the  further  rapid  degradation  and  absorption.  The  more  quickly 
these  processes  are  carried  out,  the  less  opportunity  do  the  bacteria  have 
to  attack  the  cleavage-products.  That  this  is  the  correct  assumption, 
is  evident  from  the  researches  of  Ortweiler.3  He  found  that  two  patients 
afflicted  with  carcinoma  of  the  stomach  —  a  tumorous  formation  in  which 
the  free  hydrochloric  acid  is  generally  absent  —  showed  a  smaller  elimina- 
tion of  indican  after  the  administration  of  hydrochloric  acid.  Indican  is  one 
of  the  putrefactive  products  of  albumin,  as  we  shall  shortly  see.  That  this 
retardation  is  not  due  to  any  direct  action  of  hydrochloric  acid  on  the 
bacteria  is  evident  from  the  fact  that  the  administration  of  pepsin  will 
have  the  same  effect.  The  preliminary  decomposition  of  the  albuminous 
bodies  was,  therefore,  the  cause  of  the  diminished  putrefaction.  The 
putrefactive  bacteria  could  not  develop  their  activity  in  the  stomach 
under  normal  conditions.  We  also  introduce  air  into  the  stomach  with 
the  food.  This  is  the  reason  why  the  aerobic  bacteria  develop  there.  They 
themselves  cannot  cause  putrefaction.  Their  action  is  confined  mainly  to 

1  Nadina  Sieber:  J.  pract.  Chem.  19,  433  (1879). 

*  Spallanzani:  Experiences  sur  la  digestion.    Trad,  par  Senebier.     Nouvelle  Edition, 
Geneve,  1784;  in  German:  Versuche  iiber  das  Verdauungsgeschaft,  Leipzig,  1875. 
8  Ortweiler:  Mitteil.  a.  d.  med.  Klinik  zu  Wiirzburg,  2,  1886. 


220  LECTURE  X. 

the  carbohydrates,  whose  fermentation  is  an  especially  vigorous  one  when 
the  free  hydrochloric  acid  is  absent,  as  is  indicated  by  the  appearance  of 
butyric  and  lactic  acids  in  such  cases.  The  antiseptic  action  of  hydro- 
chloric acid  is,  therefore,  more  to  be  sought  for  in  this  direction. 

To  the  bile,  and  especially  the  acid  present  in  it,  has  also  been  ascribed 
an  influence  on  the  putrefactive  changes  in  the  intestines.  There  are, 
however,  many  observations  which  do  not  support  this  view.  Friedrich 
Miiller  *  observed  no  increase  in  the  amount  of  indican  excreted  in  a  case 
of  icterus,  i.e.  an  obstruction  in  the  biliary  passages,  thus  preventing  the 
flowing  of  bile  into  the  intestine;  nor  was  there  any  appreciable  increase 
in  putrefactive  changes  observed  in  the  case  of  a  dog  in  which  a  biliary 
fistula  was  made. 

The  putrefactive  processes  increase  in  the  intestines  only  when  some 
stagnation  of  the  intestinal  contents  exists.  Jaffe,  who  first  called 
attention  to  this  phenomenon,  also  showed  that  only  when  a  stoppage 
occurred  in  the  small  intestine  did  any  marked  increase  of  indican  appear 
in  the  urine.  If  we  observe  any  increase  in  the  elimination  of  indican, 
and  there  is  an  obstruction  in  the  large  intestine,  we  are,  therefore,  justi- 
fied in  concluding  that  the  stoppage  reacts  back  upon  the  contents  of 
the  smaller  intestine.  That  a  stoppage  of  the  large  intestine  of  itself  has 
but  little  effect  upon  the  elimination  of  indican,  is  evident  from  the  fact 
that  the  greater  part  of  the  albumin  is  absorbed  in  the  small  intestine, 
while  only  small  amounts,  depending  on  the  nature  of  the  food,  succeed 
in  reaching  the  large  intestine.  Ellinger  and  Prutz 2  have  determined  the 
effect  of  stoppages  in  various  parts  of  the  alimentary  tract  in  a  very 
ingenious  manner.  They  cut  out  pieces  of  the  intestine  of  a  dog,  and 
replaced  them  so  that  the  oral  end  of  each  excised  piece  was  joined  to 
the  distal  end  of  the  whole  intestine;  and,  conversely,  the  distal  end  was 
joined  to  the  portion  remaining  attached  to  the  stomach.  Such  a  piece 
of  intestine  retains  its  original  peristalsis  and  prevents  the  further  pro- 
gress of  the  chyme  and  fseces,  in  that  it  continually  opposes  the  activity 
of  the  remainder  of  the  intestine.  We  shall  subsequently  take  up  in  detail 
the  compounds  resulting  from  the  putrefactive  processes  upon  the  cleavage- 
products  of  albumin. 


1  Z.  klin.  Med.  12. 

»  Z.  physiol.  Chem.  38,  399  (1903). 


LECTURE   XI. 

ALBUMINS    OR   PROTEINS. 
V. 

DECOMPOSITION   OF    PROTEINS    IN   THE    TISSUES.     THE    END-PRODUCTS 
OF   ALBUMIN   METABOLISM. 

ACCORDING  to  our  present  conception  of  the  digestion  and  assimilation 
of  albuminous  substances,  we  must  assume  that  the  different  proteins  of 
our  food  are  converted  into  the  albuminous  bodies  of  the  plasma.  In  this 
form  the  individual  cells  obtain  the  nitrogenous  material  which  is  abso- 
lutely necessary  for  its  maintenance,  and,  from  our  knowledge  of 
metabolism  during  fasting,1  we  must  conclude  that  the  cells  themselves 
give  up  their  albumin  only  in  this  form  to  the  blood  for  further  transpor- 
tation. We  know  as  little  about  the  manner  in  which  the  cells  produce 
their  albumin  from  the  proteins  of  the  blood  as  we  do  of  the  reason 
why  the  animal  organism,  under  all  conditions,  requires  such  relatively 
large  amounts  of  albumin  for  the  proper  maintenance  of  its  corporal 
existence.  In  this  connection  it  is  especially  noteworthy  that  the  growing 
nursling  consumes  as  much  albumin,  proportionately,  as  does  the  fully 
developed  organism.  E.  Feer3  gives  951  grams  as  the  daily  quantity  of 
milk  consumed  by  a  boy  29  to  30  weeks  old,  and  weighing  8.23  kilograms. 
This  amount  would  contain  15.2  grams  albumin,  32.3  grams  fat,  58.0 
grams  sugar,  and  1 . 9  grams  ash.  At  this  rate  a  grown-up  person  weighing 
70  kilograms  would  consume  daily: 

Albumin 129  grams 

Fat      275     " 

Sugar 494     " 

Ash 16     " 

The  following  values  have  been  found  actually  to  be  the  average  food 
requirement  of  an  adult: 

Albumin 118  grams 

Fat      56     " 

Sugar 500     " 


1  See  Lecture  on  Metabolism. 
1  Jahrbuch  f.  Kinderheilkunde,  X.  F.  42,  195,  196. 

221 


222  LECTURE  XL 

The  fully  developed  organism  has,  of  course,  losses.  We  need  only 
refer  to  its  secretions,  to  the  constant  changes  of  the  epidermal  struc- 
tures, the  cells  of  the  mucous  membrane,  and  to  all  of  the  observa- 
tions regarding  the  organs  themselves,  which  participate  in  a  continuous 
decomposition  and  reconstruction  in  the  tissues.  It  is,  of  course,  possible 
that  these  latter  processes  are  much  more  extensive  than  we  have  any 
idea,  and  that  new  groups  are  constantly  entering  the  cell  contents, 
and  others  leaving.  This  is  in  accord  with  the  fact  that  the  animal 
organism  disintegrates  the  nutrients  to  such  an  extent  and  adapts  them 
to  all  of  the  bodily  requirements.  On  the  other  hand,  we  can  form 
no  clear  conception  of  the  manner  in  which  protoplasm  and  its  com- 
ponents are  used  up,  nor  understand  at  present  why  the  cells  should  tear 
down  its  own  components  in  order  to  make  way  for  the  constituents  of 
the  nourishment.  As  the  different  cells,  according  to  the  tissues  of  which 
they  are  a  part,  and  the  function  which  they  serve,  have  a  specific 
structure,  and  above  all  possess  individualized  protein  materials,  we  must 
consequently  assume  that  the  cells  at  every  moment  take  their  own  char- 
acteristic building  material  from  the  homogeneous  mixture  of  the  blood 
proteins,  and  to  some  extent  transform  them  in  a  quite  complicated 
manner.  It  is  possible  that  the  whole  phenomenon  is  an  hereditary  one. 
The  single-celled  organisms  are  constantly  engaged  in  multiplying  them- 
selves. They  develop  rapidly,  producing  new  individuals  in  quick  suc- 
cession. We  meet  the  same  phenomenon  in  some  of  the  more  highly 
organized  invertebrates.  From  a  single  individual,  thousands  and  tens  of 
thousands  of  new,  rapidly  growing  creatures  are  formed.  The  whole  cell 
material  is  engaged  in  constant  growth  and  change.  We  also  find  analo- 
gous phenomena  among  the  vertebrates.  In  these  cases  they  are  confined 
in  the  grown  individual  to  the  sexual  organs.  Here,  also,  we  observe  a 
constant  increase  in  the  number  of  cells,  and  a  continual  delivery  of  cell 
material,  on  the  one  hand  eggs,  and  on  the  other  spermatozoa.  The 
cooperative  efficiency  of  the  other  body-cells,  in  promptly  preparing  thou- 
sands and  tens  of  thousands  of  new  cells,  is  evident  from  the  tremendous 
production  of  leucocytes  at  the  beginning  of  any  infection.  The  invading 
army  is  surrounded  in  the  shortest  space  of  time  by  thousands  of  white 
blood-corpuscles.  They  form  a  thick  wall,  and  protect  the  remainder  of 
the  organism.  The  leucocytes  also  play  some  other,  as  yet  undiscovered, 
important  role  in  the  animal  organism.  For  instance,  they  are  present  in 
the  intestines  in  large  numbers  during  digestion.  Every  one  of  these 
newly  formed  cells  must  have  a  completely-constructed  protoplasm.  They 
must  in  every  case  contain  all  the  elementary  components;  moreover,  they 
also  contain  proteins,  which  alone  are  capable  of  giving  to  their  compli- 
cated structure  its  true  individuality. 

The  great  facility  with  which  the  animal  organism  produces  new  cells 


ALBUMINS  OR  PROTEINS.  223 

from  its  tissues  may  possibly  throw  some  light  on  the  fact  that  the  animal 
cell  is  continuously  using  up  proteins  in  its  economy.  Every  individual 
body-cell  is  capable  of  forming  new  cells,  either  in  renewing  its  own 
structure,  or  in  giving  off  cells.  It  obtains  the  other  necessary  elementary 
constituents  from  the  storehouses  of  the  tissues.  Fats  and  carbohy- 
drates are  held  in  reserve.  The  animal  organism  has  no  storeroom  for 
its  albumin.  It  is  only  capable  of  accumulating  albumin  under  very 
specific  conditions.  Even  these  stores  are  removed  when  the  nutrition 
returns  to  its  normal  state.  Every  cell  is  evidently  restricted  to  a  definite 
amount  of  albumin,  to  which  it  closely  adheres.  If  the  animal  organism 
possesses  more  fat  or  carbohydrate  than  it  requires,  it  will  store  them  up. 
There  is  no  increase  in  the  metabolism.  If,  on  the  other  hand,  the  amount 
of  albumin  administered  be  increased,  then  the  metabolic  changes  are 
increased.  The  albumin  governs  the  whole  animal  organism.  We  will 
add,  that  from  the  chemical  point  of  view  it  is  perfectly  possible  for  the 
cell,  under  certain  conditions,  to  produce  all  its  other  organic  requirements 
from  albumin.  It  is  possible  that  it  may  produce  fats  and  carbohydrates 
from  albumin.  Albumin,  from  this  point  of  view  alone,  is  therefore  a 
valuable  food-material.  Whether  such  changes  actually  occur  under 
normal  feeding,  that  is,  with  a  sufficiency  of  fats  and  carbohydrates,  is 
very  problematical,  in  fact  hardly  to  be  assumed. 

We  will  furthermore  add  that  the  albumin  in  the  nourishment,  which 
certainly  serves  for  manifold  purposes,  may  not  alt  participate  in  the 
true  cell  metabolism.  We  arrive  at  this  conclusion,  from  the  fact  that 
the  animal  organism  evidently  produces  its  body  albumin  from  such 
differently  constituted  proteins  in  our  foods.  Waste  products  may  very 
easily  arise.  Let  us  recall  the  experiment  of  feeding  a  horse  with  gliadine, 
which  is  so  rich  in  glutamic  acid.  As  this  animal  was  only  capable  of 
utilizing  one-fifth  of  this  amino  acid  for  the  synthesis  of  serum-albumins, 
the  remainder  must  have  been  consumed  in  some  other  manner.  It  is 
possible  that  the  animal  cells  possess  the  ability  of  producing  other  amino 
acids  from  a  specific  one,  but  we  can  also  imagine  that  when  the  nutrient 
albumin  is  transformed  into  body  albumin,  many  of  the  elementary  com- 
ponents are  cast  aside  and  directly  consumed.  We  must  not  forget  that 
we  are  now  entering  into  a  realm  which  has  so  far  been  but  little  investi- 
gated. We  might  expect  from  this  assumption  that  the  animal  organism 
would  be  satisfied  with  the  smallest  amounts  of  those  albuminous  sub- 
stances whose  compositions  were  closely  related  to  its  own  proteins.  In 
this  case  most  of  the  elementary  components  would  be  available.  At  any 
rate,  we  are  not  justified  in  drawing  the  conclusion  that  the  proteins 
in  the  food  take  part  in  the  metabolism  of  the  cells  from  the  fact  that 
the  nitrogen  —  in  the  case  of  mammals  —  reappears  in  a  short  time  as 
urea.  We  find  that  amino  acids  and  polypeptides  are  eventually  broken 


224  LECTURE  XI. 

down  in  the  same  way  as  the  proteins  themselves,  although  they  hardly 
ever  come  into  intimate  contact  with  the  cells.  It  has,  moreover,  never 
been  found  possible  to  spare  albumin  by  means  of  a  mixture  of  amino 
acids.  The  animal  organism  is  evidently  unable  to  build  up  its  own 
albumin  from  such  material  because  other  essential  components  are  want- 
ing.1 Why  should  not  groups  result  under  normal  conditions  which  are 
unsuitable  for  further  synthesis  and  which  are,  therefore,  immediately 
deprived  of  the  amino  group  and  consumed  ? 

The  large  albumin-requirement  of  the  animal  organism  would  be  partly 
explained  by  its  constantly  striving  to  obtain  as  much  as  possible  of  its 
individual  building-material.  Here  also  the  Law  of  the  Minimum  holds, 
i.e.  the  extent  of  the  syntheses  taking  place  depends  upon  the  amount  of 
that  substance  which  is  present  relatively  to  the  least  extent.  Again, 
in  the  formation  of  the  cell  material  from  the  serum-albumin,  all  of  the 
components  of  the  latter  are  not  utilized  to  the  same  extent.  Under  some 
circumstances  entire  large  groups  may  not  be  used  at  all.  According  to 
this  conception,  it  might  be  that  a  cell  decomposition  and  replacement, 
which  of  itself  was  not  very  extensive,  might  require  a  large  amount  of 
proteins.  But  even  with  this  assumption  we  are  still  unable  to  explain 
the  fact  that  a  definite  amount  of  albumin  is  necessary  to  maintain 
an  equilibrium  in  the  metabolism.  We  would  expect  that  the  amount  of 
albumin  used  would  be  now  more,  now  less.  But  the  grown  organism 
maintains  its  metabolism  in  a  very  definite  manner,  and  keeps  it,  with 
very  little  variation,  at  a  constant  level.  We  ought  to  get  a  good  idea  of 
all  of  these  relations  by  exactly  following  the  course  of  nitrogen  metab- 
olism of  the  salmon  during  its  stay  in  fresh  water.  Remarkable  trans- 
formations occur  in  its  organism.  Its  muscle-albumins  finally  produce 
the  protamines  of  entirely  different  composition.  Are  all  of  the  elemen- 
tary components  of  the  former  utilized?  If  this  be  so,  then  the  animal 
organism  must  be  capable  of  converting  one  component  into  another. 
These  suggestions,  needless  to  state,  are  insufficient  to  remove  the  haze 
which  still  thickly  envelops  the  whole  metabolism  of  albumin. 

If  we  wish  to  consider  this  entire  problem  which  is  so  important  to 
biology,  we  cannot  neglect  any  single  phase  of  the  whole  subject  of  the 
transformation  of  material;  and  from  this  point  of  view  it  will  be  worth 
our  while  to  follow  the  utilization  of  the  nutrient  proteins  and  their  value 
in  the  animal  organism. 

Although,  in  considering  the  questions  concerning  the  assimilation  of 
the  albumin  from  food,  we  met  with  great  difficulties,  these  become  appar- 
ently unsurmountable  when  we  attempt  to  follow  the  proteins  till  they 
are  taken  up  by  the  cells  of  the  body.  The  enigmas  begin  with  the 


E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  47    (1906) 


ALBUMINS  OR  PROTEINS.  225 

cell  itself.  Here  are  problems  wholly  unsolved.  We  cannot  be  led  away 
from  this  fact  by  the  discovery  of  more  and  more  nerve  fermentation 
processes  and  new  cell-ferments.  They  only  suggest  the  way  in  which 
the  cell  disintegrates  material,  and  leave  us  to  imagine  the  process  by 
which  the  cells  obtain  their  energy  from  the  nourishment.  We  know  very 
little  about  their  real  metabolism. 

We  must,  therefore,  give  up  trying  to  trace  the  further  behavior  of 
absorbed  albumin  in  the  animal  organism,  and  confine  ourselves  to  the 
discussion  of  the  metabolic  end-products.  We  may  be  able  to  obtain 
some  information  of  cell-metabolism  in  this  way.  The  albuminous  bodies 
contain  characteristic  elements,  namely  nitrogen  and  sulphur,  which  aid 
us  in  recognizing  their  decomposition  products.  We  know,  to  be  sure,  of 
other  nitrogenous  substances  besides  proteins,  which  participate  in  metabo- 
lism, and  need  only  refer  to  the  lecithins  and  nucleins,  etc.,  as  examples. 
Their  amounts,  however,  are  extremely  small  in  comparison  with  the 
proteins,  and  we  are  able,  from  the  chemical  constitution  of  the  end- 
products  of  metabolism,  to  indicate  definitely  their  origin.  The  extent  of 
the  decomposition  of  proteins  in  the  animal  organism  varies,  depending  on 
the  kind  of  animal;  this  at  least  applies  to  the  final  end-products.  In 
mammals  we  find  the  larger  part  of  the  nitrogen  introduced  into  the 

/NH2 
organism  reappears  in  the  urine  in  the  form  of  urea,  CO         .    The  amounts 

\NH2 

are  especially  large  in  the  case  of  the  carnivora,  and  less  so  with  the  her- 
bivora.  Only  a  very  small  amount  of  urea  occurs  in  the  urine  of  birds 
and  reptiles,  while  it  plays  a  very  important  part  in  the  economy  of  the 
amphibia  and  many  varieties  of  fishes.  Urea  has  also  been  found  in  the 
tissues  and  the  blood  of  mammalia.  It  is  very  striking  that  the  blood 
and  tissues  of  many  fishes,  especially  the  selachia,  contain  very  large 
amounts  of  urea.1  The  part  they  play  in  the  economy  of  these  animals 
has  not  yet  been  determined. 

That  urea  is  one  of  the  end-products  in  the  albumin  metabolism,  is 
evident  from  the  fact  that  its  amount  is  dependent  on  the  extent  of  albu- 
min decomposition  taking  place  in  the  tissues.  The  human  urine  for 
twenty-four  hours  contains,  under  normal  conditions  of  nutrition,  about 
thirty  grams  urea.  The  quantity  of  urea  is  greater  on  increasing  the 
amounts  of  albumin  administered,  or  by  reason  of  an  increased  decom- 
position of  the  albumin;  and,  conversely,  any  diminution  of  changes  in 
the  albumin  will  produce  less.  This  applies  only  within  certain  limits. 
In  many  cases  an  increased  disintegration  of  albumin  is  accompanied  by 


1  W.  v.  Schroder:  Z.  physiol.  Chem.  14,  576  (1890).  Cf.  also  O.  Hammarsten: 
Z.  physiol.  Chem.  24,  322  (1898).  S.  Baglioni:  Zentr.  Physiol.  19,  385  (1905).  V. 
Diamare:  ibid.  19,  545  (1805). 


226  LECTURE  XI. 

a  small,  or  even  no,  increase  in  the  amount  of  urea  in  the  urine,  for  the 
reason  that  other  nitrogenous  decomposition  products  are  also  formed, 
which,  in  part,  are  direct  indications  of  incomplete  combustion  of  the 
albumin.  We  observe  an  increased  albumin  disintegration  during  many 
pathological  processes,  such  as  fevers,  phosphorus,  arsenic  and  antimony 
poisoning,  and  also  with  an  insufficient  supply  of  oxygen.  We  shall  see 
later  that  an  increased  elimination  of  nitrogen  follows  the  administration 
of  the  thyroid  gland,  and  of  the  hypophysis,  or  of  extracts  obtained  from 
these  organs.  In  Morbus  Basedowii  we  shall  become  acquainted  with  a 
disease,  which  is  evidently  related  to  the  changes  in  metabolism  of  the 
thyroid  gland,  and  is  characterized  by  an  increased  disintegration  of 
albumin. 

We  are  here  chiefly  interested  in  this  question:  How  is  urea  produced 
from  albumin?  We  cannot  give  a  direct  answer.  We  may  in  fact  add 
that  the  formation  of  urea  from  albumin  has  never  been  satisfactorily 
explained.  We  are  accustomed  to  assume  that  a  hydrolytic  cleavage  pre- 
cedes the  oxidation  of  the  absorbed  and  assimilated  nourishment.  The 
cell  evidently  does  not  consume  glycogen,  but  d-glucose,  and  perhaps  not 
even  this  directly,  but  only  after  the  cell  has  altered  it  in  a  manner  as  yet 
undetermined  so  that  oxygen  can  attack  it.  We  assume  likewise  that  the 
fats  are  decomposed  into  their  components  and  are  then  completely  oxi- 
dized. Many  observations  indicate  that  the  proteins  in  the  cell-metabo- 
lism are  first  hydrolyzed  and  then  the  cleavage-products  are  consumed. 

An  observation  by  Drechsel *  seemed  to  place  the  proteins  in  an  excep- 
tional position.  Drechsel  obtained  urea  from  albumin  simply  by  hy- 
drolysis, although  the  yield  was  very  small.  We  know  to-day  that  the 
amount  of  urea  thus  formed  is  dependent  on  the  quantity  of  arginine 
present  in  the  protein. 

A.  Kossel  and  H.  D.  Dakin  2  have  also  recently  shown  that  urea  may  be 
obtained  from  arginine  in  the  tissues.  They  permitted  erepsin  to  act  on 
clupein  sulphate,  and  found  that  this  protamine  was  attacked  by  the 
ferment.  After  a  time  all  of  the  arginine  present  in  the  molecule  was 
found  in  the  digesting  fluid.  A  repetition  of  the  experiment,  using  another 
erepsin  preparation,  failed  to  remove  the  biuret  reaction,  even  when  the 
process  was  allowed  to  continue  through  a  long  period  of  time.  Higher 
complexes  remained  unattacked. 

On  analyzing  the  digesting  mixture  Kossel  and  Dakin  found  the  follow- 
ing products:  (1)  protone,  the  peptone  of  the  protamine;  (2)  arginine;  (3) 
ornithine;  (4)  urea;  and  (5)  amino- valeric  acid.  This  discovery  indi- 
cates that  the  erepsin  further  hydrolyzes  a  portion  of  the  arginine  into 

1  Ber.  23,  3096  (1890). 

J  Z.  physiol.  Chem.  41,  321  (1904) ;  42, 181  (1904).  Munchener  med.  Wochenschrift 
No.  13,  1904. 


ALBUMINS  OR  PROTEINS. 


227 


its  components.  These  investigators  also  succeeded  in  showing  that  the 
splitting  off  of  urea  was  due  to  the  action  of  a  specific  ferment  which  they 
called  arginase.  This  ferment  has  been  isolated  from  the  liver,  kidneys, 
thymus  and  lymphatic  glands,  and  the  chopped-up  intestine  of  the  dog. 
Small  amounts  are  also  present  in  the  blood  and  muscles,  but  it  is  absent 
in  the  suprarenal  glands,  in  the  spleen,  and  in  the  pancreatic  juice.  The 
formation  of  urea  from  arginine  proceeds  according  to  the  following  scheme: 

,NH2 


C  =  NH  i>xi2 

"  NH  .  CH2  .  CH2  .  CH2  .  CH  .  COOH  +  H2O 

Arginine 
,  NH2          NH2  NH2 

=  0   +        CH2  .  CH2  .  CH2 .  CH  .  COOH 


Urea  Ornithine     (Diaminovaleric  acid) 

Now  arginine  is  formed  in  the  alimentary  tract  by  the  action  of  trypsin, 
and  we  can  easily  imagine  that  this  diamino  acid  is  also  formed  in  the 
tissues  by  the  breaking  up  of  the  proteins.  One  of  the  sources  of  urea  is, 
therefore,  explained  by  this  discovery.  But  the  proteins  used  as  food- 
material  contain  far  less  arginine  than  they  do  of  protamines.  Only  the 
smallest  part  of  urea  present  in  the  urine  can  originate  from  this  source, 
as  the  following  table  shows: 


• 

100  gms.  Albumin 

contains  gins.  Arginine. 

Salmine                            

87.4 

Histon  from  the  thvrnus  glands               ....        .        .        ... 

15.5 

Gliadin                                               •••••"« 

3.4 

Gluten-casein                            

'  4.4 

4.8 

Edestin                    

11.7 

Gelatin                                                               '•    . 

7.6 

Another  interesting  discovery  accompanied  the  conclusion  that  urea 
was  split  off  from  arginine  in  the  tissues;  namely,  the  formation  of  ornithine. 
Jaffe  had  already  proved  that  as  a  matter  of  fact  this  diamino  valeric  acid 
is  formed  in  the  organism,  by  showing  that  ornithuric  acid  was  excreted 
when  benzoic  acid  was  fed  to  birds.  Ornithuric  acid  is  the  dibenzoyl 
derivative  of  ornithine,  and  has  the  formula  C5Hio(C6H5CO)2  .  N2O2. 
The  intermediate  product  of  metabolism,  ornithine,  is  undoubtedly 


228  LECTURE  XI. 

protected  against  further  oxidation  by  its  combination  with  benzoic  acid, 
and  is  excreted  as  such. 

The  question  now  arises  regarding  the  manner  in  which  urea  is  formed 
from  ornithine,  and  the  other  amino  acids.  We  can  say  that  it  has  been 
shown  that  urea  is  actually  formed  from  amino  acids  in  the  animal 
organism.1  This  discovery  is  of  great  significance.  It  had  always  been 
thought  possible  that  the  proteins  were  broken  down,  not  through  the 
amino  acids,  but  in  some  other,  still  unknown,  manner,  and  that  the  secret 
of  urea  formation  was  hidden  somewhere  in  such  decomposition.  If  we 
administer  glyeocoll,  alanine,  leucine,  glutamic  acid,  aspartic  acid,  aspara- 
gine,  or  arginine,  to  a  mammal,  either  by  the  mouth  or  subcutaneously,  we 
find  an  increase  of  urea  in  the  urine  corresponding  to  the  amounts  of  nitro- 
gen added  in  the  form  of  amino  acids.  We  observe  the  same  result  when 
we  use  the  polypeptides  instead  of  the  amino  acids,  e.g.  glycyl-glycine, 
diglycyl-glycine,  alanyl-alanine,  and  leucyl-leucine.2  Even  the  anhydrides 
so  far  investigated,  glycine  anhydride  and  alanine  anhydride,  are  disinte- 
grated by  the  organism  of  the  dog  into  urea.  An  especially  interesting 
case  is  that  of  arginine,  already  referred  to,  which  is  composed  of  two  parts, 
guanidine  and  diaminovaleric  acid  (ornithine).  We  have  already  called 
attention  to  the  ease  with  which  urea  is  formed  from  the  first  sub- 
stance. W.  H.  Thompson  has  shown 3  that  when  arginine  is  administered 
to  a  dog,  the  nitrogen  of  the  first  component,  guanidine,  quickly  reappears 
in  the  urine  as  urea.  Ornithine  itself  is  more  slowly  converted  into  urea. 
Even  100  per  cent  of  the  nitrogen  of  arginine  can  be  found  in  the  urine  of 
dogs  as  urea.  Very  appreciable  differences  sometimes  occur  in  different 
individuals.  S.  Salaskin  4  has  shown  that  the  liver  probably  plays  an 
important  part  in  the  production  of  urea  from  the  amino  acids.  He  passed 
glyeocoll,  leucine  and  aspartic  acid  through  a  dog's  liver  and  found  that 
the  blood  used  as  a  circulating  medium  showed  an  increase  in  its  content 
of  urea.  His  method  of  proof  is  not  very  satisfactory,  owing  to  the  fact 
that  his  method  of  estimating  urea  is  not  free  from  criticism. 

Before  discussing  the  statements  which  give  us  an  idea  of  the  chemical 
processes  participating  in  the  formation  of  urea,  we  wish  to  mention  those 
hypotheses,  which,  being  based  upon  experimental  results,  will  give  us  the 
best  conception  of  the  formation  of  urea  from  albumin  and  its  cleavage- 
products.  We  find  it  necessary  to  add  that  it  is  extremely  difficult,  from 


1  O.  Schultzen  and  M.  Nencki:  Ber.  2,  566  (1869),  and  Z.  Biol.  8,  124  (1872).  M. 
Nencki:  Ber.  5,  890  (1872).  W.  Knieriem:  Z.  Biol.  10,264  (1874).  E.  Salkowski:  ibid. 
4,  54  and  100  (1880). 

3  E.  Abderhalden  and  Y.  Teruuchi:  loc.  cit.  E.  Abderhalden  and  Franz  Samuely: 
loc.  cit.  E.  Abderhalden  and  B.  Babkin:  Z.  physiol.  Chem.  47  (1906). 

3  J.  Physiol.  32,  137  (1905),  and  33,  106  (1905). 

4  Z.  physiol.  Chem.  25,  128  (1898). 


ALBUMINS  OR  PROTEINS.  229 

the  literature  at  hand,  to  draw  a  correct  conclusion  regarding  the  subject. 
In  very  many  cases  we  have  contented  ourselves  with  a  more  or  less 
exact  method  of  determining  the  urea  or  its  antecedents.  This  proof  is 
generally  an  indirect  one.  We  shall,  therefore,  confine  ourselves  to  the 
most  important  investigations,  abstracting  only  the  essentials  from  each 
of  them. 

M.  Nencki *  characterizes  the  urea  formation  as  analogous  to  a  type  of 
synthesis,  which  takes  place  to  a  considerable  extent  in  the  animal  organ- 
ism; namely,  the  combination  of  two  substances  with  elimination  of  water. 
He  uses  the  formation  of  hippuric  acid  from  glycocoll  and  benzoic  acid,  as 
an  example: 


C6H5  .  CO  .jOH  +  HjNH .  CH2  .  COOH=C6H5CO  .  NH  .CH2  .  COOH  +  H20. 


Benzoie  acid  Glycocoll  Hippuric  acid 

Again, 

C23H39O3  .  COOH  +  H  .  NH  .  CH2  .  COOH 


Cholic  acid  Glycocoll 

=  C23H39O3  •  CO  .  NH  .  CH2  .COOH  +  H20. 
Glycocholic  acid. 

We  can  add  other  innumerable  examples  to  these.  We  need  only  refer 
to  the  formation  of  glycogen,  fats,  and  albumin  from  their  components, 
and  to  the  numerous  examples  of  the  conjugation  of  glycocoll,  glucuronic 
acid,  and  sulphuric  acid,  with  other  foreign  bodies.  Thus,  we  have  as  an 
example  of  each  : 

C6H5OH  +  HO  .  S03K  -  C6H5  .  0  .  S03K  +  H20. 
Phenol  Pot.  phenolsulphate 

CioH7COOH  +  NH2  .  CH2  .  COOH=Ci0H7CO  .  NH  .  CH2  .  COOH  +  H2O 

V  -  r  -  /  V  -  v  -  /  V  -  -  -^-  --  .  -  / 

Naphthoic  acid          Glycocoll  Naphthuric  acid 

3  .COH  +  C6H1007  =  (CH3)3  .  CO  .  C6H906  +  H20. 


Trimethyl-       Glucuronic     Conjugated  Glucuronic  acid 
carbinol  acid 

M.  Nencki  considers  the  formation  of  urea  from  ammonium  carbamate 
to  take  place  similarly  by  the  elimination  of  water: 

NH2  .  CO  .  O  .  NH4  =  NH2  .  CO  .  NH2  +  H20. 

Ammonium-  Urea 

bamate 


Ber.  6,  890  (1872). 


230  LECTURE  XI. 

Schmiedeberg  *  is  of  the  same  mind,  only  he  believes  that  the  urea  is 
produced  from  ammonium  carbonate.  We  can  imagine  that  the  ammo- 
nium carbarn  ate  is  an  intermediate  product,  as  indicated  by  the  following 
formulae : 

X0(NH4)  /0(NH4)  xNH2 

C=O  ->          C=0  ->  C=O+  H2O 

X0(NH4)  XNH2  XNH2 

Ammonium  Ammonium  Urea 

carbonate  carbamate 

Consequently  no  important  difference  seems  to  exist  between  the  last 
two  views.  Hoppe-Seyler  2  and  Salkowski 3  look  upon  the  formation  of 
urea  in  another  manner.  They  assume  that  cyanic  acid  and  ammonia  are 
first  produced  from  albumin: 

/NH2 

NCOH    +  NH3        ->        CN  .  O  .  NH4          ->    CO 

v— *— '  * '  VNH2 

Cyanic  acid  Ammonium  cyanate  Urea 

F.  Hofmeister  4  has  finally  proposed  a  third  hypothesis.  He  assumes 
that  urea  is  produced  by  an  oxidation  synthesis.  From  this  point  of 
view,  a  CONH2  group  is  formed  by  the  oxidation  of  albumin  or  its  amino 
acid,  which,  at  the  moment  of  its  formation,  unites  with  the  NH2  residue 
of  ammonia,  when  the  latter  is  oxidized,  thus  producing  urea. 

Of  the  three  theories  mentioned,  that  of  Hoppe-Seyler  and  Salkowski 
seems  to  us  the  least  probable.  It  has  the  least  experimental  support. 
Again,  cyanic  acid  has  not  been  discovered  in  the  organism.  The  Nencki- 
Schultze-Schmiedeberg  and  the  Hofmeister  hypotheses,  on  the  other  hand, 
have  many  observations  substantiating  their  claims.  In  the  first  place, 
numerous  experiments  have  established  the  fact  that  ammonium  carbonate, 
and  all  those  other  ammonium  salts  which  are  capable  of  being  converted 
into  it  in  the  tissues,  are  changed  into  urea  by  the  animal  organism.5 
This  applies  to  the  carnivora  as  well  as  to  the  herbivora.  It  had  seemed, 
it  is  true,  as  if  the  former  were  an  exception.  After  the  administration  of 
sal-ammoniac,  NH4C1,  to  rabbits,  the  increased  elimination  of  urea  corre- 

Arch.  exp.  Path.  Pharm.  8,  1  (1879). 

Physiologische  Chemie,  Berlin,  1881,  pp.  809  and  810. 

Z.  physiol.  Chem.  1,  1  and  374  (1877). 

Arch.  exp.  Path.  Pharm.  33,  198  (1894);  37,  426  (1896). 

W.  v.  Knieriem:  Z.  Biol.  10,  263  (1874).  E.  Salkowski:  Z.  physiol.  Chem.  1,  1 
(1877).  Cf.  also  L.  Feder:  Z.  Biol.  13,  256  (1877).  I.  Munk:  Z.  physiol.  Chem.  2,  29 
(1878-70).  E.  Hallervorden:  Arch.  exp.  Path.  Pharm.  10, 124  (1879).  F.  Walter:  ibid. 
7,  148  (1877).  Corander:  ibid.  12,  76  (1880).  J.  Pohl  and  E.  Miinzer:  ibid.  43,  28 
(1900). 


ALBUMINS  OR  PROTEINS.  231 

sponded  exactly  with  the  amount  of  nitrogen  added  in  the  form  of  sal- 
ammoniac.  The  results  were  not  so  definite  with  human  beings  and  dogs. 
A  part  of  the  ammonia  appeared  in  the  urine,  and,  from  the  uncertain 
increase  of  urea,  it  remained  undecided  whether  this  was  due  to  the  am- 
monia diet  or  an  increased  disintegration  of  albumin.  The  cause  of  the 
different  behavior  between  the  carnivora  and  the  herbivora  was  soon  dis- 
covered. It  depends  on  the  following:  The  food  of  the  herbivora  yields 
an  alkaline  ash,  and  during  its  combustion  in  the  organism  it  forms  potas- 
sium carbonate  which  can  react  with  ammonium  chloride.  Ammonia 
is  liberated,  and  can  then  be  utilized  for  the  production  of  urea.  The 
conditions  are  entirely  different  with  the  carnivora.  Its  food  furnishes 
an  acid  ash.  The  hydrochloric  acid  is  not  separated  from  the  ammonia 
in  the  tissues,  and  consequently  the  latter  is  not  available  for  the  produc- 
tion of  urea.  If,  on  the  other  hand,  we  feed  some  ammonium  carbonate 
to  a  dog,  we  likewise  observe  an  increase  of  urea.  These  experiments, 
therefore,  indicate  that  the  organism  of  mammals  is  capable  of  utilizing 
ammonia  for  the  production  of  urea. 

The  observations  of  N.  Nencki,  J.  Pawlow,  and  J.  Zaleski  *  have  indicated 
the  probability  that  ammonia  normally  —  i.e.  without  being  artificially 
administered  —  participates  in  the  formation  of  urea.  They  showed  that 
portal  blood  contained  much  more  ammonia  than  did  the  venous  blood  of 
the  liver.  The  intestine  evidently  sends  ammonia  to  the  liver,  where  it  is 
transformed.  If  the  liver  be  extirpated,  we  no  longer  observe  any  dif- 
ference between  portal  blood  and  that  obtained  from  any  other  part  of 
the  body. 

W.  v.  Schroder  2  has  shown  that  the  liver  can  produce  urea  from  am- 
monium carbonate  and  ammonium  formate.  He  passed  blood,  to  which 
he  had  added  these  ammonium  compounds,  through  the  liver  of  a  dog,  and 
could  soon  detect  an  increase  in  the  amount  of  urea  therein.  There  can, 
therefore,  no  longer  be  any  doubt  that  the  liver  plays  a  very  important 
part  in  the  production  of  urea.  Analogous  experiments  were  carried  out 
with  the  kidneys  and  muscles,  without,  however,  showing  any  increase  in 
the  formation  of  urea  in  these  organs. 

That  the  liver  is  not  to  be  looked  upon  as  the  only  place  where  urea  is 
formed,  is  evident  from  the  fact  that  its  production  is  continued,  even  if 
less  in  amount,  after  the  liver  has  been  entirely  extirpated.  These  dis- 
coveries only  became  possible  after  it  was  known  how  to  make  the  so- 
called  "  Eck's  fistula."  3  Mammals  do  not  tolerate  the  complete  extir- 
pation of  the  liver.  They  die  shortly  after  the  operation.  They  can, 

1  Arch.  exp.  Path.  Pharm.  37,  26  (1895). 

2  Arch.  exp.  Path.  Pharm.  15,  364  (1882);  19,  373  (1885). 

3  M.  Hahn,  O.  Massen,  M.  Nencki,  and  J.  Pawlow.     Arch.  exp.  Path.  Pharm.  32, 
161  (1892). 


232  LECTURE  XI. 

however,  be  kept  alive  for  a  considerable  time,  if  the  liver  is  cut  off  from 
the  general  circulation  while  the  portal  vein  is  sewed  to  the  Vena  cava 
inferior  near  the  hilus  of  the  liver,  and  communication  then  established 
between  the  two  veins.  The  blood  then  passes  directly  from  the  intestine 
into  the  general  circulation.  The  experimental  results  obtained  after 
this  operation  are  not  always  uniform,  owing  to  the  fact  that  some  of 
the  blood  will  often  find  its  way  through  the  liver  on  account  of  a  collateral 
circulation  which  may  develop. 

If,  thus,  the  utilization  of  ammonia  in  the  formation  of  urea  has  been 
established,  we  must  now  determine  whether  it  is  to  be  assumed  that  all, 
or  at  least  the  greater  part,  of  the  amino  groups  present  in  the  tissues  are 
split  off  as  ammonia,  and  thus  take  part  in  the  production  of  urea.  Such 
an  assumption  has  much  in  its  favor.  In  recent  years  a  number  of  pro- 
cesses have  been  discovered  in  the  animal  organism  which  indicate  the 
presence  of  ferments  which  cause  the  removal  of  the  amino  group,  and, 
in  fact,  such  processes  are  known  in  the  vegetable  as  well  as  in  the  animal 
kingdom.  We  can  imagine  that  entirely  analogous  to  the  breaking  down 
of  carbohydrates  and  fats  in  the  tissues,  the  proteins  are  first  hydrolysed 
with  the  formation  of  the  separate  amino  acids,  from  which  ammonia  is 
split  off.  Nitrogen-free  carbon  chains  would  then  remain,  by  the  com- 
bustion of  which  the  cells  could  then  obtain  their  energy.  Unfortunately, 
we  know  nothing  further  about  these  carbon  chains.  It  is  possible  that 
they  enter  into  relations  with  the  carbohydrates  and  with  the  fats.  The 
CO  group  for  the  production  of  urea  does  not  necessarily  have  to  orig- 
inate from  the  albumin  itself. 

We  have  already  called  attention  to  the  assumption  that  carbamic  acid 
may  occur  as  an  intermediate  product  between  the  amino  acids  and  urea. 

/NH2 

It  is  not  known  as  the  free  acid:   CO        ,    but   as  its  ammonium  salt. 

XOH 

/  NH2  /  NH2 

The  close  relations  between  carbamic  acid,  CO       ,  and  urea,  CO         ,  are 

x  OH  X  NH2 

evident  without  further  comment.  We  may  consider  urea  as  the  amide 
of  carbamic  acid.  It  is  difficult  to  decide,  from  the  investigations  at  hand, 
whether  this  acid  is  a  normal  metabolic  product.  There  are  many  obser- 
vations at  hand  which  indicate  that  carbamic  acid  is  present  in  urine,  —  in 
fact,  normally  so.  Abel l  states  that  he  has  succeeded  in  obtaining  this 


1  E.  Drechsel  and  J.  J.  Abel:  Arch.  Anat.  Physiol.  1891,  236.  J.  J.  Abel  and  A. 
Muirhead:  Arch.  exp.  Path.  Pharm.  31,  15  (1893).  Cf.  also  E.  Drechsel:  J.  pract. 
Chem.  12,  417  (1875);  22,  476  (1880). 


ALBUMINS  OR  PROTEINS.  233 

acid  in  large  amounts  from  the  urine  of  human  beings  and  dogs  after  the 
administration  of  milk  of  lime.  Furthermore,  it  has  been  observed  that 
dogs  with  an  Eck's  fistula  showed  severe  indications  of  poisoning,  and  that 
the  same  symptoms  could  be  obtained  by  the  introduction  of  carbamates 
into  the  blood-stream.  This  method  of  proof  is  not  convincing.  Macleod 
and  Haskins  *  have  recently  indicated  the  normal  presence  of  carbamates  in 
the  urine  and  of  an  increased  appearance  after  extirpation  of  the  liver. 
We  must  admit  that  the  estimation  of  the  carbamic  acid  was  only  an 
indirect  one.  On  the  other  hand,  the  formation  of  carbamates  corre- 
sponds very  well  with  the  assumption  of  the  production  of  urea  from 
ammonium  carbonate,  as  previously  mentioned.  We  wish  to  emphasize, 
however,  that  its  normal  occurrence  and  its  relations  to  the  production  of 
urea  have  not  yet  been  absolutely  proved. 

It  will  be  appropriate  at  this  point  to  call  attention  to  the  observa- 
tion of  M.  Siegfried,2  which  may  have  some  bearing  on  the  formation  of 
urea  as  indicated  above.  M.  Siegfried  found  that  when  carbon  dioxide 
was  led  into  a  mixture  of  equal  parts  of  normal  glycocoll  and  baryta 
solutions  no  immediate  precipitation  of  barium  carbonate  appeared,  as 
was  to  be  expected,  but  the  mixture  remained  clear  for  some  time.  It 
gradually  became  turbid  on  standing.  In  studying  this  subject  further, 
Siegfried  found  that  salts  of  the  following  type  were  formed: 

R— N' 

|  XCOOH 
COOH 

Siegfried  analyzed  several  of  these  salts,  for  instance,  calcium  glycocoll- 
carbonate  (calcium  carbamoacetate) : 

/H 
CH2— N— COO 

COO— Ca/ 

Also  the  calcium  alanine-carbonate  (calcium  carbamopropionate) : 

CH3 


C— NH— COO 

COO— Ca/ 
The  composition  of  calcium  leucine-carbonate  is: 

(CH3)2  .  CH  .  CH2  .  CH  .  NH  .  COO 

COO— Ca 


1  Am.  J.  Physiol.  12,  444  (1905). 

2  Z.  physiol.  Chem.  44,  85  (1905);  46,  401  (1905). 


234  LECTURE  XI 

We  will  only  refer  here  to  these  interesting  investigations,  and  await 
further  developments. 

We  must  also  consider  Hofmeister's  hypothesis  and  its  claims.  Hof- 
meister  succeeded  first  of  all  in  producing  urea  by  the  oxidation  of  albu- 
min, and  then  also  of  amino  acids,  in  the  presence  of  ammonia.  From  10 
grams  glycocoll  he  obtained  3  grams  urea.  The  assumption  of  an  oxidizing 
synthesis  in  the  formation  of  urea  has  much  in  its  favor.  On  the  one 
hand,  the  conditions  in  the  animal  organism  are  very  favorable  for  such  a 
production  of  urea  from  amino  acids;  and  then  again,  the  whole  process 
harmonizes  very  well  with  our  conception  of  the  degradation  of  the  proteins. 
The  hypothesis,  however,  has  not  yet  been  proved. 

If  we  take  everything  that  we  know  about  the  formation  of  urea  in  the 
animal  organism,  into  consideration,  we  can  conclude  that  a  part  of  urea 
is  directly  produced  by  the  hydrolytic  cleavage  of  albumin,  the  amount 
depending  on  the  nature  of  the  latter.  Arginine  is  the  only  source  so  far 
known  for  this  process.  This  does  not,  however,  exclude  the  possibility 
that  other  analogous  complexes  to  that  of  this  amino  acid  may  be  present 
among  the  as  yet  unknown  elementary  constituents  of  albumin.  We 
also  know  that  amino  acids  and  polypeptides,  when  incorporated  in  the 
animal  organism,  go  over  into  urea.  We  do  not,  however,  know  the  manner 
in  which  this  further  decomposition  is  accomplished.  It  is  not  impossible 
that  the  anhydride  formation,  or  the  oxidizing  synthesis,  plays  an  impor- 
tant part.  Both  assumptions  are  supported  by  experimental  evidence.  As 
far  as  the  place  of  formation  of  the  urea  is  concerned,  we  are  certain  that 
the  liver  produces  it.  We  do  not  know  whether  other  organs  also  par- 
ticipate in  its  formation. 

It  has  been  desired  to  draw  definite  conclusions  from  the  presence  of  the 
following  compounds  in  the  urine.  If  we  administer  aminobenzoic  acid 
to  the  animal  organism  we  will  find  carbaminobenzoic  acid  in  the  urine: 

NH2  .  C6H4  .  COOH  -->    NH2  .  CO  .  NH  .  C6H4  .  COOH.1 

After  the  administration  of  ethylamine  (carbona-te)  we  find  ethylurea: 
C2H5NH2  -*    C2H5  .  NH  .  CO  .  NH2. 2 

Taurine,  under  analogous  conditions,  goes  over  into  carbaminoisethionic 
acid,  sulphanilic  acid  into  sulphanilcarbamic  acid,  and  o-  and  p-amino-sal- 
icylic  acid  into  the  corresponding  carb amino  acids. 

We  can  easily  imagine  a  conjugation  of  urea  with  the  compounds  in 
question,  and  ascribe  an  analogous  role  to  it,  as  to  glycocoll,  sulphuric 

1  E.  Salkowski:  Z.  physiol.  Chem.  7,  93  (1883-83).     Cf.  also  R.  Cohn:  ibid.  17,  274, 
292  (1893). 

2  O.  Schmiedeberg:  Arch.  exp.  Path.  Pharm.  8,  1  (1877). 


ALBUMINS  OR  PROTEINS.  235 

acid,  and  glucuronic  acid.  The  three  last  compounds  unite  with  a  large 
number  of  other  substances,  as  is  well  known,  thus  protecting  the  tissue- 
cells  from  being  attacked.  Effort  has  been  made  to  utilize  the  above 
observations  as  proof  of  the  occurrence  of  cyanic  acid,  while,  on  the  other 
hand,  Hofmeister  has  looked  upon  it  in  the  light  of  his  assumption  of  an 
oxidizing  synthesis.  We  are,  therefore,  still  unable  to  decide  the  exact 
manner  in  which  urea  is  produced. 

We  also  desire  to  call  attention  to  a  compound  present  in  urine,  although 
only  in  small  amount,  which  has  often  been  mentioned  in  relation  to  urea. 

This  is  creatinine: 

NH      -  CO 
/ 
C=  NH 

\ 

N(CH3)CH2 

The  amount  excreted  daily  by  human  beings  varies  from  0.6  to  1.3 
gram.  It  is  the  anhydride  of  creatine,  which  is  present  in  the  muscles, 
and  is  a  methyl-guanidine-acetic  acid: 

NH2 
/ 

C=  NH 
\ 
N(CH3)  .CH2.COOH. 

On  boiling  with  baryta  water  creatine  decomposes,  adding  water,  and 
forms  urea,  sarcosin,  and  other  products.  It  may  also  be  obtained  syn- 
thetically by  heating  sarcosine  (methyl-glycocoll)  with  cyanamide  in  a 
sealed  tube  to  100  degrees,1  or  by  adding  a  few  drops  of  ammonia  in  the 
cold  to  a  saturated  solution  of  sarcosine  containing  the  equivalent  amount 
of  cyanamide,  and  allowing  the  mixture  to  stand : 2 
NH2  CH3  NH2 

CN      +      N— H  C  =  NH 

CH2  .  COOH          N  (CH3)  .  CH2  .  COOH. 


Cyanamide       Sarcosine  Creatine 

Creatine  may  also  be  considered  a  substituted  guanidin,  as  the  following 


formula  shows: 

NH2 


\^r 

In 


NH 


H2 
Guanidine 


1  J.  Volhard:  Zeit.  f.  Chem.  1869,  318. 
3  A  Strecker:  Jsb.  Chem.  1868,  686. 


236  LECTURE  XI. 

We  have  already  indicated,  while  discussing  arginine  and  arginase,  that 
urea  can  be  formed  from  guanidine.  Creatine,  therefore,  may  also  be 
looked  upon  as  an  antecedent  of  urea,  although  we  do  not  possess  any 
confirmatory  proof  of  this.  The  position  of  creatine  in  the  general 
metabolism  is,  in  fact,  extremely  uncertain.  We  do  not  even  know  its 
source.  It  is  generally  considered  as  being  directly  related  to  the  proteins. 
Its  formation  from  albumin  has,  as  yet,  never  been  proven.  It  appears 
far  more  probable  that  it  is  more  directly  related  to  the  nourishment;  at 
any  rate,  the  elimination  of  creatine  depends  upon  the  introduction  of 
food.  It  is  principally  found  in  the  muscles,  although  it  has  also  been 
isolated  from  the  blood,  brain,  transudates,  and  in  the  amniotic  fluid. 
It  is  stated  that  the  amount  of  creatine  is  increased  by  muscular  work. 
This  has  given  rise  to  the  assumption  that  its  formation  is  related  to 
muscular  contraction.  It  is,  however,  also  possible  that  its  elimination 
may  be  due  to  an  increased  circulation  of  the  blood  and  the  changes  which 
occur  in  a  working  muscle. 

Uric  acid  must  also  be  looked  upon  as  a  source  of  urea.  It  has  been 
shown  that  a  part,  at  least,  of  this  substance  when  administered  to  the 
organism  of  mammals,  is  changed  into  urea.1  This  form  of  urea  produc- 
tion plays  only  an  insignificant  part  in  mammals.  It  was  long  thought 
that  uric  acid  was  first  formed  from  albumin,  and  that  this  was  then  con- 
verted into  urea.  It  was  believed  to  have  been  observed  that  a  dimin- 
ished oxidation  in  the  tissues  was  responsible  for  an  increase  in  the 
amount  of  uric  acid  at  the  expense  of  urea.  Such  an  assumption  was 
supported  by  the  observation  that  those  animals,  namely  the  reptiles, 
whose  metabolism  is  very  slow,  showed  only  uric  acid  in  their  excreta. 
Opposed  to  this  assumption  was  the  fact  that  birds,  whose  metabolism 
we  generally  consider  to  be  a  very  rapid  one,  likewise  excreted  the  larger 
part  of  the  nitrogen  from  their  food  in  the  form  of  uric  acid.  To-day, 
the  question  of  uric  acid  production  in  the  organism  of  mammals,  and 
also  the  other  vertebrates,  has  been  more  satisfactorily  explained.  It  is 
quite  independent  from  that  of  urea.  We  shall  see  later,  that  the  uric 
acid  of  mammals,  in  contradistinction  to  that  of  birds  and  reptiles,  has 
no  relation  whatever  to  albumin-metabolism,  but  is  derived  from  the 
nucleins.  We  shall  consider  this  in  connection  with  the  constitution  of 
uric  acid  and  related  compounds,  and  shall  deal  with  the  subject  here  only 
in  so  far  as  is  related  to  the  metabolism  of  albumin. 

There  are,  undoubtedly,  direct  relations  between  the  decomposition  of 
albumin  and  the  elimination  of  uric  acid  in  those  animals  in  which  the 
larger  part  of  the  nitrogen  administered  reappears  in  the  form  of  uric 
acid.  This  is  especially  noticeable  with  reptiles.  Here  the  elimination  of 
uric  acid  stands  in  the  same  relation  to  the  albumin  taken  into  the 

1  Wohler  and  Frerichs:  Ann.  65,  335  (1848);  Neubauer:  Ann.  99,  206  (1856). 


ALBUMINS  OR  PROTEINS.  237 

system,  as  does  urea  in  the  case  of  mammals.  The  analogy  between  uric 
acid  and  urea  has  received  further  support  from  the  discovery  that  the 
same  materials  which  produce  an  increase  in  urea  in  mammals,  will  cause 
an  increased  elimination  of  uric  acid  in  birds.  Thus,  von  Knieriem 1  showed 
such  an  influence  by  the  administration  of  amino  acids,  while  von  Schroder 2 
observed  the  same  thing  by  feeding  ammonium  salts.  Urea,3  also,  will 
cause  an  increased  elimination  of  uric  acid. 

Minkowski 4  obtained  a  further  insight  into  the  production  of  uric  acid 
in  birds,  by  extirpating  the  liver  of  geese.  These  animals  will  survive 
the  operation  for  20  hours,  because,  in  them,  the  portal  vein  is  not  the 
only  outlet  of  the  splanchnic  vessels,  but  is  supplemented  by  another, 
the  Vena  communicans.  The  elimination  of  nitrogen  during  this  opera- 
tion was  somewhat  diminished.  The  greatest  change  occurred  in  the 
uric  acid  of  the  urine.  Normal  geese  eliminate  from  60-70  per  cent  of 
the  total  nitrogen  in  the  urine  as  uric  acid,  while  those  whose  livers  had 
been  removed  showed  only  3.6  per  cent.  Ammonia,  in  large  amounts, 
took  the  place  of  uric  acid.  Minkowski  also  noticed  at  the  same  time  a 
large  amount  of  sarcolactic  acid  in  the  urine,  a  substance  which  is  en- 
tirely absent  in  the  urine  of  normal  geese.  The  question  now  arises,  What 
relation  do  the  eliminated  ammonia  and  lactic  acid  bear  to  the  formation 
of  uric  acid? 

We  can  imagine  that  the  increased  formation  of  ammonia  arises  from 
a  secondary  process  due  to  the  appearance  of  the  lactic  acid.  We  are 
aware  of  the  fact  that  in  ammonia  the  animal  organism  has  a  valuable 
weapon  to  protect  itself  against  acids.  An  increased  appearance  of 
ammonia  in  the  urine  is  very  often  a  direct  indication  of  an  increased 
production  of  acid  in  the  organism.  That  the  presence  of  the  lactic  acid 
was  an  important  factor  in  the  increased  production  of  ammonia  is  evident 
from  the  fact  that  an  addition  of  alkali  caused  an  appreciable  diminution 
of  the  amount  of  ammonia  in  the  urine.5  At  any  rate,  a  part  of  the  am- 
monia must  be  looked  upon  as  exerting  a  neutralizing  effect. 

Hoppe-Seyler  6  has  shown  that  the  presence  of  the  lactic  acid  was  due 
to  a  diminished  oxidation  in  the  tissues,  as  a  result  of  the  operation.  It 
is  well  known  that  a  lactic  acid  formation  often  accompanies  a  dimin- 
ished supply  of  oxygen.  Minkowski 7  has  replied  to  this  objection  by 
showing  that  the  total  extirpation  of  the  liver  is  not  the  only  way  an 


Z.  Biol.  13,  36  (1877). 

Z.  physiol.  Chem.  2,  228  (1878). 

H.  Meyer:  Inaug.  Diss.  Konigsberg,  1877. 

Arch.,  exp.  Path.  Pharm.  21,  89  (1886);  31,  214  (1893). 

S.  Lang:  Z.  physiol.  Chem.  32,  320  (1901). 

Festschrift  zu  Vichow's  70  Geburtstag,  1891.     Cf.  also  Araki:  loc.  cit. 

Arch.  exp.  Path.  Pharm.  31,  214  (1893). 


238  LECTURE  XI. 

excretion  of  lactic  acid  can  be  caused,  but  that  even  ligating  the  vessels 
of  the  liver  is  sufficient  to  bring  this  about.  Lactic  acid  will  only  appear 
in  the  urine  at  the  moment  when  the  last  branch  of  the  hepatic  artery  has 
been  tied.  There  is  no  lactic  acid  formed,  if  a  single  branch  is  left  free. 

Kowalewski  and  Salaskin  l  have  shown  that  the  appearance  of  lactic 
acid  after  the  extirpation  of  the  liver  is  actually  to  be  traced  back  to  a 
disturbance  in  the  formation  of  uric  acid.  They  could  detect  the  forma- 
tion of  lactic  acid  by  merely  leading  ammonium-lactate  through  the  liver 
of  birds.  H.  Wiener2  also  showed  relations  between  the  lactic  acid  and 
the  formation  of  uric  acid.  He  fed  lactic  acid  and  urea  to  birds,  and 
noticed  an  increase  in  the  uric  acid. 

In  order  to  give  an  idea  of  the  relationship  of  lactic  acid  to  uric  acid 
it  will  be  necessary  to  give  the  constitution  of  uric  acid.  It  is  a  2,  6,  8 
trioxypurine:  HN— C  =  O 

I      I 
O=C    C— NH 

I     I     >co 

HN— C— NH 

Uric  acid 

Horbaczewski  has  obtained  it  synthetically  by  heating  urea  and  glycocoll 
together,  and  also  by  heating  trichlorlactamide  with  an  excess  of  urea. 
Uric  acid  is  decomposed  on  strongly  heating  into  urea,  hydrocyanic  acid, 
cyanuric  acid,  and  ammonia.  If  uric  acid  is  heated  with  concentrated 
sulphuric  acid  in  a  sealed  tube  at  170°  C.  it  breaks  up  into  glycocoll,  carbon 
dioxide,  and  ammonia.  Strecker,3  to  whom  we  owe  this  discovery,  com- 
pares the  uric  acid  production  from  the  components  glycocoll  and  cyanic 
acid  with  the  production  of  hippuric  acid  from  glycocoll  and  benzoic  acid. 

We  observe  from  this  that  the  synthesis  of  uric  acid  from  lactic  acid 
and  ammonia,  or  urea,  is  a  very  plausible  one.  The  standpoint  that 
uric  acid  is  a  direct  degradation  product  of  albumin  has  long  been  dis- 
carded. Uric  acid,  which  obtains  its  nitrogen  from  albumin,  can  only  be 
produced  synthetically.  We  wish  to  call  attention  at  this  point  to  the 
very  close  analogy  between  the  production  of  uric  acid  and  that  of  urea. 
It  can  be  shown  in  both  cases  that  ammonia,  directly  or  indirectly,  plays 
a  part,  as  does  also  an  acid  (carbonic  acid  or  lactic  acid) .  The  ammonia 
in  both  cases  may  have  the  same  origin,  being  derived  from  albumin  or  its 
cleavage-products.  The  organisms  of  the  birds  and  reptiles  evidently  are 
also  capable  of  causing  the  removal  of  the  NH2  group.  This  is  appar- 

1  Z.  physiol.  Chem.  33,  210  (1901). 

2  Verb.  XVII,  Kong.  Med.   1889,  p.  622,  and  Arch.  exp.   Path.  Pharm.  42,   375 
(1899);  Verb.  XIX,  Kong.  Med.  1901,  383.     Hofmeister's  Beit.  2,  42  (1902).     Cf.  also 
H.  Wiener:  Die  Harnsaure,  Ergebnisse  der  Physiologic  (Asher  and  Spiro)  1,  I,  555 
(1902). 

3  Ann.  146,  142  (1868). 


ALBUMINS  OR  PROTEINS.  239 

ent  from  the  comparatively  large  production  of  lactic  acid.  The  latter 
may  be  derived  from  various  sources.  Here,  the  carbohydrates,  as  well  as 
the  amino  acids,  come  into  consideration.  We  know  some  of  these  which 
are  closely  related  to  lactic  acid.  We  would  refer  especially  to  alanine: 

CH2  .  SH 

CH  .  NH2 

COOH 
Cysteine 

We  can  also  imagine  that  serine  and  cysteine  may  bear  some  relation  to 
the  formation  of  lactic  acid.  Leucine  might  also  produce  lactic  acid,  if  we 
assume  that  its  carbon  chain  is  broken  in  the  middle: 

3     ,CH3 
^CR 


CH3 

CH3 

CH2  .  OH 

CH  .  NH2 

CHOH 

CH  .  NH2 

COOH 

COOH 

COOH 

Alanine 

Lactic  Acid 

Serine 

CH2 
H  .  NH2 > Alanine 

COOH 

Leucine 

We  can,  therefore,  easily  derive  all  of  the  components  of  uric  acid 
direct  from  albumin.  It  is  not  to  be  implied,  however,  that  lactic  acid 
may  not  also  arise  from  other  sources. 

It  might  be  thought  that  some  idea  of  the  formation  of  urea  could  be 
obtained  from  the  way  uric  acid  is  produced.  We,  however,  know  that 
there  are  several  ways  in  which  the  uric  acid  formation  may  be  explained. 
We  can  take  all  of  our  theories  for  the  formation  of  urea  and  apply  them 
directly  to  that  of  uric  acid.  It  is  possible  that  the  synthesis  in  this  case 
is  primarily  carried  out  with  the  elimination  of  water;  although  it  is  also 
conceivable  that  an  oxidation  synthesis  may  be  a  factor.  It  is  not  at  all 
impossible  that  the  formation  of  urea  may  play  a  part  in  the  synthesis  of 
uric  acid. 

Wiener's  investigations  will  give  us  an  idea  of  these  relations.  He 
found  that  tartronic  acid: 


C 


HOH 

COOH 
and  its  ureide  (dialuric  acid) : 

NH— CO 

CO     CHOH 
NH— CO 


240  LECTURE  XI. 

easily  go  over  into  uric  acid;  in  fact,  when  isolated  organs  are  used,  this 
result  has  been  accomplished.     Wiener  assumes  from  this  that  lactic  acid: 


CH3 
HOH 

OOH 
goes  over  into  tartronic  acid: 

COOH 


CHOH 


which  then  forms  dialuric  acid: 

NH— CO 


CHOH 

,4, 


NH— CO 

and  finally,  by  ihe  addition  of  the  urea  radical,  produces  uric  acid: 

NH— CO 
CO     C— NH 

I       II     >co 

NH— C— NH 

We  should,  therefore,  have  to  assume  that  the  main  cause  of  the  disturb- 
ance in  the  synthesis  of  uric  acid,  after  the  liver  had  been  removed,  was 
the  non-oxidation  of  lactic  acid  into  tartronic  acid,  and,  evidently,  also,  the 
non-formation  of  urea. 

It  is  clear  that  we  are  not  yet  prepared  to  state  that  the  formation 
of  uric  acid  proceeds  normally  in  this  manner.  Wiener's  investigations 
at  all  events  indicate  the  manner  in  which  the  synthesis  may  proceed. 
Wiener  also  advances  the  opinion  that  the  organisms  of  human  beings 
and  mammals  in  general  synthesize  at  least  a  part  of  their  uric  acid,  and 
he  sees  no  real  difference  in  principle  between  their  metabolism  of  albumin 
and  especially  in  the  formation  of  their  end-products  from  that  of  birds 
and  reptiles.  The  distinction  is  rather  a  quantitative  one.  Birds  and 
reptiles  likewise  produce  urea,  but  the  amount  formed  is  less  than  that  of 
uric  acid.  On  the  other  hand,  urea  predominates  in  human  beings  and 
mammalia.  It  cannot  be  denied  that  such  an  assumption  has  much  to 
commend  it.  Nowhere  in  the  animal  kingdom  do  we  observe  any  sharp 
demarcations,  especially  in  those  processes  which  are  of  such  great  impor- 
tance as  is  the  case  with  metabolism.  The  synthetic  formation  of  uric 
acid  among  mammals,  according  to  our  present  knowledge,  must,  never- 


ALBUMINS  OR  PROTEINS.  241 

theless,  be  relegated  to  the  background.  Even  if  such  a  process  does 
take  place,  the  amount  produced  thereby  is  so  small  in  comparison  with 
that  obtained  from  other  sources,  that  it  possesses  little  significance. 
Wiener  has  also  tried  to  show  that  uric  acid  is  synthetically  produced  by 
mammals.  His  conclusions  have,  however,  been  contradicted.1  The 
synthetic  production  of  uric  acid  by  the  mammalian  organism  cannot,  at 
present,  be  accepted  with  certainty. 

The  question  now  arises,  In  what  organs  does  the  uric  acid  formation 
take  place?  The  liver  seems  to  play  an  important  part  in  this  process 
among  birds.  W.  v.  Schroder 2  extirpated  the  kidneys  from  hens,  and 
succeeded  in  keeping  these  birds  alive  for  5-10  hours.  Schroder  examined 
after  their  death  the  blood  and  organs  for  uric  acid,  and  found  that  a  very 
appreciable  accumulation  of  this  acid  had  resulted.  The  uric  acid  pro- 
duction had  evidently  continued  after  the  extirpation  of  the  kidneys. 
The  same  behavior  was  noticed  with  snakes.  It  seems,  therefore,  that 
the  kidneys  are  of  little,  or  even  no,  service  in  this  process.  This  de- 
cision was  the  more  striking,  as  the  kidneys  were  for  a  long  time  looked 
upon  as  the  most  important  place  for  the  production  of  uric  acid.  This 
opinion  had  originated  from  the  way  uric  acid  is  distributed  after  the 
ureter  has  been  ligated. 

Both  of  the  albumin  metabolic  substances  so  far  considered  are  con- 
nected with  the  whole  albumin  molecule  and  all  its  cleavage-products. 
Ammonia  ought  also  to  be  included  in  this  group,  as  it  occurs  in  varying 
quantities  in  urine.  It  was  formerly  believed  that  an  increased  elim- 
ination of  ammonia  indicated  an  insufficient  production  of  urea.  Little 
by  little  the  cause  was  more  accurately  investigated,  and  it  was  dis- 
covered that  the  increase  in  the  amount  of  ammonia  was  not  a  primary 
effect,  but  that  it  was  due  to  an  increased  production  of  acid.  Thus,  in 
a  diabetic,  the  appearance  of  acetoacetic  acid  and  of  /5-hydroxy-butyric 
acid  is  associated  with  an  increased  elimination  of  ammonia.  F.  Walter  3 
even  showed  that  the  administration  of  hydrochloric  acid  to  human 
beings  and  dogs  caused  an  increased  elimination  of  ammonia.  A. 
Schittenhelm  and  A.  Katzenstein  4  have  recently  shown  that  the  amount 
of  ammonia  present  in  the  urine  is  directly  related  to  the  total  nitrogen  of 
the  urine.  It  rises  and  falls  with  the  consumption  of  albumin,  so  that  the 
ratio  of  ammonia  to  the  total  nitrogen  remains  constant  within  narrow 
limits.  The  amount  of  ammonia  excreted  is  not  affected  by  the  admin- 
istration of  urea,  or  ammonium  carbonate.  It  is  also  interesting  to  note 
that,  not  only  does  an  increased  elimination  of  ammonia  follow  an  increased 


1  Cf.  R.  Burian:  Z.  physiol.  Chem.  43,  497  (1905). 

2  Arch.  Anat.  Physiol.  1880,  p.  113,  Supplement. 

3  Loc.  cit. 

4  Arch.  exp.  Path.  Therapie,  2,  541  (1905). 


242  LECTURE  XI. 

diet  of  albuminous  material,  but  that  this  also  occurs  after  the  addition 
of  the  free  ammo  acids,  glycocoll  and  alanine.  It  is  very  significant  that 
the  administration  of  ammonium  carbonate  is  followed  by  a  sharp  decline 
in  the  formation  of  ammonia,  so  that  the  ratio  of  ammonia-nitrogen  to 
the  total  nitrogen  in  the  urine  becomes  less  than  under  normal  conditions. 
We  cannot  conceive  that  the  amino  acids  mentioned  are  capable  of  pro- 
ducing acidosis  on  their  own  account,  although  we  can  imagine  that 
Siegfried's  discovery,  that  the  amino  acids  take  on  carbon  dioxide  forming 
carbamic  acids,  is  here  expressed.  On  the  other  hand,  this  intermediate 
acidosis  gives  us  an  indication  of  the  manner  in  which  the  decomposition  of 
the  albumin  cleavage-products  is  carried  out  in  the  tissues.  It  does  not 
seem  improbable  that  acids  are  temporarily  formed  after  the  ammonia 
has  been  split  off,  which  cause  an  increase  in  the  production  of  ammonia. 
Our  knowledge  of  the  intermediate  metabolism  of  albumin  is  so  slight 
at  present  that  we  have  hardly  any  conception  of  these  relations. 

We  will  now  consider  the  end-products  of  albumin  metabolism,  which 
occupy  a  different  position  from  those  just  mentioned  in  that  they  are 
not  derived  from  the  albumin  cleavage-products  as  a  whole,  but  can  be 
traced  to  definite  amino  acids.  Among  these  is  hippuric  acid.  It  was 
discovered  in  horse  urine  by  Liebig.  Its  method  of  formation  was  known 
to  Keller  and  Wohler.1  These  authors  noticed  that  when  benzoic  acid 
was  administered  per  os,  it  did  not  reappear  as  such  in  the  urine,  nor 
could  cleavage-products  be  found  which  were  related  to  it.  Keller  and 
Wohler,  however,  noticed  an  appreciable  increase  in  the  amount  of  hip- 
puric acid.  Its  manner  of  formation  is  evident  from  its  constitution.  It 
is  broken  down  on  boiling  with  strong  mineral  acids  or  alkalies,  with  the 
addition  of  water,  into  benzoic  acid  and  glycocoll: 

C6H5.CO.NH.CH2.COOH  +  H2O  =  C6H5.COOH  +  NH2.CH2.COOH 
Hippuric  acid  Benzoic  acid  Glycocoll 

It  may  be  synthetically  produced  from  benzamide  and  monochlor- 
acetic  acid: 

C6H5.CONH2  +  C1.CH2.COOH  =  C6H5.CO.NH.CH2.COOH  -f  HC1 

Benzamide         Monochloracetic  Hippuric  acid 

acid 

It  may  also  be  obtained  by  heating  glycocoll  with  benzoic  acid  in  a 
sealed  tube  for  1  or  2  hours  at  160  degrees. 

The  observation  of  Keller  and  Wohler,  that  benzoic  acid  appears  in  the 
urine  united  to  glycocoll,  has  been  confirmed  by  numerous  investigations 


1  Ann.  43,  108  (1842);  Wohler  and  Frerichs;  66,  335  (1848);  Wilhelm  Wiechowski; 
Hofmeister's   Beit.  7,  204  (1905). 


ALBUMINS  OR  PROTEINS.  243 

through  administrations  by  the  mouth,  as  well  as  by  subcutaneous  injec- 
tions. We  know  to-day  that  this  synthesis,  which  at  that  time  created 
much  excitement  on  account  of  the  fact  that  it  was  the  first  instance  in 
which  a  synthetic  process  had  been  shown  to  take  place  in  the  animal 
organism,  is  not  unique.  Thus,  R.  Cohn  l  found  that  naphthoic  acid 
administered  to  rabbits  and  to  dogs  reappeared  in  the  urine  as  naphturic 
acid.  Its  formation  is  exactly  analogous  to  that  of  hippuric  acid: 

CioH7.COOH  +  NH2.CH2.COOH  =  Ci0H7.CO.NH.CH2.COOH  +  H2O 
Naphthoic  acid  Glycocoll  Naphturic  acid 

Salicylic  acid  unites  with  glycocoll  in  the  same  manner.2  Hydroxy- 
hippuric  acid  is  formed: 

OH.C6H4.COOH  +  H2N.CH2.COOH  =  OH.C6H4.CO.NH.CH2.COOH 

Salicylic  acid  Glycocoll  Hydroxyhippuric  acid 

+  H2O 

It  is  also  interesting  to  note  that  alkylated  benzoic  acids,  for  instance, 
toluic  acid,3  likewise  unite  with  glycocoll,  reappearing  as  alkylated  hippuric 
acids  : 

CH3.C6H4.COOH  +  NH2.CH2.COOH 


Toluic  acid  Glycocoll  Toluric  acid 

+  H20 

Phenylacetic  acid  similarly  appears  in  the  urine  as  phenaceturic  acid:4 
C6H5.CH2.COOH  +  NH2.CH2.COOH  =  C6H5.CH2.CO.NH.CH2.COOH 

Phenylacetic  acid  Glycocoll  Phenaceturic  acid 

+  H20 

We  have  already  seen,  when  discussing  glucuronic  acid,  which  plays  a 
role  in  the  animal  organism  very  analogous  to  that  of  glycocoll,  that  the 
cells  are  able  to  adapt  compounds,  which  of  themselves  would  not  unite 
together,  partly  by  oxidation,  partly  by  reduction,  and  sometimes  by  both 
methods.  Thus,  toluene  is  first  converted  into  benzoic  acid  and  then 
united  to  glycocoll.  Ethyl-  and  propylbenzenes  are  changed  in  the  same* 
manner.5  Xylene  is  likewise  oxidized  to  toluic  acid.  It  is  interesting  to 
note  that  aldehydes  are  oxidized  to  acids;  as  an  example  we  will  cite 


1  Z.  physiol.  Chem.  18,  112  and  119  (1894). 

2  Bertagnini:  L.  Ann.  97,  248  (1856);  Z.  physiol.  Chem.  1,  244  and  253  (1877-78). 

3  Schultzen  and  Naunyn:  Du  Bois'  Arch.  1867,  352. 

4  E.  and  H.  Salkowski:  Z.  physiol.  Chem.  7,  161  (1882-83);  9,  229  (1885). 

5  M.  Nencki  and  P.  Giacosa.  ibid.  4,  325  (1880). 


244  LECTURE  XI. 

the  conversion  of  nitrobenz aldehyde  into  nitrobenzoic  acid,  and  the  sub- 
sequent formation  of  nitrohippuric  acid:1 

NO2  .  C6H4  .  CHO  +  Q      =  NO2  .  C6H4  .  COOH 
Nitrobenz  aldehyde  Nitrobenzoic  acid 

NO2.C6H4.COOH    +  NH2.CH2.COOH  =  NO2.C6H4.CO.NH.CH2.COOH 

Nitrobenzoic  acid  Glycocoll  Nitrohippuric  acid 

+  H20 

The  conversion  of  benzamide  2  into  hippuric  acid  is  especially  note- 
worthy on  account  of  the  fact  that  water  must  be  added  to  form  benzoic 

API  C\  * 

C6H4.CONH2  +  H20  =  C6H4.COOH  +  NH3 

Benzamide  Benzoic  acid 

The  ability  of  the  organism  to  unite  other  substances  with  glycocoll 
is  not  confined  to  benzoic  acid  or  its  derivatives,  but  the  same  is  true  of 
the  carboxylic  acids  of  furan-,  thiophen-  and  pyridine-nuclei.  Thus,  from 
thiophenaldehyde  3  thiophenic  acid  is  formed,  which  in  the  presence  of 
glycocoll  goes  over  into  thiophenuric  acid: 

C4H3S  .  CHO  +  O  =  C4H3S.COOH 

Thiophenaldehyde  Thiophenic  acid 

C4H3S.COOH  +  NH2.CH2.COOH  =  C4H3S.CO.NH.CH2.COOH  +  H20 

Thiophenuric  acid 

Such  reactions  in  the  animal  organism  are  of  interest  in  more  than  one 
way.  Such  investigations  give  an  idea  of  the  activity  of  the  animal  cell. 
We  notice  that  oxidation  and  reduction  processes  are  carried  out  with  the 
greatest  ease,  while  water  is  split  off,  or  added,  as  the  case  demands. 

We  ask  ourselves,  Where  does  the  animal  organism  obtain  the  glycocoll 
which  enters  into  these  combinations?  We  have  seen  that  this  amino 
acid  is  found  among  the  many  cleavage-products  of  the  albumins.  There 
can  be  no  doubt  that  the  animal  cells  obtain  the  necessary  glycocoll 
by  the  decomposition  of  proteins.  The  fact  that  glycocoll  will  unite  with 
benzoic  acid  and  analogous  compounds  under  technical  conditions,  per- 
mits us  to  draw  valuable  conclusions  regarding  the  decomposition  of 
albumins  in  the  tissues.  There  is  little  doubt  that  this  also  applies  to 
.the  amino  acids.  The  glycocoll  formed  is  usually  further  disintegrated 
into  urea;  if,  however,  benzoic  acid  happens  to  be  present  in  the  tissues, 
the  glycocoll,  produced  as  an  intermediate  substance,  is  removed  from 
further  metabolism.  We  have  already  seen  that  other  albumin  cleavage- 

1  Ibid.  17,  274  and  292  (1893). 

2  L.  v.  Nencki:  Arch.  exp.  Path.  Pharm.  1,  420  (1873). 

3  R.  Cohn:  Z.  physiol.  Chem.   17,  281   (1893).     Cf.  E.  Fromm:  Die  chemischen 
Schutzmittel  d.  Tierkorpers  bei  Vergiftungen,  K.  J.  Trubner,  Strassburg,  1903,  p.  14; 
also  M.  Nencki:  Opera  omnia  (Vieweg  and  Sohn,  Braunschweig,  1905). 


ALBUMINS  OR  PROTEINS. 


245 


products  can  be  combined  in  like  manner.  Thus,  on  administering  ben- 
zoic  acid  to  birds  we  obtain  a  definite  amount  of  ornithine.  In  this  case 
hippuric  acid  does  not  appear  in  the  urine,  being  replaced  by  ornithuric 
acid,  the  dibenzoyl  compound  of  ornithine.  As  previously  stated,  we  can 
unite  cystine  with  brombenzene,  in  a  dog,  thus  protecting  it  from  further 
oxidation.  All  of  these  discoveries  indicate  that  the  disintegration  of 
albumin  in  the  tissues  proceeds  in  an  analogous  manner  to  that  of  the 
fats  or  carbohydrates.  Glycogen  is  first  split  up  into  its  components  and 
then  consumed.  The  same  kind  of  action  takes  place  with  the  fats. 

We  might  ask  ourselves  whether  the  glycocoll  withdrawn  from  the  body 
by  the  benzoic  acid  administered  can  be  directly  derived  from  the  amount 
of  decomposed  albumin.  An  answer  to  this  question  must  be  obtained 
by  studying  the  increased  elimination  of  hippuric  acid  caused  by  the 
administration  of  benzoic  acid,  and  tracing  at  the  same  time  the  dis- 
integration of  the  albumin.  Such  experiments  have  been  made,1  and  it 
appears  that  more  glycocoll  is  excreted  than  can  be  derived  from  the  dis- 
integrated albuminous  substance.  Such  results  are  to  be  very  cautiously 
accepted,  as  we  know  comparatively  little  about  the  decomposed  albu- 
mins in  the  intermediate  metabolism.  We  must  always  consider  the 
possibility  that  the  animal  cell  may  be  capable  of  producing  glycocoll  from 
other  amino  acids.  We  have  already  called  attention  to  a  striking  example 
of  this  by  showing  that  it  was  impossible  to  change  the  composition  of  the 
individual  amino  acids  in  the  serum-albumins  by  feeding  a  protein  which 
was  especially  rich  in  a  certain  amino  acid.2  In  the  case  indicated,  the 
"  normally  "  constituted  serum-albuminous  bodies  were  evidently  produced 
from  gliadin.  A  glance  at  the  following  table  will  show  the  changes 
which  must  have  taken  place.  We  find  it  necessary  to  state,  in  order  to 
prevent  any  misunderstanding,  that  our  conclusions  were  naturally  only 
superficial  and  incomplete.  The  configuration  and  stereochemistry  will 
at  some  time  undoubtedly  be  taken  into  consideration  in  studying  such 
changes. 


• 

100  parts  of  Albumin  contain 

Serum- 
albumin. 

Gliadin. 

Glycocoll 

3.5 

2.2 
present 
18.7 
2.8 
3.8 
8.5 
2.5 
2.5 
present 

0.7 
2.7 
0.33 
6.0 
2.4 
2.6 
31.5 
1.3 
2.4 
present 

Alanine    ... 

Aminovaleric  acid    ....           .        .           

Leucine 

Proline             .    .                                                            .... 

Phenylalanine    ...           .                                  

Glutamic  acid 

Aspartic  acid                                                                   •    • 

Tyrosine                                                               .        

Tryptophane      

1  Cf.  W.  Wiechowski:  Arch.  exp.  Path.  Pharm.  53,  435  (1905). 

2  E.  Abderhalden  and  F.  Samuely:  loc.  cit. 


246  LECTURE  XI. 

The  question  arises,  What  has  become  of  the  large  amount  of  glutamic 
acid?  It  is  possible  that  it  was  completely  disintegrated  in  the  intes- 
tine. This  phenomenon  may  perhaps  indicate  the  reason  for  the  marked 
increase  in  the  amount  of  ammonia  in  the  blood  of  the  portal  vein  during 
digestion.  We  might,  however,  assume  that  the  glutamic  acid  was  con- 
verted into  other  amino  acids  and  utilized  in  the  synthesis  of  albumin. 
We  are  unable  to  form  a  definite  opinion.  It  is  important,  however,  to 
point  out  the  possibility  of  such  transformations,  because  the  conclusion 
has  been  drawn  from  the  considerable  amount  of  glycocoll  which  can  be 
withdrawn  from  the  organism  by  means  of  benzoic  acid,  that  the  breaking 
down  of  all  the  amino  acids  to  urea  passes  through  the  glycocoll  stage.1 
We  are  not  justified  in  making  any  such  assumption.  There  is  no  founda- 
tion for  it.  It  is  far  more  probable  that  the  organism  in  any  given  case 
utilizes  its  albuminous  substance  richest  in  glycocoll,  or,  in  case  of  neces- 
sity, forms  glycocoll  from  other  amino  acids.  It  must  not  be  forgotten 
that  benzoic  acid  is  a  poison  to  the  cells,  causing  an  increase  in  the  dis- 
integration of  albumin,  thus  leading  to  a  direct  increase  in  the  amount 
of  glycocoll.  We  must  also  notice  another  possible  source  of  glycocolL 
We  shall  soon  see  that  the  animal  organism  is  able,  to  a  marked  degree,  to 
decompose  uric  acid.  It  is  assumed,  to  be  sure  without  an  entirely  satis- 
factory proof,  that  glycocoll  is  formed  as  a  decomposition  product.  The 
amount  of  this  amino  acid  thus  'formed  is  necessarily  small  among 
mammals.  Finally,  we  must  consider  the  possibility  of  glycocoll  being 
produced  synthetically,  for  instance,  from  ammonia  and  acetic  acid.  We 
have,  to  be  sure,  not  yet  succeeded  in  detecting  such  a  synthesis.2 

All  of  the  benzoic  acid  administered  is  not  changed  into  hippuric  acid. 
A  part  is  excreted  as  such,  and  another  portion  cannot  be  traced,  evidently 
being  transformed  in  some  unknown  manner. 

The  next  question  is,  In  which  organ  is  the  hippuric  acid  produced? 
G.  v.  Bunge  and  0.  Schmiedeberg  3  studied  first  of  all  the  livers  of  frogs. 
These  survive  the  extirpation  of  the  liver  very  well  indeed,  and  live  for 
3  or  4  days  after  the  operation.  They  formed  hippuric  acid  when  benzoic 
acid  was  introduced  into  the  dorsal  lymph  sac,  and  particularly  large 
amounts  when  glycocoll  was  added  at  the  same  time.  Hippuric  acid  has 
never  been  obtained  from  the  organisms  of  frogs  or  their  excretions  with- 
out the  previous  administration  of  benzoic  acid.  The  liver  of  the  frog  is, 
therefore,  not  the  only  organ  in  which  the  benzoic  acid  unites  with  glycocoll, 
if,  indeed,  the  liver  participates  at  all  in  this  synthesis. 

Bunge  and  Schmiedeberg  next  tested  the  kidneys  to  see  if  they  were 
able  to  produce  hippuric  acid  from  benzoic  acid  and  glycocoll.  They 

1  W.  Wiechowski:  loc.  cit. 

2  R.  Cohn:  Arch.  exp.  Path.  Pharm.  53,  435  (1905). 

3  Arch.  exp.  Path.  Pharm.  6,  233  (1877). 


ALBUMINS  OR  PROTEINS.  247 

ligated  the  vessels  of  the  kidneys  of  dogs,  and  then  introduced  benzoic 
acid  and  glycocoll  into  the  remaining  circulation.  The  animals  experi- 
mented upon  were  killed  after  3  or  4  hours,  and  the  blood  and  liver 
tested  for  hippuric  acid.  Benzoic  acid,  but  never  hippuric  acid,  was 
found.  The  exact  proof  that  the  kidneys  of  the  dog  is  as  a  matter  of 
fact  the  place  where  the  synthesis  of  hippuric  acid  is  effected,  Bunge 
and  Schmiedeberg  determined  by  direct  experiment.  They  cut  out  the 
kidneys  from  a  dog  that  had  been  just  killed,  and  passed  defibrinated 
blood,  to  which  benzoic  acid  and  glycocoll  had  been  added,  through  the 
renal  arteries.  It  flowed  away  through  the  veins  of  the  kidneys  and 
returned  through  the  arteries,  this  process  being  continued  for  several 
hours.  Hippuric  acid  was  then  found  in  this  blood  as  well  as  in  the 
fluid  which  flowed  from  the  ureter.  The  other  kidney  and  a  part  of 
the  original  blood  were  used  as  a  control,  but  no  hippuric  acid  was 
found  in  them.  The  surviving  kidney  had,  therefore,  produced  hippuric 
acid  from  glycocoll  and  benzoic  acid.  When  the  experimenters  added 
only  benzoic  acid,  but  no  glycocoll,  they  found  that  the  amount  of 
hippuric  acid  formed  was  very  small.  This,  however,  quickly  increased 
when  glycocoll  was  added  and  passed  through  the  kidney.  The  syn- 
thesis was  just  as  satisfactory  at  the  room- temperature  as  it  was  at 
37°  C. 

The  red  blood-corpuscles  and  the  cells  of  the  kidneys  are  of  great  impor- 
tance in  the  synthesis  of  hippuric  acid.  When  the  kidney  tissues  are 
destroyed  by  chopping,  or,  better  yet,  by  rubbing  them  up  with  pulverized 
glass,  we  find  that  the  conjugation  of  glycocoll  with  benzoic  acid  no  longer 
takes  place.  When  the  kidneys  are  cooled  to  —  20  degrees  and  then  raised 
to  40  degrees,  it  is  also  found  that  hippuric  acid  is  no  longer  produced 
from  its  components.  Again,  the  synthesis  could  not  be  effected  if  the 
serum  of  the  blood,  instead  of  the  blood  itself,  was  utilized.  It  has  been 
shown,  by  the  investigations  of  A.  Hoffmann,  that  oxygen  plays  an  impor- 
tant part  in  this  synthesis.1  He  led  blood  through  the  kidneys,  in  which 
the  oxygen  had  been  displaced  by  carbon  dioxide,  and  found  that  no  syn- 
thesis of  hippuric  acid  resulted.  Quinine  also  prevented  the  kidney  cells 
from  producing  hippuric  acid. 

It  seems  very  probable  that  the  synthesis  of  hippuric  acid  from  glycocoll 
and  benzoic  acid  is  due  to  a  ferment,  water  being  split  off.  The  attempt 
has  been  made  to  isolate  such  a  ferment.  Recent  investigations  in 
which,  contrary  to  earlier  experiments,  it  was  found  possible  to  detect 
the  synthesis  in  the  chopped  up  kidneys,  lead  to  the  hope2  that  the 

1  A.  Hoffmann:  Arch.  exp.  Path.  Pharm.  7,  233  (1877). 

2  W.  Kochs:  Pfliiger's  Arch.  20,  64  (1879).     M.  R.  Berminzone:  Bol.  accad.med.  di 
Genua  16,  No.  1  (1901).     J.  E.  Abelous  and  H.  Ribaut:  Compt.  rend.  Soc.  Biol.  June  9, 
1900. 


248  LECTURE  XI. 

conjugation  of  glycocoll  with  benzole  acid  can  be  accomplished  without 
the  direct  use  of  organs  or  cells. 

As  regards  the  place  where  the  hippuric  acid  is  formed,  it  is  to  be  noted 
that  what  has  been  said  applies  only  to  dogs.  Frogs  produce  hippuric 
acid  even  after  the  extirpation  of  the  kidneys.  Salomon  l  also  observed 
hippuric  acid  in  large  amount  after  the  administration  of  benzoic  acid  to 
a  rabbit  whose  kidneys  had  been  removed.  It  is  possible  that  the  syn- 
thesis of  hippuric  acid  is  more  localized  in  the  carnivora  than  it  is  with  the 
herbivora,  because  the  formation  of  hippuric  acid  by  the  former  under 
normal  conditions  is  only  very  small  in  amount.  The  quantity  of  hippuric 
acid  daily  excreted  by  human  beings  under  an  ordinary  diet  is  about  0.7 
gram.  It  may  be  increased  to  more  than  2  grams  by  a  liberal  diet  of 
vegetables  or  fruit. 

Glycocoll  not  only  participates  in  the  production  of  hippuric  acid  and 
of  the  other  artificially  introduced  products  just  mentioned,  but  is  also  a 
component  of  glycocholic  acid  and  glycocholeic  acid.  Both  are  decom- 
posed, in  the  same  manner  as  is  hippuric  acid,  by  boiling  with  acids  or 
alkalies  into  glycocoll,  cholic  acid,  or  choleic  acid,  respectively.  These 
last  two  acids  are  both  found  as  constituents  of  the  bile. 

Besides  these,  there  is  another  acid  containing  sulphur  called  tauro- 
cholic  acid  which  is  found  in  the  bile  of  most  animals,  and  is  likewise 
related  to  one  of  the  albumin  cleavage-products;  i.e.  to  cystine.  When 
taurocholic  acid  is  heated  with  acids  or  alkalies,  it  is  decomposed  into 
taurine  and  cholic  acid.  The  relations  of  taurine,  which  is  an  amino-ethyl- 
sulphonic  acid,  to  cystine  and  cysteine,  are  evident  from  the  following 
formulae : 

CH2  .  S02OH  CH2  .  SO2  .  OH 

|  | 

CH  .  NH2  CH2  .  NH2 

COOH_  ^ 

Cysteine  Cysteinic  acid  Taurine 

Friedmann  has  succeeded,  as  previously  mentioned,  in  converting 
cysteine  into  cysteinic  acid,  and  this  into  taurine.  Shortly  after  the  chemi- 
cal relations  between  these  compounds  had  been  settled,  experiments  with 
animals  also  indicated  the  probable  derivation  of  taurine  from  cysteine. 
W.  v.  Bergmann2  fed  dogs,  in  which  he  had  made  a  complete  biliary 
fistula,  with  cysteine,  and  estimated  the  amount  of  taurocholic  acid 
separating  out  with  the  bile.  He  could  not  detect  any  increase  in  the 
sulphur  content  of  the  bile  in  these  experiments,  but  did  notice  such 

1  Z.  physiol.  Chem.  3,  365  (1879). 

2  Hofmeister's  Beitr.  4,  132  (1903). 


ALBUMINS  OR  PROTEINS.  249 

when  sodium  cholate,  that  is,  the  other  component  of  taurocholic  acid, 
was  added  at  the  same  time  with  the  cysteine.  Wohlgemuth l  confirmed 
these  experiments,  and  showed  with  rabbits  that  the  amount  of  sulphur 
in  the  bile  and  the  sulphur  content  of  the  liver  increased  with  the  admin- 
istration of  cysteine  alone. 

We  know  nothing  definite  concerning  the  further  history  of  tauro- 
cholic acid  or  of  the  taurine  contained  in  its  molecule.  Salkowski 2  found 
that,  after  the  administration  of  taurine  to  human  beings  and  dogs,  a 
part  of  this  taurine  and  a  substituted  urea, 

/NH2 
C=0 
\     /H 

N  \  CH2— CH2  .  S03H 
appeared  in  the  urine. 

Almost  all  of  the  sulphur  of  the  taurine  reappears  in  the  urine  as  sul- 
phuric and  sulphurous  acids,  when  fed  to  a  rabbit. 

Salkowski  could  not  detect  any  increased  elimination  of  sulphuric  acid 
nor  of  sulphurous  acid,  after  taurine  had  been  fed  to  human  beings 
and  dogs.  Cysteine  increases  the  elimination  of  sulphuric  acid  in  the 
urine  of  human  beings  and  dogs.3  The  same  also  is  observed  in  the  case 
of  rabbits,  while  here  salts  of  hyposulphurous  acid  are  found  in  addition. 
We  will  add  that  thiosulphuric  acid  has  been  found  in  the  urine  of  cats 
and  dogs. 

It  has  been  shown  recently 4  that  cystine,  in  the  form  of  polypeptides,  is 
apparently  decomposed  during  metabolism  in  the  same  manner  as  when 
cystine  itself  is  administered.  It  is  interesting  to  note  that  in  these  experi- 
ments there  was  a  distinct  increase  in  the  oxidized  sulphur  of  the  urine 
corresponding  to  the  duration  of  the  experiment.  The  urine  always 
contains  a  part  of  the  sulphur  in  an  unoxidized  form.  This  portion  is 
also  called  "  neutral  "  sulphur.  Its  amount  varies  and  to  some  extent  is 
directly  related  to  the  oxidized  sulphur. 

It  is  at  present  impossible  to  give  a  clear  outline  of  the  relations  of  the 
components  containing  sulphur  of  the  urine  to  albumin  or  its  cleavage- 
products,  because  we  are  not  yet  able  to  recognize  all  the  constituents  of 
proteins  which  contain  sulphur.  We  can  only  consider  the  fact  as  settled 
that  the  sulphur  in  the  cystine  administered  to  an  animal  organism  largely 
reappears  in  an  oxidized  form  in  the  urine;  in  fact,  as  sulphuric  acid. 
There  is  no  doubt  but  that  cystine  is  also  formed  during  a  normal  disinte- 


1  Z.  physiol.  Chem.  40,  81  (1903). 

2  Virchow's  Arch.  58,  460  (1873). 

3  Cf.  E.  Goldmann:  Z.  physiol.  Chem.  9,  260  (1885).     C.  H.  Rothera:  J.  Physiology, 
32,  175  (1905).     L.  Blum:  Hofmeister's  Beit.  5,  1  (1903). 

4  E.  Abderhalden  and  F.  Samuely:  Z.  physiol.  Chem.  46,  187  (1905). 


250  LECTURE  XI. 

gration  of  the  albumins,  and  that  this  is  decomposed  in  the  same  manner 
as  the  cystine  which  is  artificially  introduced. 

The  sulphuric  acid  of  the  urine  has  been  subjected  to  thorough  study. 
It  was  found  that  it  occurred  in  various  combinations.  If  we  add  barium 
chloride  to  urine  which  has  been  previously  acidified,  barium  sulphate  will 
precipitate  at  once.  A  further  turbidity  will  appear  after  filtering  this 
off  and  boiling  with  hydrochloric  acid.  E.  Baumann 1  satisfactorily 
explained  this  behavior  of  sulphuric  acid  in  urine.  The  sulphuric  acid 
at  first  precipitated  is  derived  from  sulphates  —  salts  of  sulphuric  acid. 
That  which  is  obtained  after  boiling  with  hydrochloric  acid  is  due  to 
sulphuric  acid  which  has  been  in  combination  with  different  aromatic 
substances  in  the  urine.  The  hydrochloric  acid  decomposes  these  aromatic 
compounds  —  also  called  sulphuric  acid  esters  —  into  the  aromatic  com- 
ponent and  sulphuric  acid,  the  latter  being  then  precipitated  by  barium 
chloride.  The  sulphuric  acid  esters  themselves  form  soluble  barium  salts. 
We  shall  see  that  sulphuric  acid  forms  the  same  kinds  of  compounds  with 
these  that  we  found  it  does  with  glycocoll  and  glucuronic  acid.  We  wish 
to  add  at  this  point  that  some  sulphur  compounds  still  remain  in  solution 
even  after  the  sulphur  in  the  sulphuric  acid  esters  have  been  precipitated. 
This  is  the  "  neutral  sulphur  "  mentioned  above.  In  order  to  detect  this 
sulphur  it  is  necessary  to  oxidize  it,  thus  converting  it  into  sulphuric  acid, 
when  it  will  be  precipitated  by  barium  chloride.  By  these  methods  we 
are  able  to  isolate  all  three  varieties  of  combined  sulphur  in  the  presence 
of  one  another.  The  determination  of  the  total  sulphur  together  with 
that  of  the  total  nitrogen  in  the  urine  gives  us  a  very  good  conception  of 
the  course  of  the  disintegration  of  albumin. 

We  must  not  forget  to  mention  that  sulphocyanic  acid,  or  thiocyanic 
acid,  HCNS,  also  occurs  in  urine.  Gscheidlen 2  found  it  invariably  present 
in  the  urine  of  human  beings,  horses,  calves,  dogs,  cats,  and  rabbits.  In 
human  urine  0.2  to  0.8  gram  is  eliminated  daily.  The  sulphocyanic  acid 
comes  from  the  saliva,  being  formed  in  the  salivary  glands.  This  acid 
reaches  the  blood-stream  by  absorption.  If  all  the  ducts  of  the  salivary 
glands  are  cut  and  the  saliva  discharged  externally,  sulphocyanic  acid  no 
longer  appears  in  the  urine.  Its  origin  and  significance  have  never  been 
explained. 

1  Ber.  9,  54  (1876). 

3  Tageblatt  47,  Versammlung  deutscher  Naturf,  u.  Aerzte  in  Breslau,  1874. 


LECTURE  XII. 

ALBUMINS  OR  PROTEINS. 

VI. 
METABOLIC  END-PRODUCTS. 

WE  have  already  mentioned  the  fact  that  putrefactive  processes  always 
take  place  in  the  intestines  to  a  greater  or  less  extent.  A  part  of  the 
products  thus  formed  is  absorbed  and  eliminated  in  the  urine.  Only  a 
small  proportion  of  these  compounds  is  excreted  unchanged,  or  combined 
with  alkalies.  By  far  the  largest  percentage  of  the  albuminous  cleavage- 
products  produced  by  putrefaction  appear  in  the  urine  in  the  form  of  com- 
plex combinations.  Baumann  l  and  Brieger  2  have  shown  that  here  the 
acid  esters  of  sulphuric  acid  are  most  important.  The  organism  produces 
glucuronic  acid  only  when  there  is  a  deficiency  of  sulphuric  acid.  There 
always  seems  to  be  in  the  urine  a  small  amount  of  conjugated  glucuronic 
acid  compounds.  The  decomposition  products  are  largely  the  aromatic 
components  of  albumin;  in  fact,  chiefly  tyrosine  and  probably  phenyl- 
alanine  as  well.  Tryptophane  is  likewise  an  important  factor.  We  have 
seen  that  tyrosine,  which  is  p-hydroxyphenyl-tt-aminopropionic  acid,  is 
changed  by  loss  of  ammonia  into  p-hydroxyphenylpropionic  acid;  the 
latter  on  further  oxidation  and  loss  of  carbon  dioxide  finally  decomposes 
into  p-cresol  and  phenol.  From  tryptophane  skatole  and  indole  are  the 
end-products  obtained. 

The  most  important  of  the  conjugated  sulphuric  acid  compounds  are 
phenyl-,  tolyl-,  indoxyl-,  and  skatoxyl-sulphuric  acids.  Catechoyl-sul- 
phuric  acid  is  also,  although  not  invariably,  found  in  human  urine  in 
small  quantity.  We  may  state  that  some  of  the  sulphuric  acid  combina- 
tions have  not  yet  been  identified.  The  amounts  of  such  substances  in 
horse  urine  are  especially  large.  In  human  urine,  on  the  other  hand, 
there  is  much  less  present  than  of  the  other  sulphur  compounds.  From 
0.1-0.6  gram  is  excreted  on  an  average  every  24  hours.  Experience  has 
shown  that  no  definite  values  can  be  given.  They  vary  considerably,  and 
are  naturally  dependent  on  the  putrefactive  changes  in  the  intestines. 
The  excretion  of  the  acid  esters  of  sulphuric  acid  can  be  increased  artifi- 

1  E.  Baumann:  Ber.  9,  54  (1876);  9,  1389  (1876);  9,  1715  (1876);  10,  685  (1877);  11, 
1907  (1878);  12,  2166  (1879);  Pfliiger's  Arch.  12,  63  (1876);  12,  69  (1876);  13,  285 
(1876) ;  Z.  physiol.  Chem.  1,  60  (1877-78) ;  2,  335  (1878-79) ;  3,  250  (.1879) ;  4,  304  (1880) ; 
10,  123  (1886);  17,  511  (1893). 

2  E.  Baumann  and  L.  Brieger:  ibid..  3,  254  (1879);  3,  156  (1879). 

251 


252  LECTURE  XII. 

cially,  for  instance,  by  the  administration  of  phenol.  If  this  be  introduced 
into  the  animal  organism,  it  appears  in  the  urine  as  potassium  phenyl- 
sulphate.1  We  assume  it  to  be  formed  as  follows: 

CeHsOH  +  HO  .  SO3K  =  C6H5  .  O  .  SO3K  +  H2O 
Phenol  Potassium  phenylsulphate 

We  will  add  that  not  only  substances  like  phenol  are  eliminated  in  this 
way,  but  in  place  of  phenol  we  may  find:  the  cresols,  CH3  .  CeH4OH; 
thymol,  C3H7(CH3)C6H3  .  OH,  also  the  dihydroxy-benzenes,  C6H4(OH4)2; 
methylquinol,  CH3  .  O  .  C6H4OH;  orcinol,  CH3  .  C6H3(OH)2;  pyrogallol, 
C6H3(OH)3;  tribromphenol,  Br3C6H2OH;  o-nitrophenol,  NO3.C6H4.OH; 
p-amidophenol,  NH2  .  C6H4  .  OH;  protocatechuic  acid,  COOH.C6H3(OH)2; 
tannin,  salicylamide,  m-  and  p-hydroxybenzoic  acids. 

Before  discussing  the  sulphuric  acid  esters  which  normally  occur  in 
urine,  we  will  mention  the  fact  that  in  addition  to  the  above  compounds 
produced  by  the  artificial  introduction  of  aromatic  compounds,  substitution 
products  of  the  phenols  and  hydroxyl  derivatives  of  other  cyclic  com- 
pounds may  also  appear  in  urine  conjugated  with  sulphuric  acid.  Such 
an  example  is  hydroxyquinolin  sulphate,  which,  to  some  extent  at  least, 
appears  in  urine  as  an  acid  ester  of  sulphuric  acid.  Here  also  it  is  inter- 
esting to  note  that  in  the  organism  substances  are  prepared  for  combina- 
tion which  of  themselves  are  incapable  of  reacting  together.  For  example, 
benzene  is  first  oxidized  to  phenol,  and  then  united  with  sulphuric  acid. 
We  shall  soon  see  that  indole  and  skatole  are  also  first  oxidized  to  indoxyl 
and  skatoxyl,  and  then  further  made  to  combine: 

NH  :  C8H6  +  0  =  HN  :  C8H5OH 

Indol  Indoxyl 

HN  .  C8H5  .  OH  +  OH  .  SO3K  =  HN  :  C8H5  .  O  .  SO3K+  H2O 

Indoxyl  Pot.  indoxylsulphate 

It  is  also  interesting  that  substances,  themselves  capable  of  combination, 
are  likewise  oxidized.  This  part  of  the  phenol  is  oxidized  to  quinol  and 
appears  then  as  quinol  sulphuric  acid: 

C6H5  .  OH  +  O  =  HO  .  C6H4  .  OH 

*•  1  V y 1 

Phenol  Quinol 

HO  .  C6H4  .  OH  +  HO  .  S03K  =  HO  .  C6H4  .  O  .  SO3K  +  H2O 

V ,, ' 

Potassium  quinol  sulphate 

These  reactions  indicate  that  the  formation  of  sulphuric  acid  esters  is 
dependent  on  the  presence  of  aromatic  compounds,  whether  these  are 

1  E.  Baumann  and  E.  Herter:  Ber.  9,  1747  (1876);  1,  244  (1877-78). 

2  C.  Brahm:  Z   physiol.  Chem.  28,  439  (1899). 


ALBUMINS  OR  PROTEINS.  253 

artificially  administered  or  normally  produced  from  the  food.  It  is  very 
probable  that,  under  normal  conditions,  all  the  conjugated  sulphuric  acid 
compounds  are  the  outcome  of  intestinal  putrefaction.  The  amount  of 
sulphuric  acid  esters  has  even  been  suggested  as  indicating  the  extent  of 
putrefaction  taking  place  in  the  intestines.  We  may,  however,  state  that 
a  true  conception  of  the  putrefactive  changes  in  the  intestines  cannot  be 
obtained  by  the  determination  of  sulphuric  acid  esters  alone.  Their 
amount  is  naturally  dependent,  first  of  all,  on  that  of  the  absorbed  products 
of  putrefaction,  and  the  absorption  depends  on  the  time  the  material 
remains  in  the  intestines.  During  diarrhea  large  amounts  of  putrefactive 
products  are  withdrawn  from  the  organism.  The  quantity  in  the  faeces 
would  also  have  to  be  determined.  Moreover,  only  a  part  of  the  putre- 
factive products  leave  the  organism  in  an  unaltered  condition.  If  indole 
or  phenol  is  administered  to  the  animal  organism,  it  is  partially  destroyed, 
or,  more  correctly  expressed,  it  cannot  be  detected  in  the  urine,  having 
been  evidently  transformed  in  some  manner. 

We  must  also  bear  in  mind  that  not  all  the  aromatic  putrefactive  sub- 
stances appear  in  the  urine  in  the  form  of  conjugated  sulphuric  acids,  but 
they  are  often  present  as  salts,  or  even  in  an  unaltered  condition.  We  must 
also  remember  that  the  sulphuric  acid  present  is  derived  from  the  albumins 
themselves,  and  is  necessarily  limited  in  amount.  It  is  very  probable  that 
larger  quantities  of  glucuronic  acid  than  usual  would  be  obtained  in  place 
of  the  sulphuric  acid  esters,  if  albumins,  low  in  sulphur  content,  were  fed 
to  the  organism.  On  the  other  hand,  we  must  admit  the  possibility  of 
the  organism  covering  up  any  such  deficit  in  sulphur  by  breaking  down 
proteins  rich  in  sulphur  from  its  own  tissues,  just  as  well  as  our  present 
knowledge  indicates  that,  within  certain  limits,  the  formation  of  hippuric 
acid  is  independent  of  the  glycocoll  in  the  albumin  of  the  food.  As  the 
amount  of  stored-up  sulphur  compounds  is  necessarily  small,  it  follows 
that  the  animal  organism  will  soon  have  to  rely  upon  glucuronic  acid 
when  the  amount  of  aromatic  putrefactive  products  exceeds  a  certain 
limit.  The  compounds  conjugated  with  glucuronic  acid  are  naturally 
not  detected  in  determining  the  amounts  of  sulphuric  acid  esters. 

Baumann  assumed  that  the  acid  esters  of  sulphuric  acid  were  produced 
by  the  combination  of  aromatic  substances  with  the  sulphuric  acid  residues 
which  circulated  in  the  body  in  the  form  of  sulphates.  This  theory  has 
recently  been  questioned.  Tauber 1  only  succeeded  in  obtaining  an 
increased  amount  of  phenylsulphuric  acid  in  administering  large  amounts 
of  phenol  only  when  he  introduced  sulphites  at  the  same  time;  while  this 
was  not  the  case  with  sulphates.  It  seems,  therefore,  that  the  reaction 
between  the  aromatic  compound  and  the  radical  containing  sulphur 

1  Tauber:    Arch.    exp.    Path.    Pharm.    36,    197    (1895);  Z.  physiol.  Chem.    2,  366 

(1878/89);  Habilitationsschrift,  1878. 


254  LECTURE  XII. 

occurs  before  the  latter  has  been  oxidized  to  sulphuric  acid.  It  is  very 
probable  that  the  final  oxidation  to  sulphuric  acid  only  takes  place  after 
the  substances  have  united.  We  must  not  neglect  to  call  attention  to  the 
-analogy  existing  between  the  formation  of  the  sulphuric  acid  compounds 
and  the  conjugated  glucuronic  acids.  The  latter  are  also  of  secondary 
nature,  only  appearing  after  the  dextrose  has  combined  with  some  of  the 
conjugating  substance.1 

We  shall  now  consider  those  compounds  which  are  produced  by  the 
aromatic  cleavage  substances  of  proteins  being  conjugated  with  sulphuric 
acid.  Let  us  consider  first  of  all  phenylsulphuric  acid: 

C6H5O  .  SO2  .  OH 
and  the  p-tolyl  sulphuric  acid: 


O  .S02.OH 

Both  have  the  same  origin  and  are  always  classed  together.  They  are 
found  in  urine  as  alkali  salts.  The  quantity  of  each  varies,  and  depends, 
as  can  easily  be  imagined,  on  the  intensity  of  the  intestinal  putrefaction 
and  the  amount  of  resulting  products  that  is  absorbed.  Tyrosine  is  the 
mother-substance  of  the  phenols.  As  we  have  seen,  all  the  phenol  admin- 
istered to  the  body  is  not  excreted  as  such  combined  with  sulphuric  acid 
in  the  urine.  A  part  is  changed  in  another  way,  probably  consumed,  while 
another  portion  is  in  some  cases  found  in  the  urine,  oxidized  to  quinoyl- 
sulphuric  acid.  This  cannot  be  detected  under  normal  conditions,  although 
catechoylsulphuric  acid  is  often  present  in  urine,  if  only  in  small  amount. 
Catechol  is  o-dihydroxybenzene.  It  has  never  been  definitely  decided 
whether  its  sulphuric  acid  ester  is  produced  by  the  oxidation  of  phenol, 
or  arises  from  some  constituent  in  the  food  which  is  not  directly  related 
to  the  proteins. 

There  is  some  evidence  indicating  that  catechoylsulphuric  acid  results 
from  a  vegetarian  diet,  but  is  not  formed  in  a  diet  exclusively  of  meat.  It 
has  been  suggested  that  protocatechuic  acid  is  the  mother-substance  of 
the  sulphuric  acid  ester  mentioned. 

We  will  add  to  the  phenyl-  and  tolylsulphuric  acids  the  other  decom- 
position products  of  tyrosine  which  occur  in  urine.  They  may  be  con- 
sidered as  intermediate  products  between  tyrosine  and  phenol.  Thus, 
there  has  been  found  in  urine:  p-hydroxyphenylpropionic  acid  (p-hydro- 
cumaric  acid)  :  ^^  ^  QH  ^  CIj2  ^  CH2  g  COQH^ 

and  the  p-hydroxyphenylacetic  acid:  2 

'm  _  C6H4  .  OH  .  CH2  .  COOH. 

1  Cf.  Lecture  II,  p.  33. 

3  E.  Baumann:  Z.  physiol.  Chem.  4,  304  (1880);  6,  183  and  234  (1882). 


ALBUMINS  OR  PROTEINS.  255 

They  have  both  been  obtained  from  urine,  partly  as  conjugated  sulphuric 
acids,  but  mainly  in  the  form  of  salts. 

It  is  questionable  whether  these  two  compounds  are  always  and  invari- 
ably produced  by  intestinal  putrefaction.  It  is  possible,  in  fact  probable, 
that  these  two  hydroxy-acids  are  produced  by  the  decomposition  of  tyro- 
sine  in  the  tissues.  Confirming  this  is  the  fact  noted  by  H.  Thierfelder 
and  Nuttal,1  that  these  two  acids  were  observed  in  the  urine  of  guinea  pigs 
which  had  been  kept  sterile,2  i.e.  they  had  grown  up  with  their  intestinal 
tracts  free  from  bacteria,  consequently  there  could  not  be  any  putre- 
faction. It  is  important  that  the  urine  of  these  animals  did  not  contain 
any  typical  putrefactive  products  of  proteins;  i.e.  the  phenols. 

Para-hydroxymandelic  acid, 

C6H4  .  OH  .  CH  .  (OH)  .  COOH, 

has  also  been  found  in  the  urine,  although  only  under  specific  conditions. 
Schultzen  and  Ries  3  found  it  in  acute  cases  of  atrophy  of  the  liver. 

Blendermann, 4  after  feeding  tyrosine  to  a  dog,  found  a  dihydroxyphenyl- 
propionic  acid: 

HO  .  C6H4  .  C2H3  (OH)  .  COOH, 
in  the  urine. 

If  we  review  the  investigations  just  mentioned,  we  shall  see  that  the  same 
groups  of  decomposition  products  are  obtained  by  intestinal  putrefaction 
of  tyrosine  as  are  obtained  by  the  same  process  outside  the  animal 
organism.5  From  tyrosine, 

/OH 

p-hydroxyphenylaminopropionic  acid:  C6H4 

XCH2.CH(NH2)  COOH 
we  obtain  the  following  decomposition  products: 


p-hydroxyphenylpropionic  acid:  CeH4 

XCH2.CH2.COOH 
,OK 

p-hydroxyphenylacetic  acid:  CeH4 

XCH2.COOH 
,0V 

p-cresol:  CeH4 

XCH3 
phenol:  C6H5  .  OH 


1  H.  Thierfelder  and  Nuttal:  ibid.  21,  109  (1896);  22,  62  (1897). 

2  Cf.  Lecture  IV,  p.  64. 

3  Schultzen  and  Ries:  Ueber  akute  Phosphorvergiftung u.  Leberatrophie,  Berlin,  1869. 

4  H.  Blendermann:  loc.  cit. 
6  Cf.  Lecture  VIII,  p.  171. 


256  LECTURE  XII. 

We  will  state,  once  more  that  according  to  the  experiments  at  hand, 
para-cresol  and  phenol  are  to  be  regarded  solely  as  products  of  putre- 
faction, whereas  it  is  still  a  question  with  regard  to  the  other  products  as 
to  how  much  is  formed  in  the  intestine  and  how  much  is  caused  by  the 
intermediate  breaking  down  of  albumin,  or  of  tyrosine,  in  the  cells.  It  is 
unquestionably  certain  that  p-hydroxyphenylpropionic  acid  and  p-hydroxy- 
phenyl-acetic  acid  may  be  formed  beyond  the  intestine.  This  discovery 
serves  to  give  us  an  interesting  insight  into  the  decomposition  of  tyrosine 
in  the  tissues.  We  first  observe  that  the  amino  group  is  split  off  and  that 
oxidation  then  sets  in.  It  is  still  questionable  as  to  how  far  these  observa- 
tions may  be  applied  to  the  decomposition  in  the  metabolism  of  the  cells. 
Some  observations  seem  to  indicate  that  the  elimination  of  the  amino 
group  is  the  first  stage  of  the  decomposition  of  the  amino  acids. 

We  must  refer  to  another  specific  property  of  tyrosine.  In  discussing 
the  digestion  of  albuminous  substances  by  trypsin,  we  called  attention  to 
the  fact  that  this  amino  acid,  together  with  tryptophane,  is  very  quickly 
split  off  from  the  albumin.  It  is  very  possible  that  this  fact  may  cause 
tyrosine  and  tryptophane,  —  which  we  shall  soon  learn  to  recognize  as  the 
mother-substance  of  skatole  and  indole, —  to  fall  easy  prey  to  the  putrefac- 
tive bacteria. 

Another  question  of  considerable  interest  confronts  us :  What  becomes  of 
the  other  aromatic  amino  acid,  phenylalanine?  Investigations  on  tryptic 
digestion  show  that  this  amino  acid  shows  an  entirely  different  behavior 
from  that  of  tyrosine.  It  is  not  set  free  by  trypsin.  In  the  putrefaction 
of  albumin  outside  the  body,  phenylaminopropionic  acid  breaks  down  into 
phenylpropionic  acid  and  phenylacetic  acid.  The  former  is  not  found  as 
such,  in  urine,  but  is  combined  with  glycocoll  as  phenaceturic  acid.  In 
this  form  it  has  been  isolated  from  normal  horse  urine.  Whether  it  occurs 
in  human  urine,  or  not,  has  never  been  decided.  If  it  were  present  to  a 
considerable  extent,  one  might,  aside  from  the  possibility  of  its  formation 
from  other  sources,  e.g.  from  the  decomposition  products  of  tyrosine,  and 
its  formation  during  the  decomposition  processes  in  the  tissues,  draw  the 
conclusion  that  albumin,  or  a  higher  complex  of  amino  acids  such  as  a 
polypeptide,  is  attacked  by  the  bacteria  of  putrefaction.  The  increased 
appearance  of  the  other  two  acids  would  be  an  indication  of  intense  putre- 
factive changes  taking  place  in  the  intestines. 

Tyrosine  and  phenylalanine  have  also  been  supposed  to  participate  in 
the  production  of  hippuric  acid.  If  so,  they  would  furnish  the  benzoic 
acid  radical.  According  to  the  above,  it  is  evident  that  phenylalanine  can 
hardly  play  a  part  here,  —  at  least,  as  far  as  it  is  a  question  of  putrefactive 
processes  in  the  intestines.  Tyrosine  alone  is  to  be  considered  in  this  con- 
nection. It  is,  of  course,  possible  that  phenylalanine,  and  tyrosine  as  well, 
are  used  for  the  production  of  hippuric  acid  in  the  metabolism  of  the  cell. 


ALBUMINS  OR  PROTEINS.  257 

In  this  connection  we  would  add,  that  two  other  acids,  closely  related 
to  tyrosine  and  phenylalanine,  namely,  homogentisic  acid  and  uroleucic 
acid,  have  also  been  found  in  rare  cases  in  urine.  The  former  is  a  dihy- 

droxyphenylacetic  acid: 

XOH 

C6H3—  OH 

XCH2.COOH 

the  latter,  a  dihydroxyphenyllactic  acid.     They  are  both  found  during  an 
abnormal  metabolism  in  the  so-called  "  alcaptonuria." 

Let  us  turn  from  our  discussion  of  the  tyrosine  and  phenylalanine  de- 
composition products  to  the  sulphuric  acid  esters.  We  have  already  con- 
sidered the  occurrence  of  indoxyl-  and  skatoxyl-sulphuric  acids  in  urine. 
Intestinal  putrefaction  of  albumin  produces  indole: 

CH 

//       \ 
HC  C—  CH 

I  II      II 

HC  C    CH 

^        /  \  / 
CH        NH 

and  skatole  (methyl-indole)  : 

CH 

HC  C—  C  .  CH3 

I  II     II 

HC  C    CH3 

^        /  \  / 
CH        NH 

They  are  oxidized  in  the  tissues  to  indoxyl: 

CH 
//       \ 

HC  C—  C(OH) 

I  II      II 

HC  C    CH 

^        /  \  / 

CH        NH 
and  skatoxyl: 


HC 
1 
HC 
^ 

\ 
C—  C  .  CH3 
II     II 
C    C(OH) 
/  \  / 
CH         NH 

and  then  combined  with  sulphuric  or  glucuronic  acids. 

We  will  at  once  state  that  skatoxylsulphuric  acid  has  not  been  detected 


258  LECTURE  XII. 

with  sufficient  certainty  in  urine.  It  is  even  problematical  whether 
skatoxyl  occurs  in  urine.  The  suggestion  has  been  made  that  it  is  present 
in  combination  with  glucuronic  acid.  At  any  rate,  its  presence  is  only 
indirectly  established.  Indoxylsulphuric  acid  is  found  as  an  alkaline  salt 
in  urine.  It  is  the  source  of  most  of  the  urine  indigo.  Jaffe  1  was  the 
first  to  discover  that  indoxylsulphuric  acid  resulted  from  the  combination 
of  indole  and  indoxyl  with  sulphuric  acid.  He  injected  in  dole  subcuta- 
neously  into  dogs,  and  then  found  large  amounts  of  indoxylsulphuric  acid 
in  the  urine.  The  suggestion  has  also  been  advanced  that  the  indoxyl- 
sulphuric acid  in  the  urine  is  not  only  produced  by  intestinal  putrefaction, 
but  that  indole  and  indoxyl  are  also  formed  in  the  tissues.  The  researches 
of  A.  Ellinger  and  M.  Gentzen  2  have  made  this  improbable.  These 
authors  showed  first  of  all  that  tryptophane,  which  is  skatoleaminoacetic 
acid,  is  the  antecedent  of  indole,  and  the  latter  is  formed  from  it  during 
putrefaction.  When  tryptophane  was  introduced  directly  into  the  small 
intestine  of  rabbits,  large  amounts  of  indoxyl  quickly  appeared  in  the 
urine.  When,  however,  the  tryptophane  was  injected  subcutaneously, 
no  indoxyl  could  be  detected  in  the  urine.  That  the  excretion  of  indoxyl- 
sulphuric acid  in  the  urine  is  very  intimately  connected  with  the  intestinal 
putrefactive  changes,  is  shown  by  the  fact  that  when  there  is  an  intestinal 
stoppage,  especially  in  the  small  intestine,  the  quantity  quickly  increases. 
Observations  with  fasting  carnivorous  animals  have  shown  that  the  elimi- 
nation of  indoxyl  continues,  and  the  inference  was  drawn  that  indole  and 
indoxyl  were  also  produced  by  the  tissues.  F.  M  tiller3  has,  however, 
shown  that,  during  fasting,  only  the  intestinal  contents  gave  an  in- 
tense indole  test,  whereas  the  organs  showed  this  only  to  a  slight  extent. 
He,  therefore,  concludes  that  indole  in  the  urine  is  exclusively  of  intestinal 
origin.  A  limitation  is  certainly  necessary,  and  this  applies  also  to  the 
phenols.  Putrefactive  products  can,  of  course,  also  be  formed  in  other 
parts  of  the  organism,  aside  from  the  intestines,  wherever  putrefactive 
processes  are  at  work;  for  instance,  in  putrid  empyema,  decomposing 
tumors,  etc. 

If  we  add  to  urine  an  equal  amount  of  hydrochloric  acid  containing  a 
little  free  chlorine  or  ferric  chloride,  a  blue  coloring  matter  is  produced, 
which  can  be  shaken  out  with  chloroform.  This  is  indigo-blue: 

xcox         xcox 


C  =     C 


NNHX 


1  Jaffe":  Z.  med.  Wiss.  1872  and  1875. 

2  A.  Ellinger  and  M.  Gentzen:  Hofmeister's  Beit.  4,  171  (1903). 

3  F.  Miiller:  Mit.  Wiirzburger  med.  Klinik,  2,  1886;  A.  Ellingsr:  Z.  physiol.  Chem. 
39,  44  (1903). 


ALBUMINS  OR  PROTEINS.  259 

It  is  produced  by  the  decomposition  of  indoxylsulphuric  and  indoxyl- 
glucuronic  acids  into  their  components,  and  the  simultaneous  oxidation  of 
the  indoxyl  to  indigo-blue.  This  coloring  matter  occurs  in  the  indigo 
plant  in  the  form  of  a  glucoside,  called  indican.1  Indigo-blue  can  occa- 
sionally be  observed  on  the  surface  of  putrid  urine  as  a  copper-red  scum, 
with  a  metallic  luster.  There  is  also  another  coloring  material  present, 
an  isomer  of  indigo-blue.  This  is  indirubin,  indigo-red.  This  coloring 
matter  has  also  been  assumed  to  be  related  to  skatoxyl,  although  this 
substance  has  not  yet  been  isolated,  as  such  from  normal  urine.  This 
question  must  be  left  open  for  the  present. 

In  the  putrefaction  of  tryptophane,  skatole  acetic.  acid  and  skatolecar- 
boxylic  acid  are  also  produced.  Up  to  the  present  time,  only  the  latter 
has  been  shown  to  be  probably  present  in  urine.2 

Furthermore,  cadaverine  and  putrescine  are  also  to  be  mentioned  among 
the  putrefactive  products  of  the  intestines.  Cadaverine  is  formed  with 
loss  of  carbon  dioxide  from  lysine  (diaminocaproic  acid)  ,  and  is  a  penta- 
methylenediamine. 

CH2  .  CH2  .  CH2  .  CH2  .  CH  .  COOH=CH2  .  CH2  .  CH2  .  CH2  .  CH2  +  CO2 
NH2  NH2  NH2  NH2 

V  --  y  /  V  .y  -  / 

Lysine  Cadaverine 

Putrescine,  tetramethylenediamine,  is  produced  from  ornithine,  diamino- 
valeric  acid,  a  constituent  of  arginine: 

CH2  .  CH2  .  CH2  .  CH  .  COOH=CH2  .  CH2  .  CH2  .  CH2  +  C02 

NH2  NH2  NH2  NH2 

Ornithine  Putrescine 

Phenylethylamine  is  produced  from  phenylalanine  : 

C6H5  .  CH2  .  CH  (NH2)  .  COOH=C6H5  .  CH2  .  CH2  .  NH2  +  CO2 
and  hydroxyphenylethylamine  from  tyrosine: 

/  OH  /  OH 

C6H4  =  C6H4  +  C02 

x  CH2  .  CH  (NH2)  COOH       x  CH2  .  CH2  .  NH2 

Recently  3  the  attempt  has  been  made  to  trace  the  production  of  phenyl- 
ethylamine  and  of  hydroxyphenylethylamine  to  the  action  of  trypsin  or 
of  pepsin.  A  great  many  experiments  have  been  carried  out,  with  pure 
pancreatic  and  gastric  juices,  taking  great  care  to  prevent  any  bacterial 


1  The  indoxyl  of  urine  is  also  wrongly  called  indican. 

2  E.  Salkowski:  Z.  physiol.  Chem.  9,  1,  23  (1885). 

3  R.  C.  Emmerson:  Hofmeister's  Beit.  1,  501  (1902). 


260  LECTURE  XII. 

contamination,  without  finding  any  ground  for  such  an  assumption.  That, 
on  the  contrary,  carbon  dioxide  is  split  off  by  the  action  of  putrefactive 
bacteria,  has  been  convincingly  shown  by  Ellinger.1  Cadaverine  and 
putrescine  are  only  found  in  the  faces  and  urine  under  exceptional  condi- 
tions, as,  for  example,  in  dysentery  and  acute  enteritis.  It  is  particularly 
well  known  that  these  diamines  appear  in  cystinuria,  a  disturbance  in  the 
metabolism  of  albumin  which  we  shall  soon  take  up  more  in  detail.  It  is 
still  questionable  what  the  relation  is  between  the  appearance  of  these 
two  diamines  and  this  metabolic  irregularity.  At  all  events,  these  com- 
pounds are  not  always  observed  when  cystine  is  eliminated  in  the  urine. 
We  have  now  mentioned  all  those  products  of  urine  which  are  to  be 
traced  to  putrefaction  in  the  intestines,  and  will  now  turn  our  attention 
to  an  acid  which  has  been  found  only  in  the  urine  of  certain  animals, 
especially  dogs,  namely  kynurenic  acid,  whose  mother-substance  has  been 
quite  recently  recognized  to  be  tryptophane.  It  is  y  -hydro  xyquinolin-  /?- 
carboxylic  acid:2 


HC  C          C  .  COOH 

I  II  I 

HC  C          CH 


The  formation  of  kynurenic  acid  from  tryptophane  was  proved  by 
Ellinger,  who  fed  some  of  the  tryptophane,  inclosed  in  a  gelatine  capsule, 
to  a  dog,  and  estimated  the  amounts  of  kynurenic  acid  before  and  after 
the  feeding.  The  increase  caused  by  tryptophane,  was  very  appreciable. 
Rabbits,  which  ordinarily  do  not  excrete  any  kynurenic  acid,  did  so  after 
the  administration  of  tryptophane.3  Human  beings,  on  the  other  hand, 
were  not  found  to  produce  any  kynurenic  acid. 

These  decomposition  products  give  us  a  very  good  idea  of  the  protein 
decomposition  in  the  tissues.  We  will  not  go  very  far  astray  if  we  accept 
the  following  conception  of  the  behavior  of  the  proteins  in  the  animal  or- 
ganism. In  the  stomach,  the  albuminous  substances  are  almost  entirely 
broken  down  into  a  number  of  very  complicated  products  by  the  action  of 
pepsin  and  hydrochloric  acid.  These  pass  on  to  the  intestine,  where  they 
are  attacked  further  by  trypsin.  Under  these  influences,  polypeptides  are 
produced,  a  larger  or  smaller  number  of  the  amino  acids  entering  into 
their  composition.  A  large  number  of  free  amino  acids  are  split  off  at 
the  same  time,  first,  tyrosine,  tryptophane,  and  cystine.  Then  follow 


1  A.  Ellinger:  Z.  physiol.  Chem.  29,  34  (1900);  Ber.  31,  3183  (1899);  32,  3542  (1900). 

2  J.  Liebig:  Ann.  86,  125  (1853).     R.  E.  Swain:  Am.  J.  Physiol.  13,  30  (1905). 

3  A.  Ellinger:  Z.  physiol.  Chem.  43,  325  (1904). 


ALBUMINS  OR  PROTEINS.  261 

alanine,  leucine,  glutamic  acid,  aspartic  acid,  lysine,  arginine,  histidine, 
etc.  Phenylalanine  and  proline  are  undoubtedly  present  in  combination, 
for  they  are  unacted  upon  by  trypsin.  They  remain  unattacked,  com- 
bined with  other  amino  acids  in  the  form  of  polypeptides.  All  these 
cleavage-products  are  absorbed.  The  albumin  synthesis  starts  in  the 
intestinal  walls,  the  serum-albumins  being  first  formed.  The  rapidity  of 
this  synthesis  is  dependent  on  the  presence  of  certain  amino  acids,  for,  as 
recent  investigations  have  proved,  the  relative  amounts  of  the  amino  acids 
in  the  serum-albumins  are  very  constant.  The  albumin  synthesis  would 
necessarily  be  regulated  by  the  amount  of  that  amino  acid  which  is  present 
to  the  smallest  relative  extent.  There  is  always  the  possibility  that  one 
amino  acid  may  change  into  others.  This  is  known  to  be  true  only  of 
amino  acids  of  the  aliphatic  series,  among  themselves;  but  in  the  same 
manner  we  can  imagine  the  production  of  aromatic  amino  acids  from  one 
another.  On  the  other  hand,  it  is  hardly  probable  that  relations  exist 
between  these  two  groups  or  at  most  only  in  the  sense  that  an  aromatic 
amino  acid  might  give  rise  to  an  aliphatic  one,  or  at  least,  a  fatty  acid. 
Our  knowledge  of  the  formation  of  one  food-stuff  from  another,1  e.g.  the 
production  of  fat  from  the  carbohydrates,-  forces  us  to  admit  the  pos- 
sibility of  several  amino  acids  being  produced  from  a  single  one. 

If  such  transformations  take  place  then  naturally  the  extent  of  the 
albumin  synthesis  is  considerably  widened.  Those  amino  acids  which  are 
not  utilized  for  the  production  of  new  proteins  are  evidently  already 
broken  down  in  the  walls  of  the  intestine;  i.e.  the  amino  group  is  first 
split  off  and  the  residue  consumed.  The  ammonia  thus  formed  prob- 
ably is  utilized  in  the  production  of  urea.  From  these  conceptions,  we 
should  expect  to  find  a  priori,  that  the  various  albuminous  substances 
behave  differently;  i.e.  under  certain  conditions  an  influence  upon  the 
extent  of  the  synthesis  of  albuminous  substances  in  the  intestines  might 
affect  the  entire  metabolism.  This  is  well  shown  in  the  case  of  gelatin, 
which  not  only  lacks  whole  groups  of  amino  acids,  but  at  the  same  time 
possesses  combinations  of  such,  which  affect  unfavorably  the  breaking 
down  of  the  molecule  and  indirectly  the  formation  of  new  proteins.  The 
other  proteins  might  also,  according  to  the  amino  acids  in  their  composition, 
be  more  or  less  favorable  to  the  synthesis  of  protein,  and  especially  for 
the  formation  of  the  serum-albumins.  It  could  even  be  expected  that  it 
would  not  be  possible  to  maintain  the  same  nitrogen  balance  with  every 
albuminous  substance.  Here  it  is  assumed  that  the  amino  acids  which 
are  already  broken  down  in  the  intestines  are  to  a  certain  extent  eliminated 
from  the  albumin  metabolism.2  We  have  intentionally  dwelt  on  these 


1  Cf.  Lecture  XIV. 

2  Cf.  Lecture  XI,  p.  225. 


262  LECTURE  XII. 

relations  somewhat  more  in  detail,  because  they  have  hitherto  received 
but  little  attention  in  experimental  investigation. 

The  albuminous  substances  now  produced,  together  with  the  ammonia 
that  has  been  split  off,  and,  possibly,  other  cleavage-products  from  the 
amino  acids,  pass  from  the  intestine  to  the  liver,  and  from  here  into  the 
general  circulation.  We  will  mention  that  the  liver  is  quite  generally 
considered  as  the  place  where  the  above-mentioned  aromatic  products  of 
putrefaction  are  conjugated  with  sulphuric  and  glucuronic  acids.  We 
have  already  mentioned  the  fact  that  urea  is  formed  in  the  liver  on  a  large 
scale. 

As  a  consequence  of  the  extensive  decomposition  and  reconstruction  of 
proteins  in  the  alimentary  tract,  only  those  albuminous  substances  circu- 
late in  the  organism  which  correspond  to  its  entire  construction.  Every 
cell  continually  receives  the  same  nourishment  in  the  same  composition, 
through  the  instrumentality  of  the  blood.  The  whole  mechanism  of 
the  cell  is  thereby  greatly  simplified.  The  cell  is,  in  the  widest  sense, 
independent  of  the  nature  of  the  food  in  the  exercise  of  its  functions. 
It  is,  in  its  entire  metabolism,  adjusted  to  a  nourishment  of  quite  definite 
composition,  which  is  always .  available  to  satisfy  its  demands.  A  prom- 
inent part  is  taken'  by  the  intestine  in  the  total  metabolism.  The 
nutritional  relations  of  the  entire  cell-material  depend  in  the  widest  sense 
upon  its  activity.  Its  functions  are  simplified,  in  proportion  as  the 
proteins  from  the  food  are  prepared  by  the  combined  action  of  hydro- 
chloric acid  and  pepsin  and  of  trypsin.  The  cells  of  the  intestines  will 
be  built  up  more  quickly  the  better  the  material  available  for  synthesis 
is  suited  for  the  new  proteins.  Although  any  derangement  in  the 
secretion  of  the  ferments  would  undoubtedly  affect  the  processes  in  the 
intestinal  tract,  the  disturbance  in  this  tract  must  affect  the  entire  meta- 
bolism even  more  seriously. 

The  individual  body-cell  removes  from  the  blood  such  protein  sub- 
stances as  it  requires.  It  breaks  them  down  in  the  same  manner  that 
trypsin  does.  Amino  acids  result,  which,'  on  further  decomposition, 
produce,  on  the  one  hand,  urea,  and,  on  the  other,  carbon  chains  free 
from  nitrogen,  of  whose  nature  we  still  know  but  little,  and  which, 
perhaps,  enter  into  relations  with  the  carbohydrates,  fats,  and,  possibly, 
other  organic  components  of  the  tissues.  The  breaking  down  of  the 
amino  acids  in  the  cells  is  still  an  obscure  process.  We  only  know  that 
the  total  nitrogen  soon  appears  in  the  urine.  It  is  questionable  whether 
the  total  combustion  of  the  amino  acids  is  immediately  effected  after  the 
elimination  of  the  amino  or  CO  .  NH2  groups,  or  whether  the  surviving 
carbon  chains  in  their  further  decomposition  are  independent  of  the  above 
process.  The  formation  of  the  nitrogenous  end-products,  whether  it  be 
urea  or  uric  acid,  is  also  but  imperfectly  explained.  If  we  assume  that  the 


ALBUMINS  OR  PROTEINS.  263 

liver  is  practically  the  only  organ  in  the  body  producing  urea,  we  must 
conclude  that  the  nitrogenous  cleavage-products,  whether  ammonia  or 
any  compound  containing  the  CO  .  NH2  group,  formed  by  the  cell  func- 
tions, would  have  to  be  transported  to  the  liver,  and  there  acted  upon. 
Here  is  another  large  gap  in  our  knowledge  concerning  the  decomposition 
of  albumin  in  the  tissues,  which  we  do  not  seem  able  to  bridge  over  at 
present.  Hypotheses  have,  therefore,  been  advanced  here,  which  we 
have  already  discussed  under  the  formation  of  urea  and  uric  acid. 

If  we  accept  the  foregoing  explanation  of  the  decomposition  of  albumin 
in  the  tissues,  we  must  naturally  expect  that  the  presence  of  some  of  the 
amino  acids  which  have  been  designated  as  representing  transition  stages 
may  be  detected.  As  a  matter  of  fact,  certain  observations  do  indicate 
the  presence  of  amino  acids  in  the  intermediate  metabolism  of  albumin. 
We  will,  moreover,  state,  in  order  to  prevent  any  misapprehension,  that 
when  the  proteins  are  broken  down  by  the  cells  into  the  amino  acids, 
further  decomposition  need  not  necessarily  immediately  follow,  any  more 
than  that  the  muscles  must  immediately  consume  any  dextrose  which 
may  be  presented  to  them.  Just  as  the  muscles  produce  their  glycogen 
from  dextrose,  so  the  cells  undoubtedly  utilize  the  decomposition-products 
according  to  their  requirements,  at  one  time  decomposing  them  further, 
and  at  another  time  linking  them  together  into  chains,  thus  utilizing  the 
proteins  thereby  formed  as  building  material  for  the  contents  of  their 
own  cells,  or  for  forming  new  cells.  Every  individual  cell  must  build  up 
its  own  albumin,  in  the  same  manner  as  the  intestine,  and  form  its 
own  peculiar  albumin  from  its  own  particular  nourishment,  the  serum- 
albumin.  This  probably  takes  place  in  much  the  same  way  as  in  the 
intestine,  with  its  digestive  ferments  furnished  by  the  glands.  The 
body  cells,  also,  probably  supply  themselves  with  the  necessary  materials 
for  their  cell  requirements  by  breaking  down  the  proteins  into  simpler 
portions.  Polypeptides  and  amino  acids  very  likely  appear  as  transition 
products  in  the  intermediate  metabolism  of  albumin.  Just  as  the  intes- 
tines do  not  decompose  the  albumins  entirely  into  the  lowest  cleavage- 
products,  so  we  need  not  expect  the  tissue-cells  to  decompose  all  of  the 
albumin  into  its  simplest  components.  These  cells  also  probably  only 
decompose  the  proteins  to  the  point  where  they  can  be  utilized  to  recon- 
struct new  albumins. 

The  assumption  that  cell-metabolism  also  produces  amino  acids,  has 
been  supported  by  the  fact  that  it  is  possible  to  protect  certain  of  these 
amino  acids  from  being  acted  upon  further  by  the  administration  of 
specific  compounds  which  possess  the  faculty  of  uniting  with  them,  and 
thus  to  recover  them.  In  this  way  the  presence  of  cystine  in  dogs  has  been 
verified  by  introducing  phenyl  halides  (brom-,  chlor-,  or  iodo-benzene) 
into  the  animal.  By  feeding  benzoic  acid  to  mammals,  we  obtain  a  com- 


264  LECTURE  XII. 

pound  of  glycocoll,  while  from  birds  we  get  one  of  ornithine.  Some  of  the 
amino  acids,  such  as  cystine,  have  been  directly  isolated  from  normal 
organs. 

The  question  whether  amino  acids  are  normal  constituents  of  urine,  has 
recently  been  raised  repeatedly.  Various  answers  have  been  given.  If  we 
examine  critically  the  investigations  so  far  published,  we  shall  have  to 
admit  that  there  is  no  positive  proof  yet  brought  forth  indicating  the 
presence  of  amino  acids  in  urine  under  normal  conditions.  Glycocoll  is 
the  only  one  that  has  been  identified  positively,  and  this  was  only  accom- 
plished after  the  urine  had  been  liberally  treated  with  alkali  for  many 
hours;  in  fact,  several  days.  We  can  easily  imagine  that  the  glycocoll 
may  have  been  split  off  from  some  compound.  Until  it  is  possible  to 
show  that  the  amount  of  this  product  depends  upon  the  extent  of  albumin 
decomposition  in  the  organism,  we  cannot  regard  this  discovery  as  proof 
of  the  appearance  of  glycocoll  in  cell-metabolism.  It  is  noteworthy  that 
only  glycocoll  has  so  far  been  isolated.  This  amino  acid  is  utilized  to  a 
considerable  extent  for  conjugation  with  aromatic  substances,  especially 
benzoic  acid.  We  can  easily  imagine  that  the  glycocoll  found  in  urine 
originated  from  this  source.  It  is  very  probable  that  the  organism  main- 
tains a  supply  of  glycocoll  for  just  this  coupling  process.  When  we  con- 
sider in  addition  that  the  kidneys  are  active  producers  of  hippuric  acid, 
we  can  appreciate  the  possibility  of  glycocoll  being  flushed  into  the  urine 
under  certain  conditions.  From  the  investigations  at  hand,  we  are  not 
at  all  justified  in  stating  that  amino  acids  are  normal  constituents  of 
urine.1 

Amino  acids  are,  however,  often  present  in  urine  in  large  amounts  under 
certain  pathological  conditions.  This,  for  instance,  occurs  in  the  case  of 
acute  atrophy  of  the  liver,  a  disease  in  which  the  albumin  decomposition 
is  very  rapid.  The  liver,  in  this  case,  is  flabby  and  emaciated.  The  con- 
tents of  the  capsule  of  Glisson  are  quite  soft,  and,  in  part,  semi-fluid.  An 
extensive  destruction  process  has  taken  place  in  all  the  liver  cells.  Amino 
acids  can  be  found  in  the  liver-paste,  leucine  and  tyrosine  being  easily 
isolated  on  account  of  their  insolubility.  The  remaining  elements  of  the 
albumin  molecule,  especially  those  easily  split  off,  are  also  probably  present. 
The  two  amino  acids  mentioned,  often  crystallize  out  directly  on  the  liver 
itself,  in  the  form  of  a  white  coating.  Leucine  and  tyrosine  have  been 
found  in  the  urine  at  such  times.  A  very  analogous  condition  arises  in 
phosphorus  poisoning.  Here,  again,  we  find  amino  acids  in  the  urine; 
tyrosine,  leucine,  and  glycocoll2  having  been  isolated.  Undoubtedly 


1  E.  Abderhalden  and  A.  Schittenhelm :  Z.  physiol.  Chem.  47,  1906.    G.  Embden  and 
H.  Reese:  Hofmeister's  Beitr.  7,  411  (1905). 

2  E.  Abderhalden  and  P.  Bergell:  Z.  physiol.  Chem.  39,  464  (1903).     E.  Abderhalden 
and  L.  F.  Barker:  ibid.  42,  524  (1904). 


ALBUMINS  OR  PROTEINS.  265 

there  are  other  albuminous  decomposition-products  present  in  the  urine 
of  animals  which  have  been  poisoned  by  phosphorus. 

We  will  add  that  the  sudden  destruction  of  cell-albumin  as  it  occurs 
in  acute  atrophy  of  the  liver,  phosphorus  poisoning,  and  many  other  con- 
ditions, has  been  compared  to  the  autolysis  of  dead  tissues.  By  autolysis, 
we  mean  "  self-digestion  "  of  the  organs,  which  follows  in  a  short  time, 
when  these  are  preserved  in  a  sterile  condition.  A  gradual  solution  and 
liquefaction  of  the  whole  organ  takes  place.  Among  the  end-products  of 
this  process  we  find,  for  one  thing,  decomposition  products  of  albumin,  — 
arginine  is  rarely  present,  as  it  is  further  decomposed  by  the  arginase,  — 
then  again  cleavage-products  from  the  nucleins,  and  finally  also  com- 
pounds arising  from  the  remaining  elements  of  the  tissue.  We  obtain 
the  impression,  that  all  cell-ferments  become  active  immediately  after 
death,  and  then,  when  all  the  regular  functions  have  ceased,  indiscrimi- 
nately tear  everything  to  pieces.  It  is  correct  to  assume  from  this  con- 
ception of  autolysis,  that  an  analogous  fermentation  occurs  in  the  cells. 
It  would  be,  however,  a  grave  error  to  conclude  that  the  autolytic 
decomposition  is  to  be  regarded  as  the  normal  breaking  down  of  the  cell. 
The  living  cell  unquestionably  does  not  permit  all  its  ferments  to  act  at 
one  time.  It  regulates  its  metabolism  most  carefully.  One  fermentation 
process  is  carried  out,  another  then  follows.  By  one  of  these  processes 
a  certain  cleavage-product  is  formed,  while  the  action  of  another  ferment 
breaks  it  down  further.  All  these  processes  cooperate  with  one  another. 
The  reconstruction  proceeds  uninterruptedly  together  with  the  decompo- 
sition. In  the  dead  tissues  all  this  regulating  mechanism  is  wanting. 
Decomposition  alone  takes  place.  We  are  not  justified  in  considering  the 
severe  destruction  which  occurs  in  the  above-mentioned  liver  tissues  as 
parallel  to  autolysis.  It  is  possible  that  the  whole  process  is  a  similar 
one,  that  the  solution  of  the  cell  structure  precedes  the  death  of  the  cells; 
on  the  other  hand,  it  must  be  remembered  that  we  have,  as  yet,  only 
established  a  restricted  decomposition  of  cell  proteins,  while  an  absolute 
confirmation  of  the  total  dissolution  of  the  cell  tissues,  which  characterizes 
autolysis,  is  missing.  The  cell  destruction,  under  the  pathological  condi- 
tions mentioned,  is  also  much  more  rapid  in  autolysis  than  under  normal 
conditions. 

Autolysis  also  seems  to  play  a  part  in  the  living  organism,  —  in  fact, 
assisting  in  the  removal  of  dead  matter;  for  example,  of  the  fibrin  produced 
by  pneumonia  in  the  lungs;1  in  the  reduction  of  the  uterus  after  childbirth ; 
very  probably  in  the  absorption  of  copious  exudations  of  corpuscular 
elements  and  the  decomposition  of  decaying  neoplasms,  which  have  been 
cut  off  from  the  circulation,  etc.  It  is  questionable  whether  we  are  justi- 


1  F.  Miiller:  Verb.  XX,  Kon.   Med.  Wiesbaden,  1902. 


266  LECTURE  XII. 

fied  in  calling  these  processes  autolytic.  We  only  know  that  the  organism 
is  capable  of  mobilizing  ferments  which  take  care  of  foreign  material,  and 
by  decomposing  and  reducing  the  complex  molecules,  prepare  it  for  assimi- 
lation. In  fact,  in  pneumonia,  during  resolution  the  bronchial  tubes  seem 
to  possess  functions  very  analogous  to  those  of  the  intestine.  It  would 
be  better,  for  the  present,  to  restrict  the  term  "  autolysis  "  to  the  ferment 
action  of  the  cells  in  the  tissues,  which  follows  some  time  after  death. 
It  is  like  the  works  of  a  clock,  whose  spring  has  been  released  and  sud- 
denly runs  down. 

Amino  acids  have  recently  been  found  in  the  urine  during  various  dis- 
eases. If  we  summarize  these  observations,  we  will  obtain  the  impression 
that  the  metabolism  has  been  deranged  by  lack  of  oxygen.  Thus,  tyrosine 
is  found  in  the  urine  after  prolonged,  deep  narcosis,  during  the  coma  of 
a  diabetic,  etc.1 

While  these  cases  represent  merely  isolated  cases  of  the  appearance  of 
individual  amino  acids,  due  to  temporary  derangements,  and  which  are  not 
at  all  permanent,  we,  however,  also  know  of  a  derangement  in  metabolism 
in  which  a  greater  or  less  amount  of  an  amino  acid  is  always  present  in 
the  urine.  This  occurs  during  cystinuria.  Cystine 2  is  found  in  the  urine 
during  this  rather  rare  disturbance  in  the  decomposition  of  albumin. 
Small  amounts  of  this  compound  seem  to  be  always  present  in  urine.3  In 
cystinuria,  however,  the  quantity  is  very  largely  increased,  and  often 
leads  to  the  formation  of  calculi.  There  is  not  the  least  doubt  but  that 
this  cystine  originates  from  albumin.  It,  like  the  albuminous  cystine,  is 
an  a-diamino-/?-dithio'dilactylic  acid.  Emil  Fischer  and  Umetaro  Suzuki 4 
have  recently  established  the  identity  of  the  two  substances. 

The  significance  of  cystinuria  was  long  in  doubt.  The  discovery  of 
L.  von  Udransky  and  E.  Baumann 5  that  other  di-amines  (putrescine  and 
cadaverine)  are  present  in  the  urine  during  cystinuria,  for  a  long  time  led 
to  the  assumption  that  cystinuria  is  caused  by  an  increased  intestinal  putre- 
faction. Cystine,  according  to  this  assumption,  is  split  off  from  albumin 
in  the  intestines  and  absorbed  as  such.  To-day  we  know  that  the  forma- 
tion of  amino  acids  is  a  normal  function  of  the  alimentary  tract,  in  no  case 
causing  their  elimination  in  the  urine.  The  di-amines  mentioned  are  by 

1  E.  Abderhalden:  Z.  physiol.  Chem.  44,  17  and  40  (1905);  45,  468  and  471  (1905). 

2  W.  F.  Lobisch:  Ann.  182,  231  (1876).     A.  Niemann:  Deut.  Arch.  klin.  Med.  18, 
232  (1876).     W.  Ebstein:  19,  138  (1877);  30,  594  (1882).     B.  Hester:  Z.  physiol.  Chem. 
14,  109  (1890).     A.  Loewy  and  C.  Neuberg:  ibid.  43,  338  (1904).     C.  Alsberg  and  O. 
Folin:  Am.  J.  Physiol.  14,  54  (1905).     E.  Abderhalden:  Z.  physiol.  Chem.  38,  557  (1903). 
E.  Abderhalden  and  A.  Schittenhelm :  ibid.  45,  468  (1905). 

3  Stadthagen:  ibid.  9,  29  (1885).     E.  Goldmann  and  E.  Baumann:  ibid.  12,  254 
(1888). 

4  E.  Fischer  and  U.  Suzuki:  ibid.  45,  405  (1905). 

6  L.  v.  Udransky  and  E.  Baumann:  Z.  physiol.  Chem.  13,  562  (1889). 


ALBUMINS  OR  PROTEINS.  267 

no  means  found  in  all  cases  of  cystinuria.  It  is  far  more  probable  that  the 
disease  is  to  be  regarded  as  a  disturbance  in  the  breaking  down  of  albumin, 
on  the  part  of  the  tissues.  That  the  cystine  from  the  albuminous  sub- 
stances in  the  food  is  absorbed  and  assimilated  is  evident  from  the  fact 
that  the  albuminous  material  in  the  tissues  of  a  patient  afflicted  with 
cystinuria,  certainly  contains  cystine;  and  that  no  diminution  in  the 
amount  of  this  amino  acid  can  be  detected.  Cystine  is  evidently  produced 
in  the  decomposition  of  proteins  during  cell-metabolism,  and  is  not 
further  worked  over.  It  is  difficult  to  say  why,  in  these  cases,  cystine 
is  not  decomposed.  A  patient  afflicted  with  cystinuria  consumes  any 
cystine  administered  to  him,  and  does  not  eliminate  all  the  cystine-sulphur 
as  such.  It  would  be  easy  to  imagine  some  change  in  the  cystine  molecule, 
such  that  the  cell  ferments  are  unable  to  find  any  point  of  attack.  We 
have  seen  that  the  cystine  from  albumin,  and  that  of  the  urine,  are 
identical.  This  question  must  be  left  unsettled  for  the  present.  It  may, 
of  course,  be  possible,  that  the  ferments  capable  of  decomposing  cystine 
are  absent  from  some  cells,  and  that  this  substance  is,  therefore,  eliminated 
unchanged.  Such  an  assumption  has  not,  however,  been  experimentally 
confirmed.  It  would  start  with  the  hypothesis  that  each  cell  possessed 
a  distinct  ferment  to  produce  each  different  amino  acid,  or  group  of  amino 
acids.  We  must  say  that  we  have  absolutely  no  proof  of  such  a  condition 
of  affairs.  We  can  imagine  that  cystine  might  occupy  an  isolated  position 
on  account  of  its  difficult  solubility.  It  is,  however,  possible  that  con- 
ditions may  exist  in  the  cells  of  a  person  afflicted  with  cystinuria,  which 
may  cause  cystine  to  be  thrown  out.  That  cystine  may,  in  time,  accu- 
mulate in  the  tissues  to  large  proportions,  has  recently  been  proved  in  the 
case  of  a  boy  21  \  months  old.1  He  died  with  indications  of  gradual 
inanition.  A  post-mortem  examination  showed  all  the  organs  permeated 
with  crystals  of  cystine.  The  spleen,  for  example,  was  saturated  with 
cystine,  and  from  this  organ  the  pure  amino  acid  could  easily  be  isolated 
in  large  quantities.  It  was  interesting  that  this  was  a  case  of  inherited 
cystine  diathesis, —  in  fact,  in  a  progressive  form.  Perhaps  some  light 
may  be  shed  upon  this  rare  derangement  in  metabolism  by  the  obser- 
vation that  other  amino  acids,  besides  cystine,  may  be  found  in  the  urine 
during  this  disease.2  Thus,  in  one  case,  cystine,  leucine,  and  tyrosine  were 
found.  Apparently  from  this  discovery  cystinuria  corresponds  to  a  more 
general  disturbance  in  the  breaking  down  of  albumins  than  is  usually 
assumed,  and  that,  to  a  certain  extent,  this  disease  is  to  be  considered  as 
the  simplest  form  of  such  derangement.  We  must  again  state,  however, 


1  E.  Abderhalden:  ibid.  38,  557  (1903). 

2  E.  Fischer  and  U.  Suzuki:  Z.  physiol.  Chem.  45,  405  (1905).     E.  Abderhalden  and 
A.  Schittenhelm:  ibid.  45,  468  (1905). 


268  LECTURE  XII. 

that  it  is  impossible  to  give  a  perfectly  clear  picture  of  the  metabolic 
disturbance  in  question,  which  shall  be  based  upon  our  present  experi- 
mental knowledge.  If  we  base  our  judgment  concerning  this  anomaly  in 
albumin-metabolism  not  only  upon  the  observations  made  upon  those 
afflicted  with  cystinuria,  but  upon  our  general  knowledge  of  the  total 
metabolism  of  albumin  in  the  tissues,  it  then  appears  as  most  probable 
that  we  have  in  cystinuria  a  disturbance  in  the  decomposition  of  proteins 
in  the  cell-metabolism.  Conversely,  we  can  consider  the  appearance  of 
cystine  in  this  disease  as  further  evidence  of  the  formation  of  amino  acids 
from  albumin  in  the  intermediate  metabolism,  always  remembering  that 
one  supposition  is  dependent  on  the  other,  and  thus  it  is  not  a  definitive 
proof. 

Our  insight  into  the  intermediate  decomposition  of  albuminous  bodies 
is  by  no  means  limited  to  the  discovery  of  amino  acids  in  the  urine 
under  specific  conditions,  and  to  the  recognition  of  the  final  albumin 
cleavage-products,  —  urea,  in  the  case  of  mammals,  and  uric  acid  in  birds 
and  fishes.  There  are  other  products  present  in  the  urine,  as  yet  largely 
unknown,  which  contain  nitrogen  and  sulphur,  and  are  undoubtedly 
closely  related  to  albumin-metabolism.  We  will  disregard  the  fact  that 
there  are  albuminous  substances  in  urine  which  have  been  variously  inter- 
preted. They  are  probably  not  simple  substances.  They  belong  partly 
to  the  mucins,  and  in  part  to  the  group  of  nucleo-albumins,  and  probably 
originate  in  the  urinary  passages.  They  have  no  bearing  on  the  subject 
of  albumin-metabolism.  This  applies  especially  to  the  large  quantities 
of  albumin  which  appear  in  the  urine  under  pathological  conditions,  and 
especially  in  diseases  of  the  kidneys.  These  only  affect  the  albumin- 
metabolism  indirectly,  inasmuch  as  they  continually  withdraw  this  valuable 
material  from  the  body,  thus  depriving  the  organism  of  the  energy  con- 
tained therein.  It  is  indeed  possible,  that  an  exact  examination  of  these 
substances  would  give  us  an  insight  into  the  course  of  albumin  decompo- 
sition in  the  tissues.  It  would  certainly  be  of  the  greatest  interest  to 
know  the  origin  of  the  albumin  always  present  in  the  various  forms  of 
nephritis.1  We  usually  assume  that  the  serum-proteins  (serum-globulin, 
and  serum-albumin)  under  pathological  conditions  pass  into  the  urine. 
Although  this  assumption  is  very  plausible,  it  must  be  said  it  does  not 
necessarily  explain  all  the  cases  arising.  That  albumin  does  not  normally 
appear  in  urine,  excepting,  of  course,  in  traces,  is  due  to  the  fact  that  the 
epithelial  cells  of  the  kidney,  or  those  of  the  glomeruli,  will  not  permit  the 
colloidal  albumin  to  pass  through.  This  simple  explanation  is  not  inva- 
riably true,  as  is  shown  by  the  appearance  of  a  very  well-defined  albumi- 
nous substance,  the  so-called  "  Bence- Jones  albumin,"  in  the  urine.  It  is 


1  E.  Abderhalden:  Z.  exper.  Path.  u.  Therapie,  2,  642  (1905). 


ALBUMINS  OR  PROTEINS.  269 

principally  present  in  cases  of  sarcoma  formations  in  the  bone  marrow 
(Sarcomatosis  ossium).  It  is  usually  found  only  in  the  urine,  the  epi- 
thelia  of  the  glomeruli  permitting  this  substance  to  pass  through,  at  the 
same  time  retaining  all  the  serum-albumins.  It  might  be  thought  that 
the  Bence-Jones  albumin  represents  a  lower  albumin,  and  consequently 
diffuses  through  the  urinary  passages.1  This  assumption  is,  however,  in- 
correct, because  this  albumin  contains  all  of  the  usual  amino  acids,  which 
seems  to  indicate  that  the  albumin  has  not  in  any  way  undergone  much 
decomposition.  Tyrosine  is  one  of  these  amino  acids,  and  this  amino 
acid,  as  is  well  known,  is  very  easily  split  off  from  the  rest  of  the  molecule. 
The  objection  might  be  raised,  of  course,  that  the  tyrosine-is  linked  in  a 
different  manner  in  the  Bence-Jones  albumin  from  that  in  other  varieties 
of  albumin.  There  is  at  present  no  ground  for  such  an  assumption. 
According  to  its  content  of  amino  acids,  the  Bence-Jones  albumin  does 
not  correspond  to  either  of  the  two  serum-proteins,  and  may  be  con- 
sidered as  one  of  the  tissue-albumins,  which,  without  being  broken  down 
or  changed  into  one  of  the  serum-albumins,  is  transmitted  to  the  blood, 
and  then  is  probably  eliminated  as  an  albumin  foreign  to  the  blood 
although  suitable  for  the  body.  It  would  be  interesting  to  investigate 
other  analogous  albuminous  excretions  from  the  kidneys. 

Although  such  products  are  only  found  under  specific  conditions,  normal 
urine,  nevertheless,  contains  other  complicated  compounds,  whose  nature 
has  not  yet  been  determined,  but  which,  from  their  elementary  composition, 
must  be  closely  related  to  albumin-metabolism.  Their  high  percentage 
of  oxygen  stamps  them  as  albumin  oxidation  products.  Their  presence 
indicates  the  possibility  that  the  disintegration  of  the  albumin  molecule 
may  proceed  in  different  ways,  and  that  our  assumption,  that  albumin  is 
broken  down  in  cell-metabolism  through  the  amino  acid  stage,  does  not 
apply  to  all  albumin  decomposition.  It  is  indeed  possible  that  a  part  of 
the  albumin  is  oxidized  in  a  manner  unknown  to  us  without  undergoing 
previous  cleavage.  It  is  not  impossible  that,  for  this  kind  of  albumin 
decomposition,  those  complexes  come  into  consideration  which,  as  we 
have  seen,  strongly  resist  the  action  of  the  proteolytic  ferments.  At  all 
events,  we  shall  expect  that  when  these  products  are  explained,  we  shall 
receive  further  insight  into  the  intermediate  metabolism.  Here  we  can 
only  mention  the  names  of  these  various  compounds,  and  assert  that  no 
proof  exists  of  their  individuality.  Bondrizyski  and  Gottlieb  2  distinguish 

1  E.  Abderhalden  and  O.  Rostoski:  Z.  physiol.  Chem.  46,  125  (1905).  Cf.  A. 
Ellinger:  Deut.  Arch.  klin.  Med.  62,  255  (1899).  A.  Magnus-Levy:  Z.  physiol.  Chem. 
30,  200  (1900).  F.  Reach:  Deut.  Arch.  klin.  Med.  82,  390  (1905). 

3  St.  Bondzyriski  and  Gottlieb:  Zentr.  Med.  Wiss.  (1897)  No.  33, 577.  St.  Bondzyriski 
and  Panek:  Bull,  de  1'Acad.  d.  sciences  de  Crascovie,  Oct.  1902.  St.  Bondzyriski,  St. 
Dombrowski,  and  K.  Panek:  Z.  physiol.  Chem.  45, 83  (1905).  F.  Pregl:  Pfluger's  Arch. 
76,  87  (1899). 


270  LECTURE  XII. 

first  of  all  between  an  oxy-proteinic  acid  and  an  alloxy-proteinic  acid. 
Antoxy-proteinic  acid  has  recently  been  added  to  these.  All  three  acids 
contain  sulphur,  nitrogen,  and  large  amounts  of  oxygen. 

The  following  figures  will  give  some  idea  of  their  composition.  The 
antoxy-proteinic  acid  contains  43.21  per  cent  C,  4 . 91  per  cent  H,  24 . 40  per 
cent  N,  0.61  per  cent  S,  and  26.33  per  cent  O;  the  oxy-proteinic  acid  39 . 62 
per  cent  C,  5 . 64  per  cent  H,  18 . 08  per  cent  N,  1.12  per  cent  S,  and  35 . 54 
per  cent  O;  and  the  alloxy-proteinic  acid  41.33  per  cent  C,  5.70  per  cent 
H,  13.55  per  cent  N,  2.19  per  cent  S,  and  37.23  per  cent  0.  We  must 
also  add  that  O.  Thiele  1  has  described  a  uroferric  acid  occurring  in  urine, 
which  undoubtedly  belongs  to  this  group  of  compounds.  By  heating  it 
with  hydrochloric  acid  in  a  sealed  tube  it  decomposes,  producing  melanin 
substances,  carbon  dioxide,  ammonia,  organic  sulphur  compounds,  hydro- 
gen sulphide,  and  aspartic  acid.  We  must  also  add  that  these  substances 
do  not  give  any  albumin  reactions.  The  biuret  test,  Millon's  reaction, 
and  the  remaining  characteristic  test  for  albumins  and  their  closely- 
related  cleavage-products,  all  give  negative  results.  We  must  content  our- 
selves for  the  present  with  the  mere  enumeration  of  these  substances.  It 
is  possible  that  perhaps  some  light  is  thrown  upon  the  formation  of  them 
by  the  fact  that  a  difficultly-dialyzable  body  containing  no  amino  acids2 
may  be  isolated  from  urine,  in  the  same  way  as  alloxy-proteinic  acid 
and  oxy-proteinic  acid  were  obtained.  Such  acids  may,  however,  be 
obtained  from  this  substance  by  boiling  it  with  concentrated  hydrochloric 
acid.  Glycocoll,  leucine,  and  glutamic  acid  are  then  isolated,  and  the 
presence  of  phenyl-alanine  and  aspartic  acid  indicated.  The  substance 
did  not  contain  any  tyrosine.  It  is  very  probable  that  this  product  is 
a  residue  of  a  partially  disintegrated  albumin  molecule,  which  has  escaped 
further  disintegration.  We  know  nothing  further  about  its  relations  with 
the  other  acids  just  mentioned. 

In  the  discussion  of  the  decomposition  products  of  tyrosine  and  phenyl- 
alanine,  we  called  attention  to  two  hydroxy-acids  which  occur  in  the  urine 
during  the  very  rare  metabolic  disturbance  known  as  alcaptonuria.  Alcap- 
ton  was  the  name  which  Bodeker 3  gave  to  a  substance  which  he  isolated 
from  the  urine  of  a  man  afflicted  with  diabetes.  It  gave  to  the  urine  two 
distinguishing  characteristics.  The  urine  showed  a  very  appreciable  reduc- 
ing power,  and  had  the  property  of  turning  dark  brown  or  black,  taking  on 
oxygen,  when  alkali  was  added.  This  alcapton  has  been  isolated  from 
urine  by  M.  Wolkow  and  E.  Baumann,4  and  its  composition  ascertained 


1  O.  Thiele:  Z.  physiol.  Chem.  37,  251  (1903). 

2  E.  Abderhalden  and  F.  Pregl:  ibid.  46,  19  (1905). 

8  Bodeker:  Z.  rat.  Med.  7,  130  (1859);  Ann.  17,  98  (1861). 

4  M.  Wolkow  and  E.  Baumann:  Z.  physiol.  Chem.  15,  228  (1891).     Here  are  given 
references  to  the  older  literature. 


ALBUMINS  OR  PROTEINS.  271 

after  Kirk  1  had  previously  shown  that  a  crystallized  acid  could  be  obtained 
from  the  urine  of  three  children  in  the  same  family.  He  soon  recognized 
the  fact  that  it  was  a  mixture  of  uroleucic  acid  and  uroxanthic  acid.  The 
latter  is,  undoubtedly,  identical  with  the  homogentisic  acid  of  Wolkow  and 
Baumann,  who  have  established  its  constitution.2  It  is  a  di-hydroxy- 
phenyl-acetic  acid.  Uroleucic  acid,  on  the  other  hand,  is  a  di-hydroxy- 
phenyl-lactic  acid.  The  latter  has  only  occasionally  been  found  in  alcap- 
tonuric  urine,  and  is,  undoubtedly,  the  antecedent  of  homogentisic  acid. 
Wolkow  and  Baumann  have  discovered  the  source  of  these  acids,  and  also 
the  conception  of  the  whole  phenomenon.  Alcaptonuria  is  not  to  be  looked 
upon  as  a  disease;  it  is  more  to  be  considered  as  indicative  of  an  anomalous 
metabolism,  which,  without  causing  any  noticeable  derangement,  may 
continue  for  the  entire  lifetime.  It  is  of  considerable  interest  to  note  its 
appearance  in  several  members  of  the  same  family.  As  far  as  the  origin 
of  the  homogentisic  and  uroleucic  acids  are  concerned,  it  is  natural  to 
look  to  the  aromatic  groups  derived  from  the  albumin  molecule.  We 
have  already  called  attention  to  the  fact  that  a  large  number  of  decompo- 
sition products  may  be  obtained  directly  from  this  source  and  appear  in 
the  urine. 

Tyrosine,  until  recently,  was  the  only  elementary,  aromatic  constituent  of 
albumin,  which  was  invariably  found  present  and  easily  obtained.  From  it 
are  derived  p-hydroxy-phenyl-propionic  acid,  p-hydroxyphenylacetic  acid, 
p-cresol  and  phenol.  Wolkow  and  Baumann,  by  means  of  feeding  experi- 
ments, showed  that  the  acids  of  alcaptonuric  urine  were  also  formed  from 
tyrosine.  They  found  that  the  administration  of  tyrosine  to  a  man  afflicted 
with  alcaptonuria  caused  an  appreciable  increase  in  the  amounts  of  alcap- 
ton  acids  excreted.  Wolkow  and  Baumann  also  indicate  phenyl-alanine 
(phenyl-amino-propionic  acid  )3  as  another  source  of  these  alcapton  acids. 
These  investigators  did  not  have  a  sufficient  quantity  of  this  aromatic  acid, 
and  they  had  to  confine  their  researches  to  the  relation  of  the  alcapton 
acids  to  tyrosine.  The  methods  recently  introduced  by  Emil  Fischer, 
for  the  isolation  of  the  cleavage-products  of  proteins,  made  it  possible  not 
only  to  obtain  phenyl-alanine  in  larger  quantities,  but  also  showed  its 
universal  distribution  as  an  elementary  constituent  of  albuminous  sub- 
stances. Very  little  albuminous  material  is  free  from  it,  and  it  is  even 
more  widely  distributed  than  tyrosine.  On  the  basis  of  this  knowledge, 
and  because  of  the  recent  discovery  of  the  easy  accessibility  of  phenyl- 
alanine,  the  relations  between  it  and  the  alcapton  acids  have  been  inves- 
tigated anew.  W.  Falta  and  Leo  Langstein  4  found  that  when  this  amino 


1  Kirk:  Brit.  Med.  Jour.  2,  1017  (1886);  J.  Anat.  and  Physiol.  23,  69  (1889). 

2  E.  Baumann  and  S.  Fraenkel:  Z.  physiol.  Chem.  20,  219  (1894). 

3  M.  Wolkow  and  E.  Baumann:  loc.  cit.  p.  266. 

4  W.  Falta  and  L.  Langstein:  Z.  physiol.  Chem.  37,  513  (1903). 


272  LECTURE  XII. 

acid  was  administered  to  a  man  afflicted  with  alcaptonuria,  the  elimination 
of  the  homogentisic  acid  increased  in  the  same  manner  as  when  tyrosine 
was  used.  Both  of  these  elementary  aromatic  constituents  of  albumin 
are,  therefore,  to  be  considered  as  forming  the  basis  for  the  formation  of 
the  alcapton  acids.1  It  is  very  important  to  note  that  as  far  as  our  present 
knowledge  is  concerned,  all  the  phenyl-alanine  and  tyrosine  in  the  food 
materials  are  converted  by  persons  afflicted  with  alcaptonuria,  into  the 
alcapton  acids,  so  that  the  disturbance  in  the  disintegration  of  these  amino 
acids  seems  to  be  very  complete. 

A  comparison  of  the  constitution  of  tyrosine  and  of  phenyl-alanine  with 
that  of  the  alcapton  acids  shows  us  that  the  formation  of  the  latter  from 
the  former  is  not  an  altogether  simple  process. 

A  AOH 


CH2  .  CH  .  NH2  .  COOH  CH2  .  CH  .  NH2  .COOH 

phenyl-alanine  Tyrosine 

HO  /,  HO  ^ 


OH  VOH 

CH2  .  CH(OH)  .  COOH  CH2  .  COOH 

Uroleucic  acid  Homogentisic  acid 

Tyrosine  is  para-hydroxyphenyl-a-aminopropionic  acid,  and  phenyl- 
alanine  is  a  phenyl-a-aminopropionic  acid.  All  the  decomposition  products 
of  tyrosine  which  we  have  met  with,  partly  as  putrefactive  products,  and 
partly  as  products  arising  from  intermediate  metabolism,  belong,  as 
tyrosine  itself  does,  to  the  para  compounds.  The  constitutional  formulae 
of  homogentisic  and  uroleucic  acids,  as  shown  above,  indicate  that  this 
is  not  true  of  them.  It  is  difficult  to  understand  the  formation  of  both 
of  these  alcapton  acids  from  any  of  the  known  aromatic  components  of  the 
proteins.  In  the  transformation  of  tyrosine  into  homogentisic  acid,  the 
hydroxyl  group  must  certainly  be  eliminated,  either  by  being  split  off 
or  by  migrating.  Two  other  places  in  the  benzene  ring  are  then  oxidized, 
hydroxyl  groups  being  formed  para  to  one  another.  Altering  the  side- 
chain  of  the  amino-propionic  acid  into  an  acetic  acid  residue  presents 
nothing  unusual,  and  can  easily  arise  by  merely  removing  the  amino  group. 

It  is  very  probable  that  the  homogentisic  acid  is  not  directly  produced 
from  tyrosin,  but  from  its  derivative,  p-hydroxyphenylacetic  acid.  It  is 
here  evidently  that  the  anomaly  in  the  further  degradation  of  tyrosine 
occurs.  The  corresponding  compound  from  phenyl-alanine  is  phenylacetic 


1  Cf.  also  A.  C.  Garrod  and  T.  S.  Hele:  J.  Physiol.  33,  198  (1905). 


ALBUMINS  OR  PROTEINS.  273 

acid.  Embden  1  has  shown  that  the  alcapton  acids  are  not  produced  when 
the  latter  is  administered.  This  investigation  does  not,  however,  pre- 
clude the  possibility  that  phenyl-acetic  acid  is  one  of  the  first  degradation 
products  of  phenyl-alanine,  even  from  persons  affected  with  alcaptonuria, 
or  that  the  disintegration  of  this  amino  acid  does  not  proceed  abnormally 
from  the  very  beginning.  Efforts  have  been  made  to  establish  homogen- 
tisic  acid  as  a  normal  intermediate  cleavage-product  of  phenyl-alanine 
and  tyrosine.2  From  this  point  of  view,  alcaptonuria  would  be  looked 
upon  as  a  check  on  the  complete  combustion  of  the  benzene  nucleus.  The 
formation  of  homogentisic  acid  would  then  be  looked  upon  as  an  oxidation 
preceding  the  disruption  of  the  benzene  ring.  The  person  afflicted  with 
alcaptonuria  would  not  be  capable  of  carrying  this  process  to  the  end,  as 
a  result  of  which,  this  anomalous  metabolism  produces  a  decomposition 
product  in  the  intermediate  metamorphosis  which  would  otherwise  have 
been  lost  to  us. 

There  is  something  very  attractive  in  the  suggestion  that  alcaptonuria 
acts  as  a  simple  restraining  influence  in  the  normal  disintegration  of  tyrosine 
and  phenyl-alanine.  We  must  admit  that  this  assumption  has  received 
some  support  in  the  researches  of  Otto  Neubauer  and  W.  Falta.  On  the 
other  hand,  we  must  remember  that  the  manner  of  formation  of  the 
alcaptonuric  acids  still  remains  a  hypothesis,  and  that  no  absolute  proof 
of  its  truth  has  as  yet  been  presented. 

The  place  of  formation  of  the  alcapton  acids  in  the  organism  of  a 
patient  afflicted  with  alcaptonuria  was  for  a  long  time  very  much  in 
question.  Wolkow  and  Baumann  claimed  that  they  were  produced  in 
the  upper  part  of  the  intestine,  by  the  aid  of  micro-organisms.  We 
to-day  believe  that  the  alcapton  acids  are  probably  formed  in  the 
tissues  themselves.  This  conclusion  follows  from  the  fact  that  phenyl- 
alanine,  as  far  as  known,  is  not  set  free  by  proteolytic  ferments  in  the 
alimentary  tract.  -The  conditions  are  different  with  tyrosine.  Large 
quantities  of  this  are  set  free  in  the  intestine.  This,  under  normal  con- 
ditions, is  very  largely  assimilated,  being  even  utilized  by  those  affected 
with  alcaptonuria  in  the  production  of  albumin,  which  is  indicated  by 
the  fact  that  the  albuminous  components  of  their  blood  show  the  same 
amounts  of  tyrosine  and  phenyl-alanine,  as  do  those  of  normal  persons.3 
A  small  portion  of  the  tyrosine  is  undoubtedly  attacked  by  bacteria  in  the 
intestine,  in  this  way  producing  the  various  decomposition-products,  until 
phenol  is  reached.  The  intermediate  products,  p-hydroxyphenylpropionic 
acid,  and  p-hydroxyphenylacetic  acid,  may  also  act  as  sources  for  the  pro- 

1  H.  Embden:  Z.  physiol.  Chem.  18,  304  and  317  (1894). 

2  L.  Gamier  and  S.  Voisin:  Arch,  physiol.  Ges.  6,  224  (1892).      O.  Neubauer  and 
W.  Falta:  Z.  physiol.  Chem.  42,  81  (1904). 

3  E.  Abderhalden  and  W.  Falta:  Z.  physiol.  Chem.  39,  143  (1903). 


274  LECTURE  XII. 

duction  of  the  alcapton  acids.  The  largest  amounts  are,  however,  produced 
in  cell-metabolism,  after  the  cell  has  disintegrated  the  proteins  into  their 
components,  and  now  completes  the  decomposition  of  the  amino  acids. 
This  is  where  the  anomaly,  or  restriction,  occurs. 

If  we  combine  all  our  knowledge  of  the  proteins,  their  composition,  and 
their  decomposition,  with  what  we  know  experimentally  about  the  diges- 
tion, absorption,  and  assimilation  of  the  albuminous  materials  of  our  food, 
together  with  the  information  gleaned  from  our  study  of  their  changes 
and  their  final  disintegration  in  the  tissues,  we  shall  find  that  we  are 
obtaining  a  very  good  idea  of  the  whole  subject  of  albumin-metabolism. 
To  be  sure,  many  bridges  have  been  built  purely  provisionally  from  analo- 
gous conclusions  and  probable  relations,  to  enable  us  to  pass  from  one 
well-founded  principle  to  another,  and  hypotheses  still  permeate  all  of 
our  views.  We,  however,  do  not  doubt  that  the  progress  of  albumin 
chemistry  will  strengthen  one  position  after  another,  and  that  eventually 
facts  will  supplant  our  assumptions. 


LECTURE   XIII. 
THE  NUCLEOPROTEIDS  AND  THEIR  CLEAVAGE-PRODUCTS. 

IN  discussing  the  proteins,  we  have  only  briefly  referred  to  those  which 
do  not  occur  by  themselves,  in  the  tissues,  but  are  united  to  a  second 
atomic  complex.  To  these  compound  proteins,  also  called  proteids,  belong 
the  nucleoproteids.  They  occupy  an  important  position,  not  only  in  animal 
economy,  but  in  that  of  the  plant  cell  as  well.  They  are  widely  distrib- 
uted, and  are  mainly  found  in  the  nuclei  of  cells.  It  is  at  present  very 
difficult  to  decide  whether  the  materials  classified  under  the  name  of 
nucleoproteids  are  of  an  individual  nature,  within  certain  limits.  They 
are  purified  with  difficulty,  and  are  mainly  characterized  by  their  cleavage- 
products.  From  what  we  know,  it  appears  that  the  albuminous  compo- 
nent may  vary  widely  in  character.  For  example,  we  find  histones  and 
varieties  of  protamines.  The  other  component,  which  we  shall  shortly 
consider,  also  shows  differences  in  composition  according  to  the  nature 
and  derivation  of  the  nucleoproteid.  When  we  recollect  all  that  has  been 
said  regarding  this  class  of  substances,  we  are  involuntarily  forced  to  the 
conclusion  that  an  exact  decision  as  to  the  construction  of  the  nucleo- 
proteids is  not  possible,  largely  because  it  is  certain  that  these  proteids  are 
obtained  in  various  degrees  of  purity,  according  to  the  method  used  for  iso- 
lating them ;  or,  perhaps  better  expressed,  because  in  certain  investigations 
products  have  been  worked  with  which  had  already  undergone  considerable 
change.  The  albumin  component  shows  all  the  characteristics  common  to 
the  proteins.  Above  all,  it  possesses  the  property  of  "  denaturizing,"  which 
often  serves  to  impart  an  entirely  new  property  to  an  isolated  product, 
thus  apparently  indicating  a  new  compound.  We  are  forced  to  obtain 
the  nucleoproteids  from  the  cells  themselves,  i.e.,  from  a  very  complex 
mixture  of  proteins.  The  fact  that  in  the  different  nucleoproteids  the 
two  components  are  combined  with  different  degrees  of  firmness,  may 
likewise  lead  to  errors,  and  prevents,  more  than  anything  else,  any  energetic 
attack  in  the  attempt  to  purify  the  isolated  products. 

When  we  take  all  these  facts  into  consideration,  there  is  little  wonder 
that  the  existence  of  the  nucleoproteids  should  be  repeatedly  questioned. 
We  have  to  thank  F.  Miescher  for  much  of  our  knowledge  about  these 
bodies.  The  non-albuminous  component,  nucleic  acid,  will  precipitate 
albumin.  It  is  conceivable  that  it  shows  its  precipitating  power  during 
the  isolation  of  the  proteids,  and  is  thus  brought  to  our  attention  as 

275 


276  LECTURE  XIII. 

apparently  combined  with  albumin.  Nucleoproteids  have,  however,  been 
obtained  by  salting  them  out.  Although  we  have  no  doubt  that  such 
compounds  with  nucleic  acid  exist,  especially  of  the  basic  proteins,  like 
the  histones  and  protamines,  still  we  must  admit  that  no  convincing  proof 
has  yet  been  presented  that  there  is  such  a  state  of  combination  in  the  cells 
themselves.  We  are  accustomed  to  look  upon  substances  which  we  always 
find  in  given  localities,  and  are  never  absent,  as  being  particularly  important 
for  the  functions  of  the  cells  and  tissues,  especially  when  we  find  these  in 
the  parts  of  cells  to  which  we  assign  great  importance.  Although  such  an 
assumption  is  probably  true,  we  should  be  concealing  the  actual  state  of 
our  knowledge,  if  we  failed  to  mention  the  fact  that  the  exact  significance 
of  the  nucleoproteids  is  still  unknown  to  us,  and  that  we  do  not,  at  present, 
understand  their  relations  in  cell-metabolism. 

We  have  already  stated  that  the  nucleoproteids  are  composed  of  two 
constituents,  one  of  which  is  an  albumin,  and  the  other  nucleic  acid.  It 
is  not  yet  clear  to  us  how  we  shall  conceive  the  formation  of  the  proteids 
from  these  two  components.  It  has  been  shown  that  the  decomposition 
into  albumin  and  nucleic  acid  portions  does  not  always  take  place  as  if  it 
were  a  simple  process.  We  obtain  the  impression  that  the  nucleic  acid  is 
united  with  two  parts  of  albumin.  One  part  can  be  easily  split  off,  the 
other  with  much  more  difficulty.  The  following  scheme  expresses  this 
conception: 

Nucleoproteids 


Albumin      Nuclein 

/\ 
Albumin     Nucleic  acid. 

When  albumin  is  split  off  from  the  nucleoproteid,  a  part  of  the  protein 
remains  combined  with  the  nucleic  acid.  This  product  is  called  nuclein. 
This  was  first  observed  by  Miescher  on  digesting  a  nucleoproteid  with 
pepsin  and  hydrochloric  acid.  The  albuminous  portion,  which  is  most 
easily  split  off,  is  decomposed,  while  the  nuclein  precipitates.  More  recent 
investigations  have  shown  that  active  pepsin  may  even  disintegrate  the 
nuclein,  thus  leaving  the  pure  nucleic  acids  behind. 

We  are  especially  interested  here  in  the  nucleic  acids.  We  have  already 
considered  the  protein  constituent  as  far  as  it  is  known.  All  the  nucleic 
acids  contain  phosphorus.  When  decomposed,  they  produce  phosphoric 
acid  and  nuclein  bases.  Other  products  are  also  formed  when  the  nucleic 
acids  are  decomposed.  A  carbohydrate  group  has  been  split  off  in  some 
cases,  while  from  others  pyrimidine  groups  have  been  obtained.  We  shall 
here  first  consider  all  of  the  known  cleavage-products  of  the  different 
nucleic  acids,  and  not  pay  any  attention  at  present  to  the  composition  of 
these  different  acids.  All  of  these  nucleic  acids  which  have  been  studied, 


THE  NUCLEOPROTEIDS.  277 

except  inosic  acid  (from  extract  of  beef)  which  forms  crystalline  salts,1 
are  amorphous  and  react  acid.  They  are  easily  dissolved  in  water  con- 
taining ammonia  or  alkali,  and  form  insoluble  salts  with  the  heavy  metals. 

Phosphoric  acid  is,  as  we  have  said,  quite  generally  found  among  the 
cleavage-products  of  the  nucleic  acids.  We  do  not  know  how  it  is  united 
in  the  molecule.  The  occurrence  of  representatives  of  the  group  of  purine 
bases  is  especially  important.  They  vary  according  to  their  origin,  and 
the  number  of  bases  participating  in  the  constitution  of  the  nucleic  acids 
is  also  a  variable  one.  J.  Piccard  2  early  met  with  these  compounds  in  his 
investigations  of  the  nucleins.  The  numerous  observations  of  A.  Kossel 3 
have  indicated  their  wide  distribution,  and  also  the  nature  of  the  purine 
bases  present. 

We  wish  to  state  in  advance  that  the  purine  bases  are  very  closely  related 
to  an  important  metabolic  end-product,  uric  acid,  not  only  from  a  purely 
chemical  point  of  view,  but  also  because  recent  experiments  have  indicated 
intimate  biological  connections.  We  wish,  therefore,  to  describe  briefly 
the  most  important  points  with  regard  to  the  constitution  of  this  class  of 
bodies.  It  will  then  be  easier  for  us  to  follow  the  individual  purine  bases 
in  their  course  through  the  organism,  and  to  judge  of  the  part  they  play  in 
metabolism. 

Uric  acid,  the  earliest  known  member  of  this  series,  was  discovered  in 
urine  and  bladder  stones,  as  far  back  as  1776,  by  Scheele 4  and  Bergmann.5 
We  will  add  that  Pearson6  has  shown  the  presence  of  uric  acid  in  "chalk- 
stones,"  and  that  Fourcroy  and  Vauquelin 7  shortly  after  proved  it  to  be  an 
essential  constituent  of  the  excrement  of  birds.  Finally  William  Prout,8 
in  1815,  found  that  the  excrement  of  the  boa-constrictor  contained  as 
much  as  90  per  cent  of  uric  acid. 

Uric  acid  was  thoroughly  investigated  by  Liebig.  A  large  number  of 
its  important  decomposition  products  also  became  known,  without,  how- 
ever, indicating  the  true  constitution  of  the  acid  itself.  Wohler  and  Liebig  9 
mention  its  close  relation  to  allantoine,  even  then  regarded  as  a  component 
of  the  allantoic  fluid.  They  obtained  urea  and  alloxan  by  treating  uric  acid 

1  J.  von  Siebig:  Ann.  62,  317  (1847)  and  Haiser:  Monatsh.  16,  190  (1895). 

2  J.  Piccard:  Ber.  7,  1714  (1874). 

3  A.  Kossel:  Z.  physiol.  Chem.  4,  290  (1880);  find.  7,  7  (1882);  find.  10,  248  (1886); 
12,  241  (1888). 

4  K.  W.  Scheele:  Examen  chimicum  Calculi  urinarii,  Opuscula  II,  73  (1876). 

6  T.  Bergmann:  Opuscula  IV,  232  (1876).     Cf.  E.  Fischer:  Ber.  32,  435  (1899).      Cf. 
also  Synthesen  in  der  Purin-  und  Zuckergruppe,  F.  Vieweg  &  Sohn,  Braunschweig, 
1903,  and  Untersuchungen  in  die  Puringruppe  (1882-1906),  J.  Springer,  Berlin,  1907. 
K.  Bunte:  Inaug.  Diss.  Berlin,  1905. 

8  Pearson:  Phil.  Trans,  of  the  Royal  Soc.  London,  15,  1798. 

7  Ann.  de  chim.  56,  258  (1905). 

8  Ann.  Phil.  5,  413  (1815). 

9  Ann.  26,  241  (1838). 


278  LECTURE  XIII. 

with  nitric  acid.  From  alloxan  they  obtained  a  large  number  of  closely 
related  compounds.  We  are  indebted  to  Adolf  Baeyer *  for  establishing 
the  constitution  of  alloxan  and  its  closely  allied  derivatives.  We  will  also 
mention  the  discovery  of  A.  Strecker,2  that  heating  uric  acid  with  concen- 
trated hydrochloric  acid  in  a  sealed  tube  to  170  degrees,  produces  glycocoll, 
carbon  dioxide,  and  ammonia,  water  entering  into  the  reaction: 

C5H4N4O3  +  5  H2O  =  CH2.(NH2)  .COOH  +  3  CO2  +  3  NH3. 
Uric  acid  Glycocoll 

From  this  fact,  Strecker  regarded  uric  acid  as  a  glycocoll  united  with 
cyanic  acid,  and  assumed  that  the  uric  acid  first  broke  down  into  glycocoll 
and  cyanic  acid;  the  latter  then  being  further  decomposed  into  carbon 
dioxide  and  ammonia: 

C5H4N403  =  CH2  .  (NH2)  .  COOH  +  3  HCNO. 

This  decomposition  of  uric  acid  was  of  great  significance,  because,  using 
it  as  a  basis,  Horbaczewski 3  next  produced  uric  acid  by  fusing  glycocoll 
with  urea  at  220°-230°  C.: 

/NH2 

3  CO     +  CH2  .  NH2  .  COOH  =  C5H4N403  +  3  NH3  +  2  H2O. 
\NH2 

On  heating  urea,  ammonia  is  set  free,  cyanic  acid  also  being  formed, 
which  can  then  act  further  on  the  glycocoll.  Another  synthesis  was  accom- 
plished by  melting  urea  with  tri-chlor-lactamid: 

/NH2 

2  CO     +C3C13O2H2  .  NH2  =  H2O  +  NH4Cl  +  2  HC1+C5H4N4O3. 
\NH2 

These  syntheses  did  not  lead  to  an  exact  conception  of  the  constitution  of 
uric  acid.  It  was  only  through  the  carefully-planned,  systematic  inves- 
tigations of  Emil  Fischer,  that  light  was  suddenly  thrown  on  the  whole 
group  of  the  purines  and  their  derivatives.  Not  only  does  the  entire  chem- 
istry of  all  the  compounds  of  this  group  depend  on  his  work,  but  also  all 
biological  research  in  this  field. 

We  cannot  at  this  place  trace  the  development  of  all  of  Emil  Fischer's 
work,  but  will  merely  single  out  the  points  which  are  most  important  in 
our  study.4  It  is  necessary  in  the  first  place  to  establish  the  relations 
which  exist  between  the  various  members  of  this  group.  Emil  Fischer 
based  his  work  upon  the  relations  of  all  the  members  of  this  group  to 
purine.  He  finally  succeeded  in  obtaining  purine  itself,  thus  laying  the 

1  Cf.  his  complete  works,  F.  Vieweg  &  Sohn,  Braunschweig,  1905,  vol.  i,  p.  57. 

2  Ann.  146,  142  (1868). 

3  Monatsh.  3,  796  (1882);  6,  356  (1885). 

4  Cf.  E.  Fischer:  Ber.  30,  549,  1839,  2226  (1897),  and  31,  104  (1898). 


THE  NUCLEOPROTEIDS  279 

cornerstone  for  his  whole  investigation  of  the  uric  acid  group,  Purine  is 
a  strong  base,  readily  soluble  in  water.  Its  constitution  is  evident  from 
its  preparation.  It  has  the  following  structure: 

N  =  CH 

HC     C— NH 

II  II  \CH 
N— C— N^bil 
Purine 

In  order  to  make  it  possible  to  have  a  uniform  nomenclature  for  the 
numerous  representatives  of  this  group,  Emil  Fischer  numbered  the  purine 
ring  in  the  following  manner : 


v/6 

C5-N7 


N3— C4— N9^ 

We  shall  make  use  of  this  scheme. 

Uric  acid  itself  has  the  following  structural  formula: 

HN— CO 


COC— 1 


;co 


-NH 

HU-NH 

Uric  acid  (2,  6,  8-trioxypurine) 

This  formula  harmonizes  with  the  following  important  transformations 
of  uric  acid. 

By  heating  with  hydriodic  acid  and  fuming  hydrochloric  acid  in  a  sealed 
tube,  glycocoll,  carbon  dioxide,  and  ammonia  are  produced. 

Oxidizing  with  nitric  acid  or  chlorine  produces  alloxan  and  urea. 
Alloxan  is  mesoxalyl  urea: 

HN— CO  NH— CO  MTT 

I  /NH2 

NH  CO     CO  +  CO 

NCO  +  O  +  H2O  =|  \MTT 

NHX  NH— CO 

Uric  acid  Alloxan 

By  oxidation  of  alloxan  we  obtain  parabanic  acid,  which  is  oxalyl  urea : 

CO— NH 

)co 

CO— NH 

Parabanic  acid 

which  decomposes,  on  boiling  with  water,  into  urea  and  oxalic  acid. 


280  LECTURE  XIII. 

The  transformation  of  uric  acid  into  allantoine  by  oxidation  is  very 
important:  NH-CH-NH 

CO'  XCO. 

NNH— CO    NH/ 
Allantoine 

There  are  a  large  number  of  compounds  important  to  the  biologist  which 
are  very  closely  related  to  uric  acid.  We  have  mentioned  that  the  nucleic 
acids,  when  decomposed,  produced  purine  bases;  in  fact,  the  following: 
xanthine,  hypo-xanthine,  adenine,  and  guanine.  Their  structural  formula 
are  as  follows : 


2, 

HN—  CO 
COC—  NH 

1    II        ^co 

HN—  C—  NH' 
Uric  acid  = 
6,  8-trioxypurine 

HN—  CO 

CO  C—  NH 

1      II            )CH 
HN—  C—  N    ^ 
Xanthine  = 
2,  6-dioxypurine 

HN—  CO 

HC     C—  NH  , 

II      II 
N—  C—  N     < 
Hypoxanthine 
6-oxypurine 

NH— CO  N=C— NH2 

II  II 

NH2.C        C— NH  HC    C— NH 


N    — C    —  N"  N— C— N 

Guanine  =  Adenine  = 

2-amino-6-oxypurine  6-aminopurine 

In  this  connection  we  will  add  that  substances  closely  related  to  the 
purines  have  also  been  separated  from  the  vegetable  kingdom.  These  are 
caffeine,  theobromine,  and  theophylline.  The  first  two  are  found  in  table 
accessories,  caffeine  being  present  in  coffee  and  tea,  while  theobromine  is 
a  constituent  of  cocoa.  The  relation  of  these  three  compounds  to  one 
another  is  indicated  by  their  formulae: 

CH3.N— CO  HN— CO 

I       I         /CH3  |       |  CH3 

co  c— N'  co  c— N; 

I    ii      )CH  |    ii      ;CH 

CH3  .  N— C— N  *  CH3  .  N— C— N  ' 

Caffeine  =  Theobromine  = 

1,  3,  7-trimethyl-2,  6-dioxypurine     3,  7-dimethyl-2,  6-dioxypurine 

CH3  .  N— CO 

1       II 

JO  C— NH 


CH3.N— C— 
Theophylline  = 
1,  3-dimethyl-2,  6-dioxypurine 


THE  NUCLEOPROTEIDS.  281 

Very  closely  related  to  this  group  of  nucleic  acid  cleavage-products  are 
other  compounds,  which,  instead  of  having  a  purine  ring,  contain  one  of 

pyrimidine : 

(1)  N  =  CH     (6) 

(2)  HC    CH     (5) 

II       II 

(3)  N— CH      (4) 
Pyrimidine 

The  syntheses  of  the  members  of  this  series  and  their  constitution  indi- 
cate their  close  relation  to  the  purine  derivatives.  We  are  mainly  indebted 
to  A.  Kossel  for  their  discovery.  Ascoli 1  first  found  uracyl  in  yeast- 
nucleic  acid.  It  has  the  following  constitution: 

NH— CO 

CO      CH 

.1          II 
NH— CH 

Uracyl  = 
2,  6-dioxypyrimidine 

Emil  Fischer  and  Georg  Roeder  2  succeeded  in  synthesizing  it.  These 
same  authors  also  established  the  constitution  of  another  pyrimidine  base, 
thy  mine.  It  is  a  5-methyluracyl, 

NH— CO 

O      C  .  CH3 

I          II 
NH— CH 

Thymine  = 
5-methyluracyl     (5-methyl-2,  6-dioxypyrimidine) 

This  compound  was  first  isolated  from  thymus  nucleic  acid  by  A.  Kossel 
and  Neumann.3 

Finally,  we  are  acquainted  with  a  third  pyrimidine  derivative,  cytosine, 
which  was  also  separated  from  thymus  nucleic  acid  by  Kossel  and 
Neumann.4  It  has  been  synthetically  prepared  by  Wheeler  and  Johnson,5 


1  A.  Ascoli:  Z.  physiol.  Chem.  31,  161  (1900-01).     A.  Kossel  and  H.  Steudel:  ibid. 
37,  245  (1902). 

2  E.  Fischer  and  G.  Roeder:  Ber.  34,  3752  (1901). 

3  A.  Kossel  and  A.  Neumann:  ibid.  26,  2753  (1893);  Z.  physiol.  Chem.  22,  188  (1896). 
H.  Steudel  and  A.  Kossel:  ibid.  29,  303  (1900).     H.  Steudel:  ibid.  30,  539  (1900);  32, 
241  (1901).     W.  Jones:  ibid.  29,  20  (1899);  30,  461  (1900).     W.  Gulewitsch:  ibid.  27, 
292  (1899);  27,  368  (1899).     O.  Gerngross:  Ber.  38,  3408  (1905). 

4  A.  Kossel  and  A.  Neumann:  Ber.  27,  2215  (1894).     A.  Kossel  and  H.  Steudel: 
Z.  physiol.  Chem.  37,  177  (1902);  37,  377  (1903);  38,  49  (1903). 

5  H.  L.  Wheeler  and  T.  B.  Johnson:  Am.  Chem.  J.  29,  492  and  505  (1903). 


282  LECTURE  XIII. 

and  has  the  following  structural  formula: 

HN   -  C  .  NH2 

I          II 
CO      CH 

I          I 
N   =  CH 
Cytosine  =  6-amino-2-oxypyrimidine 

Carbohydrates  —  in  fact  mostly  pentoses  —  have  also  been  obtained 
from  the  nucleic  acids  in  conjunction  with  the  purine,  and  pyrimidine  bases, 
and  phosphoric  acid.  Such  a  typical  pentose  is  xylose.  Yeast  nucleic  acid 
is  supposed  to  contain  an  hexose.  It  is  also  assumed  that  an  hexose  par- 
ticipates in  the  constitution  of  the  thymus  nucleic  acid.  Lsevulic  acid 
is  obtained  therefrom  by  an  energetic  decomposition. 

It  has  recently  become  questionable  whether  all  of  the  above  com- 
pounds are  to  be  regarded  as  primary  cleavage-products  of  the  nucleic 
acids.  Steudel l  has  shown  it  to  be  probably  true  that  adenine  and  guanine 
are  the  only  primary  building  stones  of  the  purine  bases,  and  thymine 
and  cytosine  of  the  pyrimidine  bases.  Hypoxanthine,  xanthine,  and 
uracyl  are  formed  secondarily  by  oxidation  in  the  breaking  down  of  the 
nucleic  acids.  This  discovery  lessens  the  value  of  the  numerous  inves- 
tigations concerning  the  purine  and  pyrimidine  bases  in  the  different 
nucleic  acids.  It  also  explains  why  different  authors  have  obtained 
divergent  results  in  the  study  of  nucleic  acids  from  the  same  source. 
Although  this  indicates  a  great  gap  in  our  knowledge  concerning  the 
amount  of  individual  building  stones  present  in  the  nucleic  acids,  which 
can  be  filled  only  by  the  assumption  of  secondary  transformations,  still 
on  the  other  hand,  it  is  very  good  news  to  find  that  Neuberg  and  Brahn2 
and  Bauer3  have  succeeded  in  clearing  up  the  constitution  of  inosic  acid. 
From  the  latter,  one  molecule  each  of  hypoxanthine,  phosphoric  acid, 
and  xylose  or  arabinose  is  always  obtained.  It  is  at  present  an  open 
question  whether  the  purine  bases  here  observed  are  to  be  regarded  as 
of  primary  or  secondary  formation,  and  whether  perhaps  adenine  is  not 
here  also  the  primary  building  stone.  The  question  that  next  arises  is 
with  regard  to  the  way  the  components  of  the  nucleic  acids  are  held 
together  in  the  molecule.  Undoubtedly  this  again  will  only  be  answered 
when  synthesis  has  established  the  relations. 

Burian4  attempted  to  decide  how  the  purine  bases  are  held  in  the 
nucleic  acid  molecules.  In  one  case  he  based  his  observations  upon  the 
fact  that  the  purine  bases,  unlike  the  other  components  of  the  nucleic 

1  H.  Steudel:  Z.  physiol.  Chem.  49,  406  (1906). 

2  C.  Neuberg  and  B.  Brahn:  Biochem.  Z.  5,  438  (1907). 

3  Friedrich  Bauer:  Beitr.  chem.  Physiol.  Path.  10,  345  (1907). 

4  R.  Burian:  Ber.  37,  696  and  708  (i904);  Z.  physiol.  Chem.  42,  297  (1904). 


THE  NUCLEOPROTEIDS.  283 

acid  molecule,  are  very  easily  split  off.  Purine  bases  can  be  detected  even 
when  the  material  is  merely  dissolved  in  water  at  60  degrees.  Boiling 
with  water  for  ten  minutes  is  sufficient  to  separate  practically  all  the 
purine  bases.  We  are  justified  in  looking  upon  the  purines  as  being 
primary  cleavage-products  of  the  nucleic  acid  molecule,  rather  than 
resulting  from  secondary  causes.  We  may  consider  them  as  being  com- 
posed of  a  condensed  nucleus,  consisting  of  a  pyrimidine  and  an  imidazole 
ring,  as  may  be  seen  by  the  following  structural  formula?: 

(1)  N=(6)CH  (1)      N-(6)CH 

(2)  HC      (5)  C— (7)  NH  (2)  HC     (5)  CH     (a)HC— NH(n) 

^(8)CH  ^CHO*). 

(3)  N—  (4)  C— (9)  N  (3)     N— (4)  CH     (/?)  HC— N 

Purine  Pyrimidine  Imidazole 

Corresponding  to  this  assumption,  the  purines  show  reactions,  which  are 
characteristic  of  one  or  the  other  component.  Imidazole  possesses  the 
property  of  reacting  with  diazo-benzene  chloride,  forming  a  red,  crystalline 
product,  which  is  (n)  diazo-benzene-imidazole.  This  reaction  also  applies 
to  those  imidazoles  whose  a,  /?,  or  /u.  positions  have  been  substituted;  but 
not  to  those  in  which  the  n-position  is  substituted.  The  purines  act  in 
a  very  analogous  manner.  Substitution  in  the  pyrimidine  ring  is  without 
influence  on  the  appearance  of  this  reaction.  On  the  other  hand,  the  re- 
action is  negative  when  the  imide  hydrogen  of  the  imidazole  ring,  in  position 
7,  is  replaced.  The  reaction  is  positive  in  xanthine,  hypoxanthine,  guanine, 
adenine,  theophylline ;  it  fails  with  theobromine  (3,  7-di-methyl-xanthine) 
and  with  caffeine  (1 ,  3,  7-tri-methyl-xanthine) .  The  nucleic  acids,  however, 
even  if  liberally  endowed  with  bases,  do  not  react  with  diazo-benzene- 
sulphonic  acid.  This  last  reaction  only  takes  place  when  purines  are  being 
split  off  at  the  same  time.  Taking  the  above  facts  into  consideration, 
we  arrive  at  the  conclusion  that  the  purine  bases  are  united  with  the  nucleic 
acid  residue  through  its  nitrogen  atom  in  the  seventh  position.  Another 
series  of  observations  indicate  that  the  purine  bases  are  linked  in  the  first 
place  to  the  phosphoric  acid  portion.  It  is  a  very  striking  fact  that  those 
purine  bases,  which  are  so  easily  split  off  by  boiling  water,  are  only  released 
with  great  difficulty  by  boiling  with  sodium  hydroxide.  Certain  organic 
phosphoric  acid  amides  behave  similarly.  Burian  believes  that  guanine  is 
linked  in  the  nucleic  acid  molecule  in  the  following  way: 

HN— CO         P  = 

t< 

^CH 


284  LECTURE  XIII. 

The  proof  that  such  a  state  of  combination  exists  in  the  nucleic  acid 
molecule  is  not  satisfactory.  Other  possibilities  exist.  Burian  has,  never- 
theless, shown  that  such  a  linkage  is  probable. 

In  discussing  the  proteins,  we  found  that  a  knowledge  of  the  amino 
acids  participating  in  the  constitution  of  the  individual  albumins  often 
gave  us  valuable  suggestions  regarding  their  behavior  in  the  animal 
organism.  The  relations  of  most  nucleic  acids,  on  the  other  hand,  are 
as  we  have  already  stated,  not  so  clear,  because  they  have  not  all 
been  studied  in  the  same  way,  nor  with  the  same  care.  Above  all  we 
have  no  means  for  deciding  which  cleavage-products  are  to  be  regarded 
in  any  given  case  as  primary  or  secondary.  Inosic  acid  is  an  excep- 
tion, as  its  composition  has  been  established,  and  we  are  justified  in  con- 
sidering it  as  a  simple  substance.  Perhaps  this  is  also  true  of  guanylic 
acid l  isolated  by  Bang  and  Raashon  2  from  the  pancreas.  In  the  break- 
ing down  of  this  nucleic  acid,  guanine  is  the  only  purine  base  that  could 
be  detected  in  the  presence  of  phosphoric  acid  and  a  carbohydrate.  As 
to  whether  the  remaining  nucleic  acids  are  simple  substances  or  mixtures, 
we  have  no  means  of  knowing.  It  will  be  best  here  to  mention  merely 
the  most  important  nucleic  acids.  They  are  almost  always  designated  by 
the  name  of  the  organs  from  which  they  were  obtained. 

The  nucleic  acids  from  the  spermatozoa  have  been  longest  known. 
Since  F.  Miescher  3  first  called  attention  to  them,  they  have  been  the  subject 
of  frequent  investigation.4  It  appears  that  the  nucleic  acids  obtained 
from  the  various  kinds  of  spermatozoa  are  closely  related  to  one  another. 
Certain  observations  indicate  a  far-reaching  similarity.  Great  care  should 
be  taken,  however,  in  drawing  any  conclusions  regarding  the  identity  of 
the  various  nucleic  acids  from  analytical  values  or  knowledge  of  the 
cleavage-products.  According  to  the  grouping  of  the  cleavage-products, 
many  differences  may  appear  which  are  as  yet  hidden  from  our  view.  It  is 
noteworthy  that  the  percentage  of  phosphorus  present  in  the  nucleic  acids 
isolated  from  the  cells  of  ripe  semen  is,  in  general,  a  very  constant  one. 
The  values  range  between  9.11  per  cent  and  9.62  per  cent.  Salmon 
nucleic  acid,  according  to  Schmiedeberg,5  has  the  following  composition: 
C,  37.42  per  cent;  H,  4.19  per  cent;  N,  15.24  per  cent;  and  P,  9.64.  All 
the  known  purine  bases  have  been  obtained  in  the  cleavage  of  the 
spermatozoa  nucleic  acids.  The  values  are  given  on  the  following 
page. 


1  I.  Bang  Z.  physiol.  Chem.  26,  133  (1898-99);  31,  241  (1900-01). 

2  I.  Bang  and  C.  A.  Raaschon:  Hofmeister's  Beitr.  4,  175  (1903). 

3  F.  Miescher:  Verb,  naturf.  Gesell.  Basel,  6,  138  (1874).     Cf.  also  the  complete  works 
of  F.  Miescher:  loc.  ciL  2,  55;  Arch,  exper.  Path.  Pharm.  37,  100  (1896). 

4  R.  Burian:  Ergeb.  Physiol.  3,  1,  48  (1904). 

«  O.  Schmiedeberg:  Arch,  exper.  Path.  Pharm.  43,  57  (1900). 


THE  NUCLEOPROTEIDS. 


285 


100  g.  Dry  Substance  Contains 

Nucleic  acid  from  the  testes  of  the  bull1  .    . 
Spermatozoa  of  the  bull     
Spermatozoa  from  the  testes  of  a  boar1    .    . 
Spermatozoa  of  the  carp2  
Salmon  nucleic  acid.  1st  preparation1    .    .    . 
Salmon  nucleic  acid.  2d  preparation     .    .    . 
Pancreas1        

Adenlne. 

Guanine. 

Hypoxanthine. 

Xanthine. 

0.736 
0.126 
1.181 
0.360 

6.248 
0.187 

d.'l27 
0.193 

1.962 
0.207 
0.635 
0.309 
0.664 
1.208 
0.154 

6.039 
0.352 
2.057 
2.278 
2.924 
3.914 
0.740 

We  must  once  more  state  that  too  much  reliance  should  not  be  placed 
upon  these  figures.  Burian  and  Walker  Hall3  called  attention  to  the  fact 
that,  in  the  preparation  of  the  purine  bases,  oxypurines  (xanthine  and 
hypoxanthine)  might  be  formed  from  the  aminopurines  (adenine  and 
guanine).  As  we  have  seen,  Steudel  has  proved  this  directly.  This 
probably  accounts  for  the  fact  that  Schmiedeberg,  in  investigating  salmon 
nucleic  acid,  found  guanine  and  adenine,  but  no  xanthine  nor  hypo- 
xanthin. 

Thymo-nudeic  acid  from  the  thymus  gland  is  another  nucleic  acid  which 
has  been  investigated  considerably.4  Phosphoric  acid,  thymine,  cytosine, 
guanine,  adenine,  Isevulic  acid,  and  ammonia  were  obtained  by  hydrolytic 
decomposition.  Guanylic  acid,  obtained  from  the  pancreas,  broke  down 
into  guanine,  phosphoric  acid,  and  a  pentose.  A  nucleic  acid  has  also 
been  isolated  from  the  spleen.  We  may  add,  finally,  that  analogous 
products  can  also  be  obtained  from  the  plants.  Triticonucleic  5  acid, 
obtained  from  the  embryo  of  wheat,  has  been  most  studied.  It  yields 
by  hydrolysis :  guanine,  adenine,  cytosine,  uracyl,  phosphoric  acid,  and  a 
pentose.  Nucleic  acids  have  also  been  isolated  from  tubercle-bacilli  and 
from  yeast. 

We  cannot  at  present  say  anything  regarding  the  nucleic  acids  and  their 
cleavage-products,  and  shall  confine  ourselves  in  the  following  to  the  dis- 
cussion of  their  participation  in  metabolic  processes.  We  will  state,  at 
the  start,  that  there  can  no  longer  be  any  doubt  that  the  nucleo- 
proteids  are  disintegrated  in  the  cell-metabolism,  and  participate  to  the 
same  extent  in  the  reconstruction.  There  is  scarcely  any  question  but 
that  the  animal  cell  obtains  the  components  of  the  nucleoproteids  already 
formed  in  the  food.  It  does  not  seem  probable  that  the  purine  and  pyri- 


1  Y.  Inoko:  Z.  physiol.  Chem.  18,  57  (1894). 

2  S.  Schindler:  ibid.  13,  432  (1889). 

3  R.  Burian  and  W.  Hall:  ibid.  38,  366  (1903). 

4  H.  Steudel:  ibid.  42,  165  (1904);  43,  402  (1904);  46,  332  (1905);  P.  A.  Levene,  32, 
541   (1901);  37,  402  (1902-03);  38,  80  (1903);  39,  4  (1903);  39,  479  (1903);  43,  199 
(1904);  45,  370  (1905);  Am.  J.  Physiol.  12,  213  (1905). 

5  T.  B.  Osborne  and  J.  F.  Harris:  Z.  physiol.  Chem.  36,  85  (1902). 


286  LECTURE  XIII. 

midine  bases  are  synthetically  formed  by  the  cells  for  this  purpose.  To  be 
eure,  the  animal  organism  —  at  least,  that  of  the  birds  and  the  reptiles  —  is 
capable  of  building  up  uric  acid.  From  the  whole  manner  of  its  formation 
it  would  seem  very  improbable  that  the  purine  bases  have  the  same  origin. 
In  this  connection  we  must  indeed  recall  the  work  of  F.  Knoop  and 
A.  Windaus,1  from  which  we  can  easily  assume  a  synthetic  production  of  a 
compound  which  is  important  to  the  cell-metabolism.  These  two  inves- 
tigators have  shown  that  the  action  of  ammoniacal-zinc-hydroxide  on 
grape-sugar  in  the  cold  produces  an  oxygen-free  base  in  large  quantity; 
namely,  methyl-imidazole : 

CH3— C— NH 

)CH 
CH-N 

This  gives  us  a  connecting  link  between  the  carbohydrates  and  the 
purine  bases.  It  is  possible  that  analogous  reactions  may  occur  in  the 
plant  organism.  The  animal  cell  would  hardly  look  to  the  carbohydrates 
as  a  source  for  the  production  of  nitrogenous  material;  at  least,  nothing 
at  present  known  would  indicate  that  it  does.  We  will  state  here  that, 
in  spite  of.  the  large  number  of  recent  observations  in  the  field  of  purine 
metabolism,  it  is  still  impossible  for  us  to  give  an  exact  account  of  the 
influence  of  this  class  of  bodies  on  the  total  metabolism,  and  even  less  so 
in  the  case  of  the  nucleoproteids  and  nucleic  acids  in  the  individual  cells. 
We  know  that  the  animal  organism  utilizes  materials  containing  purines 
for  its  requirements.  There  are  nutrient  substances,  like  meat,  rich  in 
purine  bases,  and  others,  again,  containing  less  of  these.  Milk  belongs  to 
the  latter  class.  The  animal  cell  undoubtedly  requires  nucleic  acid  and 
also  purine  bases  for  the  purpose  of  building  up  nucleoproteids.  They  con- 
stantly decompose — as  we  shall  soon  see  —  those  constituents  which  contain 
purine  and  replace  them  again.  From  this  we  can  easily  imagine  that  the 
cell  utilizes  the  nucleic  acids  either  in  their  original  or  converted  form  to 
replace  wasted  material  or  to  construct  new  cells.  We  shall  see  later  that 
the  animal  organism  continues  to  break  down  material  containing  purines, 
even  in  cases  of  extreme  starvation,  some  of  the  derivatives  formed  by 
this  process  appearing  in  the  urine.  There  is  a  far-reaching  analogy  here 
to  the  behavior  of  the  proteins  in  the  organism.  It  is  possible  —  in  fact 
very  probable  —  that  the  nucleoproteids  in  the  form  of  nucleic  acids  are 
utilized  by  the  cells,  at  least  in  part,  in  the  manner  just  indicated.  We 
must  not  forget,  however,  that  we  have  no  absolute  proof  of  this.  In  fact 
there  are  some  observations  which  point  to  the  probability  that  the  animal 
organism,  like  the  plants,  is  also  capable  of  directly  synthesizing  the  purine 


1  F.  Knoop  and  A.  Windaus:  Ber.  36,  1166  (1905).      Hofmeister's  Beitr.  6,  392  (1905V 


THE  NUCLEOPROTEIDS.  287 

bases.  Tichomiroff  l  has  shown  that  hibernating  insect  eggs  contain  only 
traces  of  purine  bases,  while  the  maturing  eggs  show  a  much  larger  per- 
centage of  these.  A.  Kossel 2  finally  showed  that  the  yolks  of  unincubated 
eggs  contained  practically  no  purine  bases.  After  fifteen  days'  incubation 
larger  amounts  of  guanine  and  hypoxanthine  could  be  detected.  We  must 
also  refer  to  the  work  of  Burian  and  Schur.3  They  estimated  the  amounts 
of  bases  present  in  new-born  animals,  and  compared  these  values  with 
those  obtained  from  older  sucklings.  Although  the  latter  had  received 
almost  no  purine  bases  with  their  nourishment,  the  milk,  the  amount  of 
these  substances  continually  increased.  Finally,  we  must  remember  the 
work  of  F.  Miescher,4  who  found  that  even  the  salmon,  during  the  fasting 
period  when  it  remains  in  fresh  water,  not  only  builds  up  nucleins  from  the 
simplest  components,  but  newly  forms  the  purine  bases  as  well.  All  these 
important  observations  show  us  what  difficult  syntheses  the  animal  cell  is 
capable  of  effecting.  There  does  not  seem  to  be  any  reason  for  doubting 
that  the  most  varied  constituents  of  the  tissues  of  the  animal  organism  are 
built  up  of  the  simplest  components.  It  is  still  an  open  question  regarding 
the  manner  in  which  the  growing  organism  carries  out  this  process. 

It  is,  at  present,  impossible  to  make  any  definite  statements  concerning 
the  products  utilized  in  the  synthesis  of  the  purine  bases.  It  is  indeed 
possible  that  further  investigations  with  histidine  and  its  behavior  in  the 
animal  organism  may  give  us  some  clew  to  this  process.  This  albuminous 
cleavage-product,  as  we  have  seen,  is  very  probably  an  a-amino-/?-imid- 
azole-propionic  acid: 

CH— NH 

II          )CH 

C    — N 

CH2 

CH  .  NH2 

COOH 

If  this  be  true,  we  have  another  bridge  from  the  proteins  to  the  purines. 

We  specifically  call  attention  to  our  ignorance  of  the  relations  of  the 
nucleic  acids  to  the  general  metabolism,  because  recent  investigations 
on  the  disintegration  of  these  substances  in  the  tissues  have  indicated 
the  ease  with  which  these  gaps  in  our  knowledge  may  be  overlooked. 
They  immediately  become  apparent  when  we  attempt  to  explain  the 

1  A,  Tichomiroff:  Z.  physiol.  Chem.  9,  518  (1885). 

2  A.  Kossel:  Z.  physiol.  Chem.  10,  248  (1886). 


3  R.  Burian  and  H.  Schur:  ibid.  23,  55  (1897). 

4  F.  Miescher:  Arch,  exper.  Path.  Pharm.  37,  100  (1896). 


288  LECTURE  XIII. 

causes  of  the  well-known  metabolic  derangement,  gout,  which  is  un- 
doubtedly closely  related  to  a  disturbance  of  the  purine  assimilation. 
Our  uncertainty  begins  when  we  proceed  to  follow  the  behavior  of  the 
nucleic  acids  in  the  alimentary  tract,  although  we  are  a  little  better  informed 
regarding  the  decomposition  of  the  nucleoproteids  themselves.  The  latter 
are,  at  the  start,  vigorously  attacked  by  pepsin  and  hydrochloric  acid 
in  the  stomach.  The  loosely-linked  albuminous  component  is  split  off 
and  converted  into  peptones.  Nuclein  then  separates  in  an  insoluble 
form,  but  later  on  is  partially  dissolved.  Trypsin  likewise  separates 
the  albuminous  component  from  the  nucleoproteids.  The  nucleic  acids, 
however,  seem  to  remain  entirely  unaltered.  They  must,  therefore, 
occupy  a  class  by  themselves  among  the  food  materials,  because  all  the 
others  so  far  discussed  are  largely  disintegrated  in  the  intestine  in  order 
to  supply  the  tissue  cells,  and  partly  those  of  the  intestine  itself,  with 
the  necessary  material  for  their  individual  needs.  We  would  expect, 
a  priori,  that  the  nucleic  acids  would  also  have  to  be  disintegrated  to 
make  them  available.  Up  to  the  present  time  but  one  ferment  has  been 
isolated  from  the  tissues  capable  of  separating  nucleic  acids  into  their 
components.  This  is  the  so-called  nuclease.1  Trypsin  destroys  this 
ferment.  Nuclease  has  been  found  in  the  pancreas  of  the  dog  and  the 
thymus  gland  of  the  calf.  Undoubtedly,  such  ferments  must  be  widely 
distributed  in  the  tissues.  They  account  for  the  first  stages  of  the  cleavage 
and  degradation  of  the  nucleic  acids.  Recent  investigations  2  have  shown 
that  neither  the  active  nor  the  inactive  pancreatic  juice  is  able  to  decom- 
pose the  nucleic  acids  into  their  components;  both,  however,  are  capable 
of  so  altering  them  that  their  entire  characteristics  are  changed,  thus 
making  them  more  easily  dialyzable.  Even  tfye  cell  walls  of  the  intestine 
possess  ferments  which  are  capable  of  completely  decomposing  the  altered 
nucleic  acids.  The  animal  organism  evidently  treats  this  valuable  material 
in  a  very  economical  manner.  The  nucleic  acid  cleavage-products  are 
difficultly  soluble  in  water,  and  not  easily  absorbed,  as  feeding  experi- 
ments with  purine  bases  have  proved.  These  experiments  indicate  that 
the  complete  disintegration  of  these  compounds  takes  place  only  in  the 
walls  of  the  intestine.  Material,  foreign  to  the  organism,  is  there  pre- 
pared for  its  requirements.  We  are  unacquainted  with  the  exact  manner 
in  which  the  pancreatic  juice  changes  the  nucleic  acids.  It  may  possibly 
be  that  it  acts  as  the  beginning  of  a  hydrolytic  decomposition.  The 
disintegration  proceeds  in  stages,  and  we  must  expect  to  meet  complexes 
analogous  to  the  peptones,  and  dextrins.  We  have  not  the  least  doubt 
but  that  the  nucleic  acids  very  closely  resemble  the  albumins  in  their 
entire  construction  and  the  way  they  are  broken  down. 

1  F.  Sachs:  Z.  physiol.  Chem.  46,  337  (1905). 

2  E.  Abderhalden  and  A.  Schittenhelm :  ibid.  47  (1906). 


THE  NUCLEOPROTEIDS.  289 

A  part  of  the  nucleic  acid  of  the  food  is  undoubtedly  decomposed  by 
bacteria  in  the  intestines.  Purine  bases  are  present  in  the  faeces.1  Martin 
Kriiger  and  Schittenhelm 2  have  shown  that  only  a  small  part  of  the  purine 
bases  in  the  faeces  could  originate  in  this  manner.  It  has  been  found  that 
the  quantitive  distribution  of  the  various  purine  bases  in  the  faeces  corre- 
sponds very  closely  to  that  in  the  different  organs,  and  that  the  main  source 
of  supply  is  undoubtedly  the  degenerating  intestinal  epithelium  and  dead 
bacteria.  Only  small  amounts  of  bases  are  introduced  into  the  intestines 
by  means  of  the  pancreatic  and  intestinal  juices. 

Until  recently,  we  knew  but  very  little  about  the  relation  of  the  nucleo- 
proteids,  or,  rather,  of  the  nucleic  acids  and  their  cleavage-products,  to  the 
decomposition  products  of  the  general  metabolism.  Indeed,  many  scien- 
tists, largely  from  purely  chemical  considerations,  were  strongly  in  favor 
of  assigning  to  the  nucleins  a  relation  to  the  formation  of  uric  acid.  It 
remained,  however,  for  recent  experiments  to  show  that  in  man,  and 
mammals  in  general,  the  greater  part  and  perhaps  all  of  the  uric-  acid 
results  from  the  decomposition  of  the  nucleic  acids  and  their  cleavage- 
products,  especially  the  purine  bases. 

For  a  long  time  the  attempt  had  been  made  to  show  that  uric  acid  was 
the  antecedent  of  urea  in  the  breaking  down  of  proteins.  In  fact,  the 
amount  of  uric  acid  in  the  urine  was  even  considered  to  be  a  direct  expres- 
sion of  the  activity  of  oxidations  in  the  animal  organism.  The  more 
extensive  these  oxidation  processes  were,  the  less  uric  acid  would  be  found 
in  the  urine.  Evidence  against  this  assumption  was  brought  forward  from 
time  to  time,  and,  above  all,  it  was  always  claimed  that  in  no  case  could 
any  direct  relationship  be  shown  between  the  uric  acid  excreted  and  the 
disintegration  of  the  albumins,  and  that  there  was  no  evidence  that  it 
indicated  the  extent  of  the  oxidation  processes.  Scientists  always  came 
back  to  the  above  view,  however,  because  it  was  not  found  possible  to 
show  positively  that  there  was  an  increased  elimination  of  uric  acid  after 
the  administration  of  nucleic  acids  and  purine  bases.  It  was  only  by  the 
experiments  of  Horbaczewski 3  that  the  problem  was  cleared  up. 

Horbaczewski  showed  with  mammals  that  if  the  pulp  or  extract  of 
organs  were  digested  for  several  hours  out  of  contact  with  the  air,  purine 
bases  were  formed,  while  exposure  to  the  air  gave  rise  to  uric  acid.  On 
adding  nucleoproteids  a  better  yield  of  uric  acid  was  obtained.  It  was 


1  A.  Schittenhelm  and  F.  Schroter:  Z.  physiol.  Chem.  39,  203  (1903).     A.  Schitten- 
helm and  C.  Tollens:  Z.  innere  Med.  25,  No.  30  (1904). 

2  M.  Kriiger  and  A.  Schittenhelm:  Z.  physiol.  Chem.  45,  14  (1905);  35,  153  (1902). 
A.  Schittenhelm:  Dent.  Arch.  klin.  Med.  81,  423  (1904). 

3  Horbaczewski:  Monatsh.  10,  624  (1889);  12,  221  (1891).     P.Giacosa:  Att.  R.  Ace. 
Scienze  di  Torino,  25, 726  (1891).  W.  Spitzer:  Pfliiger's  Arch.  76, 192  (1899).  H.  Wiener: 
Verh.  xvii,  Kong,  innere  Med.  1889;  622  Arch,  exper.  Path.  Pharm.  42,  375  (1899). 


290  LECTURE  XIII. 

also  shown  by  feeding  experiments  that  the  administration  of  nucleo- 
proteids  and  of  purine  bases  increased  the  elimination  of  uric  acid.  Sim- 
ilarly the  formation  of  uric  acid  is  increased  when  a  food  rich  in  purine 
bases  —  e.g.,  meat,  liver,  thymus,  etc.  —  is  added  to  a  definite  diet.1 

Horbaczewski  himself  believed  that  the  uric  acid  was  derived  in  the 
first  place  from  the  nucleic  acids,  or  their  purine  bases,  obtained  from 
leucocytes,  and  his  work  was  followed  by  a  large  number  of  investigations 
concerning  this  question.  It  was,  in  fact,  found  that  there  was  a  certain 
relation  between  the  amount  of  uric  acid  eliminated  and  the  number  of 
leucocytes.  A  particularly  pregnant  example,  according  to  this  view,  is 
given  in  leucaemia,  a  disease  which  in  its  entire  aetiology  is  but  little  under- 
stood. One  of  its  most  prominent  symptoms  is  a  more  or  less  extensive 
increase  in  the  number  of  leucocytes.  The  observation  that  the  increased 
elimination  of  uric  acid,  so  often  noted  during  this  disease,  is  dependent 
on  the  destruction  of  leucocytes,  is  undoubtedly  true.  The  generalization 
that  the  uric  acid  of  urine  could  only  result  from  the  destruction  of  the 
above-mentioned  cells  was  not,  however,  correct.2  All  the  other  cells  of 
the  organism  must  be  considered  in  the  same  manner.  The  most  impor- 
tant result  of  the  investigations  of  Horbaczewski  is  that  the  purine  bases, 
in  minced  organs  and  tissue  extracts,  can,  in  the  presence  of  oxygen,  be 
converted  into  uric  acid. 

To  prevent  any  misunderstanding,  we  will  state  at  this  point,  that  the 
increased  elimination  of  uric  acid  can,  in  no  case,  be  looked  upon  as  evidence 
of  an  increased  cell  destruction.  It  may  just  as  easily  arise  from  an 
increased  cellular  metabolism;  i.e.,  from  the  breaking  down  and  recon- 
struction of  the  cell-body,  and  especially  of  the  nuclei. 

Before  discussing  the  mechanism  of  the  conversion  of  purine  bases 
into  uric  acid,  we  wish  to  devote  a  little  space  to  an  important  investiga- 
tion of  Burian  and  Schur.3  These  two  scientists  showed  that  by  a  diet 
containing  no  purine  bases  it  is  possible  to  diminish  appreciably  the  excre- 
tion of  uric  acid,  but  not  to  prevent  it  entirely.  It  is  noteworthy  that  the 
amounts  of  uric  acid  then  excreted  remain  practically  constant  for  each 
individual,  but  vary  with  different  individuals.4  Burian  and  Schur  desig- 


1  R.  Burian:  Med.  Klin.  1,  131  (1905).     E.  Salkowski:  Virchow's  Arch.  117,  570 
(1889).     C.  v.  Noorden:  Lehrbuch  d.  Path.  d.  Stoffwechsels,  54,  Berlin,  Hirshwald, 
1893  (new  ed.  1906).     C.  Dapper:  Berliner  Klin.  Wochsch.  30,  619  (1893).     W.  Cam- 
merer:   Z.  Biol.  28,  72  (1891);  Z.  physiol.  Chem.  33,  139  (1896).     A.  Schittenhelm : 
Z.  Stoffw.  u.  Verdauungskrankheiten,  5,  226  (1904).     H.  Wiener:  Ergebnisse  Physiol. 
I,  1,  555  (1902). 

2  Mares :  Monatsh.  13,  101  (1892). 

3  R.  Burian  and  H.  Schur:  Pfliiger's  Arch.  80, 241  (1900) ;  87, 239  (1901).    Cf .  E.  W. 
Rockwood:  Am.  J.  Physiol.  12,  38  (1905). 

4  Schreiber  and  Waldvogel:  Arch,  exper.  Path.  Pharm.  32,  69  (1899).     Cf.  M.  Kauf- 
mann  and  L.  Mohr:  Arch.  klin.  Med.  74,  141  (1902). 


THE  NUCLEOPROTEIDS.  291 

nate  the  amount  of  uric  acid  eliminated  with  a  diet  free  from  purine  bases 
as  endogenous  uric  acid,  and  contrast  this  part  of  the  total  uric  acid  elimina- 
tion during  an  ordinary  diet  with  that  obtained  from  the  purines  in  the 
food.  The  amount  of  the  latter,  which  they  designate  as  exogenous  uric 
acid,  naturally  varies,  and  is  dependent  upon  the  quantity  of  purine 
bases  ingested  and  absorbed.  The  amount  of  endogenous  uric  acid 
remains  constant,  even  from  a  diet  rich  in  purine  bases.  The  uric  acid 
arising  from  the  purine  bases  is  added  to  that  of  endogenous  origin. 
Burian  states  that  the  amount  of  endogenous  uric  acid  excreted  daily  by 
a  normal  adult  ranges  between  0.3—0.6  gram.  The  endogenous  uric 
acid  value  is  a  direct  expression  of  the  extent  of  cell  activity,  which,  as  we 
know  from  various  observations,  is  very  carefully  regulated  and  adjusted 
for  each  individual. 

Although  we  may  look  upon  this  conception  of  endogenous  and  exoge- 
nous uric  acid,  in  the  sense  suggested  by  Burian  and  Schur,  as  a  distinct 
advance  in  our  knowledge  of  the  course  of  cell-metabolism,  we  must, 
nevertheless,  emphasize  the  fact  that  this  separation  between  the  two- 
sources  is  merely  a  superficial  one.  In  no  case  are  we  justified  in  con- 
cluding that  the  total  purine  metabolism  is  sharply  divided  into  twa 
phases;  i.e.,  that  the  purines  in  the  food  are  immediately  converted  into 
uric  acid,  nor  that  cell-metabolism,  in  the  narrowest  sense  of  the  word, 
takes  place  independently.  We  have  no  doubt  that  the  purine  bases, 
and  the  other  components  of  nucleic  acid,  replace  continually  material 
used  in  the  building  up  of  cells,  and  particularly  their  nuclei,  and  thus 
take  part  in  the  formation  of  endogenous  uric  acid,  of  a  later  period. 
Although  we  know  that  the  total  nitrogen  of  the  food,  as  a  rule,  soon  re- 
appears in  the  urine,  we  nevertheless  assume  that  the  albumins,  at  least 
to  some  extent,  participate  in  cell-metabolism,  and  in  the  construction  of 
cells  partly  supplying  material,  and  partly  acting  as  a  source  of  energy. 
Similarly,  the  purine  bases  in  the  food  undoubtedly  participate  in  cell- 
metabolism.  The  endogenous  purine  value  may  perhaps  be  compared, 
within  certain  limits,  with  that  amount  of  albumin  which  the  cells  require 
even  during  starvation.  We  do  not  mean  to  represent  that  this  compari- 
son is  an  absolute  one.  It  merely  suggests  the  similarity  between  the 
metabolism  of  albumin  and  purine  —  both  are  very  closely  related  to 
cellular  metabolism.  We  must  be  especially  cautious  not  to  differentiate 
sharply  the  endogenous  and  exogenous  uric  acid  with  regard  to  the  total 
purine  metabolism  of  the  cells. 

The  question  arises,  What  sources  have  we  to  assume  in  particular  for 

the  endogenous  uric  acid?     In  general  it  may  be  said  that  the  endogenous 

uric  acid  may  be  traced  primarily  to  the  decomposed  nuclear  material, 

.  and  also  to  the  cells  which  have  been  completely  destroyed.     R.  Burian  l 

1  Z.  physiol.  Chem.  43,  494  (1905). 


292       .  LECTURE    XIII. 

has  recently  called  our  attention  to  the  importance  of  considering  the 
muscles  as  a  source  of  purine  bases,  and,  consequently,  they  are  related 
to  the  formation  of  uric  acid.  He  showed  in  the  first  place  that  the  endo- 
genous uric  acid  elimination  in  human  beings  during  twenty-four  hours 
was  not  appreciably  influenced  by  muscular  activity,  whereas  hourly 
values  were  distinctly  changed.  Vigorous  muscular  exertion  is  followed 
by  an  hour  of  increased  elimination  of  urinary  purine.  This  increase, 
during  the  time  of  work,  does  not  influence  the  uric  acid,  as  such,  but 
principally  the  purines.  The  noticeable  increase  in  uric  acid  elimination 
is  only  evident  some  time  later.  By  a  subsequent  diminution  of  the  uric 
acid  and  purine  eliminations,  the  daily  uric  acid  and  purine  values  are 
practically  unaffected  by  periods  of  rest  or  of  activity.  Naturally  such 
investigations  can  be  carried  out  only  when  no  food  is  eaten,  or  at  least 
none  containing  purine,  or  the  amount  of  purine  bases  in  the  food  must  be 
definitely  known.  Burian  finally,  in  order  to  establish  more  closely  the 
relations  of  the  muscles  to  purine  metabolism,  caused  blood  to  flow  through 
the  surviving  muscles  of  a  dog.  It  was  found  first  of  all  that  the  liquid 
which  was  originally  perfectly  free  from  uric  acid  always  contained  it  after 
a  short  time.  If  the  muscle  was  stimulated,  purine  bases  appeared  in 
considerable  quantity,  and  chiefly  hypoxanthine.  The  discovery  is  also 
very  important  that  the  amount  of  hypoxanthine  in  the  muscle  itself  is 
greatly  increased  when  it  is  tetanized.  From  this  we  must  assume  that 
the  muscle,  when  at  rest,  constantly  oxidizes  hypoxanthine  to  uric  acid. 
When  its  metabolism  is  increased  by  greater  demands  upon  it,  the  muscle 
cells  are  no  longer  able  to  oxidize  all  of  the  purine  bases,  and  especially 
the  hypoxanthine,  so  that  then  unchanged  hypoxanthine  is  given  up  to 
the  blood.  It  is  very  important  that  according  to  these  observations  the 
muscle  cells  are  constantly  forming  hypoxanthine.  These  investiga- 
tions are  not  to  be  regarded,  however,  as  perfectly  conclusive.  We  have 
mentioned  them  here  because  from  them  we  may  perhaps  expect  to  obtain 
the  first  explanation  of  the  part  played  by  the  purines  of  the  food  in 
cellular  metabolism,  and  concerning  the  extent  of  the  synthetic  formation 
of  purine  bases. 

We  have  been  informed  recently  concerning  the  breaking  down  of  the 
individual  purine  bases  to  uric  acid,  and  their  subsequent  fate  in  the  animal 
organism,  by  a  series  of  valuable  experiments  by  A.  Schittenhelm.1  They 
have  been  confirmed  by  further  observations  by  Richard  Burian.2  We  have 
already  mentioned  the  fact  that  Horbaczewski  could  detect  the  formation 
of  uric  acid  in  the  pulp  of  organs,  or  in  extracts  of  them,  in  the  pres- 
ence of  oxygen.  It  was  now  found  possible  to  follow  carefully  the 

1  A.  Schittenhelm:  Z.  physiol.  Chem.  42,  251  (1904);  43,  228  (1904);  45,  121,  152, 
161  (1905) ;  46,  354  (1905). 

2  R.  Burian:  Z.  physiol.  Chem.  43,  497  (1905). 


THE   NUCLEOPROTEIDS.  293 

various  phases  of  this  conversion.  We  have  also  called  attention  to  the 
fact  that  the  tissues  of  many  organs  contain  ferments  which  are  capable 
of  breaking  down  the  nucleoproteids  into  their  components,  and  finally 
disintegrating  the  separate  cleavage-products,  such  as  the  nucleic  acids, 
into  their  simpler  components.  The  individual  purine  bases  are  changed 
eventually  by  ferments  into  uric  acid,  as  has  been  unquestionably  proved 
by  the  above  investigators.  Schittenhelm  has  proved  that  when  the 
pulp,  or  extract  of  organs,  is  first  boiled,  no  uric  acid  can  be  obtained. 
He  finally  succeeded  in  isolating  the  ferment  producing  uric  acid 
from  the  organs.  Instead  of  employing  organ  extracts,  we  can  now 
utilize  active  ferment  solutions  for  the  experiments.  The  advantage  of 
this  method  is  evident  when  we  appreciate  the  fact  that  the  pulp,  or 
extract  of  organs,  necessarily  contains  varying  amounts  of  purine  bases, 
which  are  practically  absent  from  the  isolated  ferment  or  in  its  solutions. 
Schittenhelm  obtained  xanthine  on  adding  the  ferment  from  beef-spleen 
to  guanine  out  of  contact  with  the  air,  but,  by  conducting  air  through  the 
liquid,  uric  acid  resulted.  The  transformation  of  guanine  into  uric  acid 
accordingly  takes  place  with  the  intermediate  formation  of  xanthine.  The 
following  formulae  indicate  these  changes: 

HN— CO  HN CO  HN— CO 

II                               II  II 

NH2  .  C     C— NH >      C  =O  C— NH        >        CO  C— NH 


\ 


CH 


CH 


CO 


;_N  HN' C— N  HN— C— NH 

Guanine  Xanthine  Uric  acid 


Guanine  is  converted  by  hydrolysis  into  xanthine  by  the  loss  of  an  NH2 
group.  By  the  oxidation  of  xanthine,  uric  acid  is  formed.  Two  ferments, 
therefore,  participate  in  the  conversion  of  guanine  into  uric  acid.  In  the 
same  manner  adenine  goes  over  into  hypoxanthine,  which  is  then  converted 
into  xanthine,  and  the  latter  into  uric  acid: 

N=C.NH2  HN— CO 

II                                 II 
HC    C— NH     >       HC    C-NH  > 


CH 


CH 


N— C— N  N— C— N 

Adenine  Hypoxanthine 

HN— CO  HN—  CO 

II  II 

COC— NH >      CO   C-NH 


\ 


CH 


\ 


/ 

HN— C— X  HX— C— NH 

Xanthine  Uric  acid 


CO 


294  LECTURE  XIII. 

The  ferment  which  converts  guanine  into  xanthine,  and  adenine  into 
byporanthine,  is  widely  distributed.  It  is  evidently  found  in  all  organs. 
The  oxidizing  ferment,  on  the  other  hand,  which  finally  produces  the 
uric  acid,  seems  to  be  restricted  to  individual  organs.  It  has  been  found 
in  the  spleen,  lungs,  liver,  intestine,  muscles,  and  the  kidneys  of  cattle. 
Further  investigations  have  disclosed  the  remarkable  fact  that  the  same 
organs  of  different  kinds  of  animals  vary  considerably  in  this  respect,  so 
that  a  generalization  of  results  obtained  with  different  species  of  animals 
is  not  permissible.  Schittenhelm  and  Bendix  l  showed  that  the  trans- 
formation of  purine  bases  into  uric  acid  not  only  takes  place  in  this  way 
in  glass  vessels,  but  also  in  the  organism  itself,  by  injecting  guanine  sub- 
cutaneously  and  intravenously  into  a  rabbit.  They  found  a  considerable 
increase  in  the  uric  acid  of  the  urine,  and  detected  the  presence  there 
of  a  purine  base  corresponding  to  xanthine,  which  is  evidently  to  be 
regarded  as  an  intermediate  product  in  the  formation  of  uric  acid  from 
guanine. 

Up  to  this  point  we  have  not  mentioned  an  important  fact  which  makes 
it  difficult  to  trace  the  quantitative  relations  in  the  production  of  uric 
acid  from  the  purine  bases.  There  are  ferments  present  in  many  tissues 
of  the  animal  organism  which  are  capable  of  further  decomposing  the 
uric  acid  formed.  Schittenhelm  calls  them  uricoli/tical  ferments,  in  order 
to  indicate  that  we  are  dealing  with  an  entirely  different  process  from 
that  of  the  uric  acid  production.  Such  a  ferment  has  been  found  in  the 
kidneys,  liver,  and  muscles,  and  very  probably  also  in  bone  marrow.2 
Schittenhelm  has  succeeded  in  isolating  this  ferment.  It  is  evident  that 
if  a  destruction  of  uric  acid  takes  place  in  the  animal  tissues,  the  old-time 
conception  that  the  amount  of  uric  acid  excreted  is  an  index  of  the  quan- 
tity of  uric  acid  formed  in  the  organism,  can  no  longer  be  accepted.  An 
increased  excretion  of  uric  acid  in  the  urine  may,  of  course,  be  due  to  a 
greater  production  thereof;  it  may,  however,  also  indicate  a  lessened 
destruction. 

The  question  now  arises,  What  are  the  degradation  products  of  uric  acid 
when  a  decomposition  sets  in?  We  can  at  once  answer  that  we  do  not 
know  definitely.  Hugo  Wiener8  has  practically  proved  that  glycocoll 
is  produced  from  uric  acid  when  administered  to  a  rabbit.  He  found 
that  the  reserve  supply  of  glycocoll  in  this  animal  was  fairly  constant. 
An  increase  was  noted  in  the  amount  of  glycocoll  excreted  after  the  injec- 
tion of  uric  acid.  This  increase  could  be  checked  by  administering  ben- 
zoic  acid,  in  which  case  hippuric  acid  was  formed.  Wiener  has  also  shown 

1  Z.  physiol.  Chem.  43,  365  (1905). 

3  Cf.  also  Hugo  Wiener,  Arch,  exper.  Path.  Pharm.  42,  375  (1899);  also  Zentr. 
Physiol.  18,  690  (1905). 

8  Arch,  exper.  Path.  Pharm.  40,  313  (1897). 


THE  NUCLEOPROTEIDS.  295 

that  the  amount  of  glycocoll  in  beef  kidneys  could  be  appreciably  increased 
by  digesting  them  with  uric  acid.1  It  seems  probable  that  the  decom- 
position of  uric  acid  may  result  in  the  formation  of  glycocoll;  but  we, 
nevertheless,  wish  to  state  that  Wiener's  investigation  is  not  entirely  con- 
vincing, for  his  method  of  estimating  the  glycocoll  was  not  an  exact  one, 
and,  above  all,  its  production  from  other  sources  was  not  absolutely 
excluded.  As  the  proteins  participate  largely  in  the  production  of  glycocoll, 
it  is  necessarily  difficult  to  estimate  the  amount  of  glycocoll  originating 
from  the  uric  acid. 

Urine  also  contains  oxalic  acid: 

COOH 

COOH 

A  part  of  this  undoubtedly  originates  from  the  food.  Another  portion 
is  unquestionably  produced  in  the  tissues.  The  assumption  has  often 
been  made  that  oxalic  acid  may  be  a  decomposition  product  of  uric  acid, 
although  no  satisfactory  proof  has  been  presented  to  substantiate  this 
view.  From  a  chemical  standpoint  such  a  formation  of  oxalic  acid  seems 
perfectly  possible.  We  know  that  uric  acid  can  go  over  into  alloxan, 
parabanic  acid,  oxaluric  acid,  and  finally  into  oxalic  acid.  It  is  impossible 
to  say  anything  further  about  a  source  of  the  oxalic  acid  which  does  not 
come  from  the  food. 

Allantoine  has  often  been  regarded  as  a  decomposition  product  in  the 
hypothetical  formation  of  oxalic  acid  from  uric  acid.  It  was  first  found 
in  the  allantoic  fluid,  and  later  recognized  by  Wohler  2  as  a  normal  con- 
stituent of  the  urine  of  suckling  calves.  Gusserow3  has  recently  isolated 
it  from  the  urine  of  new-born  children.  Allantoine  is  also  found  in  the  urine 
of  various  full-grown  mammalia;  for  instance,  dogs,  cats,  and  rabbits.  ' 

Allantoine  is  the  diuride  of  glyoxylic  acid.  It  can  easily  be  obtained 
by  melting  glyoxylic  acid  with  urea: 


COH  / NH2         /  NH-OH— NH 

|  +  2  CO         =    CO 

COOH  \  X NH 


\ 


CO  +  2  H2O 


Glyoxylic  acid        Urea  Allantoine 

The  question  of  the  origin  of  allantoine  has  been  answered  in  various 
ways.  It  is  generally  believed  to  be  related  to  the  purine  bodies.  This 
assumption  was  strengthened  by  the  discoveries  of  Salkowski 4  and  Min- 

1  Arch,  exper.  Path.  Pharm.  43,  375  (1899). 

2  Ann.  26,  244  (1838);  70,  229  (1849);  88,  100  (1853). 

3  Arch.  Gyn.  3,  270  (1872).     G.  Pouchet:  Beitrige  zur  Kenntnis  der  Extraktivstoffe 
des  Urins,  Paris,  1880  (pp.  28  and  37). 

4  E.  Salkowski:  Zent.  Med.  Wiss.  36,  No.  53,  929  (1898). 


296  LECTURE  XIII. 

kowski,1  who  showed  that  when  a  dog  was  fed  on  material  rich  in  purine 
bases,  such  as  thymus  or  pancreas,  the  amounts  of  allantoine  eliminated 
appreciably  increased.  Cohn  2  found  that  the  administration  of  hypo- 
xanthine  to  this  animal  had  the  same  effect.  Mendel  and  White  3  have 
proved  that  intravenous  injection  of  uric  acid  into  cats  and  dogs,  as  well 
as  the  injection  of  salts  of  nucleic  acids,  caused  an  increase  in  the  allan- 
toine elimination.  Wiechowski 4  has  furnished  a  better  proof  that  uric 
acid  is  decomposed  into  allantoine.  He  succeeded  in  showing  that  in 
surviving  beef-kidney  and  dog's  liver,  uric  acid  is  changed  quantitatively 
into  allantoine.  This  shows  one  way  in  which  uric  acid  may  be  decom- 
posed, but  it  does  not  necessarily  follow  that  in  the  decomposition  of  uric 
acid  allantoine  is  formed  in  every  case;  perhaps  the  latter  is  further 
decomposed  into  urea  and  glycocoll,  and  it  is  quite  possible  that  normally 
the  decomposition  of  uric  acid  may  follow  an  entirely  different  course. 
On  the  other  hand,  we  can  hardly  assume  that  the  uric  acid  is  all 
decomposed  in  one  way.  It  is  conceivable  that,  for  example,  a  part  is 
decomposed  with  the  intermediate  formation  of  glycocoll,  while  another 
part  gives  rise  to  allantoine.5 

This  would  give  us  a  clear  conception  of  the  formation  of  uric  acid  in 
mammalia.  It  can  undoubtedly  be  traced  to  the  degradation  of  nuclein 
substances,  and  finally  to  the  purine  bases.  It  has  never  been  decided 
whether  in  birds  and  reptiles  (animals  in  which,  as  we  have  seen,  the  uric 
acid  in  its  entire  significance  and  formation  takes  the  place  of  urea)  a  part, 
if  only  a  very  small  part,  is  formed  in  the  way  we  have  just  indicated.  It 
is  hardly  to  be  doubted  that  entirely  analogous  processes  take  place  in  the 
organisms  of  birds  anc[  reptiles.  Similarly  we  have  no  reason  for  denying 
that  a  synthetic  formation  of  uric  acid  may  also  take  place  in  the  tissues  of 
mammals. 

Before  considering  the  behavior  of  the  remaining  cleavage-products 
of  the  nucleic  acids  in  the  animal  organism,  we  must  pay  some  attention 
to  the  purine  bases  appearing  in  urine.  We  have  already  mentioned, 
that,  for  example,  in  vigorous  muscular  activity,  such  large  amounts  of 
purine  bases  are  transmitted  to  the  blood  that  the  purine  content  of  the 
urine  is  increased.  The  animal  cells  do  not  have  time  to  convert  these 
bases  into  uric  acid. 

Purine  bases  are  constantly  present  in  the  urine,  some  of  which  are  to 
be  regarded  as  direct  decomposition  products  of  the  nucleic  acids,  while 

1  O.  Minkowski:  Zentr.  innere  Med.  19,  No.  19  (1898). 
3  T.  Cohn:  Z.  physiol.  Chem.  25,  507  (1898). 

3  L.  B.  Mendel  and  B.  White,  Am.  J.  Physiol.  12,  85  (1905). 

4  Wilhelm  Wiechowski:  Hofmeister's  Beitr.  9,  295  (1907),  10,  247  (1907.) 

5  It  is  interesting  to  know   that  allantoine   has    been   found    in  the  bark  of  tree- 
branches  and  in  buds.     Cf.     E.    Schulze   and  J.  Barbieri:  Ber.   14,    1602    (1881);  J. 
prakt.  Chem.  25,  145  (1882);  Z.  physiol.  Chem.  11,  420  (1886). 


THE  NUCLEOPROTEIDS. 


297 


others  are  only  indirectly  related  to  the  decomposition  products  of  nucleins. 
The  amount  of  such  substances  present  in  urine  is  small  and  varies.  It 
may  be  increased  by  a  diet  rich  in  purine  bases.  An  increased  elimination 
of  purine  bases  may  also  result  from  a  greater  destruction  of  leucocytes. 
Heteroxanthine,1  paraxanthine,1  and  /-methylxanthine 2  are  purines 
which  bear  no  relation  to  nuclein  metabolism.  They  represent  the  most 
important  constituents  of  the  so-called  alloxuric  bases  of  urine,  and  arise 
from  the  caffeine,  theobromine,  and  theophylline  present  in  our  table 
accessories.  The  following  formula?  will  give  us  an  idea  of  the  relations 
between  these  substances: 


HN— CO 

CO  C  .  N  .  CH3 

I       II       )CH 
HN— C.N^ 

Heteroxanthine 

=  7-Monomethyl- 

xanthine 


CH3  .  N— CO 

CO  C  .  NH 

\ 


CH 
HN— C.N^ 

Z-Methylxanthine 


CH3  .  N— CO 

CO  C  .  N  .  CH3 

)CH 
HN— C.N^ 

Paraxanthine  =  1 :  7-Di- 
methylxanthine 


II          ,CH3 
C( 


CH3  .  N— CO 

I      I         , 
)O  C— N  ' 

I   ii     )CH  :CH 

CH3  .  N— C— N  ^          CH3  .  N C— N 

Caffeine  Theobromine 


O  CH3  .  N— CO 

I          /CH3  | 

c— N :  co 


\ 


C— NH 

\ 


CH 


CH3  .  N— C— N 

Theophylline 


The  relation  of  these  alloxuric  bases  to  the  purine  bases  of  tea,  coffee, 
and  cocoa  has  been  established  by  means  of  feeding  experiments. 

Xanthine,  hypoxanthine,  guanine,  and  adenine  are  among  the  purine 
bases  which  can  be  derived  directly  from  the  nucleic  acids.  The  two 
latter  are  not  invariably  present.  They  evidently  appear  only  when 
there  is  an  increased  decomposition  of  material  containing  nucleins  with 
relatively  less  oxidation.  Usually  they  are  evidently  converted  into  the 
corresponding  oxy purines.  Xanthine  occasionally  participates  in  the 
formation  of  renal  calculi.  Pure  xanthine  calculi  rarely  occur.  Uric 
acid  is  usually  a  constituent  of  these  bladder  stones.  These  may  occur 
as  small  concretionary  masses,  or  as  large  stones.  They  are  often  strati- 
fied, in  which  cases  uric  acid  layers  alternate  with  those  of  calcium 
oxalate. 


1  G.  Salomon:  Arch.  Anat.  Physiol.  1882,  426;  1885,  570.     M.  Kruger  and  G.  Sal- 
omon: Z.  physiol.  Chem.  21,  169  (1895);  Ber.  16,  195  (1883);  18,  3406  (1885). 

2  M.  Kruger:  Arch.  Anat.  Physiol.  1894,  553;  M.  Kruger  and  G.  Salomon:  Z.  physiol. 
Chem.  24,  364  (1898). 


298  LECTURE  XIII. 

Two  other  alloxuric  bases,  the  so-called  episarkine  *  and  epiguanine,2  have 
also  been  isolated  from  urine.     The  latter  is  7-methylguamne: 


NH2  .  C 

II 

N 

Epiguanine 

We  must  now  attempt  to  answer  the  question  as  to  what  becomes  of  the 
remaining  constituents  of  the  nucleic  acids.  We  are  especially  interested 
in  the  fate  of  the  three  pyrimidines,  —  uracil,  thymine,  and  cytosine.  We 
should  expect  them  to  be  related  in  some  way  to  the  formation  of  uric  acid, 
although  H.  Steudel,3  on  feeding  pyrimidine  derivatives  to  dogs,  could  not 
succeed  in  transforming  them  into  purine  compounds.  We  know  nothing 
else  that  is  definite  concerning  the  behavior  of  the  pyrimidine  bases  in 
animal  economy. 

As  regards  the  phosphoric  acid  which  is  obtained  by  the  cleavage  of 
nucleic  acid,  we  can  only  surmise  what  its  relations  are  in  metabolism. 
Possibly  it  is  utilized  in  the  formation  of  lecithin. 

If  we  sum  up  all  we  know  about  the  breaking  down  of  the  nucleoproteids, 
and  especially  of  the  nucleic  acids,  we  see  that  there  are  large  gaps  in 
our  knowledge.  It  is  not  yet  perfectly  clear  to  us  how  the  nucleo- 
proteids in  the  cells  themselves  participate  in  metabolism,  nor  the 
function  of  the  nucleus  in  cell-metabolism.  Although  the  study  of  the 
uric  acid  formation  has  given  to  us  a  fairly  clear  picture  of  the  transforma- 
tion of  purine  bases,  on  the  other  hand  it  has  not  been  found  possible  from 
this  knowledge  to  shed  much  light  into  the  obscurity  enveloping  the 
metabolic  disturbances  which  occur  in  gout  and  uric  acid  diathesis.  We 
can  indeed  imagine  that  in  these  diseases  either  the  production  of  uric 
acid  is  increased  for  some  reason,  or  that  there  is  not  so  much  decomposi- 
tion of  this  acid  as  takes  place  normally.  Now  uric  acid  is  very  difficultly 
soluble  in  water,  and  its  occurrence  in  certain  tissues  —  especially  in 
cartilage  —  is  to  be  traced  to  this  fact.  His4  found  that  one  part  dissolved 
in  39,000  of  water  at  18°  C.  We  shall  study  these  relations  at  another 
place,  and  will  here  merely  mention  the  fact  that  of  the  four  hydrogen 


1  Balke:  Zur  Kenntnis  der  Xanthinkorper,  Inaug.  Diss.  Leipzig,  1893.   Georg  Salo- 
mon: Z.  physiol.  Chem.  18,  207  (1894). 

2  M.  Kriiger:  loc.  cit.  Arch.  Anat.  Physiol.  1894,  553;  Z.  physiol.  Chem.  24,  364  (1898); 
26,  389  (1898-99). 

3  Z.  physiol.  Chem.  32,  285  (1901). 

4  Verh.  xvii,  Kong.  Med.  p.  315  (1899);  Deut.  Arch.  klin.  Med.  67,  81  (1900);  Verb, 
xviii,  Kong.  Med.  425  (1900)   and   Zent.  Stoffwechsel-und  Verdauungskrankheiten,  1, 
61  (1900);  3,  434  (1901);  His  and  Paul:  Z.  physiol.  Chem.  31,  64  (1900). 


THE  NUCLEOPROTEIDS.  299 

atoms  which  are  replaceable  by  radicals  in  the  uric  acid  molecule,  only 
two  take  part  in  the  formation  of  salts.  Uric  acid  is,  therefore,  a  dibasic 
acid,  and  forms  two  series  of  salts,  the  acid  or  monobasic  salts,  and  the 
neutral  or  dibasic  salts.  Thus  we  have  acid  sodium  urate,  also  called 
monosodium  urate,  and  neutral  or  disodium  urate.  Many  speculations 
have  been  brought  forward  regarding  the  deposition  of  uric  acid  in  the 
tissues,  especially  those  of  the  joints,  in  gout,  basing  them  upon  the  diffi- 
cult solubility  of  uric  acid.  On  the  one  hand,  an  increased  formation  of 
uric  acid  may  account  for  its  elimination,  and  on  the  other  hand  the  com- 
position of  the  blood,  lymph,  and  other  constituents  of  the  tissues  may  be 
such  that  the  uric  acid  is  even  more  insoluble  than  under  normal  conditions. 
All  of  these  hypotheses  have  failed  to  be  very  fruitful.  They  have  no 
good  foundation.  For  example,  we  do  not  know  in  what  form  the  uric 
acid  is  transported  in  the  blood  and  tissues.  The  assumption  has  been 
made  that  it  circulates,  not  in  a  free  state,  but  combined  with  albumin, 
nucleic  acids,  and  other  substances,  although  no  positive  proof  has  yet 
been  presented  that  such  is  the  case.  No  conclusions  can  be  drawn  from 
the  deposits  themselves,  which  consist  of  monosodium  urate.  Great 
stress  was  formerly  laid  on  the  increased  presence  of  uric  acid  in  the  blood. 
We  know  to-day,  that  other  conditions  may  result  in  an  increase  of  uric 
acid  in  the  blood  without  causing  the  appearance  of  the  symptoms  of  gout. 
Weintraud  *  has  in  fact  shown  that  in  a  normal  individual  there  is  an 
increased  amount  of  uric  acid  in  the  blood  after  a  diet  rich  in  purine  bases. 
Again,  great  stress  was  laid  upon  the  increased  elimination  of  uric  acid  in 
gout  until  it  was  positively  shown  that  it  is  permissible  to  speak  of  an 
increased  elimination  only  during  an  acute  attack.  Otherwise  —  aside 
from  the  fact  that  in  gouty  diseases  the  purine  values  of  the  urine  vary 
more  than  under  normal  conditions  —  the  amount  of  purine  present  in 
the  urine  is  practically  the  same  during  a  long  period  of  time. 

It  is  very  noticeable  that  the  deposition  of  uric  acid,  especially  in  gouty 
inflammations,  seems  to  be  confined  to  specific  locations,  such  as  the 
smaller  joints  of  the  extremities.  The  suggestion  has  been  made  that 
the  primary  cause  of  the  whole  ailment  is  not  a  disturbed  metabolism  of 
the  purine  substances,  but  an  alteration  of  the  tissues  at  the  place  in  ques- 
tion. Just  as  it  has  been  assumed  that  the  formation  of  gall-stones  is 
due  primarily  to  an  inflammation  of  the  biliary  passages,  and  likewise  that 
renal  calculi  may  originate  from  some  organic  lesion,  the  assumption 
has  also  been  made  that  the  circulating  uric  acid  was  deposited  at  a  given 
spot  on  account  of  some  change  in  the  tissues  there. 

This  is  not  the  place  to  consider  the  pathology  of  gout,  nor  to  enter  into 
any  discussion  of  the  various  theories  concerning  it.  We  can  only  attempt 

1  Wiener  klin.  Rundschau:  10,  Nos.  1  and  2,  pp.  3  and  21  (1896).  For  further  liter- 
ature see  H.  Wiener:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  2,  1  Abt.,  p.  377  (1903). 


300  LECTURE  XIII. 

here  to  explain  pathological  processes  in  the  light  of  physiological-chemical 
investigations,  and  on  the  other  hand  obtain  from  pathological  research 
new  points  of  view  for  physiological-chemical  work.  Doubtless  the  essen- 
tial part  of  purine  metabolism  will  find  its  full  explanation  only  by  means 
of  further  studies  in  pathology  and  in  physiology.  We  must  be  satis- 
fied with  merely  sketching  the  existing  situation,  and  bring  forward  the 
fact  that  for  the  present  there  is  plenty  of  room  for  hypotheses,  a  sure 
sign  that  the  investigations  have  by  no  means  solved  the  problem.  It 
seems  certain  that  gouty  diseases  will  not  all  be  referred  to  a  single  cause, 
nor  to  a  single  disturbance  in  cellular  metabolism.  Here,  as  in  diabetes, 
various  disturbances  may  take  place  in  different  stages  of  the  total  purine 
metabolism,  which  will  all  finally  result  in  the  same  symptoms. 


LECTURE   XIV. 

THE   MUTUAL   RELATIONS   BETWEEN    FATS,   CARBO- 
HYDRATES,  AND  ALBUMINS. 

I. 

IN  our  previous  treatment  of  the  three  most  important  classes  of  organic 
food-stuffs,  the  fats,  carbohydrates,  and  albumins,  we  have  considered  each 
individual  group  by  itself,  as  regards  the  way  in  which  it  is  absorbed,  the 
place  where  it  is  assimilated,  and  the  relations  of  the  group  to  specific 
functions  of  the  body.  We  have  found  that  carbohydrates  are  the  most 
important  source  of  muscular  power,  while  in  the  fats  we  have  the  princi- 
pal source  of  heat.  The  significance  of  the  albumins  is  much  less  certain. 
We  know  that  they  are  absolutely  unreplaceable,  and  also  that  they  act 
as  building  material  for  the  cells,  being  necessary  to  replace  the  parts 
which  have  been  used  up.  We  do  not  at  present  understand  why  the 
animal  organism  requires  so  much  albumin  under  all  conditions,  nor 
why  it  so  quickly  decomposes,  up  to  a  certain  limit,  the  ingested 
albumin. 

By  more  closely  following  the  metabolism,  we  quickly  encounter  results 
which  do  not  harmonize,  for  example,  with  the  assumption  that  the  mus- 
cles are  only  capable  of  acting  by  means  of  the  energy  given  to  them  by 
the  carbohydrates.  Again,  it  was  noticed  early  that  a  portion  of  the  car- 
bohydrates disappeared  when  the  diet  was  rich  in  these  substances,  — i.e., 
this  part  could  not  be  detected  in  the  form  of  glycogen,  —  and,  moreover, 
an  exact  study  of  the  respiratory  exchange  showed  that  no  increased  com- 
bustion of  the  sugars  had  taken  place.  According  to  this  we  can  only 
assume  that  the  extra  carbohydrate  is  retained  in  some  form  other  than 
glycogen. 

Before  discussing  those  facts,  which  force  us  to  the  assumption  that  a 
transformation  of  one  group  of  food-stuffs  into  another  may  take  place 
in  the  animal  organism,  we  will  first  of  all  call  attention  to  the  relations 
existing  between  fats,  carbohydrates,  and  albumins,  according  to  our 
present  knowledge  regarding  the  chemical  composition  of  these  substances. 
Of  course,  this  will  only  show  us  the  possibility  of  such  transformations, 
and  indicate  the  manner  in  which  they  may  take  place.  The  organism 
itself  may,  naturally,  choose  an  entirely  different  course,  and  utilize  other 

301 


302  LECTURE  XIV. 

compounds,  e.g.,  certain  decomposition  products,  as  bridges  from  one 
food-stuff  to  another. 

If  we  follow  the  formation  of  the  most  varied  carbon  compounds  in 
plants,  which  are  the  prime  source  of  all  carbon  combinations  in  living 
organisms,  we  are  forced  to  the  assumption  that  the  first  product  arising 
from  the  assimilation  of  carbon  dioxide  under  the  influence  of  chlorophyll 
and  the  sun's  energy,  is  a  carbohydrate,  or  at  least  some  compound  very 
closely  related  to  this  class  of  substances.1  The  carbohydrates  undoubt- 
edly assume  a  central  position  in  plant  metabolism,  while  the  albumins 
and  fats  are  of  minor  importance.  But  it  is  not  impossible  that  the 
assimilation  of  carbon  dioxide  may  proceed  in  various  ways,  and  form 
different  primary  assimilation  products.  It  is  indeed  possible  that  the  car- 
bohydrates, i.e.,  the  large  amount  of  starch  present,  may  conceal  other 
compounds. 

Up  to  the  present  time,  because  starch  is  detected  so  easily  and  so 
positively,  this  and  analogous  substances  have  been  of  chief  interest  to 
us.  On  the  other  hand,  the  carbohydrates  impart  to  the  plant  organism 
their  individuality.  We  find  them  in  every  direction;  and  when  we 
consider  the  numerous  polysaccharides  (the  more  simple  ones  like 
starch,  which  arise  from  the  condensation  of  a  single  kind  of  sugar,  and 
the  other  innumerable,  more  complicated  sugars,  consisting  of  unlike 
components,  such  as  arabinose,  xylose,  dextrose,  etc.),  we  will  recognize 
the  fact,  immediately,  that  the  carbohydrates  occupy  the  same  pre- 
dominating position  in  plants  that  the  albumins  do  in  animal  organisms. 
At  all  events,  each  of  the  three  groups  of  food-stuffs  —  fats,  carbo- 
hydrates, and  proteins  —  is  ultimately  derived  from  the  carbonic  acid 
of  the  air,  for  that  is  the  only  source  worth  mentioning  of  the  carbon 
in  plants. 

In  considering  the  assimilation  of  carbon  dioxide  by  the  plants,  we 
referred  to  Baeyer's  hypothesis,  that  formaldehyde  is  to  be  looked  upon 
as  the  first  condensation  product.  We  stated  then  that  we  could  easily 
imagine  the  various  different  kinds  of  sugars  to  result  from  the  condensa- 
tion of  several  molecules  of  formaldehyde.  On  the  other  hand,  we  also 
mentioned  Emil  Fischer's  hypothesis,  which  includes  the  possibility  that 
the  glycerose,  discovered  by  him,  may  occupy  the  primary  stage  in  the 
whole  process  of  carbonic  acid  assimilation.  This  assumption  has  much 
in  its  favor;  and  if  glycerose,  perhaps,  does  not  actually  appear  at  this 
first  stage,  we  must  remember  the  possibility  that  it  may  result  from  the 
disintegration  of  carbohydrates.  At  any  rate  it  is  interesting  to  think 
that  glycerose  may  perhaps  occupy  an  intermediate  position  in  the  further 
syntheses  of  the  plant  organism.  From  glycerose  on,  it  is  easy  to  build 
bridges  to  the  group  of  proteins  as  well  as  to  that  of  the  fats. 

1  Cf.  Lecture  IV. 


THE  MUTUAL  RELATIONS.  303 

The  relations  to  the  fats  are  evident  from  the  following  formulae: 

CH2OH  COH  COOH 

I  I  I 

CHOH  CHOH  CHOH 

CH2OH  CH2OH  CH2OH 

Glycerol  Glycerose  Glyceric  acid. 

(Glyceraldehyde) 

Glycerose  is  simply  the  aldehyde  of  glycerol.1  Its  preparation  from 
glycerol  was  accomplished  by  Emil  Fischer.  Conversely,  we  can  imagine 
one  of  the  fat  components,  glycerol,  as  originating  from  glycerose.  The 
relations  become  much  more  complicated  if  we  attempt  to  derive  the 
fatty  acids,  the  other  components  of  fats,  from  sugar.  Emil  Fischer 2 
suggests  their  formation  in  the  following  manner:  To  produce  oleic  and 
stearic  acids,  three  molecules  of  grape-sugar  (or  six  molecules  of  glycerose) 
may  unite  at  their  aldehyde  groups,  thus  forming  a  chain  of  3  X  6  =  18 
carbon  atoms.  By  rearrangement  of  the  atoms  and  withdrawal  of  oxygen, 
i.e.,  by  reduction,  the  above-mentioned  acids  may  be  formed.  The  other 
fatty  acids,  e.g.,  palmitic  acid,  can  be  formed  perhaps  in  a  similar  manner, 
except  that  sometimes  only  hexoses  are  used  for  the  synthesis,  while,  at 
other  times,  hexoses  and  pentoses  are  both  utilized,  according  to  the 
number  of  carbon  atoms  in  the  acid  molecule.  Thus  we  can  imagine 
palmitic  acid,  with  its  16  carbon  atoms,  being  produced  from  one 
hexose  and  two  pentose  molecules.  Pentoses  are  very  widely  distributed 
in  the  vegetable  world,  and  in  large  amounts.  They  play  a  far  less 
important  part  in  the  animal  body,  although  they  may  be  formed  by 
decomposition.  We  have  already  learned  that  a  pentose,  arabinose,  may 
be  very  easily  derived  from  glucose,  or  from  gluconic  acid;  and  on  the 
other  hand,  we  have  seen  that  an  oxidation  product  of  glucose,  glucuronic 
acid,  will  easily  go  over  into  a  five-carbon  sugar  by  splitting  off  carbon- 
dioxide. 

Thus,  while  we  are  in  a  position  to  derive  one  of  the  components  of  the 
fats,  glycerol,  from  the  carbohydrate  group,  we  have  but  little  foundation 
for  the  formation  of  fatty  acids  from  the  same  group.  We  are  at  present 
confined  to  hypotheses.  We  have  not  yet  succeeded  by  any  chemical 
means  in  converting  sugars  into  fat. 


1  The  original  glycerose,  with  which  Fischer  worked,  really  contained  chiefly 
dihydroxyacetone.     von  Lippmann  and  others,  however,  prefer  to  call  glyceral- 
dehyde  (of  which  there  are  two  stereo  isomers)  glycerose  rather  than  the  dihydroxy- 
acetone.— TRANSLATORS. 

2  Die  Chemie  der  Kohlehydrate  und  ihre  Bedeutung  fur  die  Physiologic,  Berlin, 
A.  Hirschwald,  1894,  p.  28. 


304  LECTURE  XIV. 

Let  us  consider  the  relations  of  glycerose  to  the  proteins,  or  to  their 
building  materials.     The  following  formulae  will  be  helpful: 


COH 

CH2OH 

CH2SH 

CH3 

I 

| 

I 

1 

CHOH 

CHNH2 

CH  .  NH2 

CHNH2 

CH2OH 

COOH 

COOH 

COOH 

Glycerose 

a-Amino-/?-Hydroxy- 

a-Amino-/?-thio- 

a-Amino- 

propionic  acid 

propionic  acid 

propionic  acid 

=Serine 

=Cysteine 

=  Alanine 

These  formulae  show  at  once  what  slight  differences  exist  between  these 
apparently  entirely  distinct  groups.  It  would  not  be  at  all  difficult  to 
imagine  the  above  three  amino  acids  as  being  derived  from  glycerose. 
Leucine  might  be  produced  from  one  molecule  of  a  hexose  or  two  molecules 
of  glycerose,  by  the  addition  of  ammonia  and  partial  reduction;1  and  by 
oxidation,  the  dibasic  glutamic  and  aspartic  acids  may  be  formed  from 
leucine.  We  meet  with  certain  difficulties  when  we  attempt  to  account 
for  the  formation  of  these  last  compounds.  Leucine,  which  is  isobutyl- 
aminoacetic  acid,  contains  a  branched  chain.  The  difficulties  increase 
when  we  come  to  proteins  containing  an  aromatic  ring,  such  as  phenyl- 
alanine  and  tyrosine.  To  produce  the  benzene  nucleus  from  the  carbo- 
hydrates is  a  highly  complicated  process.  Such  transformations  undoubt- 
edly do  occur  in  the  organism  of  plants,  although  the  formation  of  these 
substances  is,  probably,  not  a  direct  one. 

We  must  also  consider  the  close  relation  of  alanine  to  lactic  acid,  which 
is  so  easily  produced  by  the  action  of  alkalies  or  ferments. 


CHOH  CHNH2 

COOH  COOH 

Lactic  acid  Alanine 

Plants  could  also  form  their  albumins  or  individual  amino  acids  in  this 
manner.  Conversely,  lactic  acid  may  be  easily  formed  from  alanine, 
serine,  and  cysteine  by  disintegration;  from  alanine,  for  example,  simply 
by  splitting  off  ammonia.  In  fact,  such  processes  must  take  place  in  the 
animal  organism  to  a  considerable  extent.  Lactic  acid,  therefore,  may 
arise  from  two  sources  in  the  animal  organism.  It  may  come  from  carbo- 
hydrates or  from  albumin. 

The  formation  of  albumin  in  the  animal  organism  from  the  other  kinds 


1  Cf.  E.  Fischer  and  E.  Abderhalden:  Z.  physiol.  Chem.  36,  268  (1902). 


THE  MUTUAL  RELATIONS.  305 

of  food  is  of  little  consequence,  or  at  least  all  of  our  present  knowledge 
of  albumin  metabolism  speaks  against  it.  We  need  only  think  of  the 
possibility  of  fats  and  carbohydrates  being  produced  from  albumin.  Now 
we  have  already  seen  that  a  large  part  of  the  elementary  components  of 
the  proteins  are  very  closely  related  to  the  lower  members  of  the  normal 
fatty  acid  series.  We  know  further,  that  only  a  part  of  the  carbon  leaves 
the  organism  in  combination  with  the  nitrogen  of  the  individual  amino 
acids.  A  portion  of  the  carbon  chain  must  remain  behind.  What  becomes 
of  this  is  not  yet  apparent.  Right  here  the  investigation  must  start  con- 
cerning the  transformations  of  the  albumins  into  fats  and  carbohydrates, 
for  all  such  changes  must  result  from  these  carbon  chains.  We  have,  to 
be  sure,  no  positive  proof  that  such  transformations  do  take  place. 

Perhaps  the  intermediate  product,  glucosamine,  may  throw  some  light 
upon  the  formation  of  albumin  from  carbohydrates  in  plants,  and,  con- 
versely, the  production  of  carbohydrates  from  albumins  in  the  animal 
organism.  It  is  a  derivative  of  glucose  (or  of  mannose),  and  is  closely 
related  on  the  one  hand  to  the  sugars,  and  on  the  other,  to  the  oxyamino 
acids.  It  is  certainly  not  without  significance,  that  nature  has  provided 
such  connecting  links.  We  recall  the  following  formulae: 


CH2  .  (OH) 

CH2  .  (OH) 

CH2  .  (NH2) 

CH    .  (OH) 

CH   .  (OH) 

CH2 

CH   .  (OH) 

CH    .  (OH) 

CH2 

CH   .  (OH) 

CH    .  (OH) 

CH2 

CH   .  (OH)          CH    .  (NH2)      CH  .  (NH2)  CH    .  (NH2) 

CH  :  0  CH  :  O  COOH  COOH 

d-Glucose  Glucosamine       Lysine  Leucine 

The  carbohydrates,  as  we  have  already  seen,  are  related  to  the  poly- 
hydric  alcohols  on  the  one  hand,  and  to  various  acids  of  different  char- 
acter on  the  other.  We  can  thus,  either  directly  or  indirectly,  connect 
large  groups  of  different  compounds  with  the  sugars.  We  are  still  entirely 
in  the  dark  regarding  the  method  of  formation  of  innumerable  tannins, 
ethereal  oils,  alkaloids,  etc.,  which  occur  in  the  plant  organisms.  All 
of  these  must  ultimately  be  referred  to  the  carbon  dioxide  of  the  air. 
What  relations  they  possess  to  the  carbohydrates  is  still  entirely  beyond 
our  knowledge;  in  fact,  owing  to  their  great  complexity,  we  are  almost 
forced  to  the  conclusion  that  they  are  not  at  all  related.  C.  Harries1  has 


C.  Harries:  Ber.  38,  1195  (1905). 


306  LECTURE  XIV. 

shown,  however,  that  products  of  the  vegetable  kingdom  which  appar- 
ently are  not  at  all  related  to  the  carbohydrates,  may,  nevertheless, 
have  been  derived  from  them.  He  showed  that  caoutchouc,  a  compound 
containing  an  eight-carbon  ring  (1 .5-dimethyl-cyclo-octadi-ine),  on 
hydrolysis  yielded  Isevulinaldehyde,  CH3  .  CO  .  CH2  .  CH2  .  COH,  and 
the  ozonide  of  caoutchouc  yielded  similarly  Isevulic  acid.  Now,  the  sugars 
readily  go  over  into  Isevulic  acid,  while,  on  the  other  hand,  it  is  also  possible 
that  caoutchouc  may  be  built  up  of  pentoses.  Their  reduction  to  CsH8, 
and  subsequent  condensation  into 


/CH3  .  C  .  CH2  .  CH2  .  CH         \ 
\        HC  .  CH2  .  CH2  •  C  .  CH3  /X 


CH2 

could  account  for  the  formation  of  caoutchouc.  Perhaps  the  a-methyl- 
furan,  discovered  by  Atterberg  1  from  beech-wood  tar,  which  easily  goes 
over  into  laevulinaldehyde,2  may  be  even  more  closely  related  to  the  caout- 
chouc synthesis.  At  all  events,  this  gives  us  a  new  support  for  the  assump- 
tion that  the  whole  large  group  of  terpenes  may  likewise  be  derived  from 
the  carbohydrates. 

In  this  connection  we  must  not  forget  to  mention  a  peculiar  compound 
which  occurs  in  the  vegetable  kingdom,  as  well  as  in  the  animal  organism, 
and  has  the  empirical  formula  of  the  hexoses.  We  refer  to  inositol  (or 
inosite).  It  is  found  in  the  muscles,  liver,  spleen,  kidneys,  suprarenal 
bodies,  lungs,  brain,  leucocytes,  and  the  testes,  and  has  often  been  noticed 
in  the  urine  under  normal  as  well  as  pathological  conditions.  Inositol, 
CeH^Oe,  was  formerly  looked  upon  as  a  sugar.  Maquenne  3  later  recog- 
nized it  as  a  derivative  of  hexamethylene,  with  the  following  composition: 

CHOH— CHOH 
CHOH'  ^CHOH 

x  CHOH— CHOH  ' 
Hexahydroxybenzene  =  Inositol 

It  is  indeed  possible  that  we  have  in  this  case,  one  of  the  first  stages  in 
the  conversion  of  a  carbohydrate  into  the  benzene  ring,  so  that  this 
compound  which  is  of  so  much  biological  interest  opens  up  further  possi- 
bilities for  the  formation  of  the  numerous  aromatic  compounds  in  the 
plant  organism.  Although  chemical  investigation  has  often  served  to 
give  us  better  understanding  concerning  many  obscure  biological  processes, 
we  must  not  forget  that  a  clear  conception  is  lacking  in  regard  to  the  most 


1  A.  Atterberg:  ibid.  13,  879  (1880). 

2  C.  Harries:  ibid.  31,  37  (1898). 

3  Maquenne:  Compt.  rend.  104,  1719  (1887);  ibid.  109,  812  (1889). 


THE  MUTUAL  RELATIONS.  307 

important  changes.  We  are  obliged  to  resort  here  almost  exclusively  to 
experiments  with  animals.  Certain  observations  are  also  a  result  of 
Nature's  physiological  experiment,  pathology.  In  all  such  investigations, 
we  are  dealing  with  indirect  methods  of  proof.  Experiments  with  animals 
rarely  lead  to  other  than  indirect  results.  These  are  not  entirely  con- 
clusive; they  are  merely  more  or  less  convincing,  and  in  most  cases  are 
dependent  upon  the  personal  interpretation  of  the  investigator.  This  is 
a  weak  point  in  nearly  all  biological  investigation,  which  undeniably  gives 
it  a  certain  amount  of  fundamental  uncertainty.  For  this  reason,  it  is 
difficult  to  form  a  positive  decision  from  the  numerous  experiments  which 
have  been  performed  in  the  attempt  to  decide  the  question  as  to  the 
conversion  of  one  class  of  food-stuffs  into  another.  We  can  merely 
enumerate  here  the  more  important  and  best  substantiated  conceptions 
and  those  experiments  which  have  been  carried  out  in  the  most  convinc- 
ing manner.  On  the  other  hand,  we  would  be  committing  a  grave  error 
if  we  were  to  consider  only  those  processes  and  changes  in  the  organism 
as  proved  for  which  we  have  a  purely  chemical  explanation,  and  which  we 
are  able  to  repeat,  where  possible,  outside  of  the  living  cell.  We  would 
thus  be  making  a  restriction,  which  would  hinder  the  further  develop- 
ment of  biology,  and  we  should  then  be  forgetting  that  biology  has  a 
distinct  field  of  its  own,  with  its  own  peculiar  methods  of  investigation. 
Ultimately,  of  course,  we  must  always  depend  upon  the  exact  sciences, 
chemistry  and  physics,  and  consider  a  biological  problem  as  fully  settled 
when  these  sciences  supply  the  key-stone. 

Let  us  begin  first  of  all  with  the  carbohydrates  and  their  conversion  into 
the  other  two  groups  of  food  materials,  fats  and  albumins.  The  formation 
of  albumin  from  carbohydrates  in  vegetable  organisms  comes  into  con- 
sideration only  to  the  extent  that  the  plant  cells  utilize  the  carbon  chains  of 
the  sugars  in  syntheses  together  with  the  nitrogen,  which  is  either  assimi- 
lated by  the  roots  from  the  ground,  or,  as  in  rare  cases,  is  obtained  directly 
from  the  air.  We  do  not  know  anything  definite  about  these  processes. 
In  the  animal  organism,  we  can  deny  the  possibility  of  such  transforma- 
tions. It  is  otherwise,  however,  as  regards  relations  of  the  carbohydrates 
to  the  fats.  One  of  the  first  observations  in  this  connection  was  the 
formation  of  fat  in  ripening  rape-seeds,  and  in  the  pulp  of  the  olive.  We 
know  that  unripe  rape-seeds  contain  large  amounts  of  carbohydrates,  but 
practically  no  fat.  During  the  ripening  of  the  seeds  we  find  that  the 
carbohydrates  gradually  diminish,  while  fat  takes  their  place.  This  obser- 
vation is  very  significant,  for  the  seed  is  unable  to  give  off  its  carbohydrate 
externally,  or  to  take  up  fats.  The  changes  in  nature  of  a  food  material  are 
also  attested  by  the  metabolism.  The  respiratory  quotient  changes.  Ger- 
ber1  has  shown  that  the  ratio  of  carbon  dioxide  produced  to  the  oxygen 

1  C.  Gerber:  Compt.  rend.  125,  658  and  732  (1897). 


308 


LECTURE  XIV. 


consumed,  in  the  unripe  seeds,  is  less  than  one.  More  oxygen  is  taken  up 
than  is  given  off  as  carbon  dioxide.  During  ripening  the  ratio  becomes 
greater  than  one,  only  to  fall  below  one  again  after  the  fruit  has  become 
completely  ripe.  Analogous  results  have  been  observed  in  the  ripening  of 
olives,  which  in  their  unripe  condition  contain  mannitol.  The  following 
figures  published  by  A.  Roussille 1  will  give  us  an  idea  of  the  process  which 
accompanies  the  ripening  of  olives: 


Raw  Fat. 

Albumin. 

June  20 

Per  cent.   . 
1  40 

Per  cent. 

July  30 

5  49 

August  30                 

29  19 

14  619 

September  30   

62  30 

4  189 

October  30     

67  21 

4  411 

November  25    .    „  

68  57 

4  329 

Leclerc  du  Sablon  2  found  the  following  amounts  of  carbohydrates  and 
fats  in  nuts  per  100  parts  of  the  dry  substance: 


Water. 

Oil. 

Glucose. 

Saccharose. 

Amylose. 

July  6     ... 

837. 

3. 

7.6 

0. 

21.8 

August  1    .    . 

535. 

16. 

2.4 

0.5 

14.5 

August  15  .. 

274. 

42. 

0. 

0.6 

3.2 

September  1 

48. 

59. 

0. 

0.8 

2.6 

October  4  .    . 

10. 

62. 

0. 

1.6 

2.6 

The  changes  of  carbohydrates  into  fat  in  the  almonds  were  as  follows 
on  a  basis  of  100  parts  of  dry  substance: 


Date. 

Water. 

Oil. 

Glucose. 

Saccharose. 

Amylose. 

June  9        .... 

896. 

n 

6  0 

6  7 

21  6 

July  4     

716. 

10. 

4.2 

4.9 

14.1 

August  1    .... 

219. 

37. 

0. 

2.8 

6.2 

September  1 

117. 

44. 

0. 

2.6 

5.4 

October  4  .... 

12. 

46. 

0. 

2.5 

5.3 

It  is  interesting  to  note  that  fatty  acids  —  evidently  as  intermediate 
products  —  have  been  observed  during  the  formation  of  the  fats.3  How 
the  transformation,  as  a  whole,  is  effected,  has  never  been  explained. 

We  also  know  that  the  reverse  process,  i.e.,  the  formation  of  sugars  from 
the  fats,  also  takes  place,  and  this  has  been  followed  in  the  case  of  germi- 


1  A.  Roussille:  ibid.  86,  610  (1878). 

2  Ibid.  123,  1084  (1896). 

3  von  Rechenberg:  Ber.  14,  2216  (1881). 


THE  MUTUAL  RELATIONS.  309 

nating  rape-seeds.  If  we  permit  these  to  develop  away  from  the  light,  we 
observe  the  fat  disappearing  from  the  cotyledons.  In  its  place  we  find 
carbohydrates:  starch,  cellulose,  gum,  sugar.  If  we  allow  seeds,  rich  in 
starch,  to  germinate  in  glass  tubes  sealed  under  mercury,  no  change  in  the 
volume  of  gas  can  be  observed.  During  the  germination  of  seeds  contain- 
ing oil,  on  the  other  hand,  we  notice  that  gas  is  being  consumed,  from 
the  fact  that  the  mercury  rises.  This  corresponds  to  the  amount  of 
oxygen  which  is  required  to  convert  the  fats  into  carbohydrates  which  are 
richer  in  oxygen.  These  important  observations  were  made  by  Julius 
Sachs  and  Wiesner  1  in  1859. 

There  is,  therefore,  no  doubt  that  the  plant  cell  is  capable  of  pro- 
ducing carbohydrate  from  fat,  and,  conversely,  fat  from  carbohydrate.  If 
we  assume  with  Kassowitz  2  that  the  protoplasm  absorbs,  or  assimilates, 
one  of  these  compounds,  e.g.,  the  fat,  in  order  subsequently  to  form 
in  this  case,  the  carbohydrate,  in  such  a  way  that  there  is  no  direct  con- 
nection between  the  two  compounds,  then  we  miss  the  point  at  issue,  and 
the  whole  process  is  beyond  our  understanding,  for  it  cannot  be  a  matter 
of  indifference  for  the  functions  of  the  protoplasm,  whether  at  one  time 
fat,  at  another  time  carbohydrate,  and  yet  again  albumin,  is  at  its  disposal. 
The  question  concerning  the  transformations  of  the  separate  food-stuffs 
is  only  postponed  by  such  assumptions,  and  it  becomes  more  involved  and 
obscure. 

A  much  disputed  question  is  this :  Does  the  animal  cell  possess  the  same 
abilities  as  the  plant  cells?  Can  the  animal  organism  convert  fats  into 
carbohydrates,  and,  conversely,  carbohydrates  into  fats?  The  last  ques- 
tion has  been  answered  in  the  affirmative.  We  know  that  with  a  diet 
rich  in  carbohydrates,  an  appreciable  part  of  the  ingested  carbohydrate 
is  not  stored  up  in  the  form  of  glycogen,  although  there  is  no  glucohemia. 
The  fact  forces  us  to  the  conclusion  that  carbohydrates  can  be  stored  away 
as  reserve  material  in  some  other  form  than  glycogen.  Numerous  feeding 
experiments  have  shown  that  an  accumulation  of  fat  follows  a  diet  com- 
posed largely  of  carbohydrates.3  This  decision  may  be  reached  in  two 
different  ways:  first,  by  determining  the  amounts  of  fat  formed  with 
a  diet  containing  a  definite  quantity  of  fat,  albumin,  and  carbohydrate; 
and  secondly,  by  estimating  the  daily  elimination  of  carbon  dioxide.  The 
first  proof  has  been  carried  out,  as  a  rule,  in  the  following  manner:  Two 

1  J.  Sachs:  Bot.  Zeit.  1859. 

3  Cf.  M.  Kassowitz:  Allgemeine  Biologic  (3  vols.). 

3  Cf.  also  B.  Schulze:  Landw.  Jb.  1,  57  (1882).  F.  Soxhlet:  Z.  Landw.  Vers.  Bayern. 
August  (1881).  St.  Chaniewski:  Z.  Biol.  20,  179  (1884).  H.  Weiske  and  E.  Wild: 
ibid.  10,  1  (1874).  I.  Munk:  Arch.  Path.  Anat.  101,  91  (1886).  E.  Meissl  and  F. 
Strohmer:  Sitzber.  Akad.  Wiss.  Berlin,  88,  HI  (July,  1883),  and  Monatsh.  4,  801  (1883). 
E.  Meissl,  F.  Strohmer,  and  N.  v.  Lorenz:  Z.  Biol.  22,  63  (1886).  C.  Voit:  Sitzungsber. 
Miinchener  Akad.  1886,  p.  288.  M.  Rubner:  Z.  Biol.  22,  272  (1886). 


310 


LECTURE  XIV. 


dogs  from  the  same  litter  and  about  the  same  weight,  are  permitted  to  fast 
for  quite  a  length  of  time.  One  of  the  animals  is  then  killed,  and  the 
amounts  of  albumin  and  fat  contained  in  the  carcass  are  determined. 
The  other  animal,  which  is  assumed  to  possess  approximately  like  quan- 
tities of  the  above  substances,  is  then  fed  for  a  time  on  a  definite  diet, 
the  composition  of  which  in  fat,  albumin,  and  carbohydrate  is  known. 
The  unabsorbed  part  of  this  material  can  be  estimated  by  an  analysis  of 
the  faeces.  After  several  days,  this  animal,  which  has  now  gained  in  weight, 
is  killed,  and  the  amount  of  its  fat  and  albumin  determined.  In  this 
manner  it  can  be  shown  that  as  much  as  85  per  cent  of  the  ingested  starch 
has  been  converted  into  fat.  We  must  not  place  too  much  confidence  in 
these  values,  for  the  assumption  that  the  one  animal,  at  the  termination 
of  the  fasting  period,  contained  exactly  the  same  amounts  of  fat  and 
albumin  as  the  other,  is  open  to  question.  It  is  remarkable,  nevertheless, 
that  there  should  be  such  great  differences  between  the  organisms  of  the 
two  animals,  and  that  corresponding  results  have  been  obtained  in  a 
number  of  experiments. 

Thus,  Tscherwinsky  *  obtained  the  following  values: 


Albumin. 

Fat. 

Animal  fed  4  months  with  barley  contained. 

2  52  kff 

9  25  kg 

Animal  used  as  a  "  control  "                                     .... 

0  96 

0  69 

First  animal,  therefore,  gained      

1  56  kg 

8  56  kg 

The  food  contained            .    .       

7  49 

0  66 

Difference      

-5.93  kg. 

+  7.90  kg. 

The  animal  used  in  the  experiment,  a  young  pig,  had,  therefore,  gained 
7 . 9  kilograms  fat,  which  could  not  have  come  from  the  fat  in  the  food, 
and  certainly  not  from  the  albumin.  Carbohydrates,  therefore,  were  trans- 
formed into  fat. 

We  can,  as  we  have  said,  also  follow  the  respiratory  exchange  in  an 
animal  fed  on  a  diet  rich  in  carbohydrates.  If  we  know  the  amounts  of 
carbon,  albumin,  and  carbohydrate  present  in  a  food  poor  in  fat,  but  rich 
in  carbohydrates,  we  can,  on  the  one  hand,  by  determining  the  nitrogen  in 
the  urine,  estimate  the  amount  of  albumin  retained  in  the  body,  and,  on 
the  other  hand,  we  can  estimate  the  quantity  of  carbon  remaining  in  the 
organism,  by  determining  the  amount  exhaled  as  carbon  dioxide  in  addi- 
tion to  that  eliminated  as  urea.  In  this  way  it  has  been  found  that  the 
amount  of  carbon  retained  may  be  so  large  that  the  only  possible  explana- 
tion is  that  the  ingested  carbohydrates  have  been  converted  into  fat. 

The  production  of  fat  from  the  sugars  has,  a  priori,  much  in  its  favor. 


N.  Tscherwinsky:  Landw.  Vers-sta.  29,  317  (1883). 


THE  MUTUAL  RELATIONS.  311 

The  animal  organism  has  only  a  certain  amount  of  room  in  its  tissues  for 
the  carbohydrates.  The  quantity  of  glycogen  which  can  be  stored  up  in 
the  liver,  muscles,  and  the  other  organs,  is  very  limited.  The  animal 
organism  is  often  provided  with  larger  amounts  of  carbohydrate  than  it 
is  able,  at  the  moment,  to  utilize.  It  is  here  that  the  depots  for  fat  storage 
are  utilized.  Large  amounts  of  carbohydrates  after  having  been  trans- 
formed into  fat  can  be  held  in  reserve  until  needed.  We  have  not  the 
slightest  idea  where,  in  the  animal  organism,  or  in  what  organ,  this  trans- 
formation takes  place.  It  is  possible  that  the  liver  executes  this  com- 
plicated process. 

Although  it  is  generally  admitted  that  the  animal  cell  is  able  to  convert 
carbohydrates  into  fats,  the  reverse  process  is  a  much  disputed  problem. 
We  are  accustomed  to  look  upon  most  chemical  reactions  as  reversible. 
We  also  know  that  the  animal  cells  are  capable,  directly  or  indirectly,  of 
performing  characteristic  processes.  They  build  up  and  they  tear  down 
material  only  to  reconstruct  it,  and,  finally,  by  its  complete  destruction, 
they  utilize  the  energy  contained  in  the  food.  We  have  seen  representa- 
tives of  all  three  classes  of  nutrient  materials  break  down  in  the  intestine, 
and,  again,  we  have  traced  their  reconstruction  into  more  complicated 
compounds.  The  cells  of  the  liver  produce  glycogen  from  grape-sugar, 
permitting  it  to  become  glucose  again  as  it  is  required.  Another  problem 
is  this:  Is  the  animal  organism,  under  normal  circumstances,  capable  of 
satisfying  its  carbohydrate  requirements  from  fats.  This  would  hardly 
be  the  case  under  ordinary  conditions,  for,  a  priori,  as  we  shall  later  on  see 
more  in  detail,  there  is  no  reason  at  hand  why  the  fat  should  first  go 
over  into  carbohydrate,  in  order  that  the  organism  may  utilize  its  energy 
for  specific  purposes.  On  the  other  hand,  the  possibility  of  such  a  trans- 
formation unquestionably  exists.  We  can  imagine  that  each  cell  can  only 
utilize  certain  compounds  for  specific  functions.  Thus,  we  may  assume 
that  the  muscle  cells  operate  only  by  means  of  carbohydrates.  The  selec- 
tive action  of  the  ferments  would  support  such  an  assumption.  We  know 
that,  in  many  cases,  they  are  unable  to  act  upon  substances  closely  related 
to  compounds  that  they  can  decompose.  Every  ferment  seems  peculiarly 
fitted  to  attack  only  certain  definite  compounds.  Thus  it  would  be  easy 
to  understand  that  the  muscle  cells,  which  are  especially  adapted  to  act 
upon  carbohydrates,  can  utilize  only  such  potential  energy  as  is  presented 
to  them  in  this  form.  On  the  other  hand,  we  must  remember  that  the 
cleavage  and  combustion  of  the  food  materials  are  not  the  source  of  the 
liberated  energies,  but  only  act  as  a  loosening  momentum,  or  as  a  shock. 
The  true  cause  is  the  chemical  energy  of  the  food  substances  —  ultimately 
the  sun's  energy,  transformed  sunlight.  We  cannot  understand,  a  priori, 
why  the  energy  liberated  by  the  combustion  of  the  fats  could  not  be 
just  as  well  utilized  by  the  muscle  cells  as  that  which  arises  from  the 


312  LECTURE  XIV. 

carbohydrates.  If  the  muscle  cell  possesses  the  ability  of  consuming 
the  fats,  it  hardly  seems  probable  that  it  must  first  convert  the  fats 
into  carbohydrates  in  order  to  abstract  the  energy  from  them. 

If  the  fats  were  first  changed  into  carbohydrates  before  they  could  be 
utilized  for  work,  then,  according  to  Zuntz,  a  diet  of  fats  exclusively  would 
require  about  30  per  cent  more  energy  to  perform  a  given  amount  of  work 
than  would  be  required  after  a  diet  of  carbohydrates.  This,  in  fact,  is  not 
the  case.1 

Until  recently  the  above  discussion  would  have  been  quite  unnecessary. 
The  general  conception  was  that  the  different  food  materials  in  the  organ- 
ism, i.e.,  in  the  tissues,  and  finally  in  the  cells,  were  burned  up  directly 
by  the  aid  of  oxygen.  It  was  only  necessary  that  the  food  material  and 
the  oxygen  should  both  be  present  in  such  form  that  they  could  react 
together. 

The  whole  problem  thus  became  a  very  simple  one.  The  conviction  is, 
however,  becoming  more  and  more  pronounced,  that  the  relations  are 
much  more  complicated.  The  cells  themselves  participate  far  more 
actively  in  the  combustion  of  the  food  materials  than  we  have  hitherto 
imagined.  They  prepare  the  substances  for  disintegration  and  combus- 
tion. The  fact  that  our  foods  are  not  attacked  by  the  oxygen  of  the  air, 
has  led  to  the  assumption  that  the  oxygen  is  "  activated  "  in  some  manner 
in  the  organism,  and  that  this  activated  oxygen  effects  the  combustion. 
This  problem  of  the  activation  of  oxygen  has  been  the  main  topic  of 
interest,  whereas  the  behavior  of  the  food  materials  themselves,  in  the 
oxidation  process,  has  been  entirely  neglected.  Now  it  has  only  recently 
been  shown,  as  we  have  seen,  that  the  diabetic  possesses,  as  far  as  our 
present  knowledge  is  concerned,  an  absolutely  normal  capacity  for  oxida- 
tion. Grape-sugar  alone  he  consumes  more  or  less  imperfectly.  As  soon, 
however,  as  any  slight  attack  has  been  made  upon  the  glucose  molecule,  — 
as  soon  as  it  becomes  "opened  up,"  —the  diabetic  is  able  to  consume  com- 
pletely, and  to  utilize,  the  energy  contained  therein.2  We  must  consider 
the  possibility  of  a  change  occurring  in  the  food  by  means  of  a  cell  influence 
—  either  directly  or  indirectly  by  means  of  ferments  —  before  the  oxidation 
takes  place  by  the  oxygen,  which  is  carried  to  the  tissues  with  the  blood. 
The  material  is  first  of  all  "  opened  up  "  so  that  it  can  be  oxidized.  How 
this  takes  place,  we  do  not  yet  know.  We  can  imagine,  however,  that 
the  oxygen  is  first  attached  to  the  "  opened  "  molecule,  which  is  then 
destroyed.  We  know,  from  the  investigations  of  C.  Harries,3  that  caout- 
chouc, under  the  action  of  ozone,  goes  over  into  a  compound  rich  in 


1  H.  N.  Heinemann:  Pfliiger's   Arch.  83,  44    (1901).     J.  Frentzel  and  F.   Reach: 
ibid.  83,  477  (1901). 

2  Cf.  Lecture  V,  p.  101. 

3  C.  Harries:  Ber.  37,  2708  (1904);  ibid.  38,  1195  (1905). 


THE  MUTUAL  RELATIONS.  313 

oxygen,  the  so-called  "  ozonide,"  which  can  be  looked  upon  as  a  peroxide 
of  Isevulinaldehyde. 

O  :  C  (CH3)  .  CH2  .  CH2  .  CH  :  O 


O 


It  decomposes  into  Isevulinaldehyde,  Isevulic  acid,  and  hydrogen  peroxide, 
on  prolonged  boiling  with  water.  It  is  clear  that,  in  the  animal  organism, 
such  an  energetic  action  of  oxygen  can  hardly  take  place  on  the  unaltered 
food  materials,  although  it  is  possible  that  the  cell  might  so  change  the 
food  as  to  make  it  more  susceptible  to  attack.  Such  a  conception  corre- 
sponds more  nearly  to  the  actual  functions  of  the  cells.  It  consumes  the 
substances  which  it  needs  from  time  to  time;  it  must,  therefore,  have  a 
direct  influence  on  these  processes.  Under  normal  circumstances,  oxygen 
is  invariably  present.  The  cell,  i.e.,  its  protoplasm,  either  activates  the 
oxygen,  or  else  it  seizes  the  separate  food  materials  as  it  needs  them,  and 
offers  them  to  the  oxygen  for  oxidation.  At  any  rate,  the  decomposi- 
tions, which  have  been  observed  directly,  e.g.,  that  of  the  carbohydrates, 
may  be  traced  back  directly  to  cell-activity.  The  cell  is,  therefore,  able 
in  two  ways  to  regulate  exactly  its  requirements  of  energy:  by  the  activa- 
tion of  the  oxygen,  or  by  the  preliminary  preparation  of  the  food  for 
combustion. 

We  have  intentionally  gone  into  this  matter  somewhat  in  detail,  in  order 
to  show  that  the  combustion  of  the  food  materials  in  the  tissues  is  not 
necessarily  such  a  simple  process  as  we  have  heretofore  assumed.  For 
these  reasons  it  is,  as  yet,  impossible  to  decide  whether  fats  are  normally 
converted  into  carbohydrates.  Such  a  conversion  is  hardly  probable.  It 
is  more  natural  to  imagine  a  direct  utilization  of  the  energy  in  fats  by  the 
animal  cell,  and  especially  by  the  muscle  cells. 

Experiments  have  been  made  with  animals  in  the  attempt  to  settle  the 
question  whether  fats  are  converted  into  carbohydrates.  Before  discussing 
these  we  must  show  in  general  what  deductions  can  be  safely  drawn  from 
such  investigations. 

Investigations  on  the  formation  of  sugars  from  other  compounds  than 
carbohydrates,  and  especially  from  fats,  have,  as  a  rule,  been  carried  out 
in  one  of  two  ways.  We  can  make  the  animal  chosen  for  experiment  free 
from  glycogen,  by  fasting,  hard  work,  or  strychnine  convulsions,  and  then 
feed  it  the  compound  which  is  to  be  tested  as  a  glycogen-former.  By 
subsequently  determining  the  glycogen  content  of  the  whole  animal,  it  is 
possible  to  find  out  whether  any  glycogen  has  been  formed.  Only  in 
exceptional  cases,  however,  have  these  experimental  conditions  been  satis- 
fied. Rarely  was  it  satisfactorily  proved  that  the  animal  was  free  from 
glycogen  at  the  real  beginning  of  the  experiment,  and  such  a  source  of 
error  is  serious  on  account  of  the  small  amount  of  glycogen  which  is  found 


314  LECTURE   XIV. 

at  the  end  of  the  test.  Again,  the  methods  employed  in  determining  the 
amount  of  glycogen  were  inaccurate  in  many  cases.  Finally,  the  experi- 
menters have  been  satisfied,  for  the  most  part,  with  merely  estimating 
the  amount  of  glycogen  in  the  liver,  entirely  neglecting  that  which  might 
be  retained  in  the  other  organs.  This  is  on  the  assumption  that  the  liver 
is  the  place  where  the  most  glycogen  is  formed.  We  do  not  know,  how- 
ever, how  the  animal  organism  behaves  when  it  has  been  deprived  of  its 
carbohydrate  stores.  It  is  perfectly  possible  that  the  sugar  will  first  go 
to  those  organs  which  need  it  the  most.  The  chief  objection  to  all  these 
experiments  is  always  that  the  ingested  compound  may  have  had  an 
indirect  effect,  i.e.,  when  we  add  fat,  to  determine  whether  fat  can  produce 
glycogen,  and  we  do,  as  a  matter  of  fact,  find  that  this  causes  an  increase 
in  glycogen,  then  the  objection  can  be  raised  that  perhaps  the  fat,  which  is 
itself  consumed,  has  acted  as  an  albumin-sparer,  so  that  the  glycogen 
may  have  been  produced  from  albumin.  The  method  of  proof  is,  in  every 
case,  an  indirect  one,  and  this  makes  it  far  more  difficult  to  arrive  at  the 
correct  conclusion.  In  one  arid  the  same  experiment,  the  formation  of 
sugar  may  be  traced  back  to  either  the  fats  or  albumins,  according  to  the 
point  of  view.  The  same  may  be  said  of  the  second  method  of  carrying 
out  the  experiment.  In  this  case,  glucosuria  is  first  produced,  and  then 
the  influence  of  various  substances  on  the  elimination  of  sugar  is  studied. 
Thanks  are  due  to  E.  Pfl tiger  l  for  critically  examining  all  of  the  investi- 
gations which  have  been  made  up  to  the  present  time  that  have  any 
bearing  on  this  subject,  thereby  showing  with  great  clearness  that  the 
whole  problem  is  still  in  a  very  uncertain  state. 

First  of  all,  glycerol  was  tested  with  reference  to  its  ability  to  produce 
sugar;  i.e.,  in  other  words,  the  problem  was  to  decide  whether  the  animal 
cell  is  capable  of  synthesizing  sugar  from  glycerol.  This  compound,  as  we 
have  already  seen  repeatedly,  is  related  to  sugar  in  its  composition.  We 
have  mentioned  the  hypothesis  that  glycerose  is  the  starting-point  in  the 
formation  of  glycerol  by  the  plant  cell,  and  in  the  same  way  we  can  regard 
glycerose  as  resulting  from  glycerol  when  the  plants  convert  fat  into 
sugar.  Now  the  old  idea  that  only  the  plant  cells  are  capable  of  effecting 
synthesis,  has  long  since  been  set  aside.  We  know  that  the  animal  organ- 
ism is  also  able  to  build  up.  There  is,  therefore,  no  reason  why  sugar 
could  not  be  formed  from  glycerol.  Of  the  many  experiments  which  have 
been  performed  in  this  direction,  we  will  refer  to  those  of  Cremer 2  and 
Liithje.3  They  fed  dogs,  whose  pancreas  had  been  removed,  with  glycerol, 
and  determined  the  increased  elimination  of  sugar  in  the  urine.  Liithje 

1  E.  F.  W.  Pfliiger:  Das  Glycogen  u.  s.  Beziehungen  z.  Zuckerkrankheit,  2d  ed.  Bonn., 
M.  Eager,  (1905).  Cf.  E.  Pfliiger:  Pfluger's  Arch.  103,  1  (1904). 

J  M.  Cremer:  Sitzber.  Gesel.  Morph.  u.  Physiol.  Miinchen,  May  27,  1902. 
3  H.  Luthje:  Deut.  Arch.  klin.  Med.  79,  498  (1904);  80,  101  (1905). 


THE  MUTUAL  RELATIONS.  315 

administered  as  much  as  350  grams  per  day.  The  animal  under  experi- 
ment, a  dog,  weighed  15  kilograms.  If,  in  accordance  with  common 
experience,  we  assume  that  this  animal  had  stored  up  11  grams  of  glycogen 
per  kilogram  of  weight,  at  the  beginning  of  the  experiment,  we  obtain,  as 
the  total  amount  of  glycogen  present,  165  grams,  corresponding  to  183 
grams  sugar.  If  we  take  the  maximum  value,  40  grams  of  glycogen 
per  kilogram  weight,  we  have  600  grams  glycogen,  corresponding  to  664 
grams  sugar.1  The  animal  under  experiment,  however,  excreted  1408.4 
grams  sugar.  With  the  first  assumption,  1225  grams,  and  with  the 
second,  744  grams,  of  sugar  thus  remain  unaccounted  for.  The  ingested 
albumin  and  glycerol  must  be  regarded  as  producing  this  sugar.  The 
animal  excreted  209.8  grams  nitrogen  during  the  whole  period  of  the 
experiment.  Liithje  calculated  that,  at  most,  630  grams  of  sugar  could 
have  been  produced  from  the  conversion  of  the  albumin.  This  leaves 
considerable  sugar  still  unaccounted  for  unless  we  admit  that  it  came  from 
the  glycerol.  Liithje's  experiment  is  the  only  one  which  really  proves 
that  glycerol  can  be  converted  into  sugar.2  All  of  the  other  investigations, 
namely,  those  which  showed  an  increase  in  the  glycogen  content  of  the 
liver,  are  not  above  criticism.  The  discovery  that  the  animal  cell  is 
capable  of  transforming  glycerol  into  sugar  is  another  connecting  link 
between  the  animal  and  plant  cells.  We  must  not,  however,  deceive 
ourselves  with  the  thought  that  the  conversion  of  glycerol  into  sugar  takes 
place  in  normal  metabolism  to  any  considerable  extent.  We  know  it  is 
true  that  fats,  before  being  absorbed,  are  more  or  less  disintegrated  into 
their  components,  glycerol  and  fatty  acids.  We  also  know  that  neutral 
fats  are  formed  again  in  the  intestine.  A  small  amount  of  free  fatty  acids 
remains,  and  likewise  some  glycerol.  There  is  but  very  little,  however. 
It  might  be  possible  for  fat  to  undergo  combustion  without  previous 
hydrolysis,  and  the  glycerol  therein  converted  into  glucose  instead  of  being 
consumed  with  the  rest  of  the  fat  molecule.  The  amount  of  such  glycerol 
would  be  only  11  per  cent  of  the  neutral  fat,  and  this  is  relatively  little. 

The  next  question  that  arises  is  whether  the  fat  itself,  i.e.,  the  fatty 
acid  component  also,  can  go  over  into  sugar.  Direct  experiment  indicates 
that  this  is  not  the  case.  Fat  itself  does  not  cause  any  increase  of  sugar 
in  the  urine,  even  in  the  most  severe  cases  of  diabetes.  E.  Pfluger,  who 
has  recently  come  to  the  conclusion  that  a  source  of  sugar  other  than  the 
carbohydrates  themselves  must  be  looked  for  in  bad  cases  of  glucosuria 
and  diabetes,  nevertheless  holds  to  the  opinion  that  fat  can  produce  sugar. 
He  explains  the  fact  that  fat  does  not  cause  any  increased  excretion  of 


1  E.  Pfluger  calculates  as  a  maximum  615  grams  sugar.    (See  Glycogen,  loc.  cit.  p.  537.) 

2  More   recently  Karl  Griibe,  Pluger/s  Arch.  118,  1  (1907),  has  shown  that  glycerol 
after  having  been  passed  through  the  liver  of  a  turtle   caused   an   increase   in  the 
glycogen  content  of  this  organ. 


316  LECTURE  XIV. 

sugar  during  diabetes,  by  the  behavior  of  fat  materials  in  the  general 
metabolism.  In  the  first  place,  it  is  brought  forward  that  the  animal 
organism  does  not  regulate  its  consumption  of  energy  according  to  the 
quantity  of  food  administered;  that  is,  the  combustion  in  the  organism  can- 
not be  increased  beyond  certain  limits  by  the  amount  eaten.  The  amount 
of  energy  utilized  is  dependent  on  the  work  that  the  organs  have  to  do. 
This  regulates  the  amount  of  material  consumed.  If  more  food  is  eaten 
than  is  utilized,  the  excess  can  be  stored  up.  If  all  food  is  withheld  from 
an  animal,  it  will  live  largely  upon  its  store  of  fat.  An  appreciable  fall- 
ing off  in  metabolism  immediately  follows,  which  cannot  be  entirely 
recovered  simply  by  a  diet  of  fat.  .  This  may,  however,  be  accomplished 
if  a  little  albumin  is  added.  Voit  has  also  shown  that  fat  metabolism 
ceases  when  a  sufficient  amount  of  albumin  is  fed  to  an  animal.  It 
will  then  live  solely  at  the  expense  of  albumin.  This  observation  applies, 
strictly  speaking,  only  to  the  carnivora.  The  omnivora  and  herbivora  are 
unable  to  handle  as  much  albumin  as  the  metabolism  requires.  They  con- 
sume carbohydrate  and  fat  in  proportion  as  the  albumin  alone  is  insuffi- 
cient to  fulfill  all  of  the  requirements.  The  quantities  of  carbohydrate  and 
fat  changed  over  are  regulated  by  the  supply  of  albumin  at  hand.  "  The 
extent  of  albumin  metabolism  is  dependent  on  the  amount  of  albumin 
presented;  while  fat  metabolism  is  independent  of  the  fat  supply."1  Fat 
changes  are  regulated  chiefly  by  the  supply  of  albumin,  and,  secondarily, 
the  amount  of  carbohydrates.  Every  excess  of  fat  is  deposited.  The 
reason  that  a  diet  of  fat  does  not  cause  any  increased  elimination  of  sugar 
in  a  diabetic  patient,  is  due  to  the  fact  that  the  fat  consumed  cannot  go 
beyond  prescribed  limits.  By  feeding  fats  we  only  produce  an  accumula- 
tion thereof.  The  formation  of  sugar  from  fat  is  regulated  exclusively 
by  the  amount  of  work  performed  by  the  cells  which  oxidize  fat  to  sugar. 
In  order  to  trace  the  influence  of  fat  upon  the  elimination  of  sugar,  there 
remains  the  method  proposed  by  E.  Pfliiger.2  A  dog,  with  extirpated 
pancreas,  is  fed  exclusively  on  albumin.  If  the  eliminated  sugar  is  derived 
from  the  body  fat,  we  would  expect,  as  soon  as  the  animal  had  been  freed 
of  its  fat,  that  the  elimination  of  sugar  would  cease.  Pfl tiger's  experi- 
ments in  this  direction  led  to  no  definite  conclusions,  for  his  animals  all 
died  at  a  time  when  the  fat  supplies  were  about  exhausted. 

Now  what  is  the  origin  of  the  sugar  which  the  animals  in  the  experi- 
ments of  Pfliiger  and  others  always  eliminated,  even  when  all  carbo- 
hydrates were  withheld  from  them?  Liithje,  to  whom  much  credit  is  due 
for  his  extensive  investigations  regarding  the  production  of  sugar  during 
diabetes,  is  of  the  opinion  that  the  albumins  in  the  food  are  the  source  of 
the  sugar  in  such  experiments.  This  brings  us  to  the  relations  of  the  albu- 

1  E.  Pfliiger:  Glycogen,  loc.  cit.  p.  329. 

2  E.  Pfluger:  Pfliiger's  Arch.  108,  115  (1905). 


THE  MUTUAL  RELATIONS. 


317 


mins  to  the  carbohydrates.  Clinical  experience  has  long  since  decided 
that  albumin  will  produce  sugar  during  diabetes.  In  no  case,  however, 
is  the  proof  clear  and  free  from  criticism.  We  are  compelled  to  state 
that  at  present  we  know  nothing  definite  concerning  the  way  sugar  is 
formed  from  albumin.  It  has  been  attempted  to  get  around  this  problem 
by  placing  especial  stress  upon  the  carbohydrate  groups  present  in  the 
proteins.  We  have,  however,  already  called  attention  to  the  fact  that 
the  amount  of  carbohydrate  groups  present  in  proteins  is  of  little  quanti- 
tative significance.  To  be  sure,  the  carbohydrate  content  of  the  different 
albumins  from  a  practical  standpoint  will  vary  greatly,  for  we  do  not 
feed  animals  with  "  pure  "  albumins,  but  albumin  in  the  form  of  meat, 
etc.  Even  then,  however,  if  we  were  to  assume  that  these  albuminous 
substances  may  contain  as  much  as  10  per  cent  of  carbohydrates,  this 
would  not  explain  the  appearance  of  the  large  amounts  of  sugar  which  are 
eliminated  by  diabetics.  E.  Pfltiger  himself  has  brought  forward  the  best 
proof  in  this  direction,  by  feeding  dogs  with  codfish,  which  is  practically 
free  from  glycogen  and  sugar.1  This  flesh  contains  0.55  per  cent  fat. 
The  following  table  gives  a  summary  of  such  an  experiment: 


Period  of  Time, 
1905. 

No.  of 
Days 
in  Each 
Period. 

Average 
Weight  of 
the  Dog 
in  Grams. 

Daily  In- 
take of 
Nitrogen 
in  Grams. 

Daily  Elimi- 
nation of 
Nitrogen  in 
Grams 

Daily 
Aver- 
age of 
Sugar 
in 
Grams. 

Nitrogen 
Balance. 

D* 

N 

in  the 
Urine. 

in  the 

Fu-cvs. 

1.  Jan.  14-17  .  . 
2.  Jan.  18-30  .  . 
3.  Jan.  31-Feb.  15 
4.  Feb.  16-Feb.  20 
5.  Feb.  21-Feb.  26 
6.  Feb.  27-Mar.  4 

4 

13 
16 
5 
6 
6 

8580 
8350 
8300 
8200 
8150 
7070 

15.2 
27.9 
36.1 
36.8 
39.1 
8.8 

13.2 
24.6 
30.8 
31.1 
31.0 
16.2 

4.2 
2.5 

4.1 
6.3 
6.3 
4.5 

27.8 
55.9 
69.8 
71.2 
47.3 
35.5 

-    2.2 
+   0.8 
+    1.2 
-   0.6 

+    1.8 
-11.9 

2.10 
2.27 
2.26 
2.29 
1.52 
2.20 

Here  the  case  is  perfectly  clear.  The  question  to  decide  is:  Does  the 
eliminated  sugar  arise  from  fat  or  from  albumin;  i.e.,  to  be  more  precise, 
from  the  amino  acids  in  the  albumin?  Only  these  two  classes  of  food-stuffs 
can  be  taken  into  consideration,  and  not  the  insignificant  amount  of  carbo- 
hydrate groups.  The  reverse  process,  the  production  of  amino  acids 
from  carbohydrates,  undoubtedly  takes  place  in  plants.  We  have  already 
become  acquainted  with  the  close  relations  existing  between  glycerose  (as 
well  as  lactic  acid,  a  derivative  of  the  carbohydrates)  and  alanine,  serine, 
and  cysteine,  and  have  learned  incidentally  that  the  relations  between  the 
other  known  albumin  decomposition  products  to  the  carbohydrates  still 
remain  unknown.  The  plant  cells  could  hardly  be  considered  as  produc- 
ing carbohydrates  from  albumin.  Conversely,  the  animal  cell  unques- 

1  E.  Pfluger:  Pfltiger's  Arch.  108,  p.  136.      2  Cf.  page  321. 


318  LECTURE  XIV. 

tionably  does  not  synthesize  albumin  from  carbohydrates.  It  does  not 
follow  that  the  reverse  process  may  not  take  place.  We  must  also  remem- 
ber that  the  proteins  contain  large  complexes,  the  nature  of  which  we  know 
but  little.  It  is  possible  that  more  complicated  hydroxy-acids,  such  as  di- 
amino-tri-hydroxy-dodecoic  acid,1  are  present,  the  conversion  of  which 
into  carbohydrates  would  be  easy  to  understand.  At  all  events,  we  must 
admit  that  the  conversion  of  amino  acids  into  sugars  is  no  more  difficult  to 
understand  than  is  the  transformation  of  fatty  acids  into  carbohydrates, 
and  conversely.  The  formation  of  sugar  from  amino  acids  is  connected 
with  the  question  as  to  what  becomes  of  the  carbon  of  the  amino  acids 
which  does  not  leave  the  organism  in  the  form  of  urea.  When  the  func- 
tion of  these  nitrogen-free  carbon  chains  is  explained,  the  problem  of  the 
sugar  formation  of  sugar  from  albumin  will  be  less  difficult  to  solve.  This 
is  the  vital  point  of  the  whole  question,  and  from  this  standpoint  the  whole 
subject  must  be  considered. 

We  might  think  that  feeding  amino  acids  alone  would  show,  in  the  first 
place,  whether  they  have  any  effect  upon  the  formation  of  glycogen;  and 
secondly,  whether  they  effect  the  elimination  of  sugar.  Such  experiments 
have,  in  fact,  been  made.  Alanine  and  leucine,  on  account  of  their  having 
respectively  three  and  six  carbon  atoms  in  the  molecule,  seemed  especially 
suited  for  the  experiment,  although  the  latter  has  a  methyl  side  chain. 
It  is  well  known  that  normal  carbon  chains  of  the  carbohydrates  can  easily 
go  over  into  branching  chains, — for  example,  in  the  formation  of  saccharine; 
and  so,  on  the  other  hand,  we  can  imagine  the  possibility  of  the  reverse 
process  taking  place  in  the  transformation  of  leucine  into  a  sugar.  The 
experiments  which  have  been  performed  in  this  direction  are  very  con- 
tradictory, and  have  led  to  no  positive  conclusions,2  although  apparently 
the  feeding  of  individual  amino  acids,  in  particular  leucine  and  alanine, 
does  not  cause  any  accumulation  of  glycogen. 

This  does  not  by  any  means  preclude  the  possibility  of  sugars  being 
produced  from  amino  acids.  We  can  easily  imagine  that  the  disintegration 
of  the  amino  acids  from  a  protein  proceeds  in  its  intermediate  stages  in  a 
different  manner  from  that  which  takes  place  when  we  feed  large  amounts 
of  the  individual  amino  acids,  as  such,  to  the  organism.  We  know  very 
little  as  yet  about  the  intermediate  disintegration  of  albumin,  and  are 
unable  to  state  whether  the  amino  acids,  as  such,  are  set  free,  or  whether 
the  disintegration  of  the  proteins  does  not  take  place  after  the  removal 

1  E.  Fischer  and  E.  Abderhalden:  Z.  physiol.  Chem.  42,  540  (1904). 

2  Cf.  E.  Pfluger's  criticism  (Glycogen,  loc.  cit.}.      R.  Cohn,  Z.  physiol.  Chem.  28,  211 
(1899),  found  that  feeding  rabbits  with  leucine  caused  an  increase  of  over  400  per  cent  of 
glycogen,  whereas  O.  Simon,  ibid.  35,  315  (1902),  found  no  glycogen  formation  to  take 
place.     Grube  (Pfluger's  Arch.  118, 1  (1907)  )  also  came  to  the  conclusion,  from  experi- 
ments with  the  livers  of  turtles,  that  leucine  and  alanine  did  not  increase  the  glycogen 
content. 


THE  MUTUAL  RELATIONS.  319 

of  the  amino  groups  and  oxidation.  We  should  undoubtedly  be  making  a 
great  mistake  if  we  were  to  draw  the  conclusion  that  all  such  compounds 
are  decomposed  in  the  same  way,  merely  because  in  mammals  the  greater 
part  of  the  nitrogen  from  ingested  protein,  amino  acids,  and  polypeptides 
appears  in  the  urine.  We  must  not  forget  that  the  formation  of  urea 
represents  only  one  phase  in  the  disintegration  of  the  amino  acids.  It 
certainly  does  not  explain  the  intermediate  albumin  metabolism. 

The  formation  of  sugar  from  amino  acids  has  been  regarded  as  a  safe 
conclusion  on  account  of  the  fact  that  these  acids  are  closely  related  to 
the  fatty  acids,  and  for  this  reason  it  may  seem  superfluous  to  make  such  a 
sharp  distinction  between  the  formation  of  sugar  from  fats  and  from  albu- 
min. On  the  other  hand,  the  objection  may  be  raised  that  the  amino  acids 
which  have  been  studied  are  derivatives  of  the  lower  fatty  acids.  If  we 
assume  that  the  amino  groups  are  removed  from  the  amino  acids  while  they 
are  in  the  tissues,  thus  forming  fatty  acids,  it  would  be  expected  that  an 
accumulation  of  glycogen  would  result  on  feeding  animals  with  the  fatty 
acids  in  question.  L.  Schwarz  l  has  carried  out  such  experiments,  and 
found  that  the  fatty  acids  administered  did  cause  an  increase  in  the 
acetone  bodies  eliminated,  but  not  in  the  sugars. 

Embden  and  Salomon 2  have  recently  investigated  the  influence  of 
individual  amino  acids  (alanine,  glycocoll)  of  asparagine  and  of  lactic 
acid  on  the  elimination  of  sugar  in  dogs  whose  pancreas  had  been  removed. 
They  found  that  an  increase  resulted.  It  is  possible  that  the  sugar  was 
formed,  in  this  case,  from  the  above  compounds,  and  that  this  kind  of 
experiment  is  more  suitable  for  establishing  the  formation  of  sugar  than 
the  method  of  studying  the  glycogen  formation.  It  is  certain  that  sugar 
will  be  formed  from  albumin  or  its  amino  acids  only  in  proportion  as  sugar 
is  needed  by  the  organism.  Further  experiments  will  be  necessary  to  deter- 
mine whether  the  administered  amino  acids  have  acted  in  a  direct  or 
indirect  manner. 

The  experiments  with  the  amino  acids  themselves,  therefore,  are  not 
as  yet  such  as  lead  to  definite  conclusions.  We  are  thus  brought  back  to 
our  former  question:  Is  sugar  produced  from  albumin  itself?  Claude 
Bernard  made  experiments  on  the  formation  of  glycogen  after  feeding 
albumin.  He  showed  that  a  dog,  which  had  been  fed  for  months  only  on 
meat,  contained  large  amounts  of  glycogen  in  its  liver.  He  also  raised 
fly-maggots  upon  boiled  egg-albumin  or  extracted  meat,  and  found  large 
amounts  of  glycogen.3  E.  Kiilz  4  repeated  these  last  experiments.  He 
divided  72  fresh  eggs  of  Musca  vomitoria  into  two  equal  groups,  and 

1  L.  Schwarz:  Arch.  klin.  Med.  76  (1903). 

2  G.  Embden  and  H.  Salomon:  Hofmeister's  Beitr.  6,  63  (1904);  ibid.  6,  507  (1904). 

3  C.  Bernard:  Lecons  sur  le  Diabete,  p.  464  (1877). 

4  E.  Kiilz:  Pfliiger's  Arch.  24,  71  (1881). 


320  LECTURE  XIV. 

immediately  determined  the  amount  of  glycogen  in  one  of  these,  while 
the  remainder  were  cultivated  upon  the  albumin  from  hens'  eggs.  He 
could  not  observe  any  formation  of  glycogen  in  this  case,  although  positive 
results  were  obtained  when  the  maggots  were  nourished  with  meat.  These 
experiments  do  not  furnish  a  direct  proof  that  sugar  is  formed  from  albu- 
min. We  know  now  that  neither  the  albumin  from  hens'  eggs  nor  from 
meat  is  free  from  sugar.  It  is  possible  that  the  glycogen  produced  by  the 
maggots  results  from  the  sugar  in  the  food.  Numerous  feeding  experi- 
ments with  animals  fed  exclusively  on  albumin  in  the  form  of  meat,  etc., 
have,  without  exception,  led  to  the  conclusion  that  glycogen  is  produced 
from  albumin.1  It  would  take  too  long  to  dwell  upon  all  of  these  experi- 
ments. Many  of  them  can  be  thrown  out  because  there  was  sufficient  car- 
bohydrate present  in  the  food  to  account  for  the  glycogen  found.  On 
the  other  hand,  in  many  cases  it  was  not  shown  that  the  animals  under- 
going experiment  contained  no  glycogen  at  the  beginning  of  the  test. 
Finally,  we  must  add  that  improvements  in  the  methods  of  estimating 
glycogen  have  shown  the  unreliability  of  values  formerly  obtained.  Thus, 
8.5  grams  of  glycogen  was  assumed  as  an  average  content  per  kilogram 
weight  of  a  dog.  Pfliiger  increased  this  value  to  11  grams,  while  to-day 
we  regard  41  grams  as  more  nearly  correct. 

It  will  be  sufficient  if  we  compare  the  two  series  of  experiments  of 
E.  Pfluger  and  H.  Liithje,2  which  are  free  from  criticism.  We  have  already 
given  Pfl tiger's  figures,  and  will  add  merely  that  he  in  one  experiment, 
for  example,  found  the  following  balance: 

Total  sugar  formed 3097 . 1  grams 

Explainable  as  residual  glycogen 422 . 3  grams 

Sugar  formed  from  other  sources 2674. 8  grams 

This  result  corresponds  with  that  of  Liithje,  and  proves  positively  that 
sugar  must  have  been  formed  from  some  other  source  than  carbohydrates. 
Liithje  also  fed  casein  to  a  dog  whose  pancreas  had  been  removed.  The 
animal  weighed  5.8  kilograms.  It  eliminated  1176.7  grams  of  sugar 
between  October  2  and  November  24.  E.  Pfliiger  3  subtracts  650 . 6  grams 
from  this  as  being  due  to  sugar  present  in  the  food  and  from  the  glycogen 
originally  present  in  the  body.  It  must  be  said  that  this  value  subtracted 
by  Pfliiger  is,  if  anything,  too  high  rather  than  too  low.4  Thus,  at  least, 

1  Cf.  E.  Pfliiger:  Glycogen,  loc.  cit.  p.  240,  etc. 

2  H.  Liithje:  loc.  cit.  Deut.  Arch.  klin.  Med.  79,  4999  (1904).     Pfliiger's  Arch.  106, 
160  (1904). 

3  E.  Pfluger:  Pfliiger's  Arch.  106,  168  (1904). 

4  E.  Pfluger  calculates  109  grams  sugar  from  328  grams  of  serum-albumin,  basing 
this  on  the  values  obtained  from  mucin  by  F.  Miiller.     Serum-albumin  and  serum- 
globulin  contain,  at  the  most,  2  per  cent  sugar.     If  we  take  out  7  grams  sugar  as  due 
to  the  serum-albumin,  we  would  undoubtedly  be  placing  the  sugar  value  too  high 
rather  than  too  low.     Liithje  administered  4100  cubic  centimeters  serum.     Since  1000 


THE  MUTUAL  RELATIONS.  321 

526  grams  of  sugar  remain  unaccounted  for.  Liithje  assumes  that  this 
means  that  albumin  forms  sugar.  This  assumption  of  Ltithje  corresponds 
to  the  fact  that  the  elimination  of  nitrogen,  and  likewise  that  of  sugar, 
increases  uniformly  when  the  administration  of  albumin  is  increased. 
The  ratio  of  the  sugar  (dextrose)  eliminated  to  that  of  the  nitrogen  in  the 

urine  is  usually  designated  by  the  symbol  —  . 

This  ratio  is  assumed  to  have  a  constant  value,  namely,  2 . 8.1  E.  Pfliiger 
calls  attention  to  the  fact  that  the  value  is  not  as  constant  as  is  generally 
supposed,  but  that  very  appreciable  deviations  may  arise.  Thus,  in  some 
of  his  experiments,  Pfliiger  found  the  value  to  be  less  than  1,  and  in 
other  cases  it  rose  as  high  as  14.6.  Furthermore,  it  must  be  remembered 
that  every  increase  in  the  amount  of  albumin  administered  results  in  the 
saving  of  a  corresponding  amount  of  fat  and  carbohydrate.  Every  addi- 
tion of  albumin  lessens  the  extent  to  which  carbohydrates  are  oxidized. 
Now  diabetics,  as  well  as  animals  afflicted  with  glucosuria,  have  not  lost  all 
of  their  ability  to  consume  sugar.  Some  work  is  performed  in  both  cases 
at  the  expense  of  energy  present  in  sugar.  If  now  albumin  be  fed  in  large 
amounts,  this  can  be  burned  up  in  place  of  the  carbohydrates  formerly 
required.  The  result  of  this  will  be  that  more  unconsumed  sugar  circu- 
lates in  the  blood,  and  is,  therefore,  eliminated.  This  also  would  account 
for  the  parallel  elimination  of  sugar  and  of  nitrogen.2 

If  we  consider  all  that  we  know  with  regard  to  the  formation  of  sugar 
from  substances  other  than  carbohydrates,  we  arrive  at  the  conclusion  that 
it  is  at  present  impossible  to  decide  whether  fats  or  proteins  must  be  drawn 
upon  as  a  further  source  of  supply.  We  know  merely  that  sugar  can  be 
produced  from  one  of  these  two  classes  of  compounds.  From  a  chemical 
standpoint,  the  transformation  of  fatty  acids  into  sugar  is  just  as  com- 
plicated as  is  that  from  the  amino  acids;  yes,  we  may  say,  that  the  con- 
version of  the  oxyamino  acids  into  carbohydrates  is  easier  to  understand, 
because  glucosamine  may  be  regarded  as  a  compound  intermediate  between 
the  two  latter  groups.  On  the  other  hand,  we  must  not  forget  that  a  very 
large  part  of  the  albumin  molecule  is  composed  of  simple  amino  acids. 

The  question  as  to  whether  sugar  is  produced  from  fats  or  from  albumins 
is  probably  an  unnecessary  one.  We  can  see  no  particular  reason  why 
both  should  not  be  utilized  in  this  way,  according  to  the  conditions.  Such 
an  assumption  would  explain  the  observed  irregularities,  and  enable  us  to 

understand  why  the  quotient  —  should  at  one  time  be  less  than  1,  and 


grams  serum  would  not  have  over  1.5  grams  sugar  in  a  free  form,  4100  cubic  centi- 
meters must  contain  less  than  6.15  grams. 

1  O.  Minkowski:  Arch.  exp.  Path.  Pharm.  31,  85  and  97  (1892). 

2  E.  Pfliiger:  Glycogen,  loc.  cit.  p.  325.     Cf.  also  Lecture  I,  pp.  6  and  7. 


322  LECTURE  XIV. 

again  more  than  2.8.  There  is  apparently  no  reason  why  we  should 
say  that  either  the  fats  or  albumins  do  not  produce  sugar;  and  when  we 
find  one  author  regards  fats,  and  another  albumin,  as  the  sole  producer 
of  sugar  other  than  carbohydrates,  it  only  means  that  there  is  no  direct 
proof  of  a  formation  of  sugar  from  either  one  of  these  substances,  but 
there  is  merely  an  indirect  proof  of  their  influence.  Too  much  depends 
upon  the  interpretation  of  the  results.  Whether  sugar  is  formed  normally 
from  fat  or  albumin  has  not  been  proved  by  any  of  the  experiments.  It 
is  possible  that  the  organism  of  the  diabetic  and  that  of  the  dog  suffering 
from  glucosuria,  may  behave  in  entirely  different  ways. 

We  must  consider  the  possibility  that  the  glucosuria  produced  by 
different  causes  may  have  different  effects.  We  do  not  know  the  organs 
in  which  the  transformation  of  albumin  or  fat  into  sugar  takes  place. 
This  does  not  preclude  the  possibility  that  the  process  is  carried  on  for 
both  substances  in  the  same  place,  nor  that  the  transformation  of  one 
material  is  more  affected  than  another  in  any  given  case  of  glucosuria. 
An  observation  of  G.  Rosenfeld  1  may  have  a  bearing  on  this  subject.  He 
caused  a  dog  weighing  between  3  and  5  kilograms  to  fast  for  five  days, 
and  then  on  the  sixth  and  seventh  days  injected  2  or  3  grams  of  phloridzin. 
Carbohydrates  were  fed  to  the  dog  at  the  same  time.  The  dog  was  killed 
on  the  eighth  day.  The  liver  showed  no  indication  of  fat  infiltration.  If, 
on  the  other  hand,  there  is  no  carbohydrate  in  the  food,  but  fat,  or  nothing 
at  all,  is  fed,  a  decidedly  fatty  liver  is  obtained.  While  the  amount  of  fat 
in  the  liver  of  a  fasting  dog  is  about  10  per  cent  of  the  dry  substance,  the 
livers  of  animals  used  for  the  last  experiment  have  shown  from  25  to  75 
per  cent  of  fat.  The  glycogen  had  shrunk  to  small  proportions.  The 
fatty  liver  disappeared  two  days  after  the  injection  of  the  phloridzin. 
In  these  cases,  as  was  shown  by  microscopic  examination,  the  fat 
was  not  deposited  in  the  connective  tissues,  but  directly  in  the  liver 
cells.  Here  it  is  a  transference  of  fat  from  other  organs  of  the  body,  as 
was  shown  by  Rosenfeld,  and  not  a  transformation  of  glucose  or  albumin 
into  fat. 

It  is  possible  that  this  phenomenon  has  some  connection  with  the  con- 
version of  fat  into  sugar,  although  it  need  not  apply  to  glucosuria  due  to 
other  causes.  No  fatty  liver  results,  for  example,  in  glucosuria  caused  by 
extirpation  of  the  pancreas.  It,  therefore,  appears,  a  priori,  wrong,  to  place 
the  various  forms  of  glucosuria  and  diabetes  upon  the  same  basis,  simply 
from  the  fact  that  they  have  in  common  the  predominating  symptom  of 
glucohemia  and  the  resulting  glucosuria.  The  widely  different  causes  of 
the  different  kinds  of  glucohemia  cannot  be  sufficiently  emphasized.  It  is 
possible  that  a  study  of  an  individual  case  in  different  directions,  rather 


G.  Rosenfeld:  Verb.  Kong,  innere  Med.  359  (1893). 


THE  MUTUAL  RELATIONS.  323 

than  following  solely  the  elimination  of  sugar,  would  more  likely  lead  to 
a  solution  of  the  problem.1 

In  this  connection,  the  question  arises  whether  all  carbohydrates  are 
able  to  form  glycogen.  We  have  already  seen  that  glucose  and  fruc- 
tose are  glycogen-formers.  We  also  know  that  milk-sugar  and  cane- 
sugar,2  on  being  introduced  into  the  blood,  are  eliminated  unchanged  in 
the  urine.  Cane-sugar  is  normally  disintegrated  in  the  intestine.  The 
usefulness  of  milk-sugar  is  evidently  dependent  on  the  presence  of  lactase, 
as  E.  Weinland  3  has  shown.  Glycogen  does  not  seem  to  be  formed  from 
pentoses.4  There  is  a  large  amount  of  uncertainty  concerning  these  ex- 
periments on  account  of  the  fact  that  a  compound  which  causes  an  accu- 
mulation of  glycogen,  need  not  necessarily  itself  participate  in  its  pro- 
duction. The  combustion  of  the  substance  may  indirectly  shield,  for 
example,  glucose  from  oxidation,  thus  causing  deposition  of  glycogen. 
Although  this  objection  may  seem  uncalled  for,  there  is  much  in  its- 
favor.  Perhaps  only  those  sugars  are  glycogen-formers  which  are  capable 
of  going  over  into  glucose;  for  grape-sugar  is,  probably,  the  only  building 
material  of  glycogen.  All  of  those  compounds  which  can  be  changed 
into  it,  must  be  looked  upon  as  producers  of  glycogen. 

We  now  reach  the  problem  as  to  the  relations  of  albumins  to  fats.  Is 
albumin  converted  into  fat?  There  is,  a  priori,  no  reason  why  such  a 
change  should  be  impossible.  We  know  that  the  nitrogen  in  urea  only 
carries  with  it  a  part  of  the  carbon  present  in  the  albumin,  while  the  larger 
part  of  the  carbon  in  albumin  is  transformed  in  the  body  in  some  other 
way.  It  is  conceivable  that  these  other  carbon  chains  may  be  deposited 
in  the  form  of  fat  under  certain  conditions,  in  which  case  a  direct  fat 
accumulation  might  result  from  a  diet  of  albumin.  The  assumption  of 
the  formation  of  fats  from  albumin  would  be  of  considerable  value  with 
reference  to  the  production  of  sugar  from  albumin  or  fat,  for  those  inter- 
mediate compounds  which  lead  to  the  synthesis  of  fat  from  albumin  may 
also  be  closely  related  to  the  formation  of  sugar.  We  should,  as  a  rule,  be 
rather  cautious  in  assuming  such  complicated  changes,  especially  in  view 
of  the  rapid  progress  of  albumin  metabolism.  On  the  other  hand,  the  old 
ban,  which  was  so  long  placed  on  the  animal  cell  as  not  being  in  any  man- 
ner capable  of  effecting  a  synthesis,  will  gradually  have  to  be  withdrawn. 
It  is  desirable,  therefore,  to  establish  more  proof  from  other  points  of  view. 


1  One  might  expect  the  problem  to  be  solved  by  following  the  respiratory  exchange. 
Unfortunately  there  are  no  convincing  investigations  at  hand.     Cf.  E.  Pfliiger:  Pfliiger's 
Arch.  108,  473  (1905);  Magnus  Levy:  Z.  klin.  Med.  56,  83  (1905). 

2  F.  Voit:  Deut.  Arch.  klin.  Med.  58,  523  (1897). 

3  E.  Weinland:  Z.  Biol.  38,  16  and  606  (1899);  40,  386  (1900).     Cf.  also  R.  H.  A. 
Plirnmer:  J.  Physiol.  34,  93  (1906). 

4  E.  Salkowski:  Z.  med.  Wiss.  11  (1893).     Z.  physiol.  Chem.  32,  393  (1901). 


324  LECTURE  XIV. 

The  conversion  of  albumin  into  fat  was  for  a  long  time  looked  upon  as 
an  established  fact,  albumin  being  even  considered  as  the  main  source  of 
the  body  fat.  This  conception  originated  with  Voit  and  Pettenkofer,1 
as  an  outcome  of  their  experiments  on  metabolism.  Since  the  time  when 
E.  Pfliiger  2  critically  examined  the  values  given  by  the  above  authors, 
the  belief  in  the  production  of  fat  from  albumin  has  been  more  and  more 
doubted,  this  being  especially  true  since  many  observations,  undertaken 
in  order  to  show  such  effects,  have  indicated  that  the  above  conclusions 
were  erroneous.  Pettenkofer  and  Voit  fed  dogs  with  meat  as  free  as 
possible  from  fat.  They  found  all  of  the  nitrogen  of  the  ingested  albumin 
present  in  the  excretions,  but  only  a  part  of  the  carbon.  It  was  natural 
to  conclude  from  this,  as  we  have  already  indicated,  that  the  portion  of 
carbon  which  did  not  leave  the  organism  in  combination  with  the  nitro- 
gen, was  utilized  for  the  production  of  fat.  Pettenkofer  and  Voit  reached 
this  conclusion  owing  to  the  fact  that  the}'  had  assumed  1  :  3 . 68  to  be  the 
relation  of  nitrogen  to  carbon  in  meat  free  from  fat.  Pfliiger,  after  allow- 
ing for  glycogen,  reduces  this  value  to  3 . 22,  while  Rubner  places  it  at  3 . 28. 
If  we  apply  these  changed  values  to  the  results  of  Pettenkofer  and  Voit, 
we  find  that  the  assumption  that  fat  is  produced  from  albumin  no  longer 
has  any  support. 

M.  Kumagawa 3  has  recently  tried  to  solve  the  problem  in  the  following 
manner.  He  caused  two  dogs  from  the  same  litter  to  fast  for  24  days. 
One  of  the  animals  was  then  killed  and  analyzed.  The  second  dog  for 
quite  a  long  period  was  fed  a  liberal  supply  of  horse  meat  (49  kilograms 
in  49  days).  The  body  weight  rose  from  6.08  to  10  kilograms.  The 
fat  content  of  this  animal  at  the  beginning  of  the  experiment  must 
have  been  about  120  grams.  The  other  dog  contained  this  amount. 
The  animal  under  experiment  showed  1087 . 7  grams  of  fat  on  being  killed. 
The  meat  fed  to  this  dog,  however,  contained  356  grams  of  glycogen  and 
1084  grams  of  fat.  The  amount  of  fat  in  the  food,  therefore,  would  of 
itself  have  been  sufficient  to  cause  this  increase. 

Although  we  must  admit  that  no  satisfactory  proof  has  been  obtained 
by  experiments  on  metabolism  as  regards  the  transformation  of  albumin 
into  fat,  we  must  not  forget,  on  the  other  hand,  that  these  results  merely 
give  us  a  rough  idea  of  the  whole  interchange  of  material,  but  never  the 
finer  details  of  cell  activity.  It  is  still  a  very  remarkable  fact  that  such  a 
small  portion  of  the  carbon  in  albumin  should  leave  the  organism  in  com- 

1  M.  Pettenkofer  and  C.  Voit:  Ann.  Supp.  57,  361  (1862).     C.  Voit:  Z.  Biol.  5,  106 
(1869);    6,    371    (1870);    7,    433    (1871).      Handbuch    der    Physiologic   des   Gesamt- 
stoffwechsels  und  der  Fortpflanzung,  Leipsic,  1881.      Ueber  die  Ursachen  der  Fett- 
ablagerung  im  Tierkorper,  Munich,  1883. 

2  E.  Pfliiger:  Pfliiger's  Arch.  50,98  (330  and  396)  (1891);  51,229  (1892);    52,   1 
(1892);   68,  176  (1897);   77,  521  (1899). 

3  M.  Kumagawa:  Communication  from  the  University  of  Tokio  (1890). 


THE  MUTUAL  RELATIONS.  325 

bination  with  the  relatively  large  amount  of  nitrogen.     This  must  certainly 
possess  some  deep  significance.     Let  us  consider  leucine: 


.  CH2  .  CH  .  (NH2)COOH, 
CHs 

and  urea: 


c=o 

XNH2 

The  nitrogen  united  to  C  =  O  in  the  latter  compound,  is  derived  from 
two  molecules  of  monoamino  acid.  What  becomes  of  all  of  the  rest  of 
the  carbon  chain?  We  know  nothing  about  this  nitrogen-free  residue  of 
the  amino  acids.  It  is  possible  that  it  is  immediately  consumed.  This 
has  never  been  satisfactorily  proved.  On  the  other  hand,  we  can  under- 
stand the  fact  that  nitrogen  leaves  the  organism  in  the  form  of  urea,  from 
the  standpoint  that  the  organism  has  utilized  the  energy  of  the  albumin 
to  the  fullest  possible  extent.  An  elimination  of  carbon  chains  containing 
nitrogen  would  indicate  an  incomplete  combustion  of  available  material. 
The  fact  that  the  disintegration  of  the  albumin  in  this  manner  is  a  very 
economical  one,  —  a  loss  of  energy  always  occurs  in  the  urea  itself,  —  does  not 
permit  us  to  form  any  opinion  regarding  the  utilization  of  the  remainder 
of  the  carbon.  We  call  attention  to  these  relations,  because  the  whole 
question  of  the  relation  of  albumins  to  fats  and  carbohydrates  is  dependent 
upon  this,  and  we  wish  to  emphasize  the  point  that  the  assumption  of  the 
albumin  being  rapidly  consumed  in  toto,  is  not  sufficiently  supported  by 
the  facts. 

Let  us  consider  those  investigations  and  observations  which  are  held 
to  prove  that  fat  may  be  produced  from  albumin.  We  must  state,  at  the 
start,  that  a  large  number  of  such  investigations  are  worthless,  owing  to 
the  fact  that  the  methods  employed  for  estimating  the  fat  do  not  give 
any  idea  as  to  the  actual  fat  content  of  any  individual  organ.  The  fat 
in  the  organs  is  evidently  present  in  different  forms.  A  part  of  this  may 
easily  be  extracted  by  ether.  If  we  examine  a  piece  of  tissue  which  has 
been  freed  of  fat  in  this  manner,  we  obtain  the  impression  that  all  of  the 
fat  has  been  removed.  This  is,  however,  not  the  case;  for  if  we  digest  the 
residue  with  pepsin-hydrochloric  acid,  or  boil  it  with  2  per  cent  hydro- 
chloric acid,  we  can  extract  some  more  fat  with  ether.  Instead  of  using 
ether  for  extraction  purposes,  it  has  been  recommended  to  employ  alcohol 
and  chloroform  alternately.1  The  fact  that  the  fat  is  not  entirely  extracted 


1  C.  Dormeyer:  Pfliiger's  Arch.  65,90  (1897).  J.  Nerking:  ibid.  73,  172  (1898); 
85,  330  (1901).  O.  Frank:  Z.  Biol.  35,  549  (1897).  E.  Voit:  ibid.  35,  555  (1898). 
E.  Bogdanow:  Pfliiger's  Arch.  86,  389  (1897).  G.  Rosenfeld:  Z.  in.  Med.  33  (1900). 


326  LECTURE  XIV. 

by  the  ether,  is  partly  because  some  of  the  fat  is  inclosed  in  the  cells, 
while  another  portion  is  undoubtedly  present  in  combination  with  other 
substances.  In  many  of  the  investigations  dealing  with  this  problem, 
this  latter  fact  has  not  been  sufficiently  taken  into  consideration  in  the 
estimation  of  the  total  fat  present. 

The  old  observation  of  the  formation  of  grave-wax,  or  adipocere,  has 
been  brought  forward  as  evidence  of  the  production  of  fats  from  albumin.1 
By  this  process  we  understand  the  production  of  a  wax-like  mass  from  a 
corpse.  The  albumin  disappears  little  by  little  from  the  muscles,  and  fat 
takes  its  place.  This  characteristic  change  is  especially  noticeable  in  moist 
burying-places,  where  a  slow  decomposition  proceeds  in  the  presence  of  a 
minimum  supply  of  oxygen.  By  carefully  following  this  process,  and 
especially  by  direct  experiments,  it  has  been  proved  that  there  is  no  such 
conversion  of  albumin  into  fat,  but  that  the  fat  already  present  in  the 
body  is  responsible  for  the  production  of  adipocere.  This  is  mainly  due 
to  the  fat  present  already  in  a  given  locality,  and  to  such  infiltrated  fatty 
masses  as  may  be  deposited  there  by  the  water.  Moreover,  if  it  had  been 
proved  that  the  fat  arose  from  albumin  in  this  process,  it  would  possess 
no  bearing  on  the  production  of  fat  from  albumin  in  the  living  animal 
organism.  It  would  be  conceivable  that  lower  organisms,  such  as  bacteria, 
etc.,  are  capable  of  effecting  such  conversions.  The  formation  of  fat  from 
albumin  during  the  ripening  of  cheese,  for  example,  is  attributed  to  the 
interaction  of  fungi.2 

Hoffmann,3  however,  has  carried  out  a  notable  investigation,  which  is 
considered  a  proof  of  the  transformation  of  albumin  into  fat.  He  collected 
the  eggs  of  flies,  and  determined  the  amount 'of  fat  present  in  a  number  of 
them,  while  the  others  were  cultivated  upon  defebrinated  blood.  This 
contained  0 . 032  per  cent  of  fat,  and  the  fly-eggs  4 . 9  per  cent.  The  maggots 
cultivated  upon  the  blood  finally  showed  at  least  10  times  as  much  fat  as 
was  present  in  the  eggs  and  blood.  Two  objections  can  be  raised,  for,  in 
the  first  place,  the  method  used  for  estimating  the  fat  is  not  entirely 
above  criticism,  while,  in  the  second  place,  this  conversion  of  albumin  into 
fat  may  have  been  brought  about  by  means  of  bacteria,  which  developed 
rapidly  in  the  blood.  O.  Frank,4  who  repeated  the  experiment,  using  meat, 


1  Cf.   J.   Kratter:    Z.  Biol.    16,  455    (1880).      Erman:    Vierteljahresschrift  gericht 
Med.  37,  51  (1882).     E.  Salkowski:  Festschrift  fur  Virchow's  Jubilaum,  p.  23  (1891). 
K.  B.  Lehmann:    Sitzber.  physikal.  med.  Gesel.  Wurzburg  (1888).     E.  Voit:    Sitzber. 
Gesel.    Morph.   und  Physiol.   Miinchen,  4,  50   (1888).     F.   Kraus:    Arch.  exp.   Path. 
Pharmak.  22,  174  (1887). 

2  K.   Windisch:     Arbeiten    aus  dem    Kaiserl.    Gesundheitsamte,    17    (1900).     H. 
Jacobsthal:  Pfliiger's  Arch.  54,  584  (1893). 

3  F.  Hofmann:  Z.  Biol.  8,  153  (1872). 

4  O.  Frank:  loc.  cit.  Z.  Biol.  35,  549  (1897). 


THE  MUTUAL  RELATIONS.  327 

which  had  been  freed  as  much  as  possible  from  fat,  could  not  obtain  any 
definite  results.  The  fat  formed  may  very  easily  have  been  derived  from 
the  fat  of  the  meat.  These  experiments  also  are  not  suitable  to  establish 
the  fact  that  fat  is  produced  from  albumin. 

Finally,  it  may  be  mentioned  that  the  fat  contents  of  the  secretions, 
those  of  the  lacteal  and  sebaceous  glands,  have  repeatedly  been  referred 
to  albumin  as  their  source.  Direct  experiments  do  not  confirm  this 
assumption.  It  is  also  difficult  to  decide  this  question,  owing  to  the  fact 
that  the  animal  organism  has  stores  of  fat  at  its  disposal,  and  is  not  depend- 
ent on  the  fat  in  the  food.  Moreover,  the  conversion  of  carbohydrates 
into  fat  must  be  taken  into  consideration. 

Now  we  happen  to  know  of  a  number  of  processes  in  which  organs, 
containing,  as  far  as  the  eye  can  see,  hardly  any  fat  at  all,  are  suddenly 
permeated  with  it.  This  is  especially  noticeable  in  the  case  of  the  liver. 
We  have  already  met  with  an  infiltration  of  fat  in  this  organ.  We  have 
seen,  that,  as  the  glycogen  disappears  after  glucosuria  has  been  brought 
about  by  phloridzin,  fat  will  take  its  place,  provided,  of  course,  that  no 
carbohydrates  are  present  in  the  food.  We  have  here  a  physiological 
infiltration  of  fat.  It  is  especially  noteworthy  owing  to  the  fact  that  it 
disappears  again  on  discontinuing  the  poisoning  by  phloridzin.  Normal 
liver  cells,  capable  of  performing  their  functions,  will  remain. 

We  know  of  a  large  number  of  poisons,  such  as  phosphorus,  arsenic, 
antimony,  chloroform,  alcohol,  English  oil  of  pennyroyal,  etc.,  all  of 
which  are  capable  of  causing  a  local  accumulation  of  fat.  Finally,  pathol- 
ogists  are  well  acquainted  with  the  appearance  of  a  "  fatty  degeneration," 
which  follows  various  disease  processes  (influence  of  toxins,  etc.).  We  can 
very  easily  imagine  that  the  appearance  of  acute  accumulations  of  fat  in 
places  where  we  would  hardly  expect  to  find  any,  would  lead  to  the  con- 
clusion that  some  substance  had  been  changed  into  fat  at  that  place.  As 
the  body  cells  are  generally  composed  of  albumin,  it  seemed  to  prove  that  a 
transformation  of  albumin  into  fat  had  taken  place.  This  conception  re- 
mained for  a  long  time  undisputed,  until  it  was  shown  both  macroscopically 
and  microscopically,  that  this  fat  could  have  no  connection  with  the  true 
fat  content  of  an  organ.  A  tissue  apparently  free  from  fat  may  yet  contain 
as  much  as  20  per  cent,  and  an  organ  seemingly  laden  with  fat  may 
actually  possess  less  than  an  apparently  fat-free  tissue.  It  was  necessary 
first  to  trace  the  formation  of  fat  by  exact  quantitative  methods.  A 
great  advance  was  also  made  in  the  discovery  that  it  was  not  sufficient 
to  determine  the  fat  content  of  any  specific  organ,  but  that  the  amount 
of  fat  in  the  entire  animal  must  be  taken  into  consideration.  We  can  pass 
over  the  earlier  experiments  in  this  direction,  which  were  characterized 
by  questionable  methods  for  estimating  the  fat,  and  confine  ourselves  to 
the  more  recent  work. 


328  LECTURE  XIV. 

Athanasiu  l  determined  the  fat  content  of  124  frogs.  He  then  poisoned 
a  like  number  of  animals  with  phosphorus,  and  again  estimated  the  amount 
of  fat  in  the  entire  collection.  He  found  no  increase  in  the  total  quantity 
of  fat.  Taylor,2  in  fact,  observed  an  actual  decrease. 

Experiments  with  mice  gave  the  same  results,3  whereas  control  animals, 
which  were  fed  in  the  same  manner,  showed  from  13.8  to  29.3  per  cent; 
those  which  had  been  poisoned  with  phosphorus  gave  only  4.13  to  7.9  per 
cent  of  fat.  The  organism  had,  therefore,  been  deprived  of  fat.  The 
livers  of  those  mice  which  had  been  poisoned  with  phosphorus  showed 
from  7.4  to  37.4  per  cent,  while  this  organ  in  normal  mice  gave  only  5.1 
to  11.8  per  cent  of  fat.  All  of  the  other  tissues  had  lost  fat  while  the  liver 
had  gained.  From  this  it  is  easy  to  assume  that  the  increased  fat  content 
of  the  liver  must  stand  in  direct  relation  to  the  diminution  in  the  fat  supply 
of  the  remaining  tissues.  Rosenfeld  4  has  proved  this  to  be  so  by  direct 
experiment.  He  observed  fat,  from  a  deposit  in  a  dog  which  had  been  fed 
with  mutton  tallow,  to  migrate  directly  into  the  liver,  and  the  composition 
of  this  fat  was  that  of  the  fat  deposited  in  the  dog's  own  tissues.  He  also 
showed  that  fasting  dogs  and  hens  after  being  poisoned  with  phosphorus 
gave  no  indication  of  any  increase  of  body  fat.  Their  fat  deposits  had 
already  been  drained.  Thus,  the  old  idea  that  albumin  is  converted  into 
fat  after  poisoning  with  phosphorus  must  be  discarded. 

We  have  already  called  attention  to  the  fact  that  the  cleavage-products 
of  albumin,  such  as  tyrosine,  leucine,  glycocoll,  etc.,  appear  in  the  urine 
after  phosphorus  poisoning.  This  circumstance  seems  to  support  the  old 
idea  that  albumin  goes  over  into  fat.  In  fact,  a  superficial  observation 
could  easily  lead  to  that  conclusion.  Albumin  is  decomposed,  while  fat 
appears  in  its  place.  The  decomposition  of  the  albumin,  however,  may 
take  place  entirely  independently  of  the  fat  infiltration.  It  is  clear,  on  the 
one  hand,  that  the  great  derangement  in  metabolism  caused  by  phos- 
phorus poisoning  also  affects  the  disintegration  of  the  albumins,  and 
causes  destruction  of  albumin;  while  the  observed  amounts  of  amino 
acids,  on  the  other  hand,  have  no  relation  to  the  amount  of  fat  present. 
Athanasiu  could  not  observe  any  increased  disintegration  of  albumin, 
although  a  noticeable  infiltration  of  fat  had  taken  place  in  the  liver.  The 
fattening  of  other  organs,  the  muscles,  heart,  etc.,  can  be  explained 
in  the  same  manner,  while  the  infiltrations  of  fat  due  to  other  harm- 
ful influences  in  no  case  point  to  a  formation  of  fat  from  albumin.  In 


1  J.  Athanasiu.  Pfliiger's  Arch.  74,  511  (1899). 

2  Taylor:  J.  exp.  Med.  4,  399  (1899). 

3  F.  Kraus  and  A.  Sommer:  Hofmeister's  Beitr.  2,  86  (1902). 

4  G.  Rosenfeld:    Verhandl.  Kong.  in.  Med.   (1894).      Allgem.  med.  Zent.  No.  60 
(1897);  No.  89    (1900).     Cf.    Fettbildung,    Part   II.     Ergebnisse  Physiol.  (Asher   and 
Spiro),  Bcrgmann,  Wiesbaden  2  (1903),  p.  50  et  seq. 


THE  MUTUAL  RELATIONS.  329 

every   case   there   is   enough   fat   already   present   to   explain   these   fat 
accumulations. 

Considering  all  the  results  of  physiological  and  pathological  experiments 
with  regard  to  the  formation  of  fat  from  albumin,  we  must  admit  that 
up  to  the  present  time  no  proof  has  been  found  which  compels  us  to 
assume  a  transformation  of  albumin  into  fat.  We  must  not  neglect  to 
remark  that,  although  the  fat  present  in  the  body  is  sufficient  to  explain 
the  accumulations  of  fat,  still,  this  fact  does  not  preclude  the  possibility 
of  its  production  from  some  other  substance.  We  arrive  at  the  above 
indirect  conclusion  as  it  seems  most  probable  to  us.  We  would,  however, 
be  making  a  grave  error  were  we  to  consider  the  problem  of  the  produc- 
tion of  fat  from  albumin  as  finally  solved.  Our  comments  only  go  to 
show  that  the  experiments  and  methods  so  far  utilized  are  insufficient 
to  confirm  such  transformation.  New  questions  and  new  points  of  view 
are  necessary  for  this  problem. 

We  have  now  reached  the  end  of  our  observations  concerning  the  con- 
version of  one  substance  into  another.  In  the  animal  organism  we  are 
absolutely  certain  only  of  the  production  of  fat  from  the  carbohydrates. 
The  reverse  process,  as  well  -as  that  of  the  production  of  sugar  from  albu- 
min, has  not  yet  been  sufficiently  demonstrated  to  warrant  any  definite 
decision.  At  any  rate,  it  will  be  necessary  to  look  for  some  other  source 
than  the  carbohydrates  for  an  explanation  of  the  elimination  of  sugar 
during  severe  cases  of  glucohemia.  We  have  developed  the  assumption 
that  both  fat  and  albumin  must  be  taken  into  consideration,  and  that  the 
great  differences  of  causes  of  glucohemia  may  correspond  to  different 
origins  of  sugar.  Finally,  we  have  seen  that  there  is  no  absolute  proof 
that  the  formation  of  fat  is  at  all  related  to  the  presence  of  albumin. 

We  have  intentionally  avoided  giving  any  definite  opinion  on  these 
important  questions,  preferring  to  take  the  opposite  stand  corresponding 
to  uncertainty  of  the  facts  in  hand.  Nothing  can  hurt  the  progress  of 
knowledge  more  than  the  desire  to  reach  conclusions  on  such  complicated 
questions  from  purely  theoretical  considerations.  We  are  greatly  indebted 
to  E.  Pfliiger,  whose  critical  observations  have  been  followed  in  every 
case  where  it  seemed  as  if  the  question  had  been  positively  answered.  He 
has  considered  all  the  previous  experiments,  and  has  to  a  certain  extent 
repeated  them. 

The  relations  are  evidently  entirely  different  in  the  plant.  It  must 
manufacture  its  carbohydrate,  fat  and  albumin,  all  from  the  same  raw 
materials.  It  easily  converts  carbohydrates  into  fats,  and  fats  into 
carbohydrates.  It  also  undoubtedly  synthesizes  its  albumin  from  sugar 
and  its  derivatives.  The  future  can  alone  decide  whether  there  is  any 
marked  fundamental  difference  between  the  activities  of  the  plant  and 
animal  cells,  or  whether  any  difference  between  them  may  be  only  quan- 


330  LECTURE  XIV. 

titative  rather  than  qualitative.  At  any  rate,  the  fact  that  the  animal 
cells  convert  carbohydrates  into  fat  indicates  that  they  possess  the  same 
functions  as  do  the  plant  cells.  The  transformation,  whether  it  be  from 
fat  or  from  albumin  into  carbohydrate,  is  a  very  complicated  process,  and 
it  is  safe  to  assume  that  the  animal  cell  is  far  more  efficient  than  we  have 
hitherto  imagined.  We  shall  have  to  take  such  relations  more  into 
account  and  synthetic  processes  will  receive  more  attention  in  the  future. 
It  is  only  by  reason  of  far-reaching  changes,  through  disintegrations  and 
reconstruction,  that  we  are  able  to  understand  why  every  species  of  animal, 
in  fact,  every  individual,  should  possess  a  specific  composition  in  spite  of 
the  fact  that  each  may  have  had  the  same  food.1  This  alone  is  sufficient 
to  warrant  us  in  assuming  complicated  synthetic  processes  as  taking  place 
in  the  animal  cell. 


Cf.  Lecture  XXIX. 


LECTURE  XV. 

MUTUAL   RELATION   BETWEEN   FATS,  CARBOHYDRATES, 
AND    ALBUMINS. 

II. 
THE  LAW  OF  ISODYNAMICS. 

So  far  we  have  considered  only  the  most  important  organic  nutrients 
from  one  point  of  view,  namely,  their  chemical  composition,  and  sought 
out  those  facts  which  led  to  the  assumption  that  one  class  of  substances 
goes  over  into  another  in  the  animal  organism.  In  such  cases  extensive 
chemical  changes  take  place  —  reduction,  oxidation,  analysis,  and  synthe- 
sis —  before  one  substance  can  replace  another.  This,  however,  is  not 
the  only  way  in  which  one  substance  may  appear  in  place  of  another. 
The  substitution  may  be  a  purely  physical  one;  i.e.,  the  energy  imparted 
to  the  body  by  the  substances  in  question  may  be  the  most  important 
factor.  In  other  words,  we  can  conceive  that  the  different  organs,  e.g., 
the  muscles,  do  not  work  with  one  single  food  material  alone  in  perform- 
ing their  prescribed  functions,  but  with  representatives  of  all  three  groups 
of  nutrients.  We  could  indeed  imagine,  as  we  have  already  mentioned,1 
that  every  individual  cell  in  the  body  is  so  adjusted  that  it  works  only  with 
a  definite  material.  We  would  then  have  to  assume  that  the  substitution 
of  one  of  these  combustible  substances  by  another  must  be  preceded  by  a 
transformation  into  the  former.  When  we  recall  the  facility  with  which 
the  vegetable  organism  converts  carbohydrates  into  fats,  and  fats  or 
albumin,  or  both  together  into  sugars,  such  a  conception  would,  a  priori, 
not  seem  so  improbable.  On  the  other  hand,  in  such  a  case  the  organism 
evidently  would  not  work  economically,  if  it  were  called  upon  first  of  all 
to  produce  deep-seated  and  far-reaching  transformations,  before  it  could 
utilize  the  food  materials.  The  entire  metabolism  would  thus  resolve 
itself  into  an  extremely  complicated  process,  and  such  transformations 
would  make  themselves  felt  especially  in  the  case  of  a  restricted  diet  with 
a  definite  kind  of  food,  e.g.,  of  fats,  which  are  deficient  in  oxygen,  or  of 
carbohydrates,  which  are  rich  in  oxygen.  One  might  cite  the  diabetic  as 
proof  of  the  fact  that  an  organ  can  perform  its  work  with  the  most  varied 


1  Cf.  Lecture  XIV,  p.  311. 

331 


332  LECTURE  XV. 

kinds  of  food,  for  the  diabetic  can  perform  muscular  work,  even  though 
he  is  not  able,  in  proportion  to  the  severity  of  the  disease,  to  utilize  to 
advantage  the  most  important  source  of  energy,  the  carbohydrates.  For 
him  the  carbohydrates  scarcely  come  into  consideration  as  a  source  of 
energy.  Evidently  the  diabetic  performs  his  work  at  the  expense  of  other 
food  material.  We  cannot  look  upon  this  proof  as  entirely  convincing, 
for  it  is  precisely  those  observations  dealing  with  diabetics  which  have  led 
to  the  assumption,  that  sugar  is  produced  from  the  two  other  organic 
nutrients:  albumin  and  fat.  Why  does  the  diabetic  patient  produce 
sugar  from  these?  Why  does  he  not  utilize  these  according  to  their 
calorific  value?  Why  does  he  carry  out  the  extremely  complicated 
chemical  changes,  some  of  which  are  so  difficult  to  understand?  Cer- 
tainly not  in  order  to  eliminate  more  sugar.  These  transformations  must 
have  a  deeper  significance.  Is  this  a  normal  process  which  comes  to  light 
because  of  an  insufficient  utilization  of  the  products  formed,  or  are  we  to 
look  upon  the  production  of  sugar  from  fat  and  albumin  as  a  derangement 
of  the  entire  metabolism?  These  are  enigmas,  the  solution  of  which  still 
reaches  into  the  far-distant  future.  At  all  events,  we  repeat  once  again, 
nowhere  else  does  the  question  appear  as  vital  as  here,  as  to  whether 
specific  atomic  groupings  are  not  normally  utilized  for  definite  purposes. 
Nothing  is  of  greater  promise  in  the  entire  field  of  biological  investigation 
than  the  clearing  up  of  just  such  uncertainties  and  contradictions.  Such 
work  must  lead  to  new  problems  and  new  results.  We  have,  on  the  one 
hand,  the  claim  that  large  amounts  of  sugar  arise  from  fats  and  proteins, 
while,  on  the  other  hand,  there  are  numerous  exact  statements  which  make 
it  seem  improbable  that  such  conversions  are,  as  a  rule,  necessary  in  normal 
metabolism  for  the  accomplishment  of  definite  work. 

If  we,  for  the  moment,  leave  out  of  consideration  the  significance  of  the 
organic  nutrients  as  building  material  for  the  worn-out  or  new  cells,  we 
find  that  their  most  important  function  is  that  of  a  source  of  energy. 
Chemical  energy  is  transmitted  to  the  animal  organism  by  means  of 
the  food.  Mechanical  work  is  performed  by  the  transformation  of  this 
energy.  Only  a  part  of  the  energy  is  utilized  in  this  way.  Another  part, 
and  in  fact  a  very  considerable  one,  is  changed  into  heat.  The  animal 
cell  can  utilize  these  sources  of  energy  in  two  ways:  first,  by  cleavage, 
and  second,  by  oxidation.  Only  a  portion  of  the  energy  can  be  trans- 
formed into  kinetic  energy  by  the  former  method;  oxidation  alone 
furnishing  the  possibility  for  a  complete  utilization  of  the  energy.  Now 
the  different  organic  food-stuffs  (carbohydrates,  fats,  and  albumins)  possess 
different  amounts  of  energy;  i.e.,  they  have  different  fuel  values.  The 
amount  of  energy  possessed  by  the  various  food  materials  can  be  deter- 
mined by  the  quantity  of  heat  which  they  liberate  when  undergoing 
combustion.  This  is  generally  expressed  in  calories,  a  small  calorie  (cal.) 


FATS,  CARBOHYDRATES,  AND  ALBUMINS.  333 

being  that  amount  of  heat  required  to  raise  1  gram  of  water  from  0°  to 
1°  C.  A  large  calorie  (Cal.)  is  the  amount  of  heat  necessary  to  raise  1  kilo- 
gram of  water  from  0°  to  1°  C.  We  shall  use  the  large  calorie  in  every 
case  to  express  the  heat  values  of  individual  food  materials. 

Complete  oxidation  of  one  gram  of  each  of  the  following  articles  of  food 
in  a  calorimetric  bomb  gave  the  following  values: 

Calories 

Casein 5.86 

Egg- albumin 5.74 

Conglutin 5.48 

Average  value  for  protein 5.71 

Animal  tissue-fat 9.50 

Butter-fat 9.23 

Cane-sugar 3.96 

Milk-sugar 3.95 

Glucose      3.74 

Starch 4.19 

The  values  given  for  the  carbohydrates  and  fats  represent  exactly  the 
amount  of  heat  which  is  liberated  during  combustion  in  the  animal  organ- 
ism. The  animal  cells  likewise  oxidize  the  carbohydrates  and  fats  to 
carbon  dioxide  and  water.  The  physiological  heat  value  of  the  fats  is 
generally  given  as  9.3  calories,  and  of  the  carbohydrates  4.1  calories 
for  each  gram  of  substance.  The  values  in  the  table  do  not  apply  to  the 
albumins  as  oxidized  in  the  living  organism.  The  animal  cell  does  not 
utilize  completely  the  energy  present  in  albumin.  A  portion  of  this  energy 
goes  to  waste,  usually  in  the  form  of  urea.  We  are  indebted  to  Rubner  l 
for  an  exact  estimation  of  the  physiological  heat  value  of  albumin.  He 
fed  a  dog  exclusively  on  washed  meat,  whose  heat  value  had  been  care- 
fully determined.  From  this  he  subtracted  the  heat  values  of  the  urine 
and  faeces,  as  well  as  that  necessary  for  the  swelling  of  the  albuminous 
material  and  for  dissolving  the  urea.  In  like  manner  Rubner  determined 
the  heat  of  combustion  of  the  decomposed  albumin  in  the  body  of  a  fasting 
rabbit.  He  found  the  following  values  for  the  physiological  heat  of  com- 
bustion for  each  gram  albumin: 

One  gram  of  dry  substance  —  Calories 

Albumin  from  meat 4.4 

Lean  meat 4.0 

Albumin  during  fasting 3.8 

The  physiological  heat  of  combustion  is  not  identical  for  the  different 
proteins.  The  normal  value  for  animal  albumin  is  estimated  as  4.23 

1  Max  Rubner:  Z.  Biol.  21,  250  and  337  (1885).  Berthelot  and  Vielle:  Compt.  rend. 
102,  1284  (1886).  Berthelot  and  Recoura:  ibid.  104,  875,  1571  (1887);  Berthelot  and 
Andre":  110,  884  and  925  (1890).  F.  Stohmann:  Z.  Biol.  31,  364  (1895). 


334  LECTURE  XV. 

calories;  3.99  for  vegetable  albumin;  and  4.1  as  an  average  value  for 
proteins  as  a  class. 

Before  discussing  the  significance  of  these  figures,  we  must  consider 
whether  the  law  of  the  conservation  of  energy  *  applies  entirely  to  the 
animal  organism.  We  have  seen  that  plants,  with  the  assistance  of  the 
kinetic  energy  of  the  sun's  rays,  are  able  to  liberate  oxygen  from  water 
and  carbon  dioxide.  They  use  up  kinetic  energy  and  form  potential 
energy.2  The  reverse  process  takes  place  in  the  animal  organism.  In  it  the 
oxygen  unites  with  the  compounds  poor  in  oxygen,  the  end  products  being 
water  and  carbon  dioxide  again.  This  applies,  at  least  as  indicated  above, 
to  the  fats  and  carbohydrates.  Potential  energy  is  utilized  and  kinetic 
energy  takes  its  place.  This  appears  partly  in  the  form  of  heat,  partly 
as  mechanical  work.  We  may  expect  that  the  sum  of  the  energies  of  the 
metabolized  food  materials  will  be  exactly  equivalent  to  the  energy  pro- 
duced by  the  animal  organism. 

The  first  experiment  in  this  direction  was  carried  out  by  Lavoisier,3  as 
early  as  1780,  with,  to  be  sure,  rather  primitive  methods.  Neither  he 
nor  the  two  later  investigators  Despretz  4  and  Dulong 5  were  able  to 
establish  a  satisfactory  agreement  between  the  amounts  of  energy  received 
and  that  produced.  We  owe  to  Max  Rubner  6  the  first  exact  proof  of 
this  relation,  while  more  recently  W.  O.  Atwater  7  has  repeated  the  exper- 
iments, eliminating  all  sources  of  error.  Atwater  compared  the  amounts 
of  potential  energy  in  the  substances  which  were  actually  oxidized  in  the 
body  with  the  amount  of  kinetic  energy  evolved  by  the  latter.  This 
appears  in  the  form  of  heat  in  the  rest  experiments,  and  as  heat  and  mus- 
cular work  in  the  work  experiments.  Even  in  the  latter  case  this  was 
measured  in  heat  units.  The  following  table  gives  a  summary  of  some  of 
Atwater's  results,  the  experimental  details  of  which  we  shall  discuss  in 
another  place.8 


1  Cf.  R.  Mayer:   Die  Mechanik   der  Warme.    Stuttgart  1867  (2d  ed.   1874);    Die 
Erhaltung  der  Energie.    Berlin,  1889. 

2  This,  of  course,  only  applies  to  the  principal  activity  of  the  parts  of  the  plants 
containing  chlorophyll.     These,  also,  require  oxygen  and  give  off  carbon  dioxide  (Cf. 
Lecture  IV). 

Lavoisier  et  de  la  Place:  Mem.  Acad.  roy.  sciences,  p.  355  (1780). 

Despretz:  Ann.  chim.  phys.  27,  337  (1824). 

Dulong:  ibid.  (3)  1,  440  (1841). 

Max  Rubner:  Z.  Biol.  30,  73  (1894). 

W.  Atwater:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  Ill,  1  Abt.  p.  497  (1904). 

See  Lecture  XXVII. 


FATS,  CARBOHYDRATES,  AND  ALBUMINS. 


335 


COMPARISON  OF  INCOME  AND  OUTGO  OF  ENERGY  IN  45  EXPERIMENTS 

ON  METABOLISM,  COVERING   143  DAYS.     AVERAGE 

AMOUNTS  PER  DAY. 


Net  In- 
come (Po- 
tential 

Net  Outgo 
(Kinetic 

Subject  and  Kind  of  Experiment. 

Number  o 
Experi- 
mental 

Energy  of 
Material 
Oxidized 

Energy 
Given 
off  from 

Difference  (in  Terms 
of  Net  Income). 

Days. 

in  Body). 

Body)  . 

Calories. 

Calories. 

Per  cent. 

Ordinary  Diet. 

Rest  experiments: 
7  experiments  with  E.  O.     .    . 
1  experiment  with  A.  W.  S.    . 
3  experiments  with  J.  F.  S.    . 
1  experiment  with  J.  C.  W.     . 

25 
3 
9 
4 

2268 
2304 
2118 
2357 

2259 
2279 
2136 
2397 

-    9 
-25 

-f  18 
+  40 

-0.4 
-1.1 

+  0.8 
+  1.7 

Average  for  experiments     .    . 

41 

2246 

2246 

0 

0 

Work  experiments: 
2  experiments  with  E.  O.    .    . 
4  experiments  with  J.  F.  S.     . 
14  experiments  with  J.  C.  W.    . 

8 
12 
46 

3865 
3539 
5120 

3829 
3540 
5120 

-36 

+   1 
0 

-0.9 
0 
0 

Average  for  20  experiments    . 

66 

4682 

4676 

-  6 

-.01 

Average  for  all  rest  and  work 

experiments   with  ordinary 
diet     

107 

3748 

3745 

-  3 

-0.1 

Special  Diet. 

Rest  experiments: 
6  experiments  with  E.  O.    .    . 
3  experiments  with  A.  W.  S.  . 
1  experiment  with  J.  F.  S.  . 

17 
6 
3 

2313 
2308 
2124 

2319 
2356 
2123 

+  6 
+  48 
-   1 

+  0.3 
+  2.1 
0 

Average  for  10  experiments    . 

26 

2290 

2305 

+  15 

+  0.7 

Work  experiments: 

1  experiment  with  E.  O. 

4 

3922 

3928 

+  6 

+  0.2 

2  experiments  with  J.  F.  S.    . 

6 

3583 

3552 

-31 

-0.9 

Average  for  3  experiments  .    . 

10 

3719 

3702 

-17 

-0.5 

Average  for  all  rest  and  work 

experiments  with  specialdiet 

36 

2687 

2695 

+  8 

+  0.3 

Average  for  all  the  above  ex- 

periments   

143 

3481 

3481 

0 

0 

336 


LECTURE  XV. 


As  the  values  show,  it  is  evident  that  the  law  of  the  conservation  of 
energy  holds  with  surprising  exactness  for  the  whole  animal  organism.  It 
was  found  possible  to  obtain  such  a  close  agreement  between  the  sum  of 
the  amounts  of  energy  introduced  into  the  body  and  that  produced  by 
combustion  within  the  organism,  only  by  extending  the  experiment 
through  quite  a  number  of  days. 

This  brings  us  to  the  important  question  as  to  whether  the  chemical 
energies  introduced  into  the  body  by  the  individual  nutrients  are  all 
equivalent,  or,  in  other  words,  whether  it  is  immaterial  in  what  form  the 
animal  organism  receives  its  chemical  energy.  After  considerable  investi- 
gation Max  Rubner1  was  able  to  show  that  the  different  organic  nutrients 
could  replace  one  another  in  amounts  corresponding  approximately  to 
their  relative  heat  values.  This  principle  comprises  the  Law  of  Isody- 
namics.  According  to  this  law  we  can  represent  each  substance  used  as 
food  in  a  common  unit  and  give  it  a  calorific  value.  Thus,  for  example, 
100  grams  of  fat  are  isodynamic  with  the  following  weights  of 


As  Deter- 
mined by  Ex- 
periments 
with  Animals. 

Heat  of  Com- 
bustion   by 
Calorimeter. 

Syntonin       

225 

213 

Dry  meat  

243 

235 

Starch                                   ....    

232 

229 

234 

235 

Grape-sugar                 

256 

255 

Strictly  speaking,  the  Law  of  Isodynamics  only  applies  to  fats  and 
carbohydrates.  It  fails  with  the  albumins.  These,  to  a  certain  extent, 
are  absolutely  necessary  for  the  animal  organism.  It  is  indeed  possible 
to  keep  a  dog  alive  for  a  long  time  on  albumin  alone;  i.e.,  the  albumin 
itself  may  be  looked  upon  as  isodynamic  with  the  fats  and  carbohydrates. 
It  is,  however,  as  we  shall  see  later  on,  impossible  to  nourish  a  dog  on 
fats  and  carbohydrates  exclusively,  even  when  more  than  sufficient  calo- 
rific units  are  provided.  Starvation  metabolism  begins  in  the  absence 
of  albuminous  material;  i.e.,  the  animal  draws  on  its  own  body  albumin, 
for  which  it  has  no  substitute. 

Studies  on  metabolism  have  shown  how  much  nourishment  is  required 
for  the  maintenance  of  a  definite  organism,  and  how  to  express  this  require- 
ment in  terms  of  calories.  We  shall  consider  these  relations  more  in  detail 
later.  Here  we  shall  only  state,  that  the  exact  formulation  of  the  total 
metabolism  obtained  by  considering  the  foods  solely  as  combustible 
material,  although  of  great  importance  for  the  entire  conception  of  meta- 

1  Cf.  Max  Rubner:  Die  Gesetze  des  Energieverbrauches  bei  der  Ernahrung.  Franz 
Deuticke,  Leipsic  and  Vienna,  1902. 


FATS,  CARBOHYDRATES,  AND  ALBUMINS.  337 

holism,  by  no  means  tells  the  whole  story.  The  calorific  values  serve 
merely  as  a  skeleton,  and  give  us  an  outline  of  the  changes  which  take 
place  in  metabolism.  These  changes  are  always  to  be  traced  back  to  the 
individual  cells.  It  is  not  the  foods  as  such  which  determine  in  general 
the  metabolism,  but  the  cells  themselves.  These,  naturally,  require  a 
•certain  amount  of  energy.  We  shall  see  later  on,  that  metabolism  varies 
in  different  individuals,  and  that  the  consumption  of  material,  to  a  large 
extent,  is  regulated  by  the  functional  activity  of  the  separate  organs. 
The  same  work  —  e.g.,  a  definite  amount  of  muscular  work  —  will  require 
a  greater  quantity  of  energy  the  first  time  it  is  performed  than  when  it  is 
repeated.  By  practice,  the  organism  adapts  itself  to  its  requirements. 
It  learns  how  to  perform  a  given  amount  of  work  with  the  least  expenditure 
of  energy.  We  must  call  attention  even  here  to  this  fact  in  order  to  show 
that  experiments  in  metabolism,  and  especially  experiments  dealing  with 
the  energy  required  for  a  definite  amount  of  work,  are  not  likely  to  give 
true  values,  unless  they  be  carried  out  through  an  extended  period  of 
time.  It  will  only  then  be  possible  to  compare  the  fluctuations  and 
irregularities  of  the  separate  daily  periods,  and  it  is  only  in  this  manner 
that  we  shall  be  able  to  obtain  values  which  will  be  comparable  with  others 
which  have  been  secured  under  different  circumstances.  In  practical 
work,  as  we  shall  see  later,  we  do  not  study  the  fats,  carbohydrates,  and 
proteins  by  themselves,  but  make  use  of  those  mixtures  which  are  present 
naturally  in  meat  and  vegetables.  The  impracticability  of  laying  too 
much  stress  upon  the  calorific  values  is  very  well  shown  by  the  significant 
discovery  that  the  whole  work  of  the  digestive  glands,  and  consequently 
digestion  itself,  is  dependent  to  a  great  extent  upon  the  nature  of  the 
ingested  food  material.  It  is  only  by  combining  the  knowledge  gained 
from  investigations  on  the  transformation  of  energy  with  that  obtained 
in  the  study  of  cell  activity  that  we  are  enabled  to  get  a  complete  conception 
of  metabolism  in  general. 

We  are  first  of  all  interested  in  the  questions:  What  relations  do  the 
foods  bear  to  one  another,  and  what  proofs  do  we  have  that  certain  organs 
are  able  to  perform  definite  functions  with  all  three  classes  of  nutrients  ? 
Let  us  first  take  up  the  last  question.  In  discussing  the  carbohydrates, 
we  have  already  drawn  the  conclusion,  from  many  experiments,  that  they 
form  an  exceptionally  important  source  of  muscular  activity.  Now,  are 
the  muscles  also  capable  of  performing  their  functions  by  utilizing  the 
energy  contained  in  representatives  of  the  two  other  kinds  of  organic 
food,  the  fats  and  proteins? 

The  fact  that  protein  may  serve  as  a  source  of  muscular  energy  was 
proved  by  Pfluger. *  For  over  seven  months  he  fed  a  dog  exclusively  on 
meat  which  contained  only  small  amounts  of  fat  and  carbohydrates,  —  in 
fact,  not  enough  to  satisfy  the  requirements  of  the  heart's  work.  Pfluger, 

1  E.  Pflt^er  Pfliiger's  Arch.  50,  98,  330,  396  (1891). 


338  LECTURE  XV. 

furthermore,  made  this  dog  do  heavy  work  for  considerable  lengths  of 
time.  The  dog,  therefore,  had  to  perform  all  of  its  muscular  work  at  the 
expense  of  protein.  This  proves  that  protein  can  also  serve  as  a  source  of 
muscular  energy.  Under  normal  conditions,  i.e.,  with  a  mixed  diet  the 
muscle  cells  will  first  make  use  of  the  carbohydrates  as  a  source  of  energy 
and,  if  this  is  exhausted,  then  attack  the  protein. 

A  much  discussed  question  is  the  value  of  the  fats  as  a  source  of  muscular 
energy.  Chauveau  1  and  others  took  the  stand  that  fat,  as  such,  can  in 
no  case  be  utilized  as  a  source  of  energy  by  the  muscle  cells  for  the  per- 
formance of  work.  The  fat  in  every  case  must  first  be  transformed  into 
sugar  before  it  can  be  used  by  the  muscle  cells.  According  to  this  assump- 
tion, the  value  of  fats  for  the  production  of  muscular  energy  could  not  be 
larger  than  that  corresponding  to  the  quantity  of  sugar  which  this  amount 
of  fat  can  form.  Now  1  gram  of  fat  is  isodynamic  with  2.56  grams  of 
dextrose  when  the  heat  units  of  both  are  taken  into  consideration. 

If  we  assume  that  the  fats,  before  they  can  be  utilized,  must  be  changed 
into  carbohydrates,  it  follows  that  1  gram  of  fat  would  correspond  to  1 . 6 
grams  of  carbohydrate,  if  the  fat  is  oxidized  directly  to  sugar.  We  might 
expect  to  be  able  to  determine  by  direct  experiment  how  much  of  the 
potential  energy  in  fats  the  body  can  transform  into  muscular  force.  This 
has  not  yet  been  satisfactorily  accomplished.  If  we  feed  an  animal  with 
a  mixture  of  albumin,  fat,  and  carbohydrate,  the  calorific  value  of  which 
we  know  exactly,  we  are. unable  to  decide  by  which  part  of  the  energy  the 
animal  organism  performs  its  different  functions.  We  do  not  know  whether 
such  a  selection  actually  does  take  place  in  the  case  of  a  mixed  diet,  or  if 
it  is  not  more  probable  that  the  organism  takes  all  of  the  energy  presented 
as  such,  and  uses  it  for  all  of  its  functions.  Atwater 2  justly  calls  attention 
to  the  fact  that  we  have  no  means  of  differentiating  internal  from  external 
muscular  work.  We  must  also  remember  that  in  every  case  only  a  part  of 
the  energy  used  for  accomplishing  work  is  shown  by  the  work  performed. 
A  large  part  of  this  energy  is  transformed  into  heat.  We  can  obtain  an 
idea  indirectly  of  the  value  of  fats  as  a  source  of  muscular  work,  if  we  regu- 
late the  conditions  of  the  experiment  so  that  an  economical  utilization 
of  the  available  energy  is  guaranteed.  If  in  the  food  only  barely  enough 
energy  is  supplied  to  the  body  to  meet  its  requirements,  or  even  less  than 
enough,  we  would  expect  it  to  utilize  all  of  the  available  energy  in  the 
most  economical  manner.  Atwater  has  carried  out  such  experiments. 
Particular  stress  is  laid  on  the  fact  that  the  albumin  in  the  food  must  be 
limited  as  much  as  possible  in  order  to  compare  the  fats  and  carbohydrates. 
Atwater,  therefore,  used  only  about  as  much  protein  in  severe  muscular 
work  as  he  found  necessary  to  maintain  the  nitrogen  equilibrium  in  a 

1  A.  Chauveau:  Cf.  Compt.  rend.  121,  26,  91  (1895);  122,  429,  504,  1098,  1163,  1169, 
1244,  1303  (1896);  123,  151,  283  (1897). 

2  Atwater:  Ergeb.  Physiol  III,  Abt.  1,  p.  497  (1904). 


FATS,  CARBOHYDRATES,  AND  ALBUMINS. 


339 


previous  "  rest  "  experiment.  This  amount  of  albumin,  with  small  quan- 
tities of  fat  and  carbohydrate,  was  the  starting  ration  of  the  "  work  " 
experiment.  In  the  principal  test,  in  one  case  a  considerable  amount  of 
fat  (butter,  cream)  was  added,  while  in  another  experiment  an  equivalent 
amount  of  carbohydrate  (milk-sugar  and  cane-sugar)  was  employed.  The 
total  energies  received  was  somewhat  less  than  the  organism  required;  that 
is,  some  of  the  body  substance  was  attacked.  These  experiments  estab- 
lished the  values  of  fats  and  carbohydrates  as  sources  of  muscular  energy 
in  two  directions.  In  both  cases  the  energy  in  the  form  of  albumin  and  the 
total  energy  received  were  the  same,  the  only  differences  being  the  predomi- 
nance of  fat  in  the  one  case,  and  of  carbohydrates  in  the  other.  The 
external  work  was  likewise  the  same  in  both  cases.  If  the  total  energy 
utilized  for  the  production  of  a  definite  amount  of  work  was  the  same  for 
a  fat  as  for  a  carbohydrate  diet,  the  fact  would  be  established  that  fats 
and  carbohydrates  have  the  same  value  as  a  source  of  muscular  energy. 
In  the  next  place  the  amount  of  energy  abstracted  from  the  body  itself  — 
the  quantity  of  energy  received  in  the  food  was,  as  already  stated,  not 
quite  enough  to  satisfy  the  requirements  —  must  be  a  measure  of  the 
relative  value  of  a  diet  in  which  either  fat  or  carbohydrate  predominates. 
If  equal  quantities  of  body  substance  were  used  up  in  both  cases,  we 
would  have  a  further  support  of  the  equality  of  carbohydrates  and  fats 
as  sources  of  muscular  energy.  The  following  table  will  give  us  an  idea 
of  the  results  obtained  by  Atwater  in  his  experiments. 

RELATIVE   VALUES    OF   FATS   AND   CARBOHYDRATES    IN    THE    FOOD 
FOR  THE   PERFORMANCE   OF  MUSCULAR  WORK. 


Energy 

Equiva- 

Energy of 

Energy 

Time. 

Energy  in 
the  Food. 

lent  to 
External 

the  Oxi- 
dized Ma- 

Equiva- 
lent to  the 

Name,  Nature  of  the  Experiment. 

Muscular 
Work. 

terial. 

Gain  (-}-) 
or  Loss 

(-)of 

Body  Sub- 

Days. 

Calories. 

stance. 

No.  40  J.  C.  W.  carbohydrate  diet 

4 

4180 

518 

5251 

-1071 

No.  41  J.  C.  W.  fat  diet  

4 

4150 

522 

5304 

-1154 

No.  44  J.  C.  W.  carbohydrate  diet 

4 

4602 

571 

5125 

-   523 

No.  43  J.  C.  W.  fat  diet  

4 

4496 

548 

5155 

-   659 

No.  47  J.  C.  W.  carbohydrate  diet 

4 

4366 

562 

5173 

-   807 

No.  46  J.  C.  W.  fat  diet  

4 

4478 

551 

5193 

-   715 

No.  53  J.  C.  W.  carbohydrate  diet 

3 

5132 

587 

5104 

+     28 

No.  52  J.  C.  W.  fat  diet  

3 

5120 

607 

5309 

-    189 

Average    of    4    experiments    with 

carbohydrate  diet     

15 

4532 

558 

5167 

-   635 

Average  of  4  experiments  with  fat 

diet           

15 

4524 

554 

5236 

—   712 

340 


LECTURE  XV. 


These  experiments  show  somewhat  higher  values  for  the  carbohydrates 
than  for  the  fats.  It  is  questionable  whether  this  is  always  true,  for 
Atwater  also  published  the  results  of  some  experiments  in  which  this  was 
not  the  case.  That,  as  a  matter  of  fact,  the  fats  are  to  be  considered  as 
direct  sources  of  muscular  work,  without  requiring  any  preliminary  con- 
version into  carbohydrates,  seems  apparent;  for  if  we  assume  that  the  fats 
are  first  transformed  into  carbohydrates,  there  will  be  a  loss  of  energy 
during  their  oxidation.  In  such  a  transformation,  36  per  cent  of  the 
potential  energy  of  the  fat  would  become  free  energy.  Now  1  gram  of 
animal  fat  produces  9.50  calories,  and  1  gram  of  cane-sugar  3.96  calories. 
By  the  combustion,  in  the  bomb  calorimeter,  10.53  grams  of  fat  and 
25 . 25  grams  sugar  are  required  to  produce  100  calories.  The  same  number 
of  calories  would,  of  course,  be  liberated  in  the  body  during  complete  com- 
bustion. If  the  carbohydrates  alone  were  the  source  of  muscular  energy, 
36  of  the  100  calories  from  the  10.53  grams  of  fat  would  not  be  utilized. 
These  would  be  set  free  in  the  body  during  the  transformation  of  the  fats 
into  carbohydrates  and  appear  as  heat.  The  ratio  of  the  10.53  grams 
fat  to  the  25.25  grams  carbohydrate  would  be  64  :  100.  This,  as  a 
matter  of  fact,  is  not  the  case,  as  the  following  table  shows.  In  it  the 
relative  values  of  a  carbohydrate  and  of  a  fat  diet,  as  shown  by  the  above 
experiments,  are  compared;  in  one  case  the  amount  of  energy  transformed 
per  day  is  given  in  calories,  and  in  the  other  the  percentage  of  utilization 
of  the  fat  diet  is  compared  with  that  of  the  carbohydrate  diet,  and  fat 
alone  is  compared  with  carbohydrate. 


PERCENTAGE   UTILIZATION   OF  ENERGY. 


Experiment. 

Energy  from  Fat  Diet 
Compared  with  that  of 
Carbohydrate  Diet. 

Energy  in  Fat  Com- 
pared with  that  in 
Carbohydrate. 

Experiments  No. 

40  and  41  

Per  cent. 
99  2 

Per  cent. 
98  3 

Experiments  No. 
Experiments  No. 
Experiments  No. 

43  and  44  
46  and  47  
52  and  53 

96.8 
98.3 
97  7 

92.8 
96.2 
94  8 

Average 

98  0 

95  5 

Instead  of  the  theoretical  ratio  of  64  :  100  we  find  that  the  fat  stands 
to  the  carbohydrate  in  the  proportion  of  95.5  :  98.0.  Thus,  it  is  evident, 
unless  we  choose  a  far  more  complicated  explanation,  that  the  energy 
which  the  body  receives  in  the  form  of  fat  is  a  direct  source  of  muscular 
energy,  and  that  a  preliminary  transformation  of  fat  into  carbohydrate 
does  not  take  place. 


FATS,  CARBOHYDRATES,  AND  ALBUMINS.  341 

If  we  apply  these  relations  to  the  metabolism  of  a  diabetic,  we  will 
appreciate  the  great  derangement  of  his  energy  economy.  In  the  severe 
form  of  this  disease,  the  organism  loses  not  only  the  greater  part  of  the 
energy  of  the  carbohydrates,  but  also  the  energy  required  to  transform 
fat  or  protein  into  sugar;  and  as  a  part  of  the  sugar  so  formed  is  eliminated 
by  the  system,  the  loss  becomes  a  double  one.  The  fact  that  the  diabetic, 
whose  blood  and  tissues  are  saturated  with  sugar,  and  who  is  already 
greatly  injured  as  regards  the  economy  of  energy  by  means  of  the  loss  he 
suffers  because  of  his  inability  to  consume  sugar,  even  prepares  more 
sugar  from  the  other  nutrients,  only  to  eliminate  it  eventually  as  such, 
shows  us  that  the  assumption  that  diabetes  is  only  a  simple  derangement 
of  carbohydrate  metabolism  does  not  satisfactorily  explain  the  disease. 
Up  to  the  present  time  the  most  prominent  symptom,  that  of  glucosuria, 
has  dominated  the  entire  investigation  of  problems  concerning  diabetes, 
and  it  is  very  probable  that  this  is  the  reason  why  the  disease,  as  a  whole, 
is  so  little  understood. 

We  have  intentionally  gone  somewhat  into  detail  concerning  these 
relations,  because  we  are  unable  to  follow  any  other  function  so  exactly 
as  that  of  muscular  work.  All  the  other  organs  are  only  indirectly  acces- 
sible to  our  observation.  We  do  not  know  whether  they  also  are  able  to 
utilize  all  three  of  these  materials,  fat,  carbohydrate,  and  protein,  in  like 
manner*  as  sources  of  energy.  O.  Cohnheim  l  has  recently  performed  an 
experiment  in  this  direction.  He  tried  to  decide  whether  the  digestive 
glands  obtained  their  energy  requirements  mainly  or  exclusively  from  pro- 
tein. As  we  shall  see  later  on,  it  is  possible  to  stimulate  the  digestive 
glands  without  introducing  into  the  alimentary  tract  food  which  would 
then  participate  in  the  metabolism.  Cohnheim  made  an  oesophageal 
fistula  in  a  dog  according  to  the  method  of  Pawlow,  and  after  a  period  of 
fasting  fed  the  animal.  The  food  eaten  by  the  animal  fell  out  through  the 
fistula  tube  at  every  swallow,  so  that  no  nourishment  was  actually  received 
by  the  dog.  Not  only  are  the  salivary  glands  stimulated  by  this  "  fictitious 
feeding,"  but  the  stomach  also.  On  account  of  the  acid  gastric  juice 
passing  from  the  stomach  into  the  duodenum,  the  pancreatic  gland  also 
begins  to  secrete  its  fluid.  By  estimating  the  amount  of  nitrogen  present 
in  the  urine  on  days  of  fasting  and  those  on  which  the  fictitious  feeding 
day  took  place,  Cohnheim  succeeded  in  showing  that  the  activities  of  the 
digestive  organs  were  without  influence  upon  the  transformation  of  albu- 
min. No  increased  elimination  of  nitrogen  took  place.  This  does  not  by 
any  means  prove  that  the  digestive  glands  do  not  work  with  albumin. 
It  is  possible  that,  while  the  digestive  glands  are  decomposing  albumin, 
an  equivalent  amount  of  albumin  is  being  "  spared  "  in  some  other  part 
of  the  body.  Such  an  assumption  becomes  all  the  more  plausible  when 

1  O.  Cohnheim:  Z.  physiol.  Chem.  46,  9  (1905). 


342  LECTURE  XV. 

we  remember  that  the  animal  was  fasting,  and  that  such  an  organism  is 
as  economical  as  possible  with  its  subsistence.  On  the  other  hand,  it  is 
possible  that  all  three  nutrients,  fat,  carbohydrate,  and  albumin,  are  drawn 
upon  as  sources  of  the  energy  required  for  the  work  of  the  glands,  and  that 
the  consumption,  of  albumin  especially,  was  so  small,  that  it  did  not 
change  the  nitrogen  content  of  the  urine  enough  to  be  shown  by  our 
present  methods  of  analysis. 

We  have  already  stated  that  the  carbohydrates  are  also  to  be  looked  upon 
as  a  source  of  heat.  It  is  possible  to  cause  glycogen  to  disappear  by  merely 
chilling  an  animal.  Albumin  may  also  act  in  this  way  as  a  source  of  heat. 

At  all  events,  the  discovery  that  the  fats  act  as  direct  sources  of  mus- 
cular force,  proves  that  the  nutrients  stand  in  intimate  relation  to  one 
another.  They  replace  one  another  partly  by  being  transformed  and 
partly  by  reason  of  their  calorific  values.  This,  however,  does  not  by  any 
means  include  all  of  the  relations  existing  between  the  individual  nutrients. 
As  we  have  already  seen,  it  is  possible  to  keep  a  dog  alive  on  meat  alone. 
In  this  case  the  organism  must  obtain  all  of  its  requirements  from  the 
albumin  (aside  from  the  small  amounts  of  fat  and  carbohydrate  contained 
in  the  meat).  If  the  quantity  of  meat  is  insufficient,  the  animal  must 
draw  upon  its  stores  of  fat  and  carbohydrate.  It  is  a  simple  matter  to 
determine  the  amount  of  meat  necessary  to  just  satisfy  the  energy  require- 
ments. If  we  exceed  to  the  slightest  degree  the  quantity  of  lean  meat 
which  is  necessary  to  keep  the  metabolism  in  equilibrium,  there  will  be 
no  accumulation  of  albumin,  but,  on  the  contrary,  there  is  an  increased 
decomposition  of  albumin  as  a  consequence.  An  accumulation  of  albumin, 
i.e.,  an  increased  amount  of  albumin  in  the  cell  material,  may  indeed  be 
brought  about  by  a  liberal  and  long-continued  feeding  of  albuminous 
material.1  It  has  been  shown,  however,  that  the  animal  organism  con- 
stantly seeks  to  maintain  its  albumin  content,  and  consequently  the  func- 
tional condition  of  its  cells,  at  a  constant  level.  As  soon  as  the  diet  ceases 
to  contain  the  excess  of  protein,  the  accumulation  of  albumin  in  the  cells 
quickly  disappears.  The  previous  equilibrium  in  the  economy  of  the 
individual  cells  will  be  reestablished. 

If  we  make  an  animal  go  hungry,  the  elimination  of  nitrogen  continues, 
and  this  is  also  true  when  an  abundance  of  fat  or  carbohydrate  is  fed  to 
the  animal.  The  albumin,  therefore,  is  not  entirely  replaceable,  although 
it  is  possible  to  reduce  the  destruction  of  albumin  by  means  of  fats.  This 
fat  may  come  from  the  food  or  from  the  body  itself.  It  is  possible  by 
means  of  fat  and  albumin  to  .establish  a  new  nitrogen  balance;  i.e.,  to 


1  More  recent  experiments  make  it  seem  doubtful  whether  the  nitrogen  retention 
and  deposition  of  albumin  correspond  to  one  another.  Great  caution  should  be  used  in 
the  estimation  of  the  nitrogen  balance  in  this  direction.  Cf.  E.  Abderhalden  and 
Bloch:  Z.  physiol.  Chem.  53.  464  (1907). 


FATS,  CARBOHYDRATES,  AND  ALBUMINS. 


343 


determine  anew  the  quantity  of  albumin  which  is  absolutely  necessary  to 
prevent  injury  to  the  albumin  content  of  the  organism.  This  amount  of 
albumin  will  be  much  less  than  is  required  in  a  diet  of  albumin  alone.  If 
we  feed  an  animal  a  definite  quantity  of  fat  and  albumin,  it  will  be  possible 
to  reduce  the  albumin  requirement  more  and  more  by  increasing  the  pro- 
portion of  fat  in  mixture.  We  finally  reach  a  minimum  amount  of  pro- 
tein, and  if  we  attempt  to  replace  it  by  fat,  we  cause  the  body  albumin 
itself  to  be  attacked.  This  limit  varies  with  different  animals  and  at 
different  times  with  the  same  animal;  in  every  organism  it  is  dependent 
upon  the  condition  of  the  body,  and,  above  all,  upon  the  fat  in  the  body  at 
the  time  of  the  experiment.  A  fat  animal  will  permit  more  albumin  to  be 
replaced  by  fat  than  will  a  lean  one,  for  the  former  can  contribute  from 
its  own  supply  of  fat.  On  the  other  hand,  by  feeding  fat  we  have  a  means 
of  causing  an  accumulation  of  albumin.  We  can  spare  albumin  not  only 
with  fat,  but  also  with  carbohydrates.  By  their  assistance  also,  provided 
sufficient  albumin  is  supplied,  the  albumin  content  of  the  body  may  be 
increased.  Voit,1  who  performed  experiments  in  this  direction,  came  to 
the  conclusion  that  the  fats  and  carbohydrates  did  not  have  an  equivalent 
effect  in  causing  an  accumulation  of  albumin.  Carbohydrates  are  more 
efficient  as  "  albumin  sparers  "  than  are  the  fats,  as  is  shown  by  the  follow- 
ing table: 


Food. 

Meat. 

Gain  (+)     Loss  (-) 

Meat. 

Fat. 

Carbohydrate. 
Starch.         Sugar. 

Transformed  into  Body 
Albumin. 

in  Body  Albumin. 

500 

250 

558 

-    58 

500 

300 

466 

+   34 

500 

200 

505 

-      5 

800 

250 

745 

+   55 

800 

200 

773 

+   27 

2000 

200-300 

1792 

+  208 

2000 

250 

... 

1883 

+  117 

Atwater 2  has  recently  determined  accurately  the  comparative  values  of 
carbohydrates  and  fats  as  sparers  of  albumin.  The  fact  that  proteins  are 
distinguished  from  the  other  nutrients  by  the  amount  of  nitrogen  which 
they  contain,  makes  it  easy  to  carry  out  the  experiment.  By  simply 
comparing  the  amount  of  nitrogen  in  the  food  with  that  of  the  urine,  we 
can  at  once  get  an  idea  as  to  how  much  albumin  has  been  decomposed. 
The  nitrogen  content  of  the  faeces  tells  us  approximately  how  much  albumin 
has  not  been  absorbed.  We  speak  of  a  "  nitrogen  equilibrium  "  when  the 
amount  of  nitrogen  ingested  in  the  form  of  food  is  equal  to  that  con- 
tained in  the  urine  and  in  the  faeces.  If  the  latter  is  greater  than  the 


1  Carl  Voit:  Hermann's  Handbuch  der  Physiologic,  6,  143  (1881).     2  loc.  dt. 


344 


LECTURE  XV. 


amount  introduced,  it  shows  that  albumin  from  the  body  has  been  decom- 
posed. Conversely,  if  the  nitrogen  eliminated  is  less  than  that  ingested, 
then  we  are  justified  in  concluding  that  albumin  has  been  accumulated. 

The  following  table  will  give  a  summary  of  some  of  Atwater's  experi- 
ments : 


Kind  of  Experiment. 

Sub- 
ject. 

Number  of  the  Ex- 
periment. 

Duration  in  Days. 

Available  Energy 
in  Food. 

<k  ^    . 

>    0  -0 

Nitrogen 

&*i 

w  2  o 

ill 

w  s* 

_c 

! 

o 

1 

P 

d 

JT 

.£  % 

O  " 

Calories. 

Grams. 

Work  experiments: 
Carbohydrate     
Fat 

J.C.W 

40 
41 
44 
"43 
47 
46 
53 
52 

4 
4 
4 
4 
4 
4 
3 
3 

4180 
4150 
4602 
4496 
4366 
4478 
5132 
5120 

518 
522 
571 
548 
562 
551 
587 
607 

17.1 
16.9 
17.8 
17.1 
17.4 
17.0 
17.9 
17.7 

2.2 
1.5 
2.6 
2.0 
2.7 
1.8 
2.3 
1.6 

17.1 
20.3 
17.3 
19.1 
16.3 
16.1 
15.4 
16.4 

-2.2 
-4.9 
-2.1 
-4.0 
-1.6 
-0.9 
+  0.2 
-0.3 

Carbohydrate     .    .    . 

Fat    

Carbohydrate     

Fat    

Carbohydrate     

Fat 

Average    for    the    experi- 
ments with  carbohydrates 
Average    for    the    experi- 
ments with  fat  

15 
15 

4532 
4524 

558 
554 

17.5 
17.1 

2.5 
1.7 

16.6 
18.1 

-1.5 

-2.7 

From  these  experiments  we  find,  in  agreement  with  those  of  Voit,  that 
carbohydrates  as  well  as  fats  act  as  sparers  of  albumin,  under  the  given 
conditions.  The  fact  that  in  the  carbohydrate  experiments  there  was 
invariably  more  nitrogen  in  the  faeces  than  in  the  experiments  with  the 
fats,  is  explained  by  the  nature  of  the  food.  Vegetables  predominated 
in  the  former  case,  and  meat  in  the  latter.  We  shall  see  later,  that  the 
protein  in  vegetables  is  utilized  to  a  less  extent  than  that  of  meat.  If  we 
subtract  the  nitrogen  in- the  faeces  from  the  total  nitrogen  of  the  food,  we 
shall  obtain  the  quantity  of  nitrogen  which  the  organism  has  evidently 
utilized.  If  we  insert  these  values  in  the  above  table,  we  shall  find  that 
less  nitrogen  was  available  when  carbohydrates  were  eaten,  than  when 
fats  predominated  in  the  food.  Nevertheless,  there  was  less  nitrogen 
present  in  the  urine  in  the  former  case  than  in  the  latter,  although  the 
difference  was  not  great. 

These  experiments  still  leave  one  question  unsolved:  How  do  the 
fats  and  carbohydrates  act  as  sparers  of  albumin,  when  they  are  eaten 
together?  In  the  above  experiments,  the  food  at  one  time  contained 
protein  and  fat,  and  at  another  time  protein  and  carbohydrate.  Under 
ordinary  conditions  all  three  kinds  of  nutrients,  fat,  carbohydrate,  and 
protein,  are  available  to  the  organism.  Tallquist 1  has,  therefore,  studied 

1  F.  W.  Tallquist:  Arch.  Hyg.  41,  177  (1902). 


FATS,  CARBOHYDRATES,  AND  ALBUMINS.  345 

the  problem  from  this  standpoint.  During  one  period,  the  food  contained 
16.08  grams  nitrogen,  44  grams  fat,  and  466  grams  carbohydrates;  and 
in  a  parallel  experiment  it  contained  16.08  grams  nitrogen,  146  grams  fat, 
and  250  grams  carbohydrates;  each  gives  the  same  number  of  calories 
(2867  and  2873  calories).  In  both  experiments  practically  the  same 
nitrogen  balance  was  reached.  It  appears  that  under  these  conditions 
the  carbohydrates  are  isodynamic  with  the  fats  in  respect  to  acting  as 
albumin  sparers.  Landergren  *  explains  the  greater  sparing  of  albumin  in 
an  exclusively  carbohydrate  diet,  as  compared  to  a  diet  of  fats  alone,  by 
the  assumption  that  the  animal  organism  constantly  requires  sugar;  and 
inasmuch  as  he  does  not  believe  fat  can  be  changed  into  sugar,  a  part  of 
the  albumin  must  be  utilized,  in  the  case  of  a  fat  diet,  for  the  formation 
of  sugar.  This  part  of  the  albumin  is  spared,  if  the  food  contains  carbo- 
hydrates, so  that  the  organism  then  has  more  albumin  at-  its  disposal  for 
its  remaining  functions.  The  total  albumin  may  be  utilized  as  such,  when 
sufficient  fat  and  carbohydrate  has  been  added  to  the  diet.  This  expla- 
nation is  at  present  only  an  hypothesis. 

The  results  as  a  whole,  which  have  been  obtained  in  studying  the  rela- 
tions of  the  carbohydrates  and  fats  to  the  transformation  of  albumin, 
show  that  we  may  conclude  with  a  great  degree  of  probability  that  the 
Law  of  Isodynamics  holds  for  these  nutrients  among  themselves.  Both 
are  able  to  spare  albumin  to  about  the  same  extent.  The  fact  that  the 
feeding  of  carbohydrate  alone,  or  fat  by  itself,  should  have  shown  a  differ- 
ence in  favor  of  the  former,  may  be  explained  by  the  assumption  that  this 
Law  of  Isodynamics  is  not  an  absolute  one;  i.e.,  the  chemical  composition 
of  the  foods  undoubtedly  plays  an  important  part. 

We  have  already  mentioned  the  most  important  relations  existing 
between  the  nitrogen-free  nutrients;  i.e.,  the  fats  and  carbohydrates. 
We  have  shown  that  with  fats  the  muscles  are  able  to  perform  their  work 
just  as  well  as  with  carbohydrates.  On  the  other  hand,  we  know  of 
experiments  which  prove  beyond  question  that  carbohydrates  can  replace 
fats;  in  fact,  according  to  the  Law  of  Isodynamics.  If  all  nourishment 
is  withheld  from  an  animal,  it  will  draw  on  its  own  body,  not  only  attack- 
ing its  own  protein,  but  especially  the  fat  deposits.  If  we  substitute  for 
the  fat  which  would  be  used  up  in  this  way  during  starvation  the  same 
quantity  of  fat  in  food,  we  find  that  a  complete  replacement  follows; 
i.e.,  the  animal  does  not  touch  its  fat  reserves.  The  same  effect  can  be 
obtained  by  substituting  for  the  fat  an  isodynamic  amount  of  carbohy- 
drate. This  is  shown  by  the  following  table,  which  gives  a  summary  of 
some  of  Atwater's  experiments. 

The  loss  of  body  fat  was  at  one  time  greater  with  a  carbohydrate  diet, 


E.  Landergren:  Skand.  Arch.  Physiol.  14,  112  (1903). 


346 


LECTURE  XV. 


and  at  another  time  greater  with  a  fat  diet.  On  an  average  it  was  less 
with  the  carbohydrate  diet.  Apparently  sugar  is  a  better  sparer  of  body 
fat  than  fat  itself.  The  difference  is,  however,  very  slight,  and  we  may 
conclude  from  the  experiments  that  isodynamic  quantities  of  fat  and 
carbohydrates  are  equivalent  in  this  respect. 


Kind  of  Experiment. 

Sub- 
ject. 

No. 

Duration  in  Days. 

Available 
in  the 
Food. 

Energy  of  Material 
Oxidized  in  the  Body. 

Energy  of  External 
Work. 

Gain  (+)  or  Loss  (—  ) 

cj 

0 

£ 
a 

J> 

si 

ii 
ii 

PEJ 

d 

3 

,M 

*    g 
03 
So   C3 

W  '$> 

1 

g 

I 

il 

^3 

15 
H 

Calories. 

Grams. 

Carbohydrate  .    .    . 
Fat 

J.C.W. 

40 
41 
44 
43 
47 
46 
53 
52 

4 
4 
4 
4 
4 
4 
3 
3 

15 
15 

17.1 
16.9 
17.8 
17.1 
17.4 
17.0 
17.9 
17.7 

17.5 
17.1 

4180 
4150 
4602 
4416 
4366 
4478 
5132 
5120 

4532 
4524 

5251 
5304 
5125 
5155 
5173 
5193 
5104 
5309 

5167 
5236 

518 
522 
571 

548 
562 
551 
587 
607 

558 
554 

-13.6 
-30.6 
-13.1 
-25.0 
-10.1 
-   5.6 
+    1.3 
-   2.1 

-   9.5 
-16.7 

-   77 
-173 
-  74 
-141 
-   58 
-   32 
+     8 
-    12 

-   54 
-   95 

-104.2 
-102.8 
-   47.1 
-   54.3 
-   78.5 
-71.6 
+     2.1 
-    18.6 

-   60.7 
-   64.7 

-994 
-981 
-449 
-518 
-749 
-683 
+  20 
-177 

-581 
-617 

Carbohydrate  .    .    . 
Fat  .    .           .... 

Carbohydrate  .    .    . 
Fat  
Carbohydrate  .    .    . 
Fat  .... 

Average  for  the  ex- 
periments     with 
carbohydrates  .    . 
Average  for  the  ex- 
Eeriments       with 
its      

The  question  that  next  arises  is  with  regard  to  the  way  in  which  carbo- 
hydrates and  fats  behave  when  they  are  fed  simultaneously.  It  would 
seem  possible  that  they  would  be  decomposed  equally,  and  the  liberated 
energy  utilized,  sometimes  for  one  purpose  and  sometimes  for  another. 
It  is  also  conceivable  that  one  substance  may  be  used  up  more  rapidly 
than  the  other.  This  is  a  very  hard  problem  to  decide.  We  may  determine 
the  amount  of  nitrogen  and  carbon  eliminated  in  the  urine  and  fseces,  and 
deduct  from  the  total  amount  of  carbon  that  corresponding  to  the  protein 
(as  indicated  by  the  nitrogen  value).  The  carbohydrates  and  fats  would 
be  represented  by  the  rest  of  the  carbon.  It  would  be  possible  to  decide 
which  nutrient  gave  rise  to  the  greater  part  of  the  carbon  dioxide  formed 
if  we  knew  the  amount  of  oxygen  which  was  consumed  at  the  same  time. 
If  carbohydrates  were  exclusively  oxidized,  the  ratio  of  the  volume  of  oxygen 
taken  up,  to  that  of  carbon  dioxide  produced,  would  be  equal  to  1.  The 
ratio  of  CO^C^  is  called  the  "  respir^atorx quotient."  It  is  only  0.71  in 
the  case  of  the  fats.  Experiments  which  have  been  made  in  this  direction 


FATS,  CARBOHYDRATES,  AND  ALBUMINS. 


347 


indicate  that  the  carbohydrates  are  attacked  immediately  after  absorption 
from  the  intestine,  thus  sparing  the  body  fat.  We  must  not  forget,  with 
regard  to  such  experiments,  that  the  conclusions  drawn  are  for  the  most 
part  indirect.  They  are  not  conclusive.  A  comparison  of  the  general 
metabolism  on  the  basis  of  income  and  outgo  alone,  must  necessarily  lead 
to  a  one-sided  decision.  The  results  of  physiological-chemical  investi- 
gations must  not  be  left  out  of  consideration,  and  the  finer  details  of  the 
work  must  not  be  forgotten  in  studying  the  coarser  outlines  of  metabolism 
as  a  whole.  We  have  seen  that  the  metabolism  of  carbohydrates  in  all 
of  its  phases  is  an  extremely  delicately  regulated  process.  Sugar  reappears, 
after  absorption,  in  the  liver,  deposited  in  the  form  of  glycogen.  This 
does  not  vanish  so  easily.  It  is  extremely  difficult  to  obtain  an  animal 
which  is  free  from  glycogen.  At  all  events,  our  knowledge  regarding  the 
transformation  of  the  carbohydrates  in  the  tissues  is  altogether  opposed  to 
the  assumption  that  they  are  rapidly  burned  up  after  absorption,  even 
during  work.  We  know  it  is  true  that  the  muscles  evidently  prefer  to 
utilize  the  energy  from  carbohydrates  in  their  performance  of  work,  but 
this  very  fact  prevents  us  from  believing  that  the  organism  consumes  this 
valuable  material  in  order  to  save  the  fats. 

Studies  on  metabolism  have  shown  us  that  there  is  a  difference  in  the 
behavior  of  the  protein  in  food  and  that  of  fats  and  carbohydrates, 
which  are  themselves  very  similar  in  their  behavior.  We  have  already 
stated  that  by  increasing  the  amount  of  protein  in  food,  there  is  an  in- 
creased metabolism.  This,  however,  is  not  the  case,  or  at  least  not  to  the 
same  extent,  if  we  increase  the  quantities  of  fat  or  carbohydrate,  as  the 
following  experiments,  carried  out  by  M.  Rubner,  show: 


Income. 

Total  Metabolism  in  Calories. 

Day. 

Nitrogen  in 
Grams. 

Fat  in  Grams. 

Carbohydrate 
in  Grams. 

In  Calories. 

Absolute. 

Per  Kilogram 
of  Body 
Weight. 

2 

969 

40.2 

3 

56.8 

1513 

1072 

44.8 

4 

947 

39.9 

5 

167 

1536 

963 

40.9 

6 

.  . 

922 

39.6 

7 

411 

1446 

982 

42.3 

8 

... 

977 

42.1 

2,  4,  6,  and  8  are  fasting  experiments.  In  them  40.4  calories  per  kilo- 
gram body  weight  is  the  average  metabolism.  The  addition  of  albumin 
causes  an  increase  in  the  number  of  calories  amounting  to  11.9  per  cent; 
the  addition  of  fat,  1.2  per  cent;  and  that  of  carbohydrates,  4.2  per  cent. 


348  LECTURE  XV. 

The  figures  show  that  the  number  of  calories  in  each  case  were  about  the 
same  in  the  three  experiments.  If  such  experiments  are  carried  out 
unaccompanied  by  muscular  work,  the  difference  between  the  effect  of 
albumin,  on  the  one  hand,  and  that  of  the  carbohydrates  and  fats,  on  the 
other,  towards  the  entire  metabolism,  becomes  more  marked. 

We  have  now  finished  all  that  we  care  to  say  with  regard  to  the  mutual 
relations  existing  among  the  three  most  important  organic  nutrients. 
We  have  discussed  two  ways  in  which  they  may  replace  one  another.  On 
the  one  hand,  it  is  possible  by  means  of  a  chemical  transformation  for  one 
nutrient  to  be  converted  into  another,  and,  again,  the  replacement  may 
be  merely  one  of  calorific  values,  without  any  such  transformation  being 
necessary.  The  latter  method  of  one  food  replacing  another  is  undoubtedly 
of  the  greatest  importance  in  the  whole  economy  of  metabolism.  It 
represents  the  greatest  possible  utilization  of  the  available  energy,  and 
guarantees  the  satisfactory  maintenance  of  the  entire  metabolism,  even 
when  one  of  the  nutrients  is  not  momentarily  available.  Albumin  is  an 
exception.  It  is  only  in  part  replaceable.  If  the  organism  is  starving, 
it  tries  to  preserve  its  albumin  by  consuming  first  the  fats  and  car- 
bohydrates available,  thus  protecting  its  tissues  against  severe  injury. 
The  former  condition  of  the  body  is  therefore  quickly  regained  as  soon  as 
food  is  eaten  again.  It  is  only  when  the  organism  draws  upon  its  own 
protein  for  the  main  supply  of  the  required  energy,  that  the  end  is  near. 
It  is  of  great  interest  to  note,  that  the  reserve  materials  held  in  store  by 
the  organism,  and  drawn  upon  during  starvation,  likewise  enter  into  metab- 
olism strictly  in  accordance  with  their  calorific  values.  As  soon  as  the 
body  substances  are  called  upon  to  act  as  combustible  material,  they  also 
follow  the  Law  of  Isodynamics. 


LECTURE   XVI. 

INORGANIC    FOODS. 

L 

IMPORTANCE    OF    INORGANIC    SUBSTANCES  AS    BUILDING    MATERIAL    OP 
THE   CELLS   AND  TISSUE.  —  WATER,   SALTS. 

ALL  of  the  food-stuffs  which  we  have  studied  up  to  the  present,  are  those 
by  means  of  which  the  animal  may  obtain  chemical  energy.  The  con- 
ception of  a  food  is,  in  fact,  closely  related  to  this  property.  We  recognize, 
however,  a  group  of  compounds  indispensable  to  the  organism  which  it 
always  receives  with  its  food,  but  from  which  it  can  obtain  no  chemical 
energy.  We  refer  to  water  and  inorganic  salts.  Thus  far  we  have  con- 
sidered the  foods  solely  with  regard  to  their  value  as  sources  of  kinetic 
energy.  We  must  not  forget,  however,  that  the  organism  is  constantly 
wearing  out  its  cell-material;  in  fact,  individual  cells  may  even  be  entirely 
thrown  off,  only  to  be  regenerated  and  built  up  anew.  Such  processes 
are  particularly  noticeable  in  the  case  of  growing  organisms.  In  such 
cases  the  new  cells  formed  in  place  of  the  old  ones  are  often  of  larger 
dimensions.  Yet,  it  must  not  be  thought  that  the  fully  developed 
organism  retains  its  cellular  condition  unchanged.  At  present  we  are  not 
in  a  position  to  explain  fully  the  metabolism  within  the  individual  cells. 
We  have  no  means  of  knowing  how  long  a  single  cell  may  live;  we  do  not 
know  how  long  it  can  exercise  its  function  with  the  same  material.  All 
that  we  can  say  is  that  there  are  certain  processes  visible  to  the  eye  which 
give  indication  of  a  continuous  breaking  down  and  building  up  of  cells. 
We  know  that  hair,  feathers,  scales,  etc.,  undergo  constant  changes, 
processes  which  take  place  in  some  species  of  animals  very  slowly,  but 
continuously;  while  in  other  cases,  as  with  the  shedding  of  feathers  in  the 
case  of  birds,  and  the  changing  of  skins  with  reptiles  and  amphibia,  such 
processes  take  place  within  a  relatively  short  time.  Again,  we  know  of 
the  constant  change  in  the  cells  of  the  epidermis,  and  in  the  cells  of  the 
mucous  membrane.  Similarly  we  know  that  there  is  a  continual  loss  of 
material  involved  in  the  exercise  of  the  function  of  numerous  glands.  In 
this  connection  we  need  merely  mention  the  glands  of  the  skin,  —  the 
sebaceous  and  sweat  glands,  —  the  salivary  glands,  and  the  numerous  little 
mucous  glands  of  the  respiratory  and  digestive  membranes.  The  same 

349 


350  LECTURE  XVI. 

is  true  of  all  the  glands  taking  part  in  the  digestive  processes,  beginning 
with  those  of  the  stomach  and  the  mucous  membrane  of  the  alimentary 
canal,  on  to  the  large  digestive  glands  of  the  pancreas  and  liver.  In  all 
such  cases  the  organism  suffers  a  constant  loss  of  material.  Again,  the 
organism  constantly  requires  the  presence  of  salts,  and  water  to  flush  out 
the  waste  material  through  the  kidneys.  Further,  we  have  to  consider 
the  specific  tasks  of  the  single  cells  and  cell-groups  by  means  of  which 
definite  products  are  developed  which  play  an  important  part  in  the  metab- 
olism of  the  organs,  whether'  it  be  a  ferment,  or  some  other  product  such 
as  adrenalin,  which  is  formed  in  the  suprarenal  gland. 

Furthermore,  the  fact  that  there  is  evidently  a  lively  breaking  down 
-and  building  up  even  in  tissues  which  we  would  scarcely  expect  to  par- 
ticipate in  active  metabolism,  is  shown  to  us  by  a  histologic  study  of  the 
bones,  which  show  evidence  of  a  continual  exchange  of  their  building 
material.  From  the  field  of  pathology,  we  find  that  the  building  up  of 
the  nerves  and  their  restitution  under  some  conditions  may  assume  con- 
siderable dimensions.  This  is  shown,  for  example,  in  the  case  of  hyper- 
trophic  activity,  which  appears  as  soon  as  there  is  an  additional  require- 
ment placed  upon  a  certain  organ,  whether  because  of  the  fact  that  it 
must  act  as  a  substitute  for  another,  or  whether  because  its  work  becomes 
increased  in  some  other  abnormal  way,  as,  for  example,  in  the  case  of  the 
heart  in  certain  kinds  of  heart  trouble.  On  the  other  hand,  in  conva- 
lescence after  certain  fevers,  particularly  typhoid,  we  find  a  sudden  reju- 
venation of  the  sunken  cell-energy.  Each  cell  takes  up  the  building 
material  from  the  circulating  nourishment,  and  this  is  particularly  true  of 
albumin,  which  in  a  certain  sense  determines  the  functional  activity  of 
the  cell.  In  a  short  time  the  organism  is  renewed.  The  loss  of  albumin 
which  the  body  has  experienced  during  the  disease  is  quickly  compen- 
sated. The  old  equilibrium  in  the  economy  of  the  cells  is  again  estab- 
lished. Again,  a  sudden  increased  production  of  cell-material  takes  place 
after  some  local  irritation.  Thus  we  find  that  the  organism  concentrates 
a  great  number  of  leucocytes  at  an  infected  point,  and  finally  perhaps 
large  masses  of  pus  are  formed,  all  at  the  cost  of  the  nourishment  and  the 
material  composing  the  organs.  On  the  other  hand,  sometimes  we  find 
the  organism  throwing  off  considerable  quantities  of  exudate,  as,  for 
example,  in  pneumonia,  which  again  uses  up  large  amounts  of  material. 
On  the  other  hand,  if  we  consider  the  continual  variations  in  the  number 
of  red  and  white  corpuscles,  and  the  variations  in  the  lymphocytes,  we 
obtain  the  impression  that  the  cell-material  of  the  fully  developed  organism 
is  never  at  rest.  We  know  practically  nothing  concerning  the  quantitative 
relations  involved  in  all  such  changes.  We  do  not  know  whether  the 
material  in  the  old  cells  is  used  to  some  extent  in  building  up  new  ones, 
or  whether  the  new  cells  are  entirely  formed  from  new  material.  We  do 


INORGANIC  FOODS. 


351 


not  know  whether  the  individual  organs  can  effect  an  exchange  of  materials, 
or  whether  the  cells  of  one  group  can  utilize  the  waste  material  of  another. 
The  interesting  studies  of  Miescher  l  on  salmon  give  us  some  information 
in  this  direction.  Previous  to  spawning,  these  fish  migrate  from  the  sea 
into  fresh  water,  for  example,  into  the  Rhine.  From  the  time  that  these 
fish  reach  the  river  up  to  the  time  that  the  eggs  are  laid,  they  take  no 
nourishment.  This  fact  was  known  to  Barfurth  2  and  to  His.3  Meischer 
estimated  that  the  majority  of  the  salmon  remained  in  the  Rhine  for  from 
six  to  nine  and  one-half  months,  a  smaller  number  stayed  up  to  twelve 
months,  while  some  were  there  as  long  as  fifteen  months.  During  all  of 
the  time  that  the  fish  remains  in  fresh  water,  nothing  is  eaten.  The  intes- 
tines are  always  found  empty;  and,  indeed,  Miescher  established  the  fact 
that  the  digestive  glands  during  this  period  do  not  yield  any  active  juices. 
A  series  of  marked  changes  take  place  in  the  appearance  of  the  fish  during 
this  period.  When  the  salmon  first  reaches  fresh  water  its  organs  of  regen- 
eration are  quite  undeveloped.  Being  provided  with  a  powerful  dorsal 
musculature,  it  is  able  to  stem  the  most  rapid  currents  in  the  Rhine.  On 
comparing  such  a  fish  with  one  that  is  taken  just  before  the  spawning 
time,  it  seems  scarcely  possible  that  they  are  the  same  kind  of  fish. 
The  large  dorsal  muscle  has  become  shrunken;  the  sexual  organs,  on 
the  other  hand,  have  become  enormously  developed.  There  is  a  parallel- 
ism between  the  two  changes.  Miescher  observed,  for  example,  that  the 
weight  of  the  ovary  increased  from  9.4  grams  to  15  grams,  while  simul- 
taneously there  was  a  diminution  in  the  dry  substance  and  in  the  albumin 
content  of  the  dorsal  muscles  as  shown  by  the  following  average  values: 


Length  in 
Milli- 
meters. 

Weight  in 
Grams. 

Weight  of 
Ovary  in 
Per  cent 
of  Body 
Weight. 

Composition  of  Dor- 
sal Muscle. 

Per  cent 
Albumin. 

Per  cent 
Dry  Sub- 
stance. 

March 

872 
886 
879 

9305 
8953 
7428 

0.061 
4.78 

18.45 
17.5 
13.2 

33.6 

26.8 
18.5 

July  and  August 

November  and  December  .... 

The  albumin  lost  by  the  muscles  is  evidently  utilized  in  building  up  the 
sexual  glands  —  in  one  case  the  eggs,  and  in  the  other  the  sperm  cells. 


1  Die  histochemischen  und  physiologischen  Arbeiten  von  Friedrich  Miescher,  vol.  ii. 
Leipsic,  1897.     Pp.  116  et.  seq. 

2  Troschel's  Arch.  Naturgeschichte,  Jg.  xli,  I,  122  (1875). 

3  Untersuchungen  iiber  das  Ei  und  die  Eientwicklung  bei  Knochenfischen.    Leipsic, 
1873. 


352  LECTURE  XVI. 

Direct  observation  confirms  this.  Microscopic  examination  of  the  ovaries 
and  of  the  testes  shows  that  most  active  processes  of  growth  and  trans- 
formation are  taking  place.  On  the  other  hand,  the  large  dorsal  muscle 
exhibits  all  the  signs  of  a  far-reaching  release  of  its  stored  material 
and  of  even  the  contents  of  its  cells,  the  muscular  fibers.  Everything  is 
not  given  up,  but  as  much  of  the  material  as  can  be  spared  is  transformed, 
leaving  enough  behind  so  that  subsequently  when  the  salmon  returns  to 
the  sea  the  muscles  may  be  regenerated.  It  is  the  large  dorsal  muscle 
which  entirely  provides  the  material  for  the  changes  taking  place  in  the 
body  of  the  starving  fish,  whereas  the  remaining  muscles  undergo  no 
change  that  indicates  in  any  way  a  migration  of  material.  It  has  never 
been  satisfactorily  explained  just  how  this  migration  takes  place.  Miescher 
describes  the  appearance  of  small  drops  of  fat  between  the  muscle  fibrils. 
The  amount  of  these  drops  may  become  so  great  that  the  whole  muscular 
fiber  becomes  opaque.  It  is  obvious  that  in  this  way  preparation  is 
being  made  for  a  migration  of  fat.  Besides  albumin  and  fat,  the  muscle 
must  give  up  phosphates  which  in  the  formation  of  eggs  evidently  become 
a  part  of  the  lecithin.  The  other  salts  and  substances,  such  as  choles- 
terol and  the  nuclein  substances  required  to  form  the  nuclei  of  the  eggs, 
must  likewise  be  obtained  from  the  dorsal  muscle.  It  is  evident,  there- 
fore, that  the  migration  of  substance  here  attains  large  dimensions. 
Undoubtedly  a  study  of  this  interesting  biological  phenomenon  by  modern 
methods  would  give  us  considerable  insight  into  the  extent  of  the  syntheses 
capable  of  being  carried  out  in  the  organism.  Every  supply  from  the 
outside  is  cut  off.  The  entire  sexual  products  are  formed  from  material 
taken  from  the  dorsal  muscle.  It  is  clear  that  a  comparison  of  the  amount 
of  lecithin,  nucleic  acids,  etc.,  contained  in  this  muscle  with  those  of  the 
sexual  products,  would  give  us  a  good  idea  of  the  metabolism  and  of  the 
chemical  processes  involved. 

These  observations  permit  us  to  draw  certain  conclusions  concerning 
metabolism  during  starvation.1  If  every  source  of  food  supply  is  cut  off 
from  an  animal,  then  the  organism  turns  to  its  own  body  for  nourishment. 
Carbon  dioxide  is  constantly  being  eliminated  and  oxygen  absorbed,  and 
likewise  the  chemical  composition  of  the  urine  gives  unmistakable  proof 
that  combustion  is  continually  taking  place,  which  in  warm-blooded 
animals  suffices  not  only  for  the  performance  of  mechanical  work,  but  also 
for  maintaining  the  temperature  of  the  body.  If  we  compare  the  relative 
proportions  by  weight  of  the  separate  organs  of  a  starving  animal  with 
those  of  one  that  is  well  nourished,  it  is  at  once  apparent  that  the  different 
organs  do  not  participate  equally  in  the  metabolism.  Thus  the  nervous 
system  and  'the  heart  show  but  slight,  if  any,  changes  in  their  composition 


1  S.  M.  Lukjanow:  Z.  physiol.  Chem.  13,  339  (1889).     C.  Voit:  Z.  Biol.  31,  510  (1894). 
A.  Hermann:  Pfl tiger's  Arch.  43,  239  (1888). 


INORGANIC  FOODS.  353 

as  regards  both  organic  and  inorganic  matter.  Evidently  these  organs 
which  are  so  indispensable  to  life  are  maintained  at  the  expense  of  the 
less  vital  tissues.  In  such  cases  there  is  a  continuous  transportation  of 
material  from  one  tissue  to  another.  The  fact  that  one  organ,  which 
during  starvation  will  normally  lose  material  to  a  considerable  extent, 
may  under  other  conditions,  i.e.,  when  its  function  is  of  especial  impor- 
tance to  the  whole  organism,  be  kept  in  full  activity  at  the  expense  of 
other  organs,  is  shown  by  an  observation  made  by  Pfliiger  l  that  the  liver 
of  dogs  after  extirpation  of  the  pancreas,  in  spite  of  the  resulting  glucosuria, 
did  not  diminish  in  weight,  whereas  all  the  other  organs  —  excepting  the 
heart  and  nervous  system  —  were  greatly  impaired.  Now  we  know 
what  an  important  part  the  liver  plays  in  the  metabolism  of  carbohydrates, 
so  that  we  can  easily  understand  that  under  the  above  conditions  the 
function  of  the  organ  is  of  especial  importance  to  the  animal. 

How  economical  the  animal  organism  is  with  its  materials  that  it  has 
once  built  up,  is  shown  by  another  of  E.  Pfluger's  2  observations.  The 
larva  of  the  nurse-frog  (Alytes  obstetricans)  is  fully  grown  at  the  end  of 
May.  It  has  then  attained  a  length  of  about  8.1  centimeters,  of  which 
about  3  centimeters  belong  to  the  real  body,  and  the  remainder  to  its 
over-sized  tail.  After  the  larva  has  reached  this  stage,  it  no  longer  takes 
any  nourishment.  At  the  same  time  the  tail  begins  to  shrivel  up.  Its  cell- 
material  is  liquefied  and  migrates  to  the  true  body;  and  as  the  tail  dis- 
appears, the  front  and  hind  legs  shoot  out.  Just  imagine  what  important 
transformations  must  take  place  in  this  process  of  developing  the  limbs  of 
the  animal  from  what  was  the  tail!  As  soon  as  the  tail  has  all  been 
absorbed,  nourishment  is  again  taken  up  from  the  outside.3 

This  suffices  to  give  us  some  idea  as  to  the  mutual  relations  in  the  metab- 
olism of  the  different  organs.  It  is  not  likely  that  the  above  observations 
represent  exceptional  cases.  It  is  far  more  probable  that  such  changes 
are  of  common  occurrence,  and  in  a  way  this  is  quite  similar  to  the  rela- 
tion known  to  exist  between  the  glycogen  in  the  muscles  and  that  of 
the  liver. 

Even  although  the  greater  part  of  the  nourishment  absorbed  is  employed 
for  the  production  of  energy,  a  certain  portion  of  it  is  taken,  as  required,  - 
whether  albumin,  carbohydrate,  lecithin,  cholesterol  or  nuclein  substances, 
—  and  utilized  for  the  building  up  and  extension  of  the  cells.  We  cer- 
tainly cannot  limit  our  conception  of  the  term  "  food  "  to  those  substances 
which  we  know  to  be  sources  of  energy.  The  function  of  serving  the 


1  E.  Pfliiger:  Pfliiger's  Arch.  108,  115  (1905). 

2  Pfluger's  Arch.  29,  78  (1882);  54,  333  and  403  (1893). 


3  The  phenomenon  is  not  peculiar  to  the  larvae  of  the  nurse-frog,  but  is  common  to 
larvae  of  amphibia  which  pass  through  this  stage.  The  larvae  of  Rana  fusca  and  of 
Rana  temporaria  at  least  show  a  similar  behavior,  although  here  the  animal  apparently 
eats  up  the  tail.  The  material  of  the  organ  is  utilized,  at  all  events. 


354  LECTURE  XVI. 

cells  must  also  be  included.  As  we  have  said,  water  and  inorganic  salts, 
neither  of  which  imparts  to  the  organism  any  chemical  energy,  must  neces- 
sarily be  considered  as  foods,  for  they  exercise  this  function  of  being  of 
use  to  the  cells.  Now  we  know  that  the  animal  organism  takes  up  a 
considerable  amount  of  salts  with  its  food,  while  on  the  other  hand  it  is 
equally  well  known  that  the  organism  constantly  eliminates  salt  in  the 
urine  and  in  the  sweat.  These  losses  must  naturally  be  replaced.  For 
the  salts  it  would  seem,  a  priori,  as  if  there  were  not  much  need  for  such 
replacement.  We  could  easily  imagine  that  the  salts  set  free  in  the  break- 
ing down  of  cell-material  could  be  used  anew  in  the  formation  of  new  cells. 
With  water  it  is  quite  another  matter,  because  the  organism  needs  water 
for  a  number  of  different  processes.  Its  importance  is  shown  by  the  fact 
that  two-thirds  of  the  animal  organism  consists  of  water.  Every  cell 
must  contain  water.  It  forms  one  of  the  prime  conditions  for  a  definite 
physical  consistency  of  the  cell.  Water  is  absolutely  necessary  as  a 
solvent  for  numerous  compounds.  It  brings  into  play  numerous  chemical 
reactions,  and  takes  part  in  the  building  up  and  breaking  down  of  sub- 
stances without  number.  It  is  a  carrier  of  nourishment  to  the  body, 
whether  through  the  blood,  the  lymph,  or  the  finest  fissures  between  the 
cell;  and,  conversely,  it  provides  the  means  for  carrying  away  the  waste 
products.  When  we  remember  in  addition  that  the  body  must  give  up 
water  to  the  air  in  the  process  of  respiration,  and  that  in  water  the  animal 
organism  possesses  its  most  important  means  of  regulating  the  temperature 
of  the  body,  by  virtue  of  its  evaporation  on  the  surface,  it  soon  becomes 
apparent  why  water  plays  such  an  all-important  part  in  the  life  process 
not  only  for  animals  but  naturally  for  plants  as  well.  In  the  combustion 
of  the  food,  naturally  some  water  is  formed  in  the  body,  but  this  amount 
is  so  small  that  it  by  no  means  suffices  to  satisfy  all  the  requirements. 
The  animal  organism  must  have  a  supply  of  water  from  without. 

Now,  are  the  inorganic  salts  also  indispensable  for  the  nourishment  of 
the  fully  developed  organism?  An  attempt  has  been  made  to  answer 
this  question  by  providing  animals  with  food  which  is  as  free  from  ash  as 
possible.  The  first  to  perform  such  experiments  was  Forster.1  As  food 
he  made  use  of  the  meat  residue  obtained  in  the  preparation  of  Liebig's 
Extract  of  Beef.  After  having  been  repeatedly  boiled  with  water,  such 
meat  contains  only  0.8  gram  of  ash,  for  each  100  grams  of  dry  substance. 
This,  together  with  fat,  sugar,  and  starch,  he  fed  to  two  dogs.  Both  of 
the  animals  experimented  upon  died  very  soon;  in  fact,  much  more  quickly 
than  if  they  had  not  been  fed  at  all.  The  same  result  was  obtained  by 
feeding  three  pigeons  with  starch  and  casein.  Against  the  conclusion 
that  death  was  caused  by  lack  of  salt,  G.  von  Bunge  2  very  properly  raised 

1  Z.  Biol.  9,  297  and  369  (1873). 

2  Ibid.  10,  111  and  130  (1874). 


INORGANIC  FOODS.  355 

the  question  that  possibly  the  lack  of  salt  may  have  had  an  indirect  action. 
In  the  catabolism  of  that  part  of  albumin  containing  sulphur,  the  cystine, 
there  is  formed,  as  we  have  seen,  a  considerable  amount  of  sulphuric  acid. 
This  under  normal  conditions  will  unite  with  the  basic  salts  contained  in 
the  nourishment  and  be  eliminated  as  a  salt  of  the  acid.  If  now  the 
nourishment  contains  none  of  these  basic  salts,  then  the  sulphuric  acid 
will  constantly  withdraw  alkali  from  the  cell  components  so  that  the 
system  will  not  only  fail  to  have  salts,  but  the  whole  structure  of  the  cells 
will  be  injured  by  taking  away  a  part  of  the  building  material.  Now  if 
such  a  hypothesis  be  correct,  then  the  addition  to  the  nourishment,  which 
is  otherwise  practically  free  from  ash,  of  sufficient  alkali  to  unite  with  this 
sulphuric  acid  should  enable  the  animal  to  live  longer.  Lunin  1  showed 
by  experiments  that  this  was  actually  the  case.  He  fed  mice  with  casein, 
fat,  and  cane-sugar.  The  amount  of  ash  contained  in  this  mixture  was 
only  one-tenth  of  that  in  the  mixture  used  by  Forster.  With  this  food 
and  distilled  water  five  mice  lived  respectively,  11,  13,  14,  15,  and  21  days. 
Other  mice  were  not  given  any  food  at  all;  two  died  in  three,  and  two  in 
four  days. 

Next  Lunin  fed  six  mice  with  the  same  mixture,  to  which  some  sodium 
carbonate  had  been  added.  These  animals  lived  16,  23,  24,  27,  and  30 
days,  or  nearly  twice  as  long  as  the  mice  did  in  the  previous  experiment. 
Now  the  objection  may  be  raised  to  this  last  experiment  that  here  the 
sodium  carbonate  may  not  act,  as  Bunge  reasoned  a  priori,  as  an  alkali, 
but  rather  as  a  salt.  In  order  to  meet  this  objection,  Lunin  fed  seven 
mice  with  the  same  mixture,  except  that  the  sodium  carbonate  was  replaced 
by  an  equivalent  amount  of  sodium  chloride  (common  salt).  These 
animals  died  at  the  end  of  6,  10,  11,  15,  17,  and  20  days;  i.e.,  they 
did  not  live  any  longer  than  the  mice  in  the  first  experiment.  The  experi- 
ments were  repeated  with  potassium  carbonate  and  potassium  chloride, 
but  with  the  same  result. 

Now  although  the  addition  of  sodium  and  potassium  carbonate  to  such 
a  diet  was  sufficient  to  prolong  the  life  of  the  animals,  it  was  not  able  to 
maintain  their  existence  for  any  length  of  time.2  Note,  however,  that, 
these  animals  had  received  only  one  salt  in  the  nourishment.  It  might 
be  thought  that  better  results  would  be  obtained  with  a  mixture  of  salts. 
Lunin,  therefore,  compared  the  lengths  of  life  of  mice  fed  upon  cow's  milk, 
with  that  of  mice  fed  with  the  above  mixture  of  casein,  fat,  and  cane- 
sugar,  plus  the  same  salts  that  are  contained  in  milk.  Care  was  taken  to 


1  Ueber  die  Bedeutung  d.  anorganischen  Salze  f.  d.  Ernahrung  d.  Tieres.     Dissert. 
Dorpat,  1880,  and  Z.  physiol.  Chem.  6,  31  (1881). 

2  Cf.  C.  A.  Socin,  Z.  physiol.  Chem.  15,  93  (1891).     Abderhalden  u.  Rona,  ibid.  42, 
528  (1904).     Henriques  and  Hansen,  ibid.  43,  417  (1905).     Falta  and  Noeggerath,  Hof- 
meister's  Beitrage,  7,  313  (1905). 


356  LECTURE  XVI. 

maintain  the  same  proportion  of  salts  to  organic  material  as  in  milk.  Fed 
with  such  a  mixture,  six  mice  lived  20,  23,  29,  30,  and  31  days,  or  about 
the  same  length  of  time  as  the  mice  fed  with  the  former  mixture  containing 
alkali  carbonate.  Two  mice,  fed  entirely  upon  cow's  milk  for  a  period  of 
2J  months,  remained  in  good  health  at  the  end  of  the  experiment. 

These  experiments  apparently  prove  that  it  is  not  possible  to  keep  mice 
alive  without  feeding  them  salts,  and,  moreover,  that  an  artificial  mixture 
of  salts  fails  to  sustain  the  lives  of  mice  for  more  than  a  short  time.  This 
result  may  be  accounted  for  in  a  number  of  different  ways.  It  has  not 
shown  that  the  early  death  of  the  mice  in  the  first  experiment  was  actually 
due  to  a  lack  of  salts  in  the  diet.  It  is  equally  conceivable  ,that  certain 
necessary  organic  constituents  were  wanting.  Milk  always  contains, 
besides  casein,  a  certain  amount  of  albumin.  It  is  possible  that  the 
albumin  is  of  great  importance  for  certain  functions.  Again,  perhaps 
lecithin  and  cholesterol  are  essential.  Possibly  milk  contains  organic 
compounds  of  a  nature  unknown  to  us.  Above  all  we  must  remember 
that  the  exceedingly  important  Law  of  the  Minimum  1  holds  for  the  nour- 
ishment of  animals  as  well  as  for  that  of  plants.  In  any  diet  the  amount 
of  each  constituent  required  by  the  organism  must  be  regulated  in  accord- 
ance with  this  principle.  Perhaps  some  inorganic  element,  such  as  fluor- 
ine was  lacking,  and  for  this  reason  the  other  inorganic  constituents  were 
not  sufficiently  utilized.  Naturally  the  same  law  holds  with  regard  to  the 
organic  constituents. 

Until  recently  but  little  was  known  concerning  the  physiological  impor- 
tance of  salts  in  the  plant  and  animal  organism.  It  was  known  that  they 
took  part  in  the  anabolism  of  the  cells.  In  fact,  potassium,  sodium,  calcium, 
magnesium,  iron,  phosphoric  acid,  fluorine,  and  chlorine  are  invariably 
found  in  every  cell.  In  some  cases,  manganese,  silicic  acid,  iodine,  and 
arsenic  are  found  in  the  animal  cells.  The  plants  receive  their  nourish- 
ment from  the  ground,  and  under  certain  conditions  may  contain  other 
elements;  for  example,  copper,  zinc,  and  aluminium.  Silicic  acid  in  many 
cases  of  plant  life  is  an  important  source  of  rigidity.  The  plant  cell 
requires  inorganic  material.  There  is  no  doubt  that  the  physiological 
importance  of  the  salts  is  the  same  in  both  the  animal  and  vegetable  king- 
doms, and  the  assumption  that  they  form  merely  a  passive  building 
material  for  the  cells  is  not  justifiable.  This  is  evidenced  by  the  fact  that 
the  distribution  of  the  inorganic  material  is  not  uniform  throughout  the 
organism.  Thus  we  find  in  certain  cells  more  potassium  and  less  sodium, 
while  in  the  liquids  of  the  body,  for  example  the  serum,  the  relative 
amounts  of  the  two  are  reversed.  In  the  cells  there  is  more  phosphoric 
acid,  but  less  chlorine.  It  is  evident  from  this  that  the  taking  up  of  salts 

1  J.  Liebig:  Die  Chemie  in  ihrer  Anwendung  auf  Agrikultur  und  Physiologic, 
p.  332  (1876). 


INORGANIC  FOODS.  357 

by  the  cells  is  an  active  process.  Thus  the  cell  withdraws  from  the  serum, 
which  is  rich  in  sodium  salts  and  contains  less  potassium,  the  potassium. 
It  is  possible  that  the  researches  of  Bokorny  l  concerning  the  behavior  of 
lower  organisms  to  solutions  of  certain  dyestuffs  may  throw  some  light 
on  these  processes. 

He  showed,  namely,  that  the  protoplasm  of  certain  cells  would  take  up 
definite  compounds  even  from  very  dilute  solutions,  so  that,  for  example, 
a  colored  solution  would  eventually  become  colorless.  Bokorny  assumed 
that  chemical  combination  took  place  between  the  protoplasm  and  the 
substances  in  question.  He  showed,  for  example,  that  the  Spirogyra  and 
Cladophora  would  absorb  silver  from  a  solution  containing  only  one  part 
in  100,000,000.  In  a  solution  of  1  :  10,000,000  enough  silver  was  taken  up 
so  that  when  treated  with  hydrochloric  acid  and  hydrogen  sulphide  the 
algae  turned  black.  Likewise  from  very  dilute  solutions  of  copper  and 
mercury  salts  the  cells  would  remove  the  inorganic  material.  Toward 
other  compounds,  e.g.  gold  salts,  the  behavior  was  quite  different.  From 
gold  solutions  containing  one  part  in  100,000  the  gold  is  not  removed  by 
the  above-mentioned  algae,  nor  by  yeast  cells.  There  is  a  specific  action 
between  these  cells  and  the  heavy  metals  which  we  cannot  explain  at 
present.  The  absorption  of  certain  salts  by  the  cells  of  the  animal  organism 
must  take  place  in  conjunction  with  certain  definite  and  specific  processes 
by  means  of  which  a  definite  selection  in  definite  proportions  is  made 
possible.  Quite  recently  we  have  become  able  to  explain  in  a  measure 
the  part  played  by  salts  in  the  life  of  the  cells.  The  function  of  the  salts 
is  undoubtedly  chiefly  an  osmotic  one.  It  is  the  task  of  the  inorganic 
salts  to  regulate  the  osmotic  pressure  of  the  cell-fluid  itself  and  of  the 
intercellular  fluid.  It  is  clear  that  any  change  taking  place  in  this  pres- 
sure, whether  by  the  taking  up  or  giving  off  of  water,  causing  a  swelling 
or  a  shrinking  of  the  cell,  or,  on  the  other  hand,  any  changing  in  the 
concentration  or  dilution  of  the  reacting  mixture  contained  in  the  proto- 
plasma,  will  immediately  lead  to  most  serious  disturbances  in  the 
progress  of  certain  reactions.  Above  all,  the  velocity  of  the  reactions  will 
be  changed. 

The  part  played  by  the  inorganic  material  is  not  restricted,  however,  to 
maintaining  this  constant  osmotic  pressure  between  the  liquids  within 
and  without  the  cell.  This  is  evident  from  the  fact  that  the  cell  requires 
certain  definite  salts.  It  is  not  possible,  for  instance,  to  replace  success- 
fully the  potassium  in  the  cell  by  an  equivalent  amount  of  sodium.  The 
individual  salts  must  exert  for  themselves  a  specific  action,  although  it  is 
not  yet  clear  as  to  just  what  this  may  be.  We  are  acquainted  with  quite 
a  number  of  isolated  facts  in  this  connection,  but  with  our  present  knowl- 
edge it  is  not  possible  to  group  them  together  and  view  them  from  one 


Chem.-Ztg.  29,  1201  (1905). 


358  LECTURE  XVI. 

standpoint  so  that  definite  conclusions  may  be  drawn.  It  may  be  well  to 
cite  one  or  two  examples  showing  that,  in  fact,  there  is  a  specific  action  of 
the  inorganic  salts.  Overton  *  has  shown  that  the  muscles  of  a  frog  will 
retain  their  normal  volume  in  a  0.7  per  cent  solution  of  common  salt,  and 
remain  excitable  at  the  end  of  40  to  48  hours.  In  concentrated  salt 
solutions  their  volume  is  diminished,  whereas  in  dilute  solutions  it  increases. 
Solutions  of  grape-sugar,  cane-sugar,  milk-sugar,  mannitol,  alanine, 
asparagine,  etc.,  having  the  same  osmotic  pressure  as  the  0.7  per  cent 
common  salt  solution,  are  equally  indifferent  as  regards  the  osmosis.  In 
such  solutions,  however,  the  excitability  of  the  muscle  is  soon  lost.  On 
adding  a  little  common  salt  to  one  of  these  solutions,  however,  it  is  again 
possible  to  excite  the  muscle.  In  fact,  0.068  to  0.074  per  cent  of  salt  suffices 
to  render  this  effect.  The  next  question  is  whether  a  change  of  the  anion 
(Cl)  keeping  the  cation  (Na)  constant  will  have  any  effect.  It  was  found 
the  chloride  could  be  replaced  successfully  by  equivalent  amounts  of  the 
bromide,  nitrate,  sulphate,  bicarbonate,  chlorate,  acetate,  and  secondary 
phosphate  of  sodium,  showing  that  the  anions  had  no  influence  here.  In 
a  series  of  further  experiments  the  cation  was  changed,  and  it  was  found 
that  the  sodium  could  be  replaced  by  lithium  alone,  while  potassium, 
calcium,  magnesium,  strontium,  and  barium  salts  were  unable  to  preserve 
the  excitability  of  the  muscle.  It  is  perfectly  obvious,  therefore,  that  the 
sodium  ions,  besides  serving  to  maintain  a  definite  osmotic  pressure,  also 
exert  a  quite  specific  action  upon  the  contractility  of  the  muscle. 

Jacques  Loeb  2  succeeded  in  performing  a  Very  pretty  experiment.  If 
the  medusa  Gonionemus  be  placed  in  a  solution  of  cane-sugar  or  of  glycerol, 
the  osmotic  pressure  of  which  corresponds  to  that  of  the  ocean,  its  rhythmic 
pulsation  ceases  immediately.  This  is  not  the  case,  however,  if  a  solution 
of  sodium  chloride  or  bromide  is  used  in  the  above  experiment. 

Loeb  showed,  moreover,  that  the  presence  of  the  sodium  ions  alone 
was  not  sufficient  to  maintain  the  contractility  of  the  muscle.  In  a  0.7  per 
cent  solution  of  common  salt  the  muscles  of  a  frog  after  about  an  hour 
exhibit  rhythmic  contractions  which  last  for  over  24  hours.  It  appears 
as  if  the  sodium  ions  irritate  in  some  way  the  muscular  fibers.  It  has 
even  been  stated  that  they  have  a  poisonous  effect.  It  is  exceedingly 
interesting  that  it  is  possible  to  combat  this  irritation  of  the  sodium  ions 
(also  obtained  with  rubidium  and  caesium  ions)  by  the  addition  of  the 
bivalent  calcium,  strontium,  magnesium  and  manganese  ions.  This 
effect  is  not,  however,  due  merely  to  the  valence  of  the  ion,  for  the  bivalent 
barium,  zinc,  cadmium,  and  lead  ions  do  not  act  in  the  same  way.  On 
the  other  hand  the  monovalent  potassium  ion  has  an  effect  opposite  to 
that  of  the  monovalent  sodium  ion.  It  is  particularly  interesting  that 

1  Pfluger's  Arch.  92,  115  and  346  (1902). 

2  Am.  J.  Physiol.  3,  383  (1900). 


INORGANIC  FOODS.  359 

such  closely  related  chemical  elements  as  sodium  and  potassium  should  act 
so  differently  physiologically. 

A  quite  similar  observation  was  made  with  the  Fundvlus  heteroclitus.1 
This  little  fish  is  not  at  all  sensitive  to  variations  in  osmotic  pressure. 
It  exists  in  salt  water  as  well  as  in  distilled  water,  while  on  the  contrary, 
when  placed  in  a  solution  of  pure  sodium  chloride  of  the  same  concentra- 
tion as  the  ocean,  it  soon  dies.  Its  eggs  behave  similarly.  If  to  the 
solution  of  pure  sodium  chloride  the  ions  of  calcium,  barium,  strontium, 
magnesium,  lead,  cobalt,  ferrous  iron,  zinc,  manganese,  chromium  or  alu- 
minium, are  added,  the  injurious  effect  of  the  sodium  chloride  is  combated 
successfully.  On  the  other  hand,  the  ions  of  mercury,  copper,  cadmium, 
nickel,  and  ferric  iron  are  without  influence. 

The  dependence  of  the  cell-function  upon  the  nature  of  the  salts  present, 
and  the  antagonistic  action  of  different  salts,  are  shown  very  well  by  the 
following  experiment:  A  salt  solution  of  the  concentration  correspond- 
ing to  sea-water  is  poisonous  to  the  eggs  of  the  fundulus.  Calcium  and 
magnesium  exert  no  recognizable  effect  upon  the  eggs.  If  a  fundulus 
egg  be  placed  in  a  pure  aqueous  solution  of  either  of  the  two  last-men- 
tioned salts,  it  does  not  develop.  Development  takes  place,  however, 
immediately  on  adding  a  sodium  salt  to  the  solution. 

At  this  place,  we  will  recall  the  experiments  of  Martin  H.  Fischer.2  By 
the  injection  of  a  J  molecular  solution  of  common  salt  into  the  veins,  he 
was  able  to  produce  a  glucosuria  which  in  its  entire  behavior  corresponded 
to  that  produced  by  the  diabetic  puncture.  Such  a  glucosuria  can,  in  the 
case  of  rabbits,  be  prevented  by  adding  a  little  calcium  chloride  to  the 
solution  which  is  injected  (975  cubic  centimeters  of  J  molecular  NaCl  solu- 
tion +  25  cubic  centimeters  of  J  molecular  CaCb  solution).  After  the 
elimination  of  sugar  has  ceased,  it  can  be  renewed  by  the  injection  of  pure 
sodium  chloride  solution,  and  again  checked  by  means  of  the  calcium 
chloride  solution. 

This  reciprocal  effect  is  interesting,  and  its  study  opens  up  new  fields  of 
investigation.  Each  cell  has  evidently  particular  salts  in  specific  appor- 
tionment. A  disturbance  of  this  relation  by  the  preponderance  of  this 
salt  at  one  time,  and  that  salt  at  another  time,  may  cause  considerable 
trouble  in  the  economy  of  the  cell.  For  the  present  it  is  necessary  for  us 
to  study  the  action  of  the  individual  ions  separately  and  in  artificial  mix- 
tures. As  regards  the  proportions  of  the  separate  ions  in  the  cells,  our 
present  methods  of  investigation  can  throw  no  light.  It  is  true  that  by 
analyzing  the  ash,  we  can  get  some  idea  as  to  the  inorganic  constituents 
of  an  organ.  Aside  from  t'he  fact  that  such  an  analysis  can  never  give  us 


1  Jacques  Loeb:  Pfliiger's  Arch.  80,  229  (1900).   Cf.  W.  A.  Osborne:  J.  Physiol.  [Proc. 
Physiol.     Soc.  33,  10  (1905)]. 

2  Pfliiger's  Arch.  106,  80  (1904),  and  109,  1  (1905). 


360  LECTURE  XVI. 

a  conception  of  the  way  the  different  elements  are  combined  in  the  cell, 
we  need  only  to  refer  to  the  extremely  delicate  mechanism  in  the  action 
of  the  individual  ions  to  make  one  realize  how  far  we  are  from  under- 
standing fully  the  mechanism  of  the  cell  itself. 

Jacques  Loeb  by  means  of  his  comprehensive  studies  deserves  great 
credit  for  having  added  so  much  to  our  knowledge  concerning  the  action 
of  salts  and  their  reciprocal  action,  and  especially  by  his  work  on  arti- 
ficial parthenogenesis.1  At  this  place  we  can  hardly  take  up  in  detail 
these  numerous  and  highly  interesting  investigations.  We  shall  come 
back  to  them  again.  A  great  number  of  such  experiments  have  been  made. 
Unfertilized  eggs  of  the  Annelida  may  be  developed  by  placing  them 
in  sea-water  to  which  a  small  amount  of  potassium  salt  has  been  added 
(e.g.,  one  or  two  cubic  centimeters  of  2J  N.KC1  or  KNO3  solution  to  100 
cubic  centimeters  of  salt  water.)  Such  eggs  develop  apparently  normal 
larvae.  Such  a  solution  has  no  action  upon  the  unfertilized  eggs  of  the 
sea-urchin. 

These  experiments  have  been  cited  to  show  that  the  presence  of  inorganic 
ions  is  indispensable  for  the  life-process.  The  manner  in  which  they 
act  is  still  unknown  to  us.  It  is  possible  that  new  light  may  be  thrown 
upon  this  question  by  a  study  of  the  other  components  of  the  cell,  and 
especially  of  their  behavior  towards  the  ions.  Now  the  cells  contain 
colloids,  and  in  fact  the  life  process  itself  is  intimately  related  to  their 
presence.  There  is  no  doubt  that  the  peculiar  physical  condition  of  the 
cell-contents  is  of  great  importance  to  all  of  the  different  processes  which 
take  place  within  the  cell.  Indeed,  this  alone  makes  it  possible  for  so 
many  different  reactions  to  take  place  side  by  side.  Colloidal  solutions 
diffuse  but  very  slowly  —  in  fact,  scarcely  at  all  —  into  one  another.  In- 
creased viscosity  of  a  medium,  however,  does  not  affect  the  rate  of  diffu- 
sions of  crystalloids  and  electrolytes,  nor  the  mobility  of  the  ions,  nor  does 
it  affect  the  degree  of  dissociation  of  electrolytes.  A  monomolecular  reac- 
tion (e.g.,  the  catalysis  of  methyl  acetate  by  dilute  hydrochloric  acid) 
takes  place  in  a  jelly  just  as  rapidly  as  in  water.  On  the  other  hand,  the 
colloid,  on  account  of  its  internal  friction,  often  prevents  the  formation 
of  precipitates.  This  is  effected,  not  by  preventing  the  reaction  from 
taking  place,  but  rather  by  keeping  the  newly  formed  molecules  in  such 
an  extremely  minute  state  of  subdivision  that  they  do  not  come  together 
to  form  visible  complexes.  The  colloids  cause  an  enormous  increase  in 
surface  tension.  • 

The  entire  conception  of  colloids  is  in  a  stage  of  rapid  development. 
There  is  no  way  of  defining  precisely  the  part  that  they  take  in  the  life  of 
the  cell.  Many  isolated  facts  indicate  that  the  future  investigation  of 


1  Cf.  Abderhalden:  Arch.  Rassen-und  Gesellschaftsbiologie,  Jg.  I,  p.  656  (1905). 


INORGANIC  FOODS.  361 

colloids'  will  undoubtedly  greatly  increase  our  knowledge  concerning  the 
work  of  the  cell.1  Here  we  are  especially  interested  in  the  behavior  of 
colloids  towards  ions.  Hardy  2  has  shown  that  ions  exert  a  particular 
influence  upon  the  condition  of  the  colloid.  Negatively  charged  colloids 
are  precipitated  by  the  electropositive  cations,  and  positively  charged 
colloids  by  anions.  In  these  relations  we  find  a  new  proof  of  how  extremely 
delicate  the  whole  mechanism  of  the  cell  is  to  enable  it  to  maintain 
between  the  individual  ions  on  the  one  hand,  and  the  colloids  on  the 
other  in  such  a  relation  that  all  of  its  functions  can  take  place  unhindered. 
It  is  perfectly  clear  without  further  explanation,  that  owing  to  the  various 
reactions  taking  place  within  the  cells,  at  one  time  the  action  of  one  ion 
is  most  prominent,  while  at  another  time  it  is  that  of  a  different  one. 
The  cell  must  always  be  able  to  neutralize  at  a  given  moment  the  action 
of  any  one  ion.  Undoubtedly  physical  chemistry  has  here  pointed  out 
new  paths  for  further  investigation,  and  there  is  no  question  but  that  it 
will  enable  us  eventually  to  draw  new  conclusions  along  lines  that  have 
already  been  studied.  Here  again  in  the  operations  of  the  delicate  mechan- 
ism of  the  cell,  it  is  not  right  to  attempt  to  distinguish  between  the  physical 
chemistry  and  physiological  chemistry  of  the  cells.  Here  and  there  it  is 
advisable  to  separate  the  two  fields  and  allow  them  to  develop  individually, 
but  again  and  again  they  must  come  back  to  a  common  basis  and 
unite  to  form  a  broader  field,  which  develops  by  different  methods  as 
a  whole. 

It  is  obvious  from  a  study  of  the  experiments  already  cited  that  salts 
and  water  are  fully  as  important  as  regards  the  life  of  the  cell  as  its  organic 
nutriment.  Just  as  the  part  played  by  the  latter  is  quite  a  varied  one, 
so  in  the  same  way  the  inorganic  substances  participate  in  a  number  of 
'different  processes.  Although  they  do  not  furnish  the  body  with  energy, 
nevertheless  they  do  come  into  play  during  the  expenditure  of  muscular 
effort,  whether  by  changes  in  the  concentration  of  the  solutions,  or  by 
variations  in  the  osmotic  pressure,  or  of  the  surface  tension,  etc. 

Inorganic  salts  are  usually  present  in  the  different  foods  to  an  extent 
entirely  sufficient  for  all  our  demands.  An  exception  to  this  general  rule 
is  the  fact  that  man  and  certain  animals  require  an  additional  supply  of 
sodium  chloride.  Sodium  chloride  is  the  only  inorganic  substance  which 
it  is  necessary  to  add  to  our  diet.  This  is  rather  remarkable,  because  both 
animal  and  vegetable  food  already  contains  considerable  sodium  and 
chlorine.  The  explanation  of  this  exceptional  requirement  in  the  case  of 


1  Cf.  Hans  Aron:  Biochem.  Zentr.  3,  15,  16,  17,  pp.  461  and  501  (1905).  R.  Zsig- 
mondy:  Zur  Erkenntnis  der  Kolloide,  Jena,  1905.  H.  J.  Hamburger:  Osmotischer 
Druck  u.  lonenlehre  in  den  medizinischen  Wissenschaften,  Wiesbaden,  1904.  R. 
Hober:  Physikalische  Chemie  d.  Zelle  u.  d.  Gewebe,  Leipsic,  1902. 

3  Z.  physikal.  Chem.  33,  385  (1900). 


362  LECTURE  XVI. 

common  salt  we  owe  to  G.  von  Bunge.1  Bunge  pointed  out  in  the  first 
place  that  among  animals  only  the  true  herbivora,  and  never  the  carnivora, 
crave  salt.  This  fact  is  familiar  to  hunters.  They  know  that  wild  her- 
bivora —  ruminants  and  solidungulates  —  frequent  the  salt  licks.  Now 
the  amount  of  sodium  chloride  which  these  animals  obtain  in  their  food 
is  about  the  same  per  unit  of  the  animal's  weight  as  that  obtained  by  the 
carnivora  in  its  diet.  It  is  hardly  to  be  said,  therefore,  that  there  is  a 
lack  of  sodium  chloride  unless  we  assume  that  this  salt  plays  a  particular 
part  in  the  organism  of  the  herbivora,  an  assumption  which,  in  the  light 
of  recent  investigations  concerning  the  action  of  the  individual  ions,  no 
longer  seems  so  improbable.  Bunge  has  shown,  however,  that  vegetable 
food  differs  from  animal  food  by  the  amount  of  potash  which  the  former 
contains.  The  herbivora  obtain  three  or  four  times  as  much  potassium 
salt  in  the  food  as  the  carnivora  do.  All  vegetables,  especially  potatoes, 
clover,  and  meadow  hay,  contain  large  amounts  of  potash.  We  know  of 
but  very  few  land  plants  which,  like  the  varieties  of  Chenopodium  and 
Atriplex,  contain  more  sodium  chloride  than  potassium  salt.  It  is  easy 
to  account  for  the  high  potash  content  of  plants  by  the  distribution  of  the 
elements  sodium  and  potassium  on  the  earth's  surface.  By  the  weathering 
of  silicate  rocks,  sodium  carbonate  is  formed,  which  dissolves  readily  in 
rain  water  and  trickles  down  into  the  earth.  The  potassium,  on  the  other 
hand,  remains  with  the  other  bases  combined  with  silica  and  aluminium  as 
an  insoluble  double  salt.  The  latter  remains  near  the  earth's  surface, 
while  the  sodium  is  flushed  out  by  springs,  brooks,  and  rivers,  and  carried 
on  to  the  ocean.  This  accounts  for  the  fact  that  potassium  salts  pre- 
dominate on  the  surface  of  the  earth,  while  the  ocean  is  rich  in  sodium 
salts,  especially  the  chloride. 

Now  why  should  an  increased  amount  of  potassium  salts  create  a  demand 
for  a  greater  supply  of  sodium  chloride?  Bunge  suggests  the  following 
ingenious  explanation:  If  a  potassium  salt,  for  example  the  carbonate, 
comes  in  contact  with  sodium  chloride,  a  partial  decomposition  takes 
place,  a  little  potassium  chloride  and  sodium  carbonate  being  formed. 
Now,  as  regards  the  inorganic  salts  of  the  blood-serum,  sodium  chloride 
ranks  foremost.  It  is  found  there  to  a  considerable  extent,  and,  as  far  as 
we  know,  the  amount  is  kept  fairly  constant.  Now,  on  bringing  the  serum 
in  contact  with  the  abundance  of  absorbed  potassium  salts  obtained  from 
the  vegetable  nourishment,  this  double  decomposition  between  the  sodium 
salt  in  the  blood  and  the  absorbed  potassium  salt  will  take  place  to  some 
extent.  In  this  way  potassium  chloride  is  formed,  and  a  part  of  the  sodium 
of  the  blood  combines  with  the  acid  which  was  previously  united  with  the 
potassium.  By  this  process  the  composition  of  the  blood  is  changed. 

1  Z.  Biol.  9,  104  (1873);  10,  111,  295  and  323  (1874);  Lehrbuch  der  Physiologic  der 
Menschen,  Bd.  ii,  p.  103  (1901). 


INORGANIC  FOODS.  363 

The  serum  now  contains  a  substance  which  did  not  occur  in  it  previously, 
or  at  any  rate  not  to  the  same  extent  as  now;  namely,  the  newly  formed 
sodium  salt.  It  is  the  duty  of  the  kidneys,  as  we  shall  see  later,  to  keep 
guard  over  the  serum  and  to  regulate  its  chemical  composition.  They 
eliminate  every  constituent  which  under  normal  conditions  is  foreign  to 
it,  and  take  away  any  excess  of  compounds  which  belong  there.  In  the 
above  case  the  kidneys  eliminate  the  newly  formed  sodium  salt  together 
with  the  potassium  salt.  This  process,  therefore,  results  in  the  serum 
being  deprived  of  sodium  chloride. 

Bunge  succeeded  in  testing  this  theory  experimentally.  He  himself  took 
18  grams  of  K2O  as  phosphate  and  citrate  in  three  doses  during  the  course 
of  the  day,  and  showed  that  as  a  result  his  body  lost  6  grams  of  sodium 
chloride.  This  does  not  constitute  an  abnormal  amount  of  potash  salts. 
A  man  fed  largely  on  potatoes  will  easily  take  40  grams  of  K2O  into  his 
system  during  the  day.  The  loss  of  sodium  chloride  is  by  no  means 
restricted  to  the  blood.  There  is  a  constant  exchange  of  material  between 
it  and  the  cells.  After  what  we  have  seen  with  regard  to  the  effect  of  the 
ions,  we  can  easily  understand  the  possibility  that  a  diminution  in  the 
amount  of  sodium  contained  in  the  cells,  which  is  in  no  way  replaceable 
by  potassium  ions,  may  lead  to  serious  disturbances.  The  organism,  at 
all  events,  will  attempt  as  soon  as  possible  to  restore  the  disturbed  equili- 
brium. 

Bunge,  to  support  his  views,  cited  numerous  facts.  He  showed,  for 
example,  that  in  France  the  country  folk  consume  three  times  as  much 
salt  per  capita  as  those  who  dwell  in  cities.  Now  it  is  a  fact  that  in  the 
country  much  larger  quantities  of  vegetables  are  eaten  than  in  the  city, 
where  the  diet  consists  largely  of  meat.  A  further  support  of  the  assump- 
tion that  the  vegetables  rich  in  potassium  were  the  cause  of  the  increased 
consumption  of  salt,  was  gained  by  a  study  of  people  who  live  almost 
entirely  upon  meat;  e.g.,  certain  races  of  hunters,  fishermen,  and  nomads. 
To  gain  this  knowledge,  Bunge  read  through  a  large  number  of  articles  on 
travels,  and  also  placed  himself  in  correspondence  with  travelers.  In  this 
way  he  established  the  fact  that  at  all  times  and  in  all  countries  where 
the  people  subsist  solely  upon  animal  nourishment,  either  they  have  no 
knowledge  of  salt,  or  do  not  care  for  it,  whereas  in  countries  in  which  the 
inhabitants  subsist  mainly  on  vegetables  there  is  always  such  an  unmis- 
takable craving  for  salt,  that  it  has  become  considered  as  one  of  the  neces- 
sities of  life.  This  is  the  case  in  both  the  north  and  south  polar  regions. 
Again,  in  countries  in  which  the  inhabitants  live  on  meat  and  rice,  there  is 
no  craving  for  salt.  Rice  contains  but  one-sixth  as  much  potash  as 
wheat,  rye,  barley,  or  Indian  corn,  one-twentieth  as  much  as  the  legumes, 
and  only  from  one-twentieth  to  one-thirtieth  as  much  as  potatoes. 

Now  what  happens  in  the  case  of  a  people  subsisting  chiefly  on  vegeta- 


364  LECTURE  XVI. 

bles,  and  yet  living  where  there  is  no  salt  supply?  Such  people  prepare 
a  salt  of  their  own.  Thus,  Bunge  x  was  able  to  procure  a  salt  obtained  by 
ignition  of  a  plant  which  was  used  by  the  negroes  in  the  southern  part  of 
Khartum,  Africa,  as  a  seasoning  for  their  vegetable  food.  The  analysis 
of  this  salt  showed  it  to  contain  19.27  per  cent  Na2O  and  4.92  per  cent 
K2O,  or  nearly  six  equivalents  of  soda  to  one  of  potash.  It  is  interesting 
here  to  find  that  the  natives  have  selected  a  plant  (Salsola,  or  salt-wort) 
which  is  especially  characterized  by  its  high  soda  content.  The  natural 
instinct,  however,  does  not  always  assert  itself  so  well  in  this  direction, 
for  there  are  other  races  which  use  for  salt  the  ash  of  a  plant  rich  in  potash. 
Lapicque  2  examined  such  a  salt.  The  inhabitants  of  the  Angoni  district 
in  British  Central  Africa  use  a  substance  prepared  by  burning  goat  manure 
and  wood.  Analysis  showed  that  it  contained  21.98  per  cent  KC1  and 
0 . 47  per  cent  NaCl.3  It  is  interesting  to  learn,  however,  that  after  Lapicque 
had  shown  the  natives  how  to  obtain  common  salt,  they  gave  up  the  prepa- 
ration of  their  own  native  condiment.  Salt,  for  the  inhabitants  of  Angoni, 
is  an  extremely  expensive  article  of  commerce.  The  natives  toil  for  salt 
upon  the  plantations. 

The  assumption  that  the  high  potash  content  of  vegetable  foods  causes 
losses  in  the  sodium  content  of  the  blood  and  indirectly  of  the  tissues,  is 
not  in  agreement  with  certain  observations.  Thus,  Landsteiner  4  fed  a 
number  of  young  rabbits  exclusively  upon  meadow  hay  for  3J  months. 
At  the  same  time  another  lot  of  similar  animals  was  fed  entirely  with 
cow's  milk,  which  contains  for  one  equivalent  of  soda  only  0.7  to  3.7 
equivalents  of  potash.  Now  although  these  two  series  of  animals  were 
fed  with  nourishment  containing  quite  different  relative  amounts  of  alkali, 
nevertheless,  at  the  end  of  the  experiment  the  soda  and  potash  content  of 
the  blood  was  the  same  in  each  case.  We  know,  furthermore,  that  in 
spite  of  the  fact  that  rabbits  and  hares  live  on  fodder  rich  in  potash,  they 
do  not  show  the  slightest  craving  after  salt,  and  under  normal  conditions 
do  not  obtain  any  in  addition  to  what  their  food  contains.  It  is  possible 
that  the  organism  of  these  animals  may  be  different  in  some  way,  so  that 
the  loss  of  sodium  is  avoided.  On  the  other  hand,  it  is  a  well-known  fact 
that  purely  herbivorous  animals,  such  as  cows  and  sheep,  can  subsist  upon 
fodder  rich  in  potash  for  a  long  time  without  any  extra  salt,  and  there  is 
no  recognizable  disturbance  in  the  development  of  these  animals.  It  is 
indeed  possible,  and  even  probable,  that  the  potassium  salts  contained  in 
the  fodder  do  not  have  such  a  marked  effect  as  pure  potassium  chloride, 
when  taken  by  itself  into  the  system  at  one  time  and  absorbed  as  such. 


1  Z.  Biol.  41,  484  (1901). 
3  L'Anthropologie  (1896). 

3  Abderhalden:  Pfliiger's  Arch.  97,  103  (1903). 

4  Z.  physiol.  Chem.  16,  13  (1892). 


INORGANIC  FOODS.  365 

We  perhaps  do  not  yet  know  all  the  different  ways  in  which  potash  can  be 
eliminated.  We  shall  see  that  for  the  heavy  metals  the  intestines  are  an 
important  vehicle  for  their  elimination.  It  is  even  possible  that  the  liver 
regulates  the  amount  of  potassium  salts,  holding  a  part  back  so  that  the 
blood  does  not  at  any  one  time  come  in  contact  with  large  amounts  of 
them.  At  all  events,  the  influence  of  potassium  salts  contained  in  the 
food  upon  the  elimination  of  sodium  salts  by  the  urine  must  be  tested  with 
some  food,  such  as  potatoes,  which  is  rich  in  potassium  salts.  The  exper- 
iment should  extend  over  a  considerable  period  in  order  to  determine 
whether  any  loss  of  sodium  chloride  is  permanent  or  only  temporary. 

The  organism  must  in  every  case  have  ways  and  means  for  keeping  the 
soda  and  potash  content  of  the  blood  constant  in  spite  of  variations  in  the 
food  supply.  It  is  worthy  of  mention  that  the  serum  of  all  species  of 
animals  *  which  have  been  investigated  up  to  the  present  time  always 
contains  the  same  amounts  of  these  two  elements;  the  serum  of  the  car- 
nivora,  as  well  as  that  of  the  herbivora,  contains  about  0 . 43  per  cent  of 
soda,  and  0.026  per  cent  of  potash.  Perhaps  the  fact  that  the  red  cor- 
puscles of  the  ruminants,  in  contrast  to  those  of  the  horse,  cow,  rabbit,  etc.r 
contain  considerable  amounts  of  soda,  may  shed  some  light  upon  the  fact 
that  the  former  crave  salt,  while  the  latter  do  not.  To  be  sure,  the  red 
corpuscles  of  the  carnivora  also  contain  larger  amounts  of  soda.  It  is 
very  interesting  that  in  the  milk  of  carnivora  the  two  alkalies  are  present 
in  approximately  equivalent  amounts,  whereas  in  the  milk  of  the  herbivora. 
and  in  human  milk  the  potash  predominates.  The  organism  of  the  her- 
bivora and  of  the  carnivora,  corresponding  to  their  later  nourishment,, 
thus  early  becomes  accustomed  to  a  definite  relation  between  the  amounts 
of  potassium  and  sodium.  The  beasts  of  prey,  which  live  upon  the  entire 
animal,  obtain  sodium  and  potassium  in  almost  equivalent  amounts.  On 
the  other  hand,  the  herbivora  and  the  human  race  receive  in  many  foods 
the  two  bases  in  the  same  relative  amounts  as  in  milk;  some  kinds  of  hay 
contain  three  equivalents  of  potash  to  one  in  soda,  while  in  milk  there  are 
from  one  to  six  equivalents  of  potash  to  one  of  soda.  We  may,  indeed, 
assume  that  the  organism  is  adjusted  to  the  general  preponderance  of 
potash  over  soda,  and  that  disturbances  take  place  only  when  the  cus- 
tomary relation  is  changed  greatly  at  the  expense  of  the  sodium,  as  would, 
for  example,  be  the  case  if  the  food  consisted  entirely  of  potatoes.  Rye, 
peas,  and  beans  likewise  contain  very  considerable  amounts  of  potassium, 
as  the  following  table  prepared  by  Bunge  shows: 


1  Abderhalden:  Z.  physiol.  Chem.  25,  65  (1898). 


366 


LECTURE  XVI. 


1  Equivalent  Na2O  Corresponds  to: 


Equivalents 
K,,O. 

Equivalents 
K,0. 

Beef-blood 

0  07 

Oats 

15  to  21 

White  of  hens'  eggs      .    .    . 

0.7 

Rice  

24 

Yolk  of  hens'  eggs    .... 

1.0 

Rye   

9  to  57 

Organism  of  mammals    .    . 

0  .  7  to  1  3 

Hay 

3  to  57 

Milk  of  carnivora     .... 

0.8  to  1.6 

Potatoes 

31  to  42 

Human  milk  

1  to  4 

Peas  ... 

44  to  50 

Milk  of  herbivora     .... 

0.8  to  6 

Strawberries  

71 

Beef 

4 

Clover 

99 

Wheat  

12  to  23 

Apples 

100 

Barley  

14  to  21 

Beans    

110 

Bunge's  conception  that  common  salt  widens  the  circle  of  our  food 
supply,  may  well  be  a  correct  one.  It  makes  it  possible  for  us  to  enjoy 
potatoes  and  many  other  foods  which  are  rich  in  potash. 

As  stated  before,  our  ordinary  food  contains  sufficient  quantities  of  the 
inorganic  salts,  and  it  is,  in  general,  not  to  be  feared  that  too  little  of  one 
or  another  salt  will  be  taken  into  the  system. 

Our  diet  is  ordinarily  a  mixed  one.  If  one  article  of  food  or  another 
contains  too  little  of  any  salt,  the  deficiency  is  made  up  by  something 
else  that  is  eaten.  The  fact  that  an  exclusive  diet  of  substances  lacking 
in  this  or  that  salt  may  lead  to  disturbances  will  be  shown  later.  Now, 
although  it  be  granted  that  we  need  take  no  thought  concerning  the  supply 
of  inorganic  material  required  by  adults,  the  question  arises  whether  the 
customary  food  of  growing  individuals  likewise  satisfies  the  requirements 
of  the  organism.  This  is  a  justifiable  question,  particularly  in  the  case  of 
mammals,  and  especially  human  children;  for  right  in  the  midst  of  their 
growing  period  a  change  takes  place  in  their  food  which  compels  us  to 
compare  the  composition  of  their  first  food,  the  milk,  with  that  which  is 
eaten  subsequently.  The  amount  of  inorganic  salts  contained  in  milk 
must  give  us  some  idea  as  to  the  requirements  of  the  young.  The  follow- 
ing table  gives  a  summary  of  the  contents  of  the  ash  from  human  milk  and 
that  of  certain  animals : 1 


100  Parts  by  Weight  of  Milk  Contain  in  Grams: 


species. 

K20 

Na2O 

Cl 

Fe2O3 

CaO 

MgO 

P,Os 

Man  

0.0795 

0.0253 

0.0468 

0  .  0008 

0.0489 

0.0065 

0.0585 

Dog   
Pig            .        .    . 

0.1382 
0  0945 

0.0779 
0  0776 

0.1656 
0  0756 

0.0020 
0  0040 

0.4545 
0  2489 

0.0195 
0  0157 

0.5078 
0  3078 

Sheep    

0  0967 

0  0864 

0  1297 

0  0041 

0  2453 

0  0148 

0  2928 

Goat      
Cow  

0.1302 
0.1776 

0.0617 
0.0972 

0.1019 
0.1368 

0.0036 
0.0021 

0.1974 
0.1671 

0.0154 
0.0231 

0.2840 
0.1911 

Horse    

0.105 

0.014 

0.031 

0.002 

0.124 

0.013 

0.131 

Guinea  pig 

0  0754 

0  0700 

0  0999 

0  0013 

0  2417 

0  0241 

0.2880 

Rabbit      

0.2516 

0.1980 

0.1355 

0.0020 

0.8914 

0.0552 

0.9966 

Emil  Abderhalden:  Z.  physiol.  Chem.  26, 487  and  498  (1899) ;  27,  408  and  356  (1899). 


INORGANIC  FOODS. 


367 


A  glance  at  the  above  table  shows  that  the  composition  of  milk  varies 
with  different  animals.  The  values  also  vary  in  the  case  of  different 
animals  of  the  same  species,  but  during  the  suckling  period  the  variation 
is  only  within  narrow  limits.  We  shall  find  that  the  amount  of  ash  and 
also  of  the  inorganic  material  bears  a  certain  relation  to  the  rapidity  with 
which  the  tissue  is  formed  as  shown  by  the  body  weight. 

It  is  interesting  now  to  trace  the  relations  between  the  composition  of 
the  milk  (especially  that  of  its  ash)  and  that  of  the  suckling.  It  is  of 
course  obvious  that  such  a  comparison  will  serve  to  give  us  merely  a  rough 
idea  of  these  relations,  for  our  present  methods  of  analysis  are  not  suffi- 
ciently delicate  for  us  to  attempt  to  explain  the  way  in  which  the  differ- 
ent elements  are  combined.  The  analysis  of  the  ash,  for  example,  merely 
shows  us  what  inorganic  material  is  present,  and  gives  us  absolutely  no 
conception  of  the  manner  in  which  these  elements  are  combined  in  the 
body.  We  do  not  know  from  this  whether  the  phosphoric  acid  that  we 
find  was  present  entirely  as  calcium  phosphate  or  other  phosphates,  or 
whether  it  represents  in  part  lecithin.  At  the  same  time  the  knowl- 
edge of  the  constituents  of  the  ash  forms  a  basis  for  further  investiga- 
tion, and  with  the  above-mentioned  limitations  gives  us  some  means  for 
comparison. 

Now  it  is  a  striking  fact,  as  the  figures  below  will  show,  that  milk  has 
such  a  different  composition  from  the  elements  out  of  which  it  is  formed; 
namely,  the  blood,  and  especially  the  blood-serum.  The  cells  of  the  milk- 
glands  must  possess  the  power  of  selection.  Now,  what  determines  the 
composition  of  the  milk?  Bunge,1  with  reference  to  this  question,  com- 
pared the  composition  of  milk-ash  with  that  of  the  suckling  itself,  and 
found  in  the  case  of  dogs  the  following  relations: 


100  Parts  by  Weight  of  Ash  Contain  in  Grams: 

Dog  a  Few 
Hours  Old. 

Dog's  Milk. 

Dog's  Blood. 

Dog's  Serum. 

K,O 

11.14 
10.6 
29.5 
1.8 
0.72 
39.4 
8.4 

15.0 
8.8 
27.2 
1.5 
0.12 
34.2 
16.9 

3.1 
45.6 
0.9 
0.4 
9.4 
13.3 
35.6 

2.4 
52.1 
2.1 
0.5 
0 
5.9 
47.6 

Na,O 

CaO       .... 

MgO  

PA'.  : 

ci  .....: 

Z.  physiol.  Chem.  13,  399  (1889)  and  Arch.  Anat.  Physiol.  1886,  539. 


368  LECTURE  XVI. 

With  rabbits  the  following  values  were  obtained:1 


100  Parts  by  Weight  of  Ash  Contain  in  Grams: 

Rabbit  14 
Days  Old.2 

Rabbit's  Milk. 

Rabbit's 
Blood.3 

Rabbit's 
Serum.3 

K2O 

10.84 
5.96 
35.02 
2.19 
0.23 
41.94 
4.94 

10.06 
7.92 
35.65 
2.20 
0.08 
39.86 
5.42 

23.75 
31.38 
0.81 
0.64 
6.93 
11.11 
32.66 

3.19 
54.72 
1.42 
0.56 
0 
2.98 
47.83 

Na,O 

CaO  

MgO  

Fe0O, 

PA      ' 

ci  i    

In  the  case  of  the  guinea  pig  we  find: 


100  Parts  by  Weight  of  Ash  Contain: 


New-Born  Guinea 
Pig. 

Guinea  Pig's 
Milk. 

K2O            

8  22 

9  69 

Na2O  . 

6  94 

8  99 

CaO     

32  21 

31  1 

MgO    

3.09 

3.1 

Fe2Oa  . 

0.23 

0.17 

PO 

42  25 

37  02 

ci      

9  1 

12  84 

Camerer  and  Soldner  5  have  made  a  similar  comparison  between  human 
milk  and  the  ash  of  infants : 


100  Parts  by  Weight  Contain  : 


Infant. 

Milk. 

Infant. 

Milk. 

K2O 

7  8 

31  4 

Fe2O3 

0  8 

0  6 

Na2O     .... 
CaO 

9.1 

36  1 

11.9 
16  4 

P205     .... 
CI     

38.9 

7.7 

13.5 
20.0 

MffO  . 

0.8 

2.6 

1  Abderhalden:  Z.  physiol.  Chem.  26,  498  (1899). 

2  G.  v.  Bunge:  Z.  Biol.  10,  323  (1874). 

8  Abderhalden:  Z.  physiol.  Chem.  25,  65  (1898). 

4  Abderhalden:  ibid.  27,  356  (1899). 

6  Z.  Biol.  40,  526  (1900);  41,  37  (1900);  44,  61  (1903). 


INORGANIC  FOODS. 


369 


L.  Hugonnenq l  obtained  quite  similiar  values : 


100  Parts  by  Weight  Contain  : 

Human 

Foetus. 

Human  Milk. 

Human 
Foetus. 

Human  Milk. 

K2O   

6.20 
8.12 
40.48 
1.51 

35.15 
10.43 
14.79 
2.87 

Fe2O3  .... 
P2O6     .... 
Cl     .... 

0.39 
35.28 
4.26 

0.18 
21.30 
10.75 

Na2O     .... 
CaO   . 

MgO  . 

Except  as  regards  the  composition  of  the  human  infant  and  human 
milk,  we  find  by  a  comparison  of  the  corresponding  values  that  there  is  a 
striking  agreement  between  the  ash  of  the  young  animal  and  that  of  the 
milk.  In  the  case  of  human  beings,  however,  we  do  not  find  any  such 
agreement.  Bunge  explains  this  fact  by  the  assumption  that  the  ash 
content  of  milk  has  not  only  the  task  of  building  up  tissue,  but  also  serves 
in  the  preparation  of  the  excreta,  especially  the  urine.  The  more  rapid 
the  growth  of  the  suckling,  the  less  apparent  will  be  the  influence  of  the 
latter  function.  It  is,  therefore,  in  general  not  to  be  expected  that  the 
percentage  composition  of  the  milk  and  that  of  the  infant  will  agree  so 
closely  in  the  case  of  human  beings  as  with  animals,  such  as  dogs,  rabbits, 
and  guinea  pigs,  which  require  the  mother's  milk  for  but  a  short  time  after 
birth,  but  are  soon  placed  upon  a  diet  of  green  fodder.  It  is  easy  to  see 
that  a  milk  corresponding  closely  to  the  chemical  composition  of  the  young 
as  regards  the  inorganic  constituents  will  be  more  suitable  for  animals 
which  develop  very  rapidly,  whereas  with  species  which  develop  more 
slowly,  the  building  up  of  the  separate  tissues  does  not  take  place  so  uni- 
formly and  there  are  not  so  many  changes  taking  place  at  the  time  when 
the  growing  organism  changes  to  another  source  of  nourishment. 

We  now  come  back  to  our  first  question:  Does  the  suckling  when  it 
abandons  the  mother's  milk  and  passes  to  other  food  receive  a  sufficient 
supply  of  inorganic  salts?  The  following  table  gives  a  summary  of  the 
amounts  of  inorganic  substances  contained  in  the  more  important  foods : 2 


100  Parts  by  Weight  of  Dry  Substance  Contain : 


K20 

NaaO 

CaO 

MgO 

Fe203 

P20S 

Cl 

Honey       

0.80 

0.0 

0  007 

0  04 

0  002 

0.09 

0.05 

Beef 

1  66 

0  32 

0  029 

0  15 

0  024 

1  83 

0  28 

Rve            .... 

0  61 

0  01 

0  062 

0  22 

0  007 

1.03 

0.03 

Wheat    

0  62 

0  06 

0  065 

0  24 

C  008 

0.94 

Potatoes  

2  28 

0  11 

0  100 

0  19 

0.009 

0.64 

0.13 

White  of  egg 

1  45 

1  45 

0  130 

0  13 

0  000 

0  20 

1.32 

Pear   

1   13 

0  03 

0  137 

0  22 

0  009 

0.99 

Human  milk    
Yolk  of  eggs    
Cow's  milk  

0.58 

0.27 
1.67 

0.17 

0.17 
1.05 

0.243 

0.380 
1.511 

0.05 

0.06 
0.20 

0.004 

0.024 
0.003 

0.35 

1.90 
1.86 

0.32 

0.35 
1.60 

1  Compt.  rend.  128,  1419  (1899).     Cf.  Cornelia  de  Lange:  Z.  Biol.  40,  526  (1900). 

2  Bunge:  Z.  Biol.  45,  532  (1902). 


370 


LECTURE  XVI. 


It  is  evident  from  these  values  that  most  of  the  foods  are  deficient  in  lime 
alone,  as  compared  with  milk.  Now  while  we  are  not  justified  in  assuming 
that  the  lime-content  of  milk  is  to  be  considered  as  the  normal  amount 
required  for  man's  later  development,  still,  on  the  other  hand,  we  must 
not  forget  that  probably  the  "  law  of  the  minimum  "  holds  for  animal 
organisms  as  well  as  for  plants.  Now  lime  plays  a  quite  particular  part 
in  the  development  of  the  organism,  especially  for  certain  tissues,  the 
bones  and  teeth.  It  is  clear,  therefore,  that  the  system  must  have  an 
adequate  supply  of  the  lime  at  its  disposal.  Of  course  the  fully  developed 
organism  requires  lime  as  well,  for  even  then,  as  we  have  already  seen, 
there  is  a  constant  building  up  and  wearing  down  of  tissue,  and  especially 
of  bony  tissue.  The  following  table  gives  the  amount  of  lime  present  in 
many  of  our  foods.  At  the  same  time  the  amounts  of  iron  they  contain 
are  also  given.  The  values  refer  to  100  grams  of  substance  dried  at  120°  C. 
They  are  arranged  with  increasing  lime-content. 


In  Milligrams: 

In  Milligrams: 

CaO 

Fe 

CaO 

Fe 

Suarar 

0 
7 
29 
33 
46 
60 
65 
62  to  71 
66 
77 
95 
100 
103 
.108 
123 
126 

0 
1.2 
16.9 
225.7 
1.5 
5.6 
5.5 
3.7  to  4.9 
1.9 
5.6 
2.0 
6.4 
1.0  to  2.0 
2.1 
1.9 
2.5 

White  of  egg    .    . 
Red  cherries     .    . 
Peas    

130 
136 
137 
154 
166 
196 
243 
380 
400 
404 
575 

717 
873 
1510 

0 
1.2 
6.4 
1.8 
2.8 
6.4 
2.3  to  3.1 
10  to  24 
4.0 
3.7 
1.5 

5.6 
8.1  to  9.3 
2.3 

Honey 

Beef                        .    . 

Pig's  blood    .... 
White  bread     .    .    . 
Malaga  grapes      .    . 
Wheat 

French  plums  .    . 
Plums     ... 

Huckleberries  .    . 
Human  milk     .    . 
Yolk  of  egg  .    .    . 
Figs 

Rye 

Apples    
Graham  bread      .    . 
Pears       

Wild  raspberries. 
Oranges     .... 
Cabbages    (light 
green  leaves)    . 
Wild  strawberries 
Cow's  milk   .   .   . 

Potatoes    

Rice     

Dates  
Black  cherries     .    . 
Cocoa  beans    .... 

These  values  show  that  it  is  by  no  means  immaterial  what  food  the 
infant  receives  at  the  time  it  leaves  the  mother's  breast.  When  the  child 
is  six  months  old,  it  takes  about  one  liter  of  milk  daily.  This  amount 
contains,  in  round  numbers,  about  0.5  gram  of  lime.  We  do  not  know 
exactly  how  much  lime  the  nursing  infant  requires  at  the  time  it  is 
weaned.  We  can  safely  assume,  however,  that  in  the  later  periods  of  its 
growth,  it  requires  relatively  less.  For  one  thing,  the  development  takes 
place  more  gradually  than  is  the  case  shortly  after  birth;  and,  again,  the 
absolute  amount  of  lime  taken  into  the  system  increases  with  the  quantity 
of  food  eaten.  The  following  figures  will  give  some  idea  of  the  rapidity  of 
the  development  shortly  after  birth.  Rabbits  double  their  weight  at  the 


INORGANIC  FOODS.  371 

end  of  six  or  seven  days.1  It  takes  nine  days  for  dogs  to  accomplish 
the  same  result;  at  the  end  of  eighteen  days  the  weight  was  three  times 
that  at  birth.  With  cats  it  requires  nine  or  ten  days  for  the  weight 
to  become  doubled;  in  one  case  the  weight  was  three  times  as  much 
at  the  end  of  19£  days,  and  four  times  as  much  at  the  end  of  29£  days. 
Pigs  develop  less  rapidly.  On  an  average,  it  requires  14  days  for 
the  original  weight  to  be  doubled;  with  sheep  15  days,  goats  32  days, 
calves  47  days,  and  60  days  in  the  case  of  a  colt.  The  slowest  devel- 
opment is  shown  in  the  case  of  the  human  offspring,  which  does  not  double 
its  weight  until  about  six  months  have  passed  away.  Observations  upon 
the  cat  show  that  the  rate  of  development  decreases  with  age.  It  is 
particularly  striking  only  at  the  time  of  birth.  The  case  of  guinea  pigs  is 
not  without  interest.  According  to  their  development,  they  scarcely 
belong  in  the  ranks  of  the  mammalia;  by  eating  green  food  shortly  after 
birth,  they  rapidly  increase  in  weight.  At  birth  they  are  already  remark- 
ably well  developed.  Even  then  they  are  able  to  eat  the  same  food  as 
that  of  the  mother,  and  thrive  on  cabbage,  etc.  The  female  of  this  animal 
possesses  only  two  mammary  glands,  situated  in  the  groin,  and  milk  plays 
but  a  subordinate  part  in  the  nourishment  of  the  new-born  guinea  pig. 
The  fact  that  the  first  development  of  these  animals  takes  place  quite  as 
rapidly  as  in  the  case  of  the  most  closely  related  animals,  leads  us  to  the 
assumption  that  in  early  times  these  animals  came  into  the  world  in  a 
much  more  undeveloped  condition,  and  were  forced  to  depend  upon  milk 
for  nourishment,  like  other  mammalia. 

It  has  often  been  suggested  that  rickets,  a  quite  common  children's 
disease,  is  caused  by  a  lack  of  lime-salts  in  the  nourishment.  In  fact,  this 
disease  appears  most  frequently  when  the  mother's  milk  for  some  reason 
is  replaced  by  some  other  form  of  nourishment.  There  is  no  doubt  that 
in  considering  the  value  of  a  food  for  replacing  the  mother's  milk,  too 
much  stress  has  been  laid  upon  the  amount  of  fat,  proteid,  and  carbo- 
hydrate. Certainly  a  mistake  is  being  made  unless  equal  attention  is  paid 
to  the  amount  of  inorganic  substances  contained  in  the  nourishment. 
According  to  general  experience,  it  is  not  possible  to  replace  the  mother's 
milk  satisfactorily  by  the  milk  of  some  other  animal.  It  is  necessary  to 
add  something  to  cow's  milk  in  order  that  there  may  not  be  any  substance 
present  in  less  than  the  proper  amount.  Then  again  it  is  particularly 
erroneous  to  judge  the  value  of  a  food  used  to  replace  the  mother's  milk 
by  its  calorific  value.  We  must  never  forget  that  the  suckling  must  build 
up  its  tissue  first  of  all.  It  is,  therefore,  by  no  means  a  matter  of  indiffer- 
ence whether  this  or  that  organic  substance  is  relegated  to  the  background, 
whether  fat  or  carbohydrate.  For  the  growing  suckling,  carbohydrates 
and  fat  cannot  be  considered  as  equivalent  in  this  sense.  They  are 

1  Abderhalden:  Z.  physiol.  Chem.  26,  487  (1899);  27,  408  and  594  (1899). 


372  LECTURE  XVI. 

isodynamic  only  as  regards  their  combustion  value.  The  law  of  isody- 
namics  would  undoubtedly  hold  in  the  case  of  sucklings  in  this  direction 
were  it  not  for  the  fact  that  its  body  substance  is  increased  so  largely 
that  it  is  necessary  to  arrange  its  diet  according  to  particular  lines.  We 
must,  to  be  sure,  admit  that  by  the  transformation  of  carbohydrates  to 
fat,  and  perhaps  also  by  the  reverse  process,  one  of  these  nutrients  may 
replace  another,  even  in  the  construction  of  the  cells. 

The  assumption  that  rickets  is  caused  by  a  lack  of  lime  in  the  nourish- 
ment is  contrary  to  numerous  observations.  Rickets  appears  sometimes 
with  a  food  that  is  rich  in  lime,  even  when  the  child  is  being  fed  upon 
mother's  milk,  though  much  less  frequently  than  with  other  food.  It 
might  be  thought  that  there  still  may  be  a  deficiency  in  lime,  and  perhaps 
on  account  of  the  fact  that,  owing  to  a  disturbed  process  of  absorption,  an 
insufficient  supply  of  lime  becomes  available  to  the  tissues.  This  brings 
us  to  the  question  as  to  the  state  of  the  lime  when  it  is  absorbed  and 
assimilated. 

We  meet  here  with  one  of  the  most  remarkable  circumstances  in 
the  entire  subject  of  physiological  nutrition.  Whereas  our  knowledge 
concerning  the  occurrence  of  organic  nutrients  is  considerable,  we  know 
very  little  concerning  the  way  in  which  the  inorganic  substances  are  com- 
bined in  the  food.  We  do  not  know  whether  they  are  present  as  inorganic 
salts,  —  in  the  animal  and  vegetable  tissue,  —  or  whether  complicated 
organic  compounds  are  at  hand  which  contain  these  inorganic  elements 
in  a  state  of  more  or  less  firm  combination.  It  is  conceivable  that  lime,  for 
example,  can  take  part  in  the  construction  of  tissue  only  when  it  is  present 
in  a  definite  state  of  combination.  Such  an  assumption  was  especially 
justifiable  at  the  time  when  it  was  not  recognized  that  it  was  possible  for 
the  human  organism  to  accomplish  syntheses.  Now  that  we  have  seen, 
however,  that  the  animal  cells  are  capable  of  accomplishing  most  com- 
plicated syntheses,  it  becomes  more  and  more  probable  that  they  are  also 
able  to  make  use  of  inorganic  salts  in  the  formation  of  their  tissue. 

Although  we  know  very  little  concerning  the  way  in  which  lime  is  con- 
tained in  the  ordinary  foods,  still,  on  the  other  hand,  it  is  to  be  expected 
that  an  explanation  of  the  way  lime  is  present  in  milk  will  throw  the  most 
light  upon  this  question.  There  are  a  number  of  possibilities  to  consider. 
It  may  be  that  the  lime  is  in  some  way  combined  with  the  protein  in  milk, 
or  that  it  may  be  dissolved  in  it  in  the  form  of  an  inorganic  salt.  At  all 
events,  the  fact  that  the  lime  is  not  present  in  any  firm  state  of  combination 
is  proved  by  the  following  experiment  performed  by  Bunge.1  On  diluting 
cow's  milk  with  water  and  precipitating  the  casein  by  careful  addition  of 
acetic  acid  in  the  cold,  only  a  trace  of  lime  is  found  in  the  albuminous 


Z.  Biol.  45,  532  (1901). 


INORGANIC  FOODS.  373 

precipitate.  By  boiling  and  concentrating  the  filtrate,  the  globulin  and 
albumin  of  milk  are  obtained.  These  proteins  likewise  contain  but  little 
lime.  It  is  not  impossible,  but  quite  probable,  that  the  small  amounts  of 
calcium  contained  in  these  precipitates  are  merely  carried  down  mechani- 
cally, without  there  being  any  state  of  combination  between  the  albumin 
or  globulin  and  the  calcium.  The  greater  part  of  the  lime  is  found  in  the 
filtrate  from  the  two  precipitations.  After  the  removal  of  the  casein  and 
of  the  two  other  protein  substances,  the  addition  of  oxalic  acid  at  once 
causes  the  formation  of  a  precipitate.  The  nitrate  from  this  last  precipi- 
tate of  calcium  oxalate  was  evaporated  to  dryness  and  ignited  with  sodium 
carbonate  in  order  to  remove  the  calcium  from  any  organic  substance 
which  might  not  have  been  precipitable  by  oxalic  acid.  This  ash,  however, 
contained  merely  a  trace  of  calcium.  This  shows  that  the  calcium,  if 
originally  combined  with  protein,  must  be  present  in  some  loose  salt-like 
combination  such  that  even  dilute  acetic  acid  suffices  to  set  it  free.  It 
has,  however,  not  been  established  definitely  whether  some  other  organic 
substance  in  the  milk  may  not  serve  to  keep  calcium  in  solution  in  the 
presence  of  phosphoric  acid.1 

From  these  observations  of  Bunge  we  may  say  that  it  is  undoubtedly 
true  that  lime  is  absorbable  and  assimilable  as  such.  Against  this  assump- 
tion the  objection  may  be  raised  that  it  is  possible  that  the  lime  in  the 
intestine  first  of  all  enters  into  combination  with  some  organic  substance 
and  is  then  ready  for  absorption,  and  that  the  latter  process  depends 
entirely  upon  the  formation  of  such  an  organic  compound.  On  the  other 
hand,  it  may  be  said  that  even  in  such  a  case  the  manner  of  combination 
in  the  alimentary  canal  must  be  a  weak  one,  for  it  is  not  to  be  assumed 
that  any  sort  of  firm  combination  is  formed.  Such  a  loose  form  of  com- 
bination would  have  the  effect  of  keeping  the  calcium  in  solution,  but  it  is 
perfectly  certain  that  they  have  no  other  effect  upon  the  process  of  assimi- 
lation. We  cannot  be  wrong  in  assuming  that  every  calcium  compound 
which  can  be  converted  into  a  soluble  condition  in  the  intestine  is  capable 
of  being  absorbed  and  assimilated. 

We  have  up  to  now  found  no  reason  for  believing  that  the  disease  of 
rickets  is  due  to  a  diminished  capacity  for  absorption  on  the  part  of  the 
alimentary  canal.2  It  is  far  more  probable  that  the  cause  of  the  faulty 
calcification  of  the  bones  is  due  to  a  diminished  assimilation  of  lime.  It 
is  highly  probable  that  the  cause  of  this  is  not  to  be  sought  in  an  unsuitable 
condition  of  the  calcium  salts  that  are  at  the  disposal  of  the  tissues.  It  is 


1  L.  Vaudin,  Ann.  inst.  Pasteur,  8,  502  (1894),  has  observed  that  the  amount  of 
citric  acid  in  milk  is  proportional  to  the  lime  content.  It  is  altogether  out  of  the  ques- 
tion to  believe  that  the  lime  is  simply  dissolved  by  this  acid,  but  possibly  citric  acid  in 
conjunction  with  other  organic  substances  may  serve  to  keep  the  lime  in  solution. 

»  T.  G.  Rey:  Deut.  med.  Wochschr.  35,  569  (1895). 


374  LECTURE  XVI. 

much  more  likely  that  the  function  of  those  cells  whose  duty  it  is  to  assimi- 
late the  required  calcium  does  not  exert  itself  normally.  All  the  facts 
known  concerning  the  bones  of  children  who  have  suffered  from  this 
disease  agree  best  with  this  conception.  Above  all  there  is  a  striking  over- 
production on  the  part  of  the  osteoplastic  tissue.  This  results  in  the 
formation  of  soft  bones  deficient  in  lime,  the  so-called  "  osteoid  tissue." 
At  the  same  time  there  is  an  abnormal  resorption  of  the  tissue  already 
formed.  We  cannot  be  far  wrong,  if  we  attribute  the  disease  of  rickets  to 
a  metabolic  disturbance  on  the  part  of  a  certain  group  of  cells;  and  here 
again  the  cells'  themselves  stand  in  the  foreground  as  organs  of  assimila- 
tion. We  may  say  in  this  connection  that  it  is  not  the  cells  which  play 
the  chief  part  in  the  assimilation  of  lime.  The  other  component,  which 
we  cannot  yet  sharply  formulate  according  to  our  present  knowledge,  and 
therefore  designate  in  general  by  the  term  "plasma,"  is  equally  important. 
We  have  said  nothing  concerning  the  condition  of  the  lime  in  the  cells; 
and,  in  fact,  we  are  not  able  at  present  to  depict  the  calcification  process 
which  takes  place  in  the  formation  of  bones.  We  do  not  know  whether 
the  osteoidal  tissue  formed  in  the  disease  of  rickets  is  capable  of  taking 
up  lime  at  all,  or  whether  it  is  able  to  deposit  calcium  salts  from  their  solu- 
tions. If  we  recall  what  was  said  concerning  the  mutual  relations  of  the 
individual  ions,  we  shall  be  tempted  to  attribute  the  over-production  of 
osteoidal  tissue  to  some  such  influence.1  We  have  seen  that  calcium 
chloride,  for  example,  acts  antagonistically  towards  sodium  chloride,  and 
have  drawn  the  conclusion  from  all  such  observations  that  only  by  means 
of  the  inorganic  substances  in  the  cell  acting  together  do  we  have  any 
guarantee  for  the  normal  exercise  of  the  functions  of  the  cell.  If  any  one 
element  is  missing,  a  disturbance  must  necessarily  follow.  A  certain 
amount  of  opposing  force  is  lost,  and  thus  the  action  of  a  certain  ion  or  a 
group  of  ions  exerting  a  similar  effect  may  be  felt.  With  these  suggestions 
we  will  merely  state  that  all  our  present  knowledge  concerning  rickets 
leads  us  to  the  conclusion  that  the  disease  cannot  be  attributed  to  a  lack 
of  lime  in  the  diet  of  the  child,  and  to-day  we  have  no  reason  for  assuming 
that  the  lime  is  present  in  the  cells  of  those  who  are  suffering  from  this 
disease  in  a  form  which  the  cells  cannot  assimilate.  The  cause  of  rickets 
is  doubtless  much  more  deeply  seated,  and  is  to  be  traced  to  the  organiza- 
tion and  metabolism  of  the  cells  and  tissues  concerned  in  the  process  of 
bone  production.  The  whole  course  of  this  disease,  which  in  fact  is  usually 
"  outgrown,"  is  in  accordance  with  this  view.  It  is  not  to  be  assumed 


1  Of.  Clowes  and  Frisbe,  Am.  J.  Physiol.  14,  173  (1905),  who  have  found  that  a 
rapidly  developing  adeno  carcinoma  in  mice  contains  considerable  potash  and  less  lime. 
Slow  development  of  the  tumor  shows  the  reverse  proportions.  It  is  not  possible  to 
draw  definite  conclusions  at  present  as  to  which  process  is  primary  and  which  secondary 
in  nature,  but  studies  in  this  direction  certainly  warrant  attention. 


INORGANIC  FOODS.  375 

that  more  lime  is  received  in  the  later  years,  for,  as  a  matter  of  fact,  milk, 
which  is  invariably  the  basis  of  infant  diet,  contains  more  lime  than  almost 
any  other  article  of  food,  so  that  the  infant  receives  relatively  more  lime 
than  at  any  subsequent  time. 

It  is  to  be  expected  that  the  formation  of  the  bones  will  be  seriously 
affected  if  the  lime  in  the  food  is  intentionally  made  inadequate.  Thus 
when  Forster  l  and  likewise  Voit 2  fed  young  dogs  with  meat,  fat,  and 
water,  free  from  calcium,  a  faulty  bone-formation  was  soon  apparent. 
Chossat,3  and  later  on  Voit,4  observed  that  fully  developed  pigeons,  which 
were  made  to  subsist  for  a  year  exclusively  upon  washed  wheat  grains 
and  distilled  water,  showed  a  deficient  skeleton.  The  bones  were  very 
fragile,  the  skull  and  breast-bone  being  very  thin,  and  penetrated  with 
sieve-like,  perforations.  These  experiments  merely  prove  that  the  bones 
require  lime  for  their  development.  Such  experiments  have  no  connection 
at  all  with  the  disease  of  rickets.  Particularly,  the  observations  made 
with  the  pigeons  remind  one  very  much  of  osteoporosis,  a  morbid  absorp- 
tion of  bone  which  often  takes  place  in  elderly  people,  especially  in  the 
region  of  the  skull,  and  is  obviously  due  to  inadequate  nourishment  of  the 
bony  tissue. 

Up  to  this  point  we  have  only  traced  the  metabolism  of  the  animal 
organism  in  two  periods,  namely,  during  growth  and  after  the  organism 
is  fully  developed.  An  especial  observation  with  regard  to  the  content 
of  the  food  in  inorganic  salts  is  furnished  by  the  organism  of  the  mother 
during  pregnancy  and  during  lactation.  At  this  time  the  organism  of 
the  child  develops  exclusively  at  the  expense  of  the  mother.  If  the  material 
received  by  the  mother  in  the  food  during  this  period  is  not  sufficient, 
then  the  stores  of  her  organism  are  attacked,  and  finally  her  own  tissue 
is  subject  to  resorption.  The  foetus  develops  continually  even  when  the 
mother  is  starving.  Remarkable  migrations  of  substance  must  take 
place  during  this  entire  process.  Our  knowledge  concerning  these  rela- 
tions is  still  very  incomplete.  The  following  table  prepared  by  Hugon- 
nenq  5  gives  an  idea  of  the  amount  of  inorganic  material  taken  up  by  the 
foetus  during  its  development. 

We  see  from  these  values  that  towards  the  end  of  pregnancy  there  is 
suddenly  a  marked  increase  in  the  amount  of  inorganic  material  taken  up 
by  the  foetus.  During  the  last  three  months  it  takes  up  almost  twice  as 
much  inorganic  material  as  during  the  first  six  months  of  its  development. 
Altogether  it  withdraws  about  100  grams  of  ash  constituents  from  the 

1  Z.  Biol.  9,  369  (1873);  12,  464  (1876). 
3  Ibid.  16,  85  (1880). 

3  Compt.  rend.  14,  451  (1842). 

4  Ber.  Vers.  Deut.  Naturforscher,  Miinchen,  1877,  243. 

5  Compt.  rend.  128,  1054  (1899). 


376 


LECTURE   XVI. 


mother.  Of  iron  it  takes  up  0.294  gram  (0.42  gram  Fe2O3).  Here 
again  the  greater  part  is  taken  up  during  the  latter  part  of  the  period  of 
pregnancy.  This  gives  one  the  impression  that  the  foetus  is  probably 
provided  with  reserves  in  order  to  fit  it  for  all  contingencies  which  may 
arise  with  regard  to  its  nourishment  after  the  birth. 


Age  of  the  Foetus. 

Sex. 

Weight 

Fe203 

of  the  Foetus 
in  kilograms. 

of  the  Ash 
in  grams. 

of  the  Entire 
Organism. 

Calculated  to 
100  grams  Ash. 

4^  months    
5  months      ..... 
5  months      
5  to  5£  months  .    .    . 
5J  months 

9 

0.52 
0.57 
0.80 
0.12 
1.29 
1.17 

2.72 
3.30 

14.00 
18.72 
18.36 
28.07 
32.98 
30.77 

96.76 
106.16 

0.06 
0.06 
0.07 
0.11 
0.13 
0.12 

0.38 
0.42 

0.43 
0.33 
0.40 
0.38 
0.38 
0.39 

0.40 
0.40 

6  months 

Towards  end  of  preg- 
nancy     
Towards  end  of  preg- 
nancy 

After  its  birth  the  child  still  receives  nourishment  at  the  expense  of  the 
mother.  Milk  now  affords  the  vehicle  for  the  transference  of  material. 
An  idea  of  the  amounts  of  material  which  the  mother  has  to  furnish  the 
child  is  shown  by  the  following  figures:  A  male  nursling  takes  about 
one  liter  of  milk  per  day  at  the  age  of  six  months.  This  contains  the 
following  amounts  of  separate  constituents: 1  Water  875.8  grams,  casein 
8.0  grams,  albumin  12.1  grams,  fat  37.4  grams,  milk-sugar  63.7  grams, 
ash  3.0  grams.  The  ash  is  composed  of  1.08  grams  potash,  0.28  gram 
soda,  0.50  gram  lime,  0.07  gram  magnesia,  0.007  gram  ferric  oxide, 
0.66  gram  phosphoric  acid,  0.53  gram  chlorine. 

This  increased  output  is  naturally  felt  by  the  organism  of  the  mother, 
and  it  must  be  taken  into  account  in  the  choice  of  her  food.  Here  again 
it  would  be  altogether  wrong,  as  regards  the  nourishing  of  the  nursling,  to 
regulate  the  diet  of  the  mother  with  regard  to  the  calorific  value  of  the 
food.  It  is  the  chemical  composition  of  the  food  which  is  of  utmost 
importance,  for  the  milk  must  provide  the  infant  not  only  with  combust- 
ible matter,  but  above  all  with  building  material  for  its  cells.  Although 
the  organism  of  the  child  can  probably  utilize  carbohydrates  for  the  pro- 
duction of  fat,  and  can  perhaps  form  sugar  from  albumin,  it  is  impossible 
to  effect  such  transformations  in  the  case  of  inorganic  salts.  Even  the 
assumption  that  the  place  of  one  salt  may  be  taken  by  another  one  which 


1  Averages  from   173  analyses.     See  J.   Koenig:    Die  menschlicher  Nahrungs-und 
Gemissmittel,  Berlin,  1904. 


INORGANIC  FOODS. 


377 


is  closely  related  to  it,  is  not  justifiable,  for  we  have  seen  that  the  ions  have 
a  quite  specific  action.  For  this  reason  it  seems  as  if  more  attention 
should  be  paid  to  the  inorganic  nature  of  the  ash  of  milk,  or  of  any  milk- 
substitute,  in  considering  its  value  as  food  for  the  child. 

It  is  not  right,  however,  to  lay  particular  stress  upon  any  one  inorganic 
salt.  At  present  we  are  not  able  to  judge  the  relative  merits  of  the  different 
salts.  As  we  have  seen,  almost  all  of  the  inorganic  substances,  with  the 
single  exception  of  lime,  are  present  in  sufficient  quantities  in  the  ordinary 
articles  of  diet. 

One  hundred  grams  of  dry  substance  contain  the  following  amounts  of 
lime  in  milligrams: * 


Beef 

29 

Plums 

166 

White  bread 

46 

Human  milk     

243 

Graham  bread      .... 

77 

Yolk  of  eggs     

380 

Potatoes    

100 

Strawberries     

483 

Peas 

137 

Cow's  milk 

1510 

This  little  summary  shows  that  a  diet  consisting  chiefly  of  meat  is  not 
suitable  for  the  nursing  mother.  Rich  in  lime  are  the  yolk  of  eggs,  and 
especially  cow's  milk.  We  can  well  imagine,  a  priori,  that  the  organism 
of  the  mother  during  the  entire  period  when  the  child  receives  its  nourish- 
ment at  her  expense  will  suffer  materially  if  there  is  lack  of  lime  in  her 
food,  and  in  such  cases  she  will  be  obliged  to  draw  upon  her  own  supplies 
of  lime  to  furnish  the  child  with  the  amount  that  it  requires. 

Osteomalacia,  a  disease  in  which  the  bones  gradually  lose  their  solid 
constituents  and  finally  become  thin  as  parchment,  soft  and  flexible, 
occasionally  occurs  during  pregnancy.  It  would  seem  probable  that  this 
disease  bears  some  relation  to  the  increased  requirement  of  lime-salts  on 
the  part  of  the  organism  of  the  mother.  The  child  develops  at  the  expense 
of  the  mother's  tissue.  All  that  we  know  concerning  the  disease,  however, 
is  contrary  to  this  assumption.  It  occurs  more  frequently  in  certain 
localities.2  Its  appearance  is  not  restricted  to  the  period  of  pregnancy. 
It  is  at  such  a  time,  however,  that  the  symptoms  are  most  pronounced,  and 
usually  the  disease  then  progresses  more  rapidly.  The  histological 
study  of  osteomalacial  bones  shows  that  it  is  not  lime  alone  that  the  bones 
have  lost.  It  is  true  that  one  of  the  most  noticeable  changes  is  the  decal- 
cification  of  the  individual  lamellae;  but  at  the  same  time  there 
takes  place,  with  varying  intensity,  a  new  formation  of  osteoidal  tissue. 
The  assumption  that  this  decalcification  of  the  bones  probably  does  not 
stand  in  any  direct  relation  to  the  development  of  the  fcetus  is  supported 


1  G.  von  Bunge:  Z.  Biol.  41,  155  (1900). 

2  Cf.  L.  Gelpke:  Die  Osteomalakie  im  Ergolztale,  Basel,  1891. 


378  LECTURE  XVI. 

by  observations  of  the  metabolism  which  takes  place  during  the  disease. 
Thus  Goldthwait,  Painter,  Osgood,  and  McCrudden l  found  that  when  the 
nourishment  contained  4.56  grams  of  lime  there  was  an  elimination  of  3.859 
grams  by  the  urine  and  of  1.80  grams  by  the  faeces.  Thus  the  organism 
lost  1.10  grams  of  lime  in  the  process.  Hand  in  hand  with  the  decalcifi- 
cation,  a  formation  of  an  organic  substance  takes  place.  This  substance  is 
characterized  by  a  high  sulphur  and  a  low  phosphorus  content.  Curiously 
enough,  while  the  calcium  is  being  carried  away  from  the  organism,  mag- 
nesium is  being  held  back.  Considering  all  these  facts  together,  we  are 
led  to  the  conclusion  that  the  disease  is  not  caused  by  a  giving  up  of  lime 
to  the  organism  of  the  child,  but  that  evidently  there  is  a  severe  metabolic 
disturbance  of  the  bony  tissue  which  naturally  must  be  influenced  indi- 
rectly by  the  important  transformations  which  are  taking  place  in  the  entire 
metabolism  of  the  organism  of  the  mother  due  to  the  presence  of  the 
new  being.  But  just  as  in  the  disease  of  richitis  the  lime  plays  a  more  or 
less  passive  part,  it  is  indeed  highly  probable  that  here  again  the  absence  of 
lime  is  not  directly  responsible  for  the  trouble,  but  that  the  loss  of  lime 
takes  place  secondarily  as  a  result  of  the  disease.  The  lime  is  loosened 
from  its  state  of  combination  in  the  bones,  and  is  eliminated  as  refuse  out 
of  the  system.  The  primary  trouble  is  a  disturbance  in  the  economy  of 
the  bony  tissue.  It  has  been  frequently  suggested  that  the  cause  of  the 
decalcification  is  due  to  the  appearance  of  acids.  This  was  deduced  from 
the  fact  that  lactic  acid  is  found  in  the  urine  of  those  suffering  from  osteoma- 
lacia.  The  appearance  of  the  lactic  acid,  however,  does  not  prove  anything 
in  this  direction.  In  fact,  cases  of  the  disease  are  known  in  which  no  lactic 
acid  could  be  detected  in  the  urine;  and  we  know,  furthermore,  that  the 
acid  may  appear  in  the  urine  for  quite  a  number  of  different  reasons  with- 
out the  lime-content  of  the  bones  being  affected  at  all.  The  appearance 
of  lactic  acid  in  the  urine  does  not  indicate  where  the  acid  originates. 
There  is  absolutely  no  foundation  for  the  assumption  that  the  acid  in 
osteomalacia  is  formed  in  the  bony  tissues  and  serves  to  dissolve  out  the 
lime.2 

Fehling's  3  observation,  that  removal  of  the  ovaries  serves  to  check  the 
disease,  has  shed  a  peculiar  light  upon  the  nature  of  the  disease.  After 
this  operation,  lime  is  once  more  retained  by  the  system,  and  the  newly 
formed  osteoidal  tissue  calcines.  At  present  we  can  merely  assume  that 
the  loss  of  the  ovaries  brings  back  the  metabolism  to  normal  paths.  We 


1  Am.  J.  Physiol.  14,  389  (1905). 

2  Cf.  C.  Schmidt,  Ann.  6l,  329  (1847).     Moers  and  Muck,  Deut.  Arch.  klin.  Med. 
6,  485  (1869).   Nencki  and  Sieber,  J.  pr.  Chem.  26,  43  (1882).     M.  Levy,  Z.  physiol. 
Chem.  19,  239  (1894). 

3  Arch.  Gynak.  39,  171  (1891);  48,  472  (1895).     Cf.  also  Winckel:  Sammlung  klini- 
scher  Vortrage  N.  F.  No.  71. 


INORGANIC  FOODS.  379 

may  suspect  that  the  ovaries  have  previously  produced  something  which 
has  caused  the  metabolic  disturbance.  Such  an  hypothesis,  however,  has 
not  up  to  the  present  time  been  established  experimentally.  We  must 
for  the  present  be  content  with  a  knowledge  of  the  observed  facts,  and 
await  a  fuller  explanation  of  the  peculiar  mutual  action  between  the 
ovaries  and  the  bony  tissue  as  a  result  of  further  investigation. 


LECTURE   XVII. 


INORGANIC    FOODS. 
II. 

WE  have  started  with  milk  as  a  standard  for  determining  the  require- 
ments of  the  animal  organism  as  regards  inorganic  material.  This  is 
justifiable  inasmuch  as  it  is  certain  that  milk  contains  in  proper  propor- 
tions all  the  inorganic  salts  which  are  necessary  for  the  development  of 
the  growing  individual.  Under  ordinary  conditions  there  is  little  fear  of 
an  insufficient  supply  of  these  elements  in  the  case  of  adults,  except, 
of  course,  during  periods  of  pregnancy  and  of  lactation.  Our  ordinary 
mixed  diet  contains  a  sufficient  amount  of  all  the  inorganic  substances, 
even  when  on  account  of  social  reasons  the  nourishment  is  obtained  from 
material  which  is  not  of  full  value.  We  shall  come  back  to  this  point. 

In  comparing  the  composition  of  milk  with  that  of  the  other  foods,  we 
left  one  important  fact  unmentioned;  namely,  the  relatively  low  iron  con- 
tent. There  are,  in  fact,  but  few  articles  of  food  which  contain  less  iron 
than  milk,  as  is  shown  by  the  following  table  arranged  with  increasing  iron 
content: l 


Milligrams  of  Iron 
per  100  Grams  Dry 
Substance. 

Milligrams  of  Iron 
per  100  Grams  Dry 
Substance. 

Sugar     

0.0 

Plums     

2.8 

Egg  albumin     .    .    . 
Honey    

0.0 
1  2 

Raspberries  
Figs       

3.7-3.9 
3.7-4.0 

Red  cherries     .    .    . 
Rice    

1.2 
1.0-2.5 

Shelled  hazel  nuts  .    . 
Rye     

4.3 
3.7-4.9 

Scotch  barley  .    .    . 
Oranges 

1.4-1.5 
1  5 

Cabbage        (etiolated 
leaves) 

4  5 

White  bread         .    . 

1  5 

Barley 

4  5 

Wheat  flour  .        .    . 
Greengage     .... 

1.6 

1  8 

Shelled  almonds      .    . 
Wheat        .        ... 

4.9 

5.5 

Black  cherries     .    . 
Apples    . 

1.9 
1  9 

Malaga  grapes     .    .    . 
Cabbage    (light-green 

5.6 

Pears  .... 

2  0 

leaves) 

5  6 

Dates  

2  1 

Huckleberries 

5  7-6.4 

Cow's  milk    .... 

2  3 

Potatoes    

6.4 

Human  milk     .    .    . 
Cocoa  beans     .    .    . 

2.3-3.1 
2.5 

Peas    
Beans  (white)  .... 

6.2-6.6 

8.3 

1  G.  von  Bunge:  Z.  Biol.  45,  532  (1901).     Cf.  Hausermann:  Z.  Physiol.  Chem.  23, 
555  (1897) 

380 


INORGANIC  FOODS. 


381 


Milligrams  of  Iron 
per  100  Grams  Dry 
Substance. 

Milligrams  of  Iron 
per  100  Grams  Dry 
Substance. 

Carrots                      .    . 

8.6 

Asparagus  

20  0 

Wild  strawberries  .    . 
Wheat-bran  
Lentils    
Almonds  (brown  skins) 

8.1-9.3 
8.8 
9.5 
9.5 

Yolk  of  eggs     .... 
Cabbage  (outer  dark- 
green  leaves  of  the 
head)  

10-24 
17-38 

Hazel  nuts   (brown 

Spinach 

33-39 

skins) 

12  7 

Pig's  blood    .    . 

•      226 

Dandelion  greens 

14.3 

Hematogen   .... 

290 

Beef    

16.9 

Hemoglobin      .... 

340 

The  remarkably  small  amount  in  milk  of  an  inorganic  element  to  which 
we  are  accustomed  to  ascribe  so  great  significance  is  very  striking.  Iron, 
we  know,  forms  an  important  constituent  of  the  hemoglobin.  Now  in 
comparing  the  composition  of  the  ash  of  the  suckling  with  that  of  the 
milk,  we  found  that  the  former  contained  considerably  more  iron.  This 
obliges  us  to  draw  the  conclusion  that  the  new-born  animal  is  already 
provided  with  a  store  of  iron.  The  organism  of  the  female  can  supply  its 
young  with  nourishment  in  two  ways,  —  at  first  through  the  placenta,  and 
later  by  way  of  the  mammary  glands.  Evidently  for  some  reason  or  other 
in  the  case  of  iron  the  former  method  is  preferred.  In  corroboration  of  this 
Bunge l  showed  that  the  amount  of  iron  contained  in  a  new-born  rabbit  is 
greatest  at  the  time  of  birth,  and  decreases  from  day  to  day  until  it  reaches 
a  minimum  at  the  end  of  the  period  of  lactation,  increasing  immediately 
as  soon  as  the  animal  changes  to  a  food  richer  in  iron.  The  following 
table  shows  the  results  obtained  by  Bunge: 


Milligrams  of  Iron 

Milligrams  of  Iron 

Age  of  Rabbit. 

per  100  Grams  of 

Age  of  Rabbit. 

per  100  Grams  of 

Body  Weight. 

Body  Weight. 

Embryo  arranged  ac- 
cording to  weight  . 

(6.4 

^8.5 
(9.0 

13  days  after  birth  . 
17  days  after  birth 
22  days  after  birth 

4.5 
4.3 
4.3 

1  hour  after  birth 

18.2 

24  days  after  birth 

3.2 

1  day  after  birth  .    . 

13.9 

27  days  after  birth 

3.4 

4  days  after  birth     . 

9.9 

35  days  after  birth 

4.5 

5  days  after  birth     . 

7.8 

41  days  after  birth 

4.2 

6  days  after  birth     . 

8.5 

46  days  after  birth 

4.1 

7  days  after  birth 

6.0 

74  days  after  birth 

4.6 

11  days  after  birth  . 

4.3 

Rabbits  are  fed  on  the  milk  of  the  mother  for  about  three  weeks.     These 
values  show  that  the  lowest  iron  content  coincides  with  the  end  of  the 


Z.  physiol.  Chem.  16,  173  (1892);  17,  63  (1893). 


382 


LECTURE  XVII. 


period  of  lactation.  If  the  assumption  be  correct  that  the  organism  of 
the  mother  ordinarily  provides  her  young  with  sufficient  iron  before  the 
birth,  and  that  the  percentage  of  iron  diminishes  during  lactation,  it 
would  seem  probable  that  in  the  case  of  guinea  pigs  there  would  be  no 
such  maximum  iron  content  at  the  time  of  birth,  for  there  is  no  need  of 
such  a  supply,  inasmuch  as  the  animal  immediately  after  birth  begins  to 
feed  on  green  fodder,  which  is  rich  in  iron.  In  fact,  as  Bunge  has  shown, 
this  assumption  is  verified  by  the  facts: 


Milligrams  of  Iron 

Milligrams  of  Iron 

Age  of  the  Animal. 

per  100  Grams  Body 

Age  of  the  Animal. 

per  100  Grams  Body 

Weight. 

Weight. 

4.6 

5  days  after  birth   . 

5.7 

Embryo           .... 

4.4 

9  days  after  birth   . 

4.4 

5.6 

15  days  after  birth   . 

4.4 

5.3 

22  days  after  birth   . 

4.4 

6  hours  after  birth    . 

5.0 

25  days  after  birth   . 

4.5 

1£  days  after  birth   . 

6.0 

53  days  after  birth   . 

5.2 

3  days  after  birth     . 

5.4 

Here,  as  we  expected,  there  is  no  maximum  of  the  iron  content  at  birth 
as  compared  with  later  periods;  there  is  likewise  no  minimum. 

Why  does  the  animal  organism  prefer,  as  a  rule,  to  supply  the  new  being 
with  such  a  store  of  iron  at  birth  as  will  permit  it  to  be  satisfied  with  a  low 
iron  content  in  the  milk?  Bunge's  idea  is  that  the  assimilation  of  iron  is  a 
difficult  process.  The  organism  of  the  mother  is,  therefore,  as  economical 
as  possible  with  its  stores  of  iron,  and  prefers  that  the  young  should  receive 
it  through  the  more  certain  path  of  the  placenta  than  through  the  alimen- 
tary canal  of  the  offspring. 

The  importance  of  the  iron  stored  in  the  organism  may,  however,  be  in 
another  direction.  First  of  all  it  is  to  be  decided  in  what  form  the  iron  is 
deposited  in  the  new-born  animal.  We  can,  indeed,  imagine  that  to  some 
extent  at  least  it  is  present  as  an  antecedent  of  hemoglobin,  so  that  it  can 
be  quickly  changed  into  the  latter  as  occasion  demands.  On  the  other 
hand,  it  is  also  possible  that  the  offspring  is  provided  with  a  large  amount 
of  hemoglobin  itself.  It  is  true  that  the  naked,  helpless  being  which  de- 
velops so  rapidly  after  birth  requires  a  large  amount  of  oxygen  to  effect 
the  various  oxidation  processes  which  take  place  within  it,  and  in  order 
to  make  use  of  all  this  oxygen  it  requires  hemoglobin.  The  following 
summary  shows  that,  as  a  matter  of  fact,  the  amount  of  hemoglobin  present 
per  kilogram  of  the  body  weight  is  greatest  at  the  time  of  birth.1 


1  Emil  Abderhalden:  Z.  physiol.  Chem.  34,  500  (1902). 


INORGANIC  FOODS. 
RABBITS,   SERIES  I. 


383 


Age  in  Days. 

Absolute  Weight  of  the  Hemoglobin 
in  the  Entire  Animal  Minus  the 
Intestine. 

Hemoglobin  per  1000  Grams 
Body  Weight. 

1      

0.675 

12.61 

3     

0.699 

10.91 

6     

0.760 

6.61 

10                        

0.773 

4.87 

14     

0.981 

3.81 

18     

1.096 

3.21 

22                                     .    . 

1.122 

2.41 

RABBITS,   SERIES  II. 


Age  in  Days. 

Absolute  Weight  of  the  Hemoglobin 
in  the  Entire  Animal  Minus  the 
Intestine. 

Hemoglobin  per  1000  Grams 
Body  Weight. 

1      
3 

0.836 
0  868 

13.37 
11  27 

8      

0.999 

6  44 

12      

1.083 

5  25 

18 

1  175 

4  08 

22 

1.384 

3.01 

28     

2.830 

5  47 

RATS.1 


Age  in  Days. 

Absolute  Weight  of  the  Hemoglobin 
in  the  Entire  Animal  Minus  the 
Intestine. 

Hemoglobin  per  1000  Grams 
Body  Weight. 

1      

0  026 

12  96 

6     
11 

0.048 
0  064 

6.42 
4  88 

22     . 

0.105 

4.64 

28     

0.221 

6  70 

32 

0  296 

7  39 

These  values  which  in  the  case  of  the  rabbits  were  obtained  with  animals 
of  one  and  the  same  litter,  whereas  in  the  case  of  the  rats  a  whole  litter  was 
analyzed  at  the  end  of  each  period,  show  that  the  absolute  amount  of 
hemoglobin  increases  slowly  after  birth.  At  the  end  of  the  lactation 
period  there  was  twice  as  much  hemoglobin  in  the  rabbits  as  at  birth.  In 
the  case  of  the  rats,  an  examination  of  the  contents  of  the  stomach  and 


The  values  for  each  day  were  those  of  a  whole  Utter. 


384 


LECTURE  XVII. 


intestines  showed  that  they  began  to  take  nourishment,  other  than  the 
milk  of  the  mother,  at  the  end  of  the  twenty-second  day.  During  this 
time  the  absolute  amount  of  hemoglobin  had  increased  more  than  three- 
fold. It  was  perfectly  possible  for  this  increase  to  arise  from  the  amount 
of  iron  contained  in  the  milk.  Now  if  we  compare  the  amounts  of  hemo- 
globin present  per  kilogram  of  the  animal's  weight,  it  is  evident  that  at 
birth  the  relative  amount  of  hemoglobin  present  was  remarkably  high; 
this  value  diminishes  little  by  little  as  the  animal  gains  in  weight,  reach- 
ing its  lowest  value  toward  th*e  end  of  lactation.  This  minimum  becomes 
all  the  more  remarkable  when  we  remember  that  with  full-grown  rabbits 
there  is  from  7  to  10  grams  of  hemoglobin  per  kilogram  of  the  animal's 
weight.  As  soon  as  the  animal's  nourishment  changes  from  milk  to 
green  fodder  rich  in  iron,  both  the  absolute  and  relative  amounts  of  hemo- 
globin increase  quite  materially. 

It  is  interesting  to  know  how  much  iron  is  present  in  the  new-born 
rabbits  in  some  other  form  than  hemoglobin.  In  the  following  table  this 
is  computed  on  the  assumption  that  the  hemoglobin  of  rabbits  contains 
0.336  per  cent  of  iron.1  The  value  thus  obtained  is  then  deducted  from 
the  amount  of  iron  that  Bunge 2  found  per  kilogram  of  the  animal's 
weight.3 

RABBITS,   SERIES  I. 


Age  in 
Days. 

Absolute  Weight 
of  the  Hemoglo- 
bin in  the  Entire 
Animal  Minus 
the  Intestine. 

Hemoglobin 
per  1000 
Grams  Body 
Weight. 

Milligrams 
Iron  as  Hemo- 
globin per 
1000  Grams 
Body  Weight. 

Milligrams  Total 
Iron  per  1000 
Grams  Body 

Weight. 
(After  Bunge). 

Milligrams  Iron 
not  Present  as 
Hemoglobin  per 
100  Grams  Body 
Weight. 

1 

0.675 

12.61 

42 

139 

97 

3 
4 

0.699 

10.91 

37 

j-99 

J62 

6 

0.760 

6.61 

22 

85 

63 

10 
11 

0.773 

4.87 

16 

|«. 

[27 

13 

14 

0*981 

3*81 

13 

}« 

}. 

17 
18 

i.m 

3.21 

11 

[« 

|  32 

22 

1.122 

2.41 

8 

43 

35 

1  O.  Zinoffsky:  Z.  physiol.  Chem.  10,  32  (1885). 

2  Loc.  cit. 

8  This  computation  is  naturally  not  accurate,  but  gives  relative  values. 


INORGANIC  FOODS. 
RABBITS,   SERIES  II. 


385 


Age  in 
Days. 

Absolute  Weight 
of  the  Hemo- 
globin in  the  En- 
tire Animal  Minus 
the  Intestine. 

Hemoglobin 
per  1000 
Grams  Body 
Weight. 

Milligrams 
Iron  as  Hemo- 
globin per 
1000  Grams 
Body  Weight. 

Milligrams  Total 
Iron  per  1000 
Grams  Body 
Weight. 

Milligrams  Iron 
not  Present  as 
Hemoglobin  per 
1000  Grams 
Body  Weight. 

1 

0.836 

13.37 

45 

139 

94 

3 
4 

0.868 

11.27 

38 

J99 

}., 

7 
8 

0^999 

6.44 

22 

[60 

J38 

11 
12 

1.083 

5.25 

18 

I43 

}25 

17 
18 

l]l75 

4.08 

14 

|43 

J29 

22 

1.384 

3.01 

10 

43 

33 

27 

) 

i 

28 

2^830 

5.47 

18 

\    * 

» 

A  glance  at  these  tables  shows  distinctly  that  shortly  after  birth  a  con- 
siderable amount  of  the  iron  is  present  in  some  other  form  than  hemo- 
globin. This  amount  of  iron  diminishes  rapidly  during  the  first  few 
days  after  birth,  and  is  evidently  transformed  into  hemoglobin.  After 
about  the  sixth  day  from  birth,  the  amount  of  iron  not  present  as  hemo- 
globin, per  1000  grams  of  the  animal's  weight,  remains  fairly  constant. 
Inasmuch  as  the  animal  is  constantly  gaining  in  weight  during  this  period, 
it  is  evident  that  iron  must  be  continuously  deposited  in  the  tissues. 
This  iron  comes  from  the  milk.  On  the  other  hand,  the  absolute  amount 
of  hemoglobin  likewise  increases.  At  all  events,  the  above  values  show 
the  minimum  amount  of  iron  which  is  in  the  tissues  of  the  rabbit  and 
which  is  held  there  most  tenaciously.  From  this  point  of  view  it  is  not 
difficult  to  understand  why  the  new-born  animal  is  provided  with  so 
great  an  amount  of  stored-up  iron.  During  the  first  few  days  consider- 
able hemoglobin  is  formed,  and,  if  there  were  not  this  supply  of  iron,  it 
would  be  necessary  for  the  milk  to  contain  much  more  iron  than  usual  in 
order  to  satisfy  the  requirement.  A  study  of  the  cells  of  the  milk-glands, 
however,  shows  that  on  the  whole  they  are  nearly  fitted  to  furnish  a  quite 
definite  secretion.  The  task  of  the  cells  in  satisfying  the  demands  of  the 
young  organism  is,  therefore,  lightened  by  the  fact  that  the  offspring 
already  has  this  extra  supply  of  iron  available.  As  Hugonnenq  l  has 
shown  in  the  case  of  the  human  foetus,  this  storing  up  of  iron  takes  place 
chiefly  during  the  last  three  months  before  birth.  There  is  nothing 
whatever  to  indicate  that  the  iron  is  stored  up  merely  because  it  is  a 
substance  difficult  for  the  young  organism  to  absorb  and  assimilate. 


Compt.  rend.  128,  1054  (1899). 


386  LECTURE  XVII. 

The  above  tables  are  of  interest  in  another  respect.  They  show  that 
the  iron  stores  of  the  suckling  plus  the  amount  of  iron  in  the  milk  are, 
towards  the  end  of  the  period  of  lactation,  no  longer  sufficient  for  the 
formation  of  the  required  amount  of  hemoglobin.  The  organism  is  evi- 
dently in  a  state  of  iron  starvation.  As  soon  as  fodder  rich  in  iron  is 
taken  into  the  system  together  with  the  milk,  the  hemoglobin  values 
increase  rapidly.  This  shows  how  undesirable  it  is  that  the  human  off- 
spring should  be  restricted  to  a  milk  diet  much  longer  than  the  ordinary 
period  of  lactation  (7  to  9  months).  The  child  then  requires  more  iron 
in  its  food. 

Iron  has,  from  days  of  antiquity,  always  been  considered  as  playing  an 
especially  important  part  in  the  nourishment  of  the  human  organism, 
and  chiefly  on  account  of  the  pathological  condition  known  as  chlorosis, 
or  green  sickness.  This  occurs  particularly  in  young  women  at,  or  near, 
the  age  of  puberty.  The  name  is  derived  from  the  peculiar,  character- 
istic, greenish-yellow  colored  skin  of  such  patients.  It  was  early  rec- 
ognized that  this  most  prominent  symptom  —  together  with  the  paleness 
of  the  mucous  membrane  —  was  to  be  traced  to  anaemia,  an  impover- 
ishment of  the  blood.  The  disease  has  always  been  combated  by  pre- 
scribing iron.  On  examining  the  blood  of  those  suffering  from  this  disease, 
it  is  found  that  there  is  a  deficiency  in  the  amount  of  hemoglobin  per 
unit  of  volume.  It  is  not,  as  in  forms  of  anaemia  caused  by  loss  of  blood, 
or  otherwise,  due  to  the  fact  that  the  total  number  of  blood  corpuscles  is 
diminished  and  consequently  the  hemoglobin  content,  but  rather  that 
the  amount  of  hemoglobin  contained  in  the  individual  corpuscles  is  too 
small.  While  in  many  cases  the  actual  number  of  red  corpuscles  remains 
normal,  still  it  often  sinks  considerably.  The  only  interest  that  this 
disease  has  for  us  at  this  place  is  to  the  extent  that  the  study  of  it,  and 
particularly  of  the  therapeutic  action  of  iron,  has  cleared  up  the  question 
concerning  the  absorption  and  assimilation  of  this  metal  and  of  the  other 
inorganic  elements  which  are  required  by  the  organism.  The  fact  that 
inorganic  iron  salts  have  a  favorable  action  upon  chlorosis  has  been  known 
for  a  long  time.  How  the  iron  acted  was  not  known,  —  it  was  merely 
taken  for  granted  that  it  was  absorbed  and  assimilated;  i.e.,  utilized  for 
the  formation  of  hemoglobin.  This  view  was  perfectly  plausible  as  long  as 
nothing  definite  was  known  concerning  the  manner  in  which  the  iron  is 
held  combined  in  the  hemoglobin  molecule.  If  the  hemoglobin  merely 
contains  the  iron  in  a  loose,  salt-like  state  of  combination,  it  would  be 
perfectly  plausible  to  think  of  an  assimilation  of  inorganic  iron  salts.  It 
is  now  known,  however,  that  the  iron  contained  in  hematin,  a  compound 
very  closely  related  to  hemoglobin,  is  in  a  very  firm  state  of  combination. 
It  resists  the  action  of  boiling,  concentrated  potassium  hydroxide  and 
boiling  hydrochloric  acid.  By  dissolving  it  in  concentrated  sulphuric 


INORGANIC  FOODS.  387 

acid  the  iron  is  split  off  and  the  hematin  is  changed  into  hematoporphyrin. 
The  assimilation  of  the  iron,  therefore,  cannot  be  a  very  simple  process, 
and  consequently  at  the  time  when  it  was  denied  that  the  animal  cells 
possessed  the  power  of  effecting  syntheses,  it  is  inconceivable  why  the 
assumption  should,  nevertheless,  have  been  made  that  inorganic  iron  as 
such  took  part  in  the  formation  of  hemoglobin.  This  standpoint  was 
emphasized  by  G.  von  Bunge,1  who  raised  the  question  as  to  the  form  in 
which  the  iron  is  contained  in  our  food  supply.  Is  it  present  in  the 
form  of  simple  inorganic  iron  salts,  or  as  complicated  organic  compounds? 
He  prepared  first  of  all  from  the  yolk  of  eggs,  which  must  of  course 
contain  the  iron  necessary  for  the  formation  of  hemoglobin  in  the  blood 
of  the  chick,  a  compound  which  by  its  entire  chemical  behavior  was 
shown  to  contain  iron  in  a  very  firm  state  of  combination.2  On  extract- 
ing the  yolk  of  a  hen's  egg  with  alcohol  and  ether,  none  of  the  iron 
goes  into  the  extract.  All  of  it  remains  in  the  residue,  which  consists 
chiefly  of  albumin  and  nucleins.  From  this  residue  the  iron  cannot  be 
extracted  by  means  of  alcohol  and  hydrochloric  acid.  Since  all  salt- 
like  compounds  containing  iron  combined  with  inorganic  or  organic  acids 
can  be  removed  by  the  above  reagents,  it  is  to  be  assumed  that  the  iron 
is  held  in  a  closer  form  of  combination  than  is  the  case  with  its  ordinary 
salts.  Bunge  next  isolated  the  compound  containing  iron  which  was 
formed  by  the  action  of  the  juices  of  the  stomach  during  the  digestion 
of  protein.  The  part  containing  iron  does  not  go  into  solution.  It  is 
indigestible,  and  corresponds  in  its  entire  behavior  to  that  of  a  nuclein 
substance.  The  iron  cannot  be  extracted  by  alcohol  containing  hydro- 
chloric acid,  but  is  dissolved  out  by  aqueous  hydrochloric  acid,  the  rate 
of  solution  increasing  with  the  concentration  of  the  acid.  Although  the 
iron  contained  in  hematin  does  not  react  with  the  ordinary  reagents  used 
for  detecting  the  presence  of  iron,  namely,  ammonium  sulphide,  and  acid 
solutions  of  potassium  ferro-  and  ferricyanides,  the  iron  contained  in  the 
nuclein  substance  does  give  these  tests.  By  dissolving  the  nuclein  in 
ammonia,  and  then  adding  potassium  ferrocyanide  and  acidifying  with 
hydrochloric  acid,  a  white  precipitate  is  produced  which  turns  blue  on 
standing.  In  the  case  of  potassium  ferricyanide  the  precipitate  remains 
white.  On  adding  ammonium  sulphide  to  the  ammoniacal  solution  of 
the  nuclein  a  green  coloration  is  formed,  gradually  turning  black  in  the 
course  of  twelve  hours.  Recently  this  compound,  to  which  Bunge  gave 
the  name  hematogen,  has  been  prepared  by  Hugonnenq  and  Morel,3  and 
purified  from  albumin  as  much  as  possible.  On  analyzing  it  they  obtained 

1  Verhandl.  des  13.  Kongresses  fur  innere  Medizin,  p.  133  (1895). 

2  Z.  physiol.  Chem.  9,  49  (1884). 

3  Compt.  rend.  140,  1065  (1905). 


388  LECTURE  XVII. 

the  following  values:  43.5  per  cent  C;  6.9  per  cent  H;  12.6  per  cent  N; 
8.7  per  cent  P;  traces  of  S;  0.455  per  cent  Fe;  0.352  per  cent  Ca;  and  0.126 
per  cent  Mg. 

It  appears  that  we  have  here  a  compound  representing  a  preliminary 
stage  in  the  formation  of  hemoglobin.  The  method  of  proving  this,  how- 
ever, is  not  entirely  satisfactory.  The  conclusion  rests  largely  upon  an 
.elementary  analysis.  It  need  hardly  be  mentioned  that  this  does  not 
mean  much  in  the  investigation  of  such  a  highly  complicated  organic 
substance.  A  quite  similar  compound  has  been  prepared  by  G.  Walter,1 
from  the  eggs  of  the  carp.  Walter  found  in  his  preparation  48 . 0  per  cent  C, 
7.2  per  cent  H,  14.7  per  cent  N,  0.30  per  cent  S,  and  2.4  per  cent  P;  in 
a  second  product  he  obtained  the  values  47 . 8  per  cent  C,  7 . 2  per  cent  H, 
12.7  per  cent  N,  2.9  per  cent  P,  and  0.25  per  cent  Fe. 

There  is  no  doubt  that  the  plants  also,  to  some  extent  at  least,  con- 
tain iron  in  the  form  of  complicated  organic  compounds;  and,  in  fact,  it 
seems  evident  that  nuclein  substances  containing  iron  are  present.  Plants 
rich  in  iron,  especially  spinach,  are  well  suited  for  the  preparation  of  such 
products.  By  a  similar  treatment  to  that  described  for  the  preparation 
of  hematogen  from  egg-yolk,  a  product  relatively  rich  in  iron  is  obtained, 
which,  like  hematin,  is  not  acted  upon  by  the  juices  of  the  stomach, 
gives  a  similar  elementary  analysis,  and  shows  corresponding  chemical 
reactions.  These  compounds  are  always  obtained  in  an  amorphous  state, 
so  that  it  is  difficult  to  judge  of  their  purity.  To  attempt  to  draw  any 
conclusions  as  to  their  identity,  or  as  to  the  relation  of  these  compounds 
to  one  another,  would  be  extremely  hazardous. 

We  do  not  know  the  form  in  which  the  iron  is  contained  in  milk.  The 
amount  present  is  so  small  that  up  to  the  present  time  it  has  not  been 
possible  to  isolate  any  compound  containing  iron. 

Starting  with  the  hypothesis  that  the  iron  in  our  food  is  present,  at 
least  to  some  extent,  in  a  state  of  firm  combination  with  organic  material, 
Bunge  next  raised  the  question  as  to  whether  the  animal  organism  is  so 
constituted  that  it  is  able  to  absorb  inorganic  iron  salts.  It  was  not  an 
easy  question  to  answer.  It  was  customary  to  recognize  the  absorption 
of  a  substance  only  when  it,  or  one  of  its  related  compounds,  was  found 
in  the  urine.  This  is  not  the  case  when  inorganic  iron  salts  are  taken 
into  the  system.2  Only  after  subcutaneous  introduction  is  there  any 
considerable  amount  of  iron  to  be  found  in  the  urine.  The  fact  that  when 
iron  is  incorporated  into  the  system  in  this  way  it  has  a  poisonous  effect 
upon  the  organism,  gives  further  support  to  the  assumption  that  inorganic 
iron  salts  cannot  pass  through  the  intact  intestine,3  for  there  has  never 

1  Z.  physiol.  Chem.  15,  477,  489  (1891). 

2  R.  Robert:  Arch,  exper.  Path.  Pharm.  16,  361  (1883). 

3  H.  Mayer  u.  Francis  Williams:  Arch,  exper.  Path.  Pharm.  13,  70  (1881). 


INORGANIC  FOODS.  389 

been  any  poisoning  observed  from  taking  iron  salts,  provided  the  doses  and 
the  manner  in  which  they  are  introduced  are  so  chosen  that  large  amounts 
of  iron  do  not  get  into  the  circulation  by  erosion  of  the  alimentary 
canal.  Little  by  little  the  view  became  accepted  that  iron  and  the 
heavy  metals  find  their  principal  place  of  elimination  not  in  the  kid- 
neys, but  in  the  intestines.  It  is  true  that  a  part  of  the  iron  leaves  the 
body  through  the  urine,  for  the  latter  invariably  contains  small  amounts 
of  iron.  The  amount,  however,  is  very  slight,  and  is  not  materially 
increased  when  iron  is  taken  as  medicine.  Long  ago  it  was  suggested 
that  probably  a  large  part  of  the  iron  was  eliminated  through  the  intes- 
tines, and  was,  therefore,  to  be  found  in  the  faeces.  The  fact  that  after 
taking  iron  into  the  system,  the  most  of  it  did  actually  appear  in  the  faeces, 
led  to  the  erroneous  conception  that  no  absorption  took  place.  It  has 
been  shown  in  the  first  place  that  subcutaneous  and  intravenous  injection 
of  iron  salts  always  result  in  a  part  of  the  iron  being  eliminated  through 
the  intestines.1  On  the  other  hand,  it  may  be  said  that  this  does  not  rep- 
resent a  normal  condition.  It  was  indeed  conceivable  that  the  organism 
seeks  to  get  rid  of  the  iron  salts  poisonous  to  it  as  quickly  as  possible  by 
all  the  means  available.  The  credit  of  having  done  the  most  towards 
explaining  the  absorption  and  elimination  of  iron  salts  belongs  chiefly  to 
Kunkel,  Quincke,  and  Hochhaus.2  These  investigators  made  use  of 
ammonium  sulphide  as  a  reagent  for  tracing  the  course  of  iron  in  the 
tissues;3  in  some  cases,  potassium  ferrocyanide  was  used  as  well.  If,  for 
example,  mice  are  fed  for  a  long  time  upon  milk  which,  as  we  have  seen, 
contains  but  little  iron,  then,  on  placing  the  alimentary  canal  of  these 
animals  in  ammonia  and  ammonium  sulphide,  the  iron  test  does  not 
appear,  or  at  most  there  is  only  a  slight  green  coloration.4  The  same  is 
true  of  the  other  organs  of  mice,  after  they  have  subsisted  upon  milk 
alone  for  a  considerable  period.  The  best  tests  for  iron  are  given  by  the 


1  Hamburger:  Z.  physiol.  Chem.  2,  191  (1878-79);  Lapicque:  Arch.  Physiol.  normals 
et  pathol.  1895. 

2  Kunkel:  Pfliiger's  Arch.  50,  1  (1891);   61,  595  (1895).     Filippi:  Arch.  exp.  Path. 
Pharm.  34,  462  (1895).     Hochhaus*  u.  Quincke:  ibid.  37,  159  (1896).     Quincke:  ibid. 
37,  183  (1896).     W.  F.  C.  Weltering:  Z.  physiol.  Chem.  21,  190  (1895-96),  and  Over  de 
resorptie  van  ijrerzonten  in  het  spysverteringskanaal,  Utrecht,   1895.     W.  S.  Hall: 
Arch.  Anat.  Physiol.  1896,  49 ;  1894,  455.    A.  Macallum:  J.  Physiol.  1894,  186.     Abder- 
halden:  Z.  Biol.  39,  113  (1899).     A.  Hofmann:  Virchow's  Arch.  151,  484  (1900).     G. 
Swirski:  Pfliiger's  Arch.  17,  466  (1899).     Tartakowsky:  ibid.  100,  586  (1903).     Hubert 
Sattler:  Ueber  Eisenresorption  u.  Ausscheidung  im  Darmkanal  bei  Hunden  u.  Katzen 
Inaug.  Diss.  Kiel,  1904,  and  Arch,  exper.  Path.  Pharm.  52,  326  (1905).     Franz  Miiller: 
Deut.  med.  Wochschr.  No.  51  (1900)  and  Deut.  Med.-Ztg.  No.  30  (1901).    Virchow'a 
Arch.  path.  Anat.  klin.  Med.  164,  436  (1901). 

3  Cf.  R.  Gottlieb:  Z.  physiol.  Chem.  15,  371  (1891). 

4  A.  Mayer  was  the  first  to  apply  this  method  (Dorpat,  1850).     Later,  Perls  (Vir- 
chow's Arch.  39,  42  (1867))  made  use  of  K4Fe(CN)B. 


390  LECTURE  XVII. 

liver  and  spleen.1  The  facts  are  quite  different  in  the  case  of  animals 
which  have  been  given  iron  with  the  milk.  In  the  stomach  there  is  ob- 
tained but  little,  if  any,  reaction  for  iron,  while  in  the  duodenum  there  is 
a  marked  green  coloration.  Often  the  reaction  is  localized  to  definite 
zones.  It  is  frequently  found,  for  example,  that  merely  the  top  of  the 
intestinal  villi  are  colored  green.  If  the  tissue  of  the  intestine  is 
examined  under  the  microscope,  numerous  little  kernels  containing  iron 
are  to  be  found  embedded  in  the  protoplasm  of  the  intestinal  epithelium, 
and  for  the  most  part  these  are  directly  beneath  the  cuticular  borders  of 
the  cells.  Now  and  then  tiny  leucocytes  may  be  seen  laden  with  innumer- 
able little  particles  of  iron.  These  are  noticed  in  the  stroma  of  the  villi. 
In  the  submucosa  also,  cells  containing  iron  may  be  noticed  once  in  a 
while.  In  the  jejunum,  however,  it  is  quite  different.  Here,  as  a  rule, 
the  iron  reaction  is  shown  only  in  the  solitary  follicles  and  in  the  Peyer's 
patches.  In  the  ileum,  the  iron  reaction  is  not,  as  a  rule,  very  pronounced, 
while  the  caecum  and  large  intestine  again  give  a  strong  test.  Coming 
from  the  intestinal  canal,  especially  the  duodenum,  lymphatics  filled 
with  cells  containing  iron  may  often  be  seen  leading  to  the  mesenteric 
glands,  which  likewise  show  a  pronounced  iron  reaction.  The  liver  and 
spleen  now  give  a  very  strong  test,  and  evidently  these  organs  serve  as 
storage  places  for  iron  salts.  The  muscles  and  bone-marrow,  etc.,  like- 
wise show  a  green  coloration  when  tested  with  ammonium  sulphide. 

Before  going  farther,  we  wish  to  emphasize  the  fact  that  the  observed 
conditions  which  were  obtained  with  mice,  rats,  rabbits,  guinea  pigs,  dogs, 
and  cats,  are  not  to  be  attributed  to  an  irritating  effect  of  the  iron.  It  is 
perfectly  clear  that  if  the  epithelium  of  the  intestines  is  injured  in  any 
way,  the  absorption  relations  which  normally  take  place  in  the  intestines 
will  be  considerably  affected.  Such  irritation  has  indeed  often  been 
observed  in  experiments  where  large  doses  of  iron  salts  were  fed  to  animals, 
but  in  the  experiments  now  in  question  the  amounts  of  iron  were  very 
small.  Thus,  rats  were  given  but  0.4  to  0.5  milligram  iron  in  the  course 
of  a  day,  rabbits  4  milligrams,  guinea  pigs  2  to  3  milligrams,  dogs  3 . 5  to 
4  milligrams,  and  cats  4  milligrams  per  day  in  the  form  of  ferric  chloride 
added  to  the  milk.  This  small  amount  of  iron  was  taken  up  gradually 
in  the  course  of  the  day. 

Now  what  is  the  significance  of  the  above  discoveries?  The  simplest 
assumption  is  that  iron  begins  to  be  absorbed  in  the  duodenum,  and  is  then, 
to  some  extent  at  least,  carried  first  of  all  to  the  lymphatic  ducts.  Obser- 
vations made  by  Gaule 2  make  it  seem  probable  that  part  of  the  iron  is 
carried  away  to  the  thoracic  duct,  and  thus  reaches  the  circulation.  It  is 


1  Abderhalden:  loc.  cit. 

3  Deut.  med.  Wochschr.  1896,  Nos.  19  and  24. 


INORGANIC  FOODS.  391 

certain  that  a  part  of  the  absorbed  iron  is  also  conducted  to  the  portal 
vein  of  the  liver.  The  latter  organ  forms  one  of  the  chief  storage  places 
of  iron  salts.  The  spleen  also  absorbs  considerable  iron.  It  is  probable 
that  the  lymph  carries  some  of  the  iron  back  to  the  intestines,  and  is 
eliminated  through  the  caecum  and  large  intestine.  Evidently  the  leuco- 
cytes play  an  important  part  in  the  processes  of  taking  up  and  trans- 
porting the  little  particles  of  iron,  for  they  are  often  observed  laden  with 
iron  particles,  both  in  the  paths  of  absorption  and  in  those  of  elimination. 
There  is  no  doubt  that  a  large  portion  of  the  iron  introduced  into  the 
organism  is  again  eliminated  through  the  intestines.  It  is  at  present 
uncertain  as  to  what  parts  of  the  intestines  share  in  this  elimination. 
This  is  particularly  true  of  the  small  intestine,  which  perhaps  partici- 
pates in  both  the  absorption  and  elimination  of  iron.  We  must  not 
forget,  above  all,  that  microchemical  reactions  have  a  limited  value. 
They  serve  merely  to  give  us  a  qualitative  picture  of  the  activity  of 
definite  compounds,  but  never  give  us  much  idea  as  to  the  amounts  of 
substances  entering  reactions.  Moreover,  the  method  used  in  the  above 
experiments  for  detecting  the  presence  of  iron  qualitatively  was  not 
entirely  satisfactory.  We  have  already  mentioned,  for  example,  that 
the  iron  in  hematin  does  not  react  with  the  ordinary  reagents  used  in 
testing  for  the  presence  of  iron,  and  that  hematogen  only  gives  a  notice- 
able reaction  after  the  solution  has  stood  for  some  time.  It  is  easy  to 
conceive  that  the  animal  organism  may  contain  its  iron  firmly  bound  in 
other  compounds  besides  hematin,  so  that  in. any  case  the  mere  fact  that 
we  do  not  detect  the  presence  of  iron  by  a  qualitative  test  does  not  prove 
that  the  tissue  tested  does  not  contain  this  element.  On  the  other  hand, 
the  fact  that  we  do  not  get  these  iron  tests  in  cases  where  other  methods 
(examination  of  the  ash)  show  that  it  is  actually  present,  does  not  give 
any  reliable  information  concerning  the  way  that  the  iron  is  held  in  com- 
bination. We  have  already  seen  that  colloids  play  an  important  part  in 
the  animal  organism,  and  that  they  are  apparently  capable  of  preventing 
certain  reactions  from  taking  place.  Thus  we  found  that  the  formation 
of  precipitates  was  often  prevented,  even  in  cases  where  the  reaction  had 
actually  taken  place.  The  precipitate  is  not  seen,  merely  because  the 
internal  friction  between  the  colloid  particles  prevents  the  tiny  parts  of 
insoluble  substance  formed  from  uniting  to  cause  a  visible  precipitate. 
This  point  is  all  too  frequently  lost  sight  of  in  scientific  work.  In  many 
cases  the  statement  that  iron  is  present  in  a  firm  state  of  "  organic  " 
combination  is  not  justifiable. 

It  is,  we  regret  to  say,  at  present  impossible  to  follow  with  sufficient 
accuracy  the  question  of  the  absorption  of  iron  and  the  distribution  of 
the  absorbed  iron  among  the  separate  organs. .  The  amounts  of  iron 
absorbed  are  so  small  that  with  our  present  methods  it  is  entirely  out  of 


392  .  LECTURE  XVII. 

the  question  for  us  to  attempt  to  picture  the  course  of  the  iron  through 
the  organism,  and  to  decide  how  much  inorganic  iron  is  absorbed,  and 
for  how  long. 

The  conditions  which  we  meet  with  in  the  case  of  iron  as  regards  its 
absorption  and  elimination  are  similar  with  other  elements.  Apparently 
other  inorganic  elements  are  taken  up  in  about  the  same  way  and  are 
similarly  eliminated.  Thus  we  know  that  if  we  add  lime  1  to  the  food,  a 
part  of  it  is  eliminated  in  the  urine,  whereas  a  considerable  portion  is 
deposited  in  the  large  intestine.  Inorganic  elements  which  are  not  usually 
found  in  the  organism  follow  the  same  course.  Thus,  Steinfeld  2  found 
that  subcutaneous  injection  of  bismuth  into  birds  caused  the  vermiform 
process  and  large  intestine  to  be  colored  black.  The  relations  of  elimi- 
nation are  similar  with  mammals.  Thus  Steinfeld  found  on  repeating 
this  experiment  with  dogs  and  cats  that  the  lymph  vessels  of  the  intestines 
were  filled  with  a  black  substance. 

The  fact  that  when  iron  was  administered,  a  part  of  the  dose  was 
absorbed  in  the  duodenum,  and  then  again  eliminated  at  the  end  of  the 
intestine,  does  not  tell  us  what  happens  to  the  iron  that  is  contained  in 
our  ordinary  food.  This  had  to  be  determined  by  a  direct  experiment. 
It  was  found  3  that  animals  fed  exclusively  upon  meat  or  exclusively  upon 
vegetables  gave  exactly  the  same  reactions  for  iron  in  the  intestines  and 
in  the  tissues  as  those  which  were  dosed  with  iron  salts.  The  behavior  of 
the  hemoglobin  and  hematin  was  particularly  interesting.  Both  of  these 
compounds  contain  iron  in  a  form  which  renders  it  impossible  to  detect 
it  by  the  ordinary  chemical  reactions.  If  now  a  rat  was  fed  with  milk 
containing  either  hematin  or  hemoglobin,  while  another  rat  was  fed  with 
milk  alone,  then  the  alimentary  canal  of  the  latter  would  not  give  any 
iron  reaction,  whereas  if  the  intestinal  tract  of  the  first  rat  was  placed 
in  a  solution  of  ammonia  and  ammonium  sulphide,  an  intense  green  color- 
ation appeared  at  once.  Thus  the  iron  has  been  loosened  from  its  state 
of  combination  in  hematin;  it  has  evidently  become  ionized.  This  shows 
it  is  extremely  probable  that  unchanged  hematin  is  not  absorbed  as  such. 
The  formation  of  hemoglobin  in  the  animal  organism  is  in  all  cases  the 
result  of  a  synthesis  or  a  change  in  the  way  in  which  the  iron  is  combined. 
This  assumption  cannot  at  present  be  verified  definitely,  because,  as  we 
have  mentioned,  it  is  possible  that  besides  the  compounds  in  which  we  are 
able  to  detect  iron  by  the  ordinary  reagents,  there  may  be  others  present 

1  R.  W.  Raudnitz:  Arch,  exper.  Path.  Pharm.  31,  343  (1893);  J.  G.  Rey:  Deut.  med. 
Wochschr.  No.  35,  569  (1895).     G.  Riidel:  Arch,  exper.  Path.  Pharm.  33,  79  (1894). 
J.  G.  Rey:  ibid.  35,  295  (1895). 

2  Dissertation,  Dorpat,  1884.     Meyer  and  Steinfeld:  Arch,  exper.  Path.  Pharm.  20, 
40  (1886). 

3  Emil  Abderhalden:  loc.  cit. 


INORGANIC  FOODS.  393 

which  are  capable  of  absorption  in  which  the  iron  is  too  firmly  bound  to 
react  with  such  chemicals  and  thus  escapes  microchemical  detection.  It 
is  at  least  decidedly  interesting  to  know  that  even  under  normal  conditions 
of  nourishment  the  tissues  of  the  animal  organism  always  contain  iron  in 
compounds  which  permit  its  detection  by  means  of  the  ordinary  reagents. 

The  mere  fact  that  inorganic  iron  salts  artificially  added  to  the  nourish- 
ment are  capable  of  absorption  and  deposition  in  the  tissues  does  not 
show  by  any  means  that  this  iron  is  actually  assimilated.  It  would  be 
insufficient  to  consider  the  assimilation  of  iron  from  the  standpoint  of  blood 
formation  alone.  There  is  no  doubt  that  iron  forms  an  integral  part  of 
all  cells  and  tissues  of  the  body.  Certainly,  this  iron  in  the  tissues  is  just 
as  essential  for  the  normal  functions  of  the  separate  organs  as  is  the  case 
with  the  iron  in  hemoglobin.  Some  idea  of  these  relations  may  be  ob- 
tained from  the  values  cited  for  the  iron  in  the  tissues  of  rabbits  during 
the  period  of  suckling.  It  is  evident  from  these  values  that  the  tissues 
hold  with  great  tenacity  to  a  definite  minimum  amount  of  iron,  even 
when  the  hemoglobin  content  of  the  entire  organism  is  so  far  diminished 
that  strong  anaemia  results.  At  present  we  have  no  definite  information 
as  to  the  part  played  by  this  iron  in  the  tissues.  We  do  not  even  know 
what  amounts  are  present  in  the  separate  organs.  It  is  likewise  difficult 
to  decide  what  portion  of  the  total  iron  has  been  introduced  and  what 
portion  is  about  to  be  eliminated.  Thus  it  is  easy  to  realize  how  the 
question  concerning  the  assimilation  of  iron  has  been  covered  by  that 
of  the  formation  of  the  hemoglobin. 

At  the  present  time  it  has  never  been  definitely  decided  whether  the 
iron  introduced  into  the  system  in  the  form  of  inorganic  salts  takes  part 
in  the  formation  of  hemoglobin  or  of  hematin.  We  find  ourselves  here, 
as  is  the  case  with  many  other  biological  experiments,  confronted  with 
the  condition  that  one  and  the  same  discovery  may  be  used,  to  support 
entirely  opposing  views.  The  old  experience  of  physicians,  that  iron  pills 
combat  chlorosis,  can  be  explained  by  the  assumption  that  the  iron  in  the 
pills  goes  to  form  the  hemoglobin.  On  the  other  hand,  judging  from 
analogy  with  other  observations,  it  is  perfectly  plausible  to  assume  that 
the  iron  in  the  pills  merely  has  an  indirect  effect  in  that  it  excites  those 
organs  which  take  part  in  the  formation  of  blood  into  increased  activity. 
First  of  all,  it  is  necessary  to  determine  whether  chlorosis  is  actually 
caused  by  a  deficiency  of  iron. 

Let  us  see  how  much  iron  there  is  in  the  human  organism.  A  mouse 
contains  100  milligrams  iron  per  kilogram  of  its  weight,  a  guinea  pig  con- 
tains but  52  milligrams  per  kilogram,  and  a  rabbit  about  46  milligrams. 
If  we  assume  that  the  last  value  is  about  right  for  a  human  being,  then  we 
would  have  in  a  person  weighing  70  kilograms  about  3.2  grams  of  iron. 
The  question  is  How  much  iron  does  the  human  organism  eliminate?  Star- 


394  LECTURE  XVII. 

vation  experiments  on  man  show  that  there  is  7  to  8  milligrams  of  iron 
eliminated  daily  from  the  intestines.1  Now  a  liter  of  milk  contains  about 
2!3  milligrams  of  iron.  With  milk  alone  as  food,  therefore,  it  would  be 
necessary  to  drink  at  least  four  liters  per  day,  for  during  starvation  the 
organism  is  extremely  economical  with  its  stores,  and  the  amount  of 
iron  then  eliminated  represents  a  minimum.  Certain  of  our  foods,  such 
as  white  bread,  rice,  cherries,  apples,  etc.,  are  very  deficient  in  iron.2  It 
is,  therefore,  easy  to  believe  that  people  subsisting  exclusively  upon  such 
nourishment  will  have  impoverished  blood;  and,  as  a  matter  of  fact,  many 
cases  of  chlorosis  may  be  accounted  for  in  this  way.  The  practising 
physician,  however,  knows  of  many  cases  of  chlorosis  in  which  unquestion- 
ably enough  iron  has  been  taken  into  the  system  to  satisfy  the  ordinary 
requirements.  In  such  cases  we  are  forced  to  assume  that  the  function 
of  absorbing  iron  has  in  some  way  become  disturbed,  or  else  that  the  iron 
compounds  taken  into  the  system  for  some  reason  are  not  utilized  by  the 
organs  which  serve  to  form  the  blood.  As  a  matter  of  fact,  disturbances 
in  the  function  of  the  intestinal  tract  have  been  observed  frequently  in 
chlorosis.  Even  in  such  cases,  however,  which  are,  by  the  way,  excep- 
tional, it  is  not  known  whether  these  intestinal  disturbances  are  of  a 
primary  nature,  or  whether  they  are  not  rather  a  result  of  the  impov- 
erished blood  and  the  disturbances  of  nutritional  relations  which  result 
therefrom. 

The  attempt  has  been  made  to  decide  by  means  of  experiments  upon 
animals  what  the  relations  are  between  iron  introduced  into  the  organism 
in  an  inorganic  form  and  the  formation  of  the  blood,  Two  different 
methods  have  been  tried.  We  have  seen  that  at  the  end  of  the  lactation 
period  the  suckling  possesses  a  low  hemoglobin  content,  and  that  this 
increases  rapidly  as  the  animal  begins  to  partake  of  food  richer  in  iron. 
If,  on  the  other  hand,  the  animal  is  kept  for  a  prolonged  period  upon  a 
milk  diet,  a  marked  anaemia  results.  That  this  is,  as  a  matter  of  fact,  the 
case,3  is  shown  by  comparing  the  amounts  of  hemoglobin  in  animals 
which  have  from  birth  been  fed  only  upon  milk,  with  that  of  animals 
which,  at  the  end  of  the  suckling  period,  have  passed  over  to  a  diet  richer 
in  iron  (vegetables).  Now  the  addition  of  inorganic  iron  salts  to  the 
milk  has  no  effect  upon  the  absolute  amount  of  hemoglobin  contained  in 
the  animals,  nor  upon  the  amount  per  kilogram  of  the  animal's  weight. 
The  added  iron,  however,  is  found  to  have  a  remarkable  effect  in  acceler- 
ating the  growth  of  the  animal.4 


1  Lehmann,  Miiller,  Munk,  Senator,  and  Zuntz:  Virchow's  Arch.  131,  Suppl.  1,  pp.  18 
and  67  (1893). 

2  Cf.  p.  380. 

3  Emil  Abderhalden:  Z.  Biol.  39,  193  (1899). 

4  Emil  Abderhalden.  Z.  Biol.  39,  483  (1899). 


INORGANIC  FOODS.  395 

A  second  method  *  for  deciding  the  question  concerning  the  assimila- 
tion of  iron  is  to  withdraw  equal  quantities  of  blood  from  two  animals  of 
the  same  age  and,  as  far  as  possible,  of  the  same  condition  of  nourishment, 
and  then  to  compare  the  regeneration  of  blood  in  one  case  where  the 
animal  is  fed  entirely  upon  milk,  and  in  another  where  iron  is  added  to  the 
milk.  Here  all  authors  agree  that  the  animal  to  which  the  inorganic 
iron  has  been  fed  is  able  to  replace  the  lost  blood  much  more  quickly 
than  the  other  animal  to  which  only  the  iron  contained  in  milk  is  avail- 
able. The  disagreement  in  this  result  with  that  obtained  in  above  experi- 
ments may  perhaps  be  due  to  the  different  conditions  of  the  animals  in 
the  two  types  of  experiments.  In  the  first  instance,  animals  were  chosen 
whose  iron  stores  at  the  beginning  of  the  experiment  were  in  a  quite 
exhausted  state.  All  of  the  iron  in  the  different  tissues  was  brought 
down  to  the  lowest  limit.  The  animals  in  the  second  cases  were  in  an 
entirely  different  condition.  These  possessed  a  considerable  supply  of 
stored-up  iron,  and  would  have  been  able  to  supply  the  loss  in  hemoglo- 
bin iron  from  these  stores  alone.  That  the  addition  of  inorganic  iron 
exerts  a  favorable  action  might  be  in  fact  explained  on  the  assumption 
that  it  excites  the  action  of  the  blood-forming  organs.  We  must  admit, 
however,  that  such  an  explanation  does  not  seem  well  founded  in  this 
case,  for  it  would  seem  probable  the  large  loss  of  blood  would  of  itself 
serve  to  incite  the  organs  which  take  part  in  the  formation  of  blood  into 
increased  activity.  On  the  other  hand,  it  is  conceivable  that  the  inorganic 
iron  replaces  the  iron  in  the  tissues,  so  that  the  latter  is  left  free  to  take 
part  in  the  formation  of  hemoglobin.  No  one  has  ever  been  able  to  prove 
this  directly,  but  it  seems  to  be  a  likely  explanation,  as  we  shall  see  from 
what  follows. 

Franz  Miiller 2  hoped  to  settle  this  question  by  an  examination  of 
bone-marrow,  one  of  the  principal  places  where  the  red  blood-corpuscles 
are  formed.  Miiller  fed  dogs,  taken  immediately  upon  the  completion  of 
the  lactation  period,  on  the  one  hand  exclusively  with  milk,  and  on  the 
other  with  milk  and  iron.  After  subsequently  killing  the  animals,  he 
found  that  the  bone-marrow  of  the  animals  fed  with  iron  contained  con- 
siderably more  nucleated,  red  blood-corpuscles  than  the  animals  fed 
with  milk  alone.  Again,  this  discovery  may  be  interpreted  in  two  differ- 
ent ways.  We  may  assume  that  the  inorganic  iron  takes  part  directly 
in  the  formation  of  hemoglobin,  or,  on  the  contrary,  that  it  merely  exerts 
an  indirect  action. 

When  we  take  into  consideration  all  of  the  different  experiments  that 
have  been  performed  in  this  connection,  we  must  unhesitatingly  admit 
that  it  has  never  been  satisfactorily  proved  whether  the  iron  taken  into 

1  Kunkel:  Pfliiger's  Arch.  61,  596  (1895).     Eger:  Z.  klin.  Med.  22,  335  (1897). 
3  Loc.  cit.     Cf.  also  A.  Hofmann:  loc.  cit. 


396  LECTURE  XVII. 

the  system  in  an  inorganic  form  can  take  part  in  the  formation  of 
hemoglobin.  The  question  then  naturally  arises,  Have  the  proper  means 
been  found  for  solving  this  problem  ?  Up  to  this  point,  in  discussing  the 
formation  of  hemoglobin,  we  have  considered  but  one  component  of  hema- 
tin;  namely,  the  iron.  It  seems  hardly  justifiable  to  limit  the  entire  dis- 
cussion to  this  one  component.  We  know  that  the  chemical  composition 
of  hematin  is  very  complicated.1  M.  Nencki  and  J.  Zaleski 2  have  sug- 
gested the  following  structural  formula  for  hemin,  the  hydrochloric  acid 
ester  of  hematin: 

CH2  CH2 

CH—  (OH)C/\°      CH 


i 

rt  lp«TT 

,\/C\/CH 
|CH2  NH 
0 

CH2 


—  (OH)C 

CH2  HN 

We  introduce  this  formula  here  merely  to  show  how  complicated  its 
synthesis  must  be  if  the  animal  cells  are  to  build  it  from  inorganic  iron. 
The  formula  also  shows  that  obviously  the  iron  itself  does  not  play  such 
an  all-important  part  in  the  synthesis;  that  is  to  say,  it  is  probably  not  so 
very  difficult  to  introduce  the  iron  into  the  molecule.  It  is  infinitely 
more  important  to  know  whether  the  organism  has  other  organic  material 
available  for  the  formation  of  the  hematin. 

In  the  above  formula  we  see  that  two  hematoporphyrin  molecules 
(the  iron-free  cleavage-products  of  hematin)  are  held  together  by  an  iron 
atom.  The  formation  of  hematin,  therefore,  depends  just  as  much  upon 
the  presence  of  material  from  which  hematoporphyrin  can  be  made  as  upon 
the  presence  of  iron.  Now  we  know,  as  will  be  explained  subsequently 
in  detail,  that  hematophorphyrin  is  closely  related  to  chlorophyll,3  for 
similar  decomposition  products  are  formed  from  each  of  these  two  com- 
pounds. This  suggests  the  thought  that  chlorophyll  can  perhaps  be 
brought  into  relation  with  hematin,  and  thus  with  the  formation  of  hemo- 
globin. There  is  absolutely  no  doubt  that  these  compounds  are  closely 
related  to  one  another.  The  fact  that  both,  as  we  shall  see  later  on, 
possess  similar  biological  functions  is  sufficient  to  explain  this  relation- 
ship, although,  as  a  matter  of  fact,  the  task  of  chlorophyll  is  quite  different, 
as  far  as  our  knowledge  goes,  from  that  of  hemoglobin.  Now,  inasmuch 

1  See  Lecture  XXIV. 

2  Ber.  34,  997  (1901). 

3  L.  Marchlewski:  Die  Chemie  des  Chlorophylls  (1895). 


INORGANIC  FOODS.  397 

as  the  original  source  of  all  substances  in  the  animal  organism  can  be 
traced  back  eventually  to  the  vegetable  kingdom,  the  thought  suggests 
itself  that  chlorophyll  serves  as  the  building  material  in  the  formation  of 
hemoglobin.  The  herbivora  devour  this  compound  in  considerable 
quantities,  and,  on  the  other  hand,  the  carnivora  receive  considerable 
amounts  of  hemoglobin  with  their  nourishment.  Unfortunately,  we 
know  nothing  definite  concerning  the  transformations  which  take  place 
with  these  two  products  in  the  alimentary  canal.  Of  hemoglobin  we  now 
know  that  in  its  absorption  it  is  so  changed  that  the  iron  in  it  becomes 
detectable  with  ordinary  chemical  reagents.  According  to  our  experi- 
ences as  regards  the  significance  of  digestion,  it  is  perfectly  possible  that 
chlorophyll  and  hemoglobin  are  broken  down  into  similar  products,  and 
thus  that  the  organs  which  form  the  blood  have  practically  the  same 
kind  of  building  material  presented  to  them  in  each  case.  The  actual 
amount  of  chlorophyll  and  hematin  available  does  not  need  to  be  very 
large.  Unfortunately,  we  do  not  know  how  much  hemoglobin  is  formed 
daily,  or  how  much  is  decomposed,  so  that  we  have  no  data  to  judge  as  to 
the  normal  extent  of  hemoglobin  formation. 

We  arrive  at  this  line  of  thought  because  evidently  the  synthesis  of 
hematin  is  a  very  complicated  one,  and  we  are  aware  of  no  material  from 
which  it  could  be  formed  apparently  so  readily  as  from  chlorophyll  or  its 
decomposition  products.1  At  all  events,  these  views  do  not  by  any  means 
imply  that  inorganic  iron  cannot  take  part  in  the  formation  of  hemo- 
globin. Even  if  we  grant  that  the  nucleoalbumins,  or  nucleoproteids, 
serve  as  the  building  material  of  hemoglobin,  it  does  not  seem  to  us  that 
this  makes  the  direct  assimilation  of  iron  impossible,  for  these  substances 
contain  iron  in  a  relatively  loose  state  of  combination.  The  formation 
of  hematin  from  albumin  compounds  containing  iron  must  necessitate 
quite  considerable  molecular  rearrangements  in  order  to  get  the  iron  in 
the  state  of  union  known  to  exist  in  hematin.  Now  the  question  arises, 
as  to  whether  milk  possesses  the  material,  other  than  iron,  in  sufficient, 
quantity  for  the  formation  of  hematin.  We  have  a  perfect  right  to  doubt, 
this.  It  would  be  perfectly  useless  to  provide  the  organism  with  a  suffi- 
cient amount  of  hematoporphyrin,  the  principal  component  of  hematin,. 
when  an  adequate  supply  of  iron,  the  minor  constituent,  is  not  available. 
It  is  far  more  probable  that  milk  contains  these  two  constituents  in  about, 
the  same  relative  amounts  as  in  hematin.  It  is  consequently  perfectly 

1  Perhaps  the  cleavage  products  of  protein  come  into  consideration  as  building 
stones.  Both  proline  and  glutamic  acid  could  furnish  material  for  the  pyrrole  ring. 
Plant  albumins  contain  large  amounts  of  glutamic  acid.  The  reserve  albumins  are  rich 
in  the  above-mentioned  amino  acids.  Perhaps  this  has  something  to  do  with  the  for- 
mation of  chlorophyll,  and  it  is  perfectly  possible  that  the  animal  organism  chooses  the 
same  way  for  preparing  its  hematin. 


398  LECTURE  XVII. 

possible  that  in  the  above-mentioned  experiments  in  which  iron  was  added 
to  the  milk,  there  was  not  much  effect  on  the  amount  of  hemoglobin 
formed,  because  there  was  an  insufficient  supply  of  the  other  building 
material  out  of  which  hemoglobin  is  formed.  Again,  we  have  up  to  this 
point  left  out  of  consideration  the  fact  that  besides  hematin,  there  is 
another  component  of  hemoglobin,  namely  globin,  which  is  an  albumin 
substance  of  highly  complicated  structure.  The  formation  of  the  hemo- 
globin molecule  is  complete  only  after  the  hematin  has  united  with  the 
globin  molecule. 

Enough  has  been  said  to  show  that  the  formation  of  hemoglobin  does 
not  solve  the  question  as  to  the  part  that  iron  plays  in  its  formation.  The 
kernel  of  the  whole  question  has  not  yet  been  attacked.  We  cannot  hope 
for  a  solution  of  the  problem  until  we  understand  clearly  the  formation  of 
hematin.  The  mere  fact  that  the  addition  of  iron  to  nutriment  poor  in 
iron  does  not  have  any  distinct  influence  upon  the  formation  of  hemo- 
globin, in  no  way  speaks  against  the  participation  of  inorganic  iron  in  the 
synthesis  of  hemoglobin  in  the  case  of  normal  nutrition,  but  it  indicates 
that  the  other  building  material  is  wanting  as  well  as  the  iron.  Further- 
more, the  fact  that  when  the  animal  passes  over  to  a  form  of  nourishment 
richer  in  iron,  there  is  a  rapid  increase  in  the  extent  of  the  hemoglobin 
formation,  is  explained. not  only  by  the  increased  amount  of  iron  in  the 
food,  but  as  well  by  the  fact  that  the  other  material  required  for  the  pro- 
duction of  this  substance  is  likewise  available  to  a  much  greater  extent. 

Let  us  now  return  to  chlorosis.  We  must  first  of  all  emphasize  the  fact 
that  the  anaemia  produced  by  an  exclusively  milk  diet,  or  by  loss  of  blood, 
has  nothing  whatever  to  do  with  the  disease  in  which  there  is  an  impov- 
erishment of  the  blood.  In  the  case  of  typical  chlorosis,  the  composition  of 
the  blood  is  abnormal  in  spite  of  the  fact  that  there  has  been  available  a 
sufficient  supply  of  substances  which  take  part  in  the  formation  of  blood. 
It  is  characteristic  of  the  disease  that  it  occurs  in  the  full-bloodedness  of 
the  female  organism's  development,  in  the  years  of  puberty,  and  it 
gradually  disappears  without  any  change  in  the  nourishment  sufficient 
to  account  for  the  correction  of  the  disorder.  One  gets  the  impres- 
sion that  demands  are  suddenly  made  upon  the  blood-forming  organs 
which  it  is  not  able  to  satisfy.  It  would  be  easy  to  conceive  that  the 
blood  losses  brought  about  by  menstruation  are  the  cause  of  the  increased 
demands  upon  the  hematopoietic  system.  It  has  been  shown,  however, 
that  the  amount  of  iron  lost  in  the  flow  of  blood  during  menstruation  l  is 
very  slight,  and  need  hardly  be  taken  into  consideration.  Bunge,  from  his 
observations  that  the  suckling  was  born  with  a  store  of  iron,  made  the 
suggestion  that  the  organism,  in  order  to  be  able  to  give  up  this  supply  of 
iron,  must  begin  to  store  up  iron  before  the  time  of  conception,  so  that  it 

1  Hoppe-Seyler,  Brodersen  and  Rudolph:  Z.  physiol.  Chem.  42,  545  (1904). 


INORGANIC  FOODS.  399 

would  have,  aside  from  its  food,  a  sufficient  supply  of  iron  during  preg- 
nancy. In  order  to  test  this  hypothesis  Bunge  l  made  a  number  of  experi- 
ments, and  determined  the  amount  of  iron  in  the  chief  storage  place,  the 
liver,  in  both  male  and  female  cats  and  dogs,  but  the  results  obtained  were 
not  altogether  harmonious. 

Although  we  are  not  in  a  position  to  assign  a  cause  for  chlorosis,  still  it 
is  perhaps  possible  to  explain  the  curative  effect  of  the  iron  preparations. 
If  we,  however,  study  closely  the  whole  process  of  the  hemoglobin  forma- 
tion, it  seems  to  us  less  probable  that  the  iron  preparations  added  to  the 
nourishment  actually  take  part  directly  in  the  making  of  blood.  It  would 
be  easy  to  understand  such  an  action,  if  chlorosis  were  actually  caused  by 
a  deficient  supply  of  iron.  We  are  perfectly  certain,  however,  that  in  the 
majority  of  cases  this  is  not  true.  We  have  every  reason  to  presume  that 
our  nourishment  in  general,  besides  containing  sufficient  iron,  likewise 
contains  enough  of  the  other  substances  required  for  the  formation  of 
hemoglobin.  Just  as  the  tissues  of  the  bones  in  richitis  are  not  capable 
of  assimilating  lime,  so,  evidently,  the  tissues  of  the  hematopoietic  organs 
are  not  able  to  utilize  the  material  which  forms  the  building  stones  of 
hemoglobin.  It  has  been  suggested  that  the  iron  added  in  the  form  of 
inorganic  salts  exerts  an  irritating  effect  upon  these  organs,  and  urges  them 
into  renewed  activity.  The  unsatisfactory  character  of  such  an  explana- 
tion is  evident.  It  assumes  that  the  iron  fed  to  the  body  in  an  inorganic 
condition,  behaves  otherwise  than  that  contained  in  "organic "  com- 
pounds. We  have,  however,  at  present  no  insight  into  the  ways  and 
means  by  which  absorbed  iron  reaches  the  circulation,  nor  as  regards  the 
form  in  which  it  is  present  in  the  different  fluids  and  tissues.  We  only 
know  that  the  iron  in  the  organs  can  be  detected  by  means  of  the  ordinary 
chemical  reagents,  irrespective  of  whether  the  animal  has  been  fed  with 
milk  and  inorganic  iron,  or  milk  and,  say,  hemoglobin.  Even  while  these 
observations  do  not  justify  the  assumption  that  the  different  iron  com- 
pounds all  behave  alike  after  reaching  the  intestine, —  i.e.,  that  they  may  be 
changed  into  the  same  state  of  combination,  —  still,  on  the  other  hand,  we 
have  no  justification  for  the  assumption  that  the  animal  organism  distin- 
guishes between  iron  that  is  fed  in  an  inorganic  condition  from  "organic" 
iron.  According  to  all  our  general  conceptions  of  the  process  of  digestion, 
it  appears  to  us  as  extremely  probable  that  even  the  formation  of  hematin 
is  preceded  by  a  deep-seated  decomposition.  In  this  case  the  animal 
organism  unquestionably  breaks  down  and  again  builds  up.  If  we  look 
at  the  formula  of  hemin  given  above,  it  seems  to  us  as  highly  improbable 
that  in  general  "  organic  "  iron  is  necessary  for  the  synthesis  of 
hematin.  Yes,  in  fact,  we  can  even  imagine  that  the  disease  of  chlorosis 
actually  depends  upon  the  fact  that  the  cells  of  the  body  are  no  longer 

1  Z.  physiol.  Chem.  17,  78  (1893). 


400  LECTURE  XVII. 

capable  of  making  use  of  iron  which  is  supplied  in  the  form  of  highly  com- 
plicated organic  compounds,  or  at  least  are  unable  to  convert  them  into 
such  a  state  that  they  can  be  utilized  for  the  formation  of  hematin.  Per- 
haps the  preparatory  decomposition  in  the  alimentary  canal  has  not  taken 
place,  and  thus  the  iron  may  circulate  to  some  extent  in  the  tissues,  but  in 
a  form  from  which  the  blood-forming  organs  are  not  able  to  set  it  free. 
From  this  point  of  view,  it  is  easy  to  understand  the  favorable  action  of 
inorganic  iron  salts.  Here  we  intentionally  break  away  from  the  older 
idea  that  the  animal  organism  is  dependent  upon  the  nature  of  the  food 
that  it  receives.  It  is  far  more  important  that  it  receives  all  the  materials 
that  it  requires.  The  way  these  elements  are  originally  combined  in  the 
food  is  more  or  less  a  matter  of  indifference,  provided  they  are  susceptible 
of  decomposition.  It  is  indeed  this  far-reaching  decomposition  and  the 
renewed  construction  which  makes  the  animal  organism  to  a  considerable 
extent  independent  of  the  kind  of  nourishment  it  receives.  To  be  sure, 
we  must  admit  that  apparently  the  animal  cells  are  not  capable  of  utilizing 
certain  kinds  of  combinations.  Thus,  it  is  improbable,  for  example,  that 
it  is  capable  of  constructing  cholesterol,  and  perhaps  not  hematoporphyrin 
from  its  simplest  components,  although  it  is  precisely  here  that  we  meet 
with  the  possibility  that  certain  decomposition  products  of  the  albumins 
may  be  utilized  for  the  syntheses.  At  all  events,  we  are  not  justified  in 
believing  that  hematogen  and  similar  substances  are  necessarily  direct 
preliminary  stages  in  the  formation  of  hemoglobin.  It  is  indeed  possible 
that  these  compounds  contain  all  the  necessary  material  for  the  formation 
of  the  red  pigment  of  the  blood,  although  this  has  never  been  proved 
directly. 

The  theory  we  have  thus  developed  concerning  the  action  of  inorganic 
iron  salts  is  not  necessarily  correct.  By  the  addition  of  iron  preparations 
to  the  food,  we  increase  the  iron  supply  for  the  entire  organism.  It  is 
conceivable  that  this  results  in  an  indirect  action  upon  the  organs  which 
produce  the  blood.  We  know  that  widely  different  organs  are  intimately 
related  to  one  another  in  their  metabolism  and  in  the  exercise  of  their 
functions.  In  this  connection,  we  need  refer  only  to  the  regulation  of  the 
sugar-content  of  the  blood  by  means  of  the  liver.  Similarly  the  amount 
of  hemoglobin  in  the  blood  is  a  very  constant  quantity.  Evidently  we 
have  here  another  case  of  regulation.  On  the  other  hand,  we  have  seen 
also  that  the  different  ions  exert  a  quite  specific  effect,  and  that  it  is, 
indeed,  possible  for  the  predominance  of  one  ion  to  cause  a  certain  specific 
action.  It  is  conceivable  that  the  heaping  up  of  iron  in  the  cells  of  the 
body,  and  perhaps  specially  in  the  cells  of  certain  organs,  may  give  a  new 
impulse  to  the  organs  which  participate  in  the  formation  of  blood. 

The  action  of  the  "  inorganic  "  iron  was  formerly  attributed  to  a  pro- 
tective effect.  Thus  the  sulphur  in  alkaline  sulphides,  instead  of  com- 


INORGANIC  FOODS.  401 

bining  with  the  more  complicated  organic  compounds  containing  iron, 
was  believed  to  unite  preferably  with  the  iron  of  inorganic  compounds. 
The  iron  in  the  nutriment  would  thereby  be  protected,  and  remain  in  the 
system  instead  of  being  eliminated  as  sulphide  of  iron.  Since  it  has  been 
shown,  however,  that  even  inorganic  iron  salts  are  absorbed,  and  it  has  been 
proved,  moreover,  that  alkaline  sulphides  are  not  present  in  the  stomach 
and  small  intestine,  this  protective  theory  may  well  be  discarded.1 

From  the  experiments  that  have  been  cited,  it  is  perfectly  clear  that  in 
reality  we  know  very  little  concerning  the  cause  of  chlorosis,  and  especially 
concerning  the  action  of  iron  preparations.  On  account  of  the  complexity 
of  the  processes  involved,  we  can  hardly  expect  at  present  to  understand 
perfectly  the  relations  between  the  iron  and  the  pathology  of  the  blood 
formation.  Above  all,  we  need  to  know  more  about  the  process  of  blood 
formation,  and  especially  as  regards  the  formation  of  hemoglobin  itself. 
At  the  same  time  the  solution  of  the  problem  of  the  formation  of  hemo- 
globin does  not  by  any  means  necessarily  solve  the  whole  problem  of  the 
formation  of  the  blood.  We  then  have  to  consider  the  formation  of  the 
blood  corpuscles.  The  stroma  of  the  blood  corpuscles  must  also  be  built 
up,  and,  in  such  a  way  that  it  can  take  up  the  hemoglobin.  A  long  chain 
of  processes  leads  from  the  separate  building  materials  of  hemoglobin, 
the  iron  and  the  organic  compounds,  to  the  finished  blood  corpuscles 
capable  of  exerting  their  important  functions.  The  chain  may  be  broken 
at  many  places,  and  thereby  the  whole  process  of  blood  formation  dis- 
turbed. This  so  infinitely  complicated  problem  has  been  attacked  only 
from  one  side,  that  of  the  iron.  Undoubtedly  iron  is  indispensable  in  the 
formation  of  blood,  but  equally  indispensable  are  all  the  remaining  and 
building  materials  which  are  far  more  complicated,  —  the  hematin,  hemo- 
globin, and  even  the  corpuscles  themselves. 

This  is  not  the  place  to  discuss  whether  iron  preparations  actually 
do  have  any  effect  upon  chlorosis.  It  is  indeed  conceivable  that  it  is  the 
dietetic  and  hygienic  measures  that  are  taken  that  are  alone  effective  in 
iron  therapeutics.  We  have  followed  chlorosis  and  iron  therapeutics 
thus  far  only  in  the  hope  that  we  would  be  able  thereby  to  get  some  idea 
of  the  relation  of  iron  to  the  formation  of  blood.  On  the  contrary,  the 
above  conclusions  apparently  lead  us  to  the  opinion  that  chlorosis 
itself  is  not  difficult  to  understand,  —  we  can  account  for  its  appearance 
if  we  assume  that  the  function  of  the  organs  producing  blood  are  in  any 
way  disturbed,  —  but  on  the  other  hand,  the  fact  that  inorganic 
iron  preparations2  are  successful* in  combating  the  disease  rather  stands 

1  Cf.  Kletzinsky:  Z.  Ges.  Aerzte  Wien  X,  II,  281  (1854).     Hannon:  Presse  medical 
(1851).     Weltering:  loc.  cit.     G.  von  Bunge:  Lehrbuch  d.  phys.  chemie,  p.  94  (1894). 

2  Nearly  all  of  the  "  organic  "  iron  preparations  on  the  market  belong  to   this  class 
of  iron  salts,  for  they  contain  the  iron  in  a  loose  state  of  combination. 


402  LECTURE  XVII. 

in  the  way  of  the  general  conception  which  prevails  concerning  its  cause. 
According  to  the  theory,  however,  that  it  is  not  the  function  of  synthesizing 
the  material  which  is  disturbed,  but  rather  the  function  of  decomposing 
the  material  containing  the  iron,  it  is  easy  to  understand  the  favorable 
action,  of  iron  salts,  for  in  them  the  organism  receives  material  which  for 
some  reason  it  cannot  itself  obtain.  At  all  events,  in  cases  of  iron  thera- 
peutics it  should  be  borne  in  mind  that  hemoglobin  cannot  be  formed  from 
iron  alone,  so  that  care  must  be  taken  to  supply  the  remaining  material 
necessary,  in  the  form  of  meat,  eggs,  and  green  vegetables. 

The  importance  of  iron  for  the  tissues  has  been  in  the  past  almost 
forgotten  in  the  discussion  of  the  relations  of  iron  to  the  formation  of 
blood.  Here  again  iron  plays  an  important  part,  but  unfortunately  we 
now  know  but  little  in  regard  to  the  way  it  is  combined  in  the  tissues  and 
cells.  It  evidently  occurs  in  different  forms.  Thus,  iron  compounds 
have  been  prepared  from  the  liver,  spleen,  and  muscles  of  man  by  P. 
Marfori l  and  0.  Schmiedeberg.2  According  to  these  investigators,  the 
iron  is  present  in  much  the  same  state  of  combination  as  in  hematin.  The 
substances  thus  prepared  were  apparently  absorbed  by  dogs  after  they  had 
been  starved,  or  fed  upon  a  diet  free  from  iron.  The  exact  nature  of 
these  iron  compounds  has  by  no  means  been  fully  explained. 

Copper  plays,  in  the  case  of  invertebrates,  a  similar  part  to  that 
taken  by  iron  in  the  vertebrates.3  It  is  found  combined  with  albumin. 
The  compound  which  corresponds  to  hemaglobin  is  called  hemocyanin. 
It  is  found  especially  in  many  mollusks  and  crustaceans.  The  blood  of 
the  cephalopoda  has  been  examined  chiefly  in  this  connection.  The 
arterial  blood  of  these  animals  is  blue,  the  venous  blood  colorless.  In 
certain  other  mollusks  (Pinna  squamosa,  Doris,  Patella,  Chiton)  manga- 
nese 4  replaces  the  copper. 

We  have,  up  to  this  point,  failed  to  mention  certain  inorganic  salts 
which  occur  in  milk,  and  unquestionably  are  indispensable  foods.  Thus, 
milk  always  contains  some  magnesium.  This  element  forms  an  integral 
part  of  plant  and  animal  cells  and  also  of  the  animal  fluids,  blood  and 
lymph.  The  amount  of  magnesium  in  milk  is  in  general  relatively  small. 
Its  function  in  the  animal  economy  is  not  yet  definitely  known.5  Appar- 

1  Arch,  exper.  Path.  Pharm.  29,  212  (1891),  and  Arch.  ital.  biol.  21,  1  (1894). 

2  Arch,  exper.  Path.  Pharm.  33,  102  (1894);  cf.  Filippi:  ibid.  34,  462  (1895). 

3  Cf.    Harless:   Muller's   Arch.    1846,    148.     Schlossberger:   Ann.    102,    86    (1857). 
Fre-dericq:  Arch.  Zool.  expe>.  7,  535  (1878);  Compt.  rend.  87,  996  (1878).     Dhere: 
Compt.  rend.  soc.  biol.  52,  458  (1900).     Griffiths:  Proc.  Roy.  Soc.  Edinburgh,  18,  288 
(1890-91) ;  19,  127  (1892) ;  Compt.  rend.  114,  496  (1892).     Cf.  Otto  v.  Fiirth:  Vergleich- 
ende  chemische  Physiologic  der  niederen  Tiere,  p.  74,  Jena,  1903. 

4  Griffiths:  Compt.  rend.  114,  840  (1892);  116,  259  and  474  (1892);  116,  1206  (1893), 
and  Respiratory  Proteids,  London,  1897. 

1   Cf.  Lecture  XVI,  p.  354  et.  seq. 


INORGANIC  FOODS.  403 

ently  it  bears  about  the  same  relation  to  calcium  as  potassium  to  sodium. 
J.  Malcolm  1  has  shown  that  the  introduction  of  soluble  magnesium  salts 
into  adult  animals  causes  a  loss  of  calcium.  In  growing  animals  it  tends 
to  prevent  the  taking  up  of  calcium.  Soluble  calcium  salts  apparently 
have  no  effect  upon  the  elimination  of  magnesium  salts.  In  osteomalacia 
we  have  also  come  to  recognize  a  certain  antagonism  between  these  two 
kinds  of  salts.2 

Fluorine 3  likewise  occurs  in  small  amounts  in  milk,  and  forms  a  regular 
constituent  of  bones  and  teeth,  besides  being  found  in  the  blood.4  In 
spite  of  the  small  amount  present  it  cannot  be  disregarded.  For  this 
element,  as  well  as  for  all  others,  the  Law  of  the  Minimum  holds. 

Phosphorus  is  of  much  greater  importance  both  for  the  growing  and 
adult  organism.  We  find  phosphorus  in  the  cells  in  the  form  of  very 
important  compounds,  namely  lecithin,  the  nucleins  and  nucleo albumins. 
We  know,  furthermore,  that  phosphorus  combined  with  the  alkaline 
earths  forms  one  of  the  most  important  constituents  of  the  human  skele- 
ton, and  is  also  present  in  the  same  form  in  other  tissues.  Phosphorus  is 
present  in  milk,  partly  in  organic  combination,  as  in  casein  which  belongs 
to  the  group  of  nucleoalbumins,  and  partly  as  inorganic  salt.  Milk  also 
contains  some  lecithin.  At  present  it  is  not  known  exactly  how  the 
phosphorus  is  distributed  between  these  different  compounds  in  the 
different  kinds  of  milk.  Apparently  the  amount  of  lecithin  present  is 
not  very  large. 

There  is  no  reasonable  doubt  that  the  living  organism  can  utilize 
phosphoric  acid  directly  in  the  formation  of  lecithin.  It  is  similarly 
possible  that  it  forms  a  part  of  its  nucleins.  from  the  latter  substance. 
The  fact  that  the  animal  organism  can  form  lecithin  from  phosphates 
without  difficulty  is  apparent  from  the  experiments  already  cited  of 
Miescher  upon  salmon.5 

Phosphorus  is  especially  important  in  the  construction  of  nervous 
tissue.  The  brain  of  a  new-born  infant  weighs  about  400  grams.  This 
weight  is  doubled  during  the  period  of  lactation.  According  to  Schloss- 
mann's  computations,6  the  nursling  assimilates  during  this  period  for 
the  building  up  of  its  central  nervous  system  alone  about  0.75  gram  of 
phosphorus.  The  skeleton  requires  much  more  of  this  element.  In 
fact,  if  we  estimate  the  total  amount  of  phosphorus  required  by  the  infant 
during  the  first  year  of  its  life,  we  shall  find  that  it  amounts  to  from  50  to 


1  J.  Physiol.  32,  183  (1905). 

2  Cf.  Lecture  XVI,  p.  377. 

3  G.  Tammann:  Z.  physiol.  Chem.  12,  325  (1888).     S.  Gabriel:  ibid.  18,  281  (1894). 

4  J.  Nickles:  Compt.  rend.  43,  885  (1886);  Tammann:  loc.  cit. 
6  Cf.  Lecture  XVI,  p.  351. 

6  Med.  Klinik.  No.  11  (1905);  Arch.  Kinderheilk.  40,  1. 


404 


LECTURE  XVII. 


60  grams.  The  amount  of  phosphorus  required  in  the  food  is  naturally 
even  far  greater,  because  in  the  above  estimate  it  was  not  taken  into  con- 
sideration that  phosphorus  is  constantly  being  eliminated  in  the  form  of 
phosphates.  In  one  liter  of  human  milk  there  is  present  0.19  gram 
phosphorus,  ass's  milk  contains  0.76  gram,  cow's  milk  0.79  gram,  and 
goat's  milk  0.96  gram.  Human  milk,  therefore,  is  deficient  in  phos- 
phorus; it  contains  less  than  any  of  the  other  kinds  of  milk  which  have 
been  analyzed.  This  is  a  remarkable  fact,  for  we  know  that  the  human 
offspring  is  able  to  construct,  while  still  nursing,  a  nervous  system  which 
is  but  slightly  developed.  Compared  to  human  milk,  that  of  the  above 
animals  is  extremely  high  in  phosphorus.  There  must  be  some  reason 
for  this  difference.  Bunge,  who  noticed  this  fact  in  his  analyses  of  differ- 
ent kinds  of  milk,  compared  the  percentage  composition  of  the  ash  with 
the  rate  of  development  of  the  species.1  It  is  to  be  assumed  a  priori  that 
an  animal  which  develops  rapidly  will  require  more  building  material 
than  one  whose  development  is  slower.  If  we  compare  the  time  required 
by  the  suckling  to  double  its  weight  at  birth  with  the  amounts  of  albumin 
and  ash  —  perhaps  the  most  essential  constituents  for  the  formation  of 
the  tissues  —  contained  in  100  parts  of  milk,  it  is  evident  at  a  glance  that 
the  amount  of  these  increases  in  proportion  as  the  development  of  the 
animal  is  rapid.  This  is  shown  by  the  following  table: 2 


100  1 

'arts  by  Weight 

of  Milk  Contaii 

i: 

Days  Re- 

Species. 

quired  to 

Double 

Weight. 

Albumin. 

Ash. 

Lime. 

Phosphoric 
Acid. 

Man     

180 

1.6 

0.2 

0.03 

0.05 

Horse      

60 

2.0 

0.4 

0.12 

0.13 

Cow 

47 

3  5 

0  7 

0  16 

0  20 

Goat4 

22 

3  7 

0  78 

0  20 

0  28 

Sheep  4 

15 

4  9 

0  84 

0  25 

0  29 

Pig4        

14 

5  2 

0  80 

0  25 

0  31 

Cat3    

9* 

7  0 

1  02 

Dog3,4    

9 

7.4 

1.33 

0.45 

0.51 

Rabbit  3.    .    . 

6 

14.4 

2.50 

0.89 

0  99 

The  composition  of  the  milk  of  a  single  species  is  by  no  means  constant. 
The  amount  of  albumin  and  ash  diminishes  with  the  age  of  the  suckling. 
This  likewise  has  an  effect  upon  the  rate  of  growth  as  shown  by  the  fol- 
lowing values : 5 


1  Fr.  Proscher:  Z.  physiol.  Chem.  24,  285  (1897). 

2  Abderhalden:  ibid.  27,  594  (1899). 

3  Abderhalden:  Z.  physiol.  Chem.  26,  487  (1899). 

4  Ibid.  27,  408  (1899). 
6  Ibid.  27,  457  (1899). 


INORGANIC  FOODS. 


405 


One  hundred  parts  by  weight   contain:    (a)   Before    the    animal  has 
doubled  its  weight  at  birth: 


Species. 

Casein. 

Albumin. 

Total 
Protein. 

Fat. 

Sugar. 

K2O. 

Pig  . 

3.71 

1.65 

5.36 

6.32 

3.19 

0  105 

Sheep      

4.08 

0.80 

4.88 

9.29 

5.04 

0.097 

Goat    

2.91 

0.76 

3.67 

4.33 

3.61 

0.130 

Species. 

Na2O. 

Cl. 

Fe203. 

CaO. 

MgO. 

P206. 

Total  Ash. 

Pig  ... 
Sheep  .  . 
Goat  .  . 

0.082 
0.086 
0.062 

0.083 
0.129 
0.102 

0.004 
0.004 
0.004 

0.268 
0.245 
0.197 

0.017 
0.015 
0.015 

0.329 
0.293 
0.284 

0.871 
0.841 
0.771 

(/>)   After  the  animal  has  doubled  its  weight: 


Species. 

Casein. 

Albumin. 

Total 
Protein. 

Fat. 

Sugar. 

K2O. 

Pig  ... 

3.23 

1.06 

4.29 

7.21 

3.71 

0  099 

Sheep 

4  07 

0  52 

4  59 

9  44 

5  22 

0  096 

Goat 

2  56 

0  58 

3  14 

2  93 

3  92 

0  133 

Species. 

Na2O. 

Cl. 

Fe203. 

CaO. 

MgO. 

P205. 

Total  Ash. 

Pig  ... 
Sheep  .  . 
Goat  .  . 

0.074 
0.085 
0.062 

0.067 
0.121 
0.111 

0.004 
0.004 
0.004 

0.241 
0.235 
0.199 

0.014 
0.015 
0.016 

0.300 
0.281 
0.285 

0.783 
0.809 
0.784 

During  lactation  the  albumin  content  of  milk  diminishes  gradually, 
while  substances  such  as  sugar  and  fat,  which  are  less  essential  as  build- 
ing material,  but  are  rather  to  be  regarded  as  sources  of  energy  and  heat, 
tend  to  increase  in  amount. 

The  remarkably  small  amount  of  phosphoric  acid  contained  in  human 
milk  is  nevertheless  sufficient  for  the  development  of  the  child,  although 
this  takes  place  much  more  slowly  than  is  the  case  with  most  mammals. 
The  above  relations  between  the  rate  of  growth  and  the  composition  of 
the  milk  make  it  perfectly  apparent  how  difficult  it  must  be  to  replace  one 
kind  of  milk  with  that  of  another  species.  Evidently  if  the  new  milk 
contains  any  constituent  in  amount  less  than  the  required  minimum, 


406  LECTURE  XVII. 

there  will  be,  necessarily,  disadvantageous  results.  The  value  of  any  milk 
substitute  should  in  no  case  be  determined  by  the  fact  that  it  contains 
all  of  the  elements  required,  nor  by  the  fact  that  it  contains  in  abundance 
something  (e.g.,  albumin,  lime  or  phosphorus)  which  we  are  accustomed 
to  regard  as  especially  essential.  It  is  of  chief  importance  that  there  is 
nothing  present  in  quantity  below  the  required  minimum.  Even  though 
a  milk  substitute  may  be  rich  in  phosphorus,  it  may  be  of  but  little  value; 
for,  in  order  that  the  cells  may  utilize  this  phosphorus,  it  is  necessary  that 
a  sufficient  amount  of  certain  other  substances  should  be  present.  This 
shows  where  the  greatest  emphasis  is  to  be  placed.  There  is  no  question  that 
the  unsuccessful  results  obtained  in  the  artificial  feeding  of  infants  have  been 
due  chiefly  to  the  non-observance  of  this  principle.  It  is  obvious  that 
the  mother's  milk  can  never  be  replaced  satisfactorily  by  some  other 
milk,  or  milk-substitute.  This  accounts  for  the  greater  mortality  among 
"  bottle  babies  "  than  among  those  that  are  breast-fed.  It  is  our  duty 
to  make  it  generally  known  that  on  the  one  hand  there  is  no  perfect  sub- 
stitute for  the  mother's  milk,  and  on  the  other  hand  to  show  that  when 
a  replacement  is  unavoidable,  the  food  should  be  adjusted  in  accordance 
with  the  requirements  established  as  a  result  of  biological  investigation. 

Chlorine  is  also  an  important  constituent  of  milk.  It  occurs  as  chloride 
of  sodium  and  of  potassium,  and  is  distributed  throughout  all  the  cells  of 
the  body.  The  alkali  chlorides,  especially  the  sodium  compound,  play 
an  important  part  in  the  formation  of  the  urine.  We  shall  come  back 
again  to  the  relations  of  chlorides  to  the  juices  of  the  stomach. 

Finalty,  milk  contains  another  element,  sulphur,  which  is  present  in 
a  firm  state  of  combination  in  the  proteins  casein,  albumin,  and  globulin. 
In  this  connection  the  reader  is  referred  to  what  was  said  concerning  the 
decomposition  products  of  protein.1 

As  far  as  we  know,  this  comprises  all  the  elements  contained  in  milk. 
It  is,  to  be  sure,  possible  that  other  elements  are  present  in  small  amounts. 
Thus,  it  has  been  suggested  that  milk  may  contain  iodine.  This  assump- 
tion was  made  merely  because  iodine  plays  an  important  part  in  the 
economy  of  the  cells.  It  is,  however,  perfectly  possible  that  the  new- 
born child  either  contains  iodine  already  stored  away,  or  else  that  it  makes 
use  of  what  it  has  only  for  later  functions. 

There  has  been  a  great  deal  of  discussion  as  to  whether  the  animal 
organism  normally  contains  arsenic.  It  is  certain,  however,  that  if  such 
be  the  case,  the  amount  present  is  extremely  small.  The  question  con- 
cerning the  arsenic  content  is  an  old  one,  and  has  been  zealously  discussed 
by  toxicologists  in  medical  jurisprudence.2  The  contradictory  results 
concerning  the  normal  occurrence  of  arsenic  in  the  thyroid  gland  is  prob- 

1  Cf.  Lecture  VIII,  p.  157. 

3  M.  Orfila:  TraitS  de  me"decin  legal,  4th  edition,  Vol.  Ill,  part  I,  p.  285  (Paris,  1848). 


INORGANIC  FOODS.  407 

ably  due  to  differences  in  the  material  examined.  The  amount  of  arsenic 
in  animal  tissues  must  depend  upon  the  nature  of  the  food.  Gautier  l 
and  Bertrand 2  have  found  arsenic,  while  others,  as,  for  example,  Kunkel,3 
have  not. 

It  should  be  mentioned  finally  that  recently  the  claim  has  been  made 
that  lithium  is  also  a  normal  constituent  of  the  human  organism.  Erich 
Herrmann  4  found  this  element  present  in  stages  of  development  where 
the  nourishment  had  been  provided  solely  from  the  blood  of  the  mother. 
The  lungs  were  found  to  be  particularly  rich  in  lithium. 

From  what  has  been  said,  it  is  apparent  that  inorganic  salts  are  of 
great  importance  as  foods,  both  for  the  developing  and  adult  organisms. 
The  cells  also  require  the  presence  of  salts  for  the  proper  exercise  of  their 
functions.  The  cells  are  constantly  being  broken  down  and  built  up  anew. 
The  more  recent  investigations  concerning  the  action  of  the  separate  salts 
make  it  seem  most  probable  that  our  knowledge  concerning  the  part  that 
inorganic  substances  play  in  the  metabolism  of  the  cells  will  shortly  be 
widened  greatly,  and  that  before  long  the  inorganic  substances  in  our  food 
will  be  the  subject  of  considerable  more  interest  corresponding  to  their 
importance. 

1  Compt.  rend.  137,  295  (1903),  and  Bull.  soc.  chim.  Paris,  29,  913  (1903).  Cf. 
also  Compt.  rend.  137,  158  and  232  (1903),  and  Bull.  soc.  chim.  Paris,  29,  639  (1903). 

3  Ann.  inst.  Pasteur,  16,  553  (1902);  17,  1  (1903);  Ann.  chim.  phys.  28,  242  (1903); 
Bull.  soc.  chim.  Paris,  29,  790  and  920  (1903),  and  Compt.  rend.  137,  266  (1903). 

3  Z.  physiol.  Chem.  44,  511  (1905). 

4  Pfliiger's  Arch.  109,  26  (1905). 


LECTURE   XVIII. 
OXYGEN.1 

ALL  the  foodstuffs  which  we  have  considered  up  to  this  point  are  intro- 
duced into  the  animal  organism  by  way  of  the  alimentary  canal.  There 
is  one  substance  required  to  nourish  the  body  which  differs  from  all  the 
other  organic  and  inorganic  foods,  not  only  in  the  form  in  which  it  is 
taken  up,  but  also  in  the  manner  of  its  introduction.  We  refer  to  oxygen, 
which  is  taken  up  as  a  gas  into  the  animal  organism  through  the  lungs 
and  carried  by  the  blood  to  the  tissues.  With  the  oxygen,  as  such,  there 
is  no  available  energy  introduced  into  the  organism.  It  possesses  no 
chemical  kinetic  energy,  so  that  it  belongs  to  the  same  class  of  substances 
in  this  respect  as  the  salts  and  water.  In  every  way,  however,  oxygen 
occupies  an  exceptional  position.  Plants  set  it  free  by  the  aid  of  chloro- 
phyll and  the  influence  of  the  sun's  rays  in  the  assimilation  of  carbon 
dioxide  and  water.  Energy  is  required  for  this  process  and  becomes 
stored  up  as  chemical  energy.  Conversely,  in  the  animal  cells  oxygen 
again  combines  with  the  substances  formed  in  the  plants,  energy  is  set 
free,  and  we  find  as  the  final  end-products,  water  and  carbon  dioxide,  both 
of  which  can  again  take  part  in  the  cycle.2 

The  first  one  to  clearly  recognize  the  importance  of  oxygen  for  the  life 
process  was  Lavoisier.  He  sharply  outlined  the  important  role  which 
this  substance  plays  in  the  combustion  processes  taking  place  within  the 
animal  organism.  With  this  knowledge,  there  was  laid  one  of  the  most 
important  foundation  stones  for  the  entire  physiology  upon  which,  in  the 
period  following,  stone  after  stone  was  piled  in  rapid  succession  until 
finally  the  structure  was  established,  the  particulars  of  which  we  are  now 
studying.  No  discovery  in  the  whole  field  of  physiology  was  so  decisive 
for  further  investigation  as  this.  Lavoisier  himself,  it  is  true,  believed 
that  the  lungs  were  the  seat  of  all  the  oxidation  processes  taking  place  in 
the  animal  organism.  The  oxygen  taken  from  the  air  was  supposed  to 
oxidize  the  substances  brought  to  the  lungs  by  means  of  the  blood.  Such 
an  assumption  was  a  priori  hardly  plausible,  for  in  this  combustion 

1  Cf.  Christian  Bohr:  Handbuch  der  Physiologie  der  Menschen,  Vol.  I,  p.  54,  1905. 

2  Fundamentally,  there  is  no  such  sharp  distinction  between  plant  and  animal  cells. 
Plants  also  utilize  chemical  energy,  but  in  them  the  reduction  processes  far  exceed  those 
of  oxidation  in  the  daytime,  though  in  the  absence  of  light  (night-time)  the  latter  pro- 
cesses are  more  prominent. 

408 


OXYGEN.  409 

energy  is  set  free  which  is  required  by  the  life-processes  taking  place  in  the 
tissues  and  cells.  If  all  combustion  took  place  in  the  lungs,  then  at  a 
single  place  the  greater  part  of  the  total  energy  would  be  set  free.  The 
tissues  and  cells  could  only  secure  for  themselves  a  part  of  this  energy  by 
means  of  certain  cleavage-processes.  An  examination  of  the  gases  in  the 
blood  would  necessarily  decide  this  question.  If  the  oxygen  actually 
combined  with  the  combustible  substances  directly  in  the  lungs,  then  it 
was  certainly  to  be  expected  that  the  blood  itself  would  contain  but 
little  if  any  oxygen.  This  idea  appealed  to  Magnus,1  who  analyzed  the 
gases  in  blood  and  showed  that  a  certain  amount  of  oxygen  was  present 
until  the  capillaries  were  reached  and  at  this  point  a  part  of  it  began  to 
disappear.  This  proved  beyond  question  that  all  of  the  combustion 
processes  could  not  take  place  in  the  lungs.  It  left  undecided  the 
question  whether  the  oxidation  processes  took  place  exclusively  in  the 
blood,  or  whether  oxygen  passed  through  the  walls  of  the  blood-vessels 
into  the  tissues.  It  is  conceivable  that  the  tissues  constantly  give  up 
these  oxidizable  substances  to  the  blood.  In  fact,  certain  discoveries 
support  this  assumption.  If  the  supply  of  oxygen  be  entirely  cut  off 
from  an  animal,  it  suffocates.  Its  blood  then  contains  but  traces  of 
oxygen.  On  exposing  such  blood  to  oxygen,  the  latter  disappears  in  a 
short  time,  and  the  amount  of  carbon  dioxide  in  the  blood  increases. 
The  blood  of  an  animal  which  has  not  been  suffocated  shows  the  same 
phenomenon,  but  to  a  much  less  extent.  Ludwig  and  Schmidt,2  who 
carried  out  these  experiments,  explained  this  discovery  on  the  assumption 
that  oxidizable  substances  were  constantly  being  given  up  to  the  blood 
which  immediately  underwent  combustion  provided  the  supply  of  oxygen 
were  adequate.  If  this  supply  were  cut  off,  these  substances  began  to 
accumulate  in  the  blood.  Now  we  know  that  the  blood  contains  cells, 
the  white  and  red  blood  corpuscles,  which  themselves  undergo  metabolism, 
and  thereby  may  easily  consume  oxygen  and  yield  carbon  dioxide.  The 
above  experiments,  therefore,  are  not  sufficient  to  prove  satisfactorily 
that  the  combustion  takes  place  chiefly  in  the  blood.  Afonassiew 3  then 
showed  that,  as  a  matter  of  fact,  only  the  blood-corpuscles  and  not  the 
serum  of  a  suffocated  animal  could  take  up  oxygen  in  this  way.  The 
assumption  that  the  combustion  takes  place  in  the  cells  and  tissues  them- 
selves was  furthermore  supported  by  the  following  experiment:  Pfliiger 
and  Oertmann 4  removed  the  blood  from  a  frog,  washed  out  the  last 
blood  corpuscles  with  a  0.75  per  cent  solution  of  common  salt,  and  finally 

1  Ann.  Physik.  40,  583  (1837);  and  64,  177  (1845). 

2  Ber.  iiber  die  Verhandl.  der  Sachs.  Ges.  Wissen.  Leipzig.     Math.-physikal  Klasse, 
19,  99  (1867). 

3  Ibid.  24,  253  (1872). 

4  E.  Oertmann:  Pfliiger's  Arch.  15,  382  (1877);  E.  Pfliiger:  ibid.  10,  251  (1875). 


410  LECTURE  XVIII. 

replaced  all  the  blood  in  the  various  vessels  by  this  saline  solution. 
This  animal  was  then  placed  in  an  atmosphere  of  pure  oxygen,  and  con- 
sumed as  much  of  the  gas  and  evolved  as  much  carbonic  acid  gas  as  a 
normal  frog. 

To-day  there  is  not  the  slightest  possible  doubt  that  oxygen  diffuses 
into  the  tissues,  and  that  the  cells  themselves  obtain  their  energy  by  the 
combustion  of  their  nutriment,  which  takes  place  in  their  immediate 
vicinity.  We  know  a  great  many  facts  which  are  in  harmony  only 
with  this  assumption.  One  of  the  principal  proofs  is  that  the  blood 
itself  possesses  no  oxidizing  properties.1  If,  for  example,  salts  of  lactic 
acid,  acetic  acid,  etc.,  are  placed  in  the  blood  they  remain  unchanged, 
whereas  in  their  passage  through  the  organism  they  are  quickly  and 
completely  oxidized.  This  experiment  becomes  more  convincing  if 
carried  out  with  surviving  organs.  If,  for  example,  blood  is  conducted 
through  the  liver  of  a  dead  animal  by  the  portal  vein,  it  can  be  shown  that 
ammonium  formate  introduced  into  the  blood  disappears  and  in  its  place 
urea  is  formed.  This  is  never  the  case,  however,  if  the  formate  is  merely 
exposed  to  the  action  of  the  blood  without  coming  in  contact  with  the 
liver-cells;  in  such  cases  the  ammonium  formate  remains  unchanged. 
Evidently  there  is  a  mutual  action  between  the  blood  and  the  cells  of  the 
liver  which  is  necessary  to  cause  this  complicated  reaction  to  take  place. 
This  is  merely  one  example  out  of  many. 

The  fact  that  oxygen  actually  passes  through  the  walls  of  the  blood- 
vessels is  strikingly  shown  by  the  way  the  fcetus  is  provided  with  this 
element.  It  is  well  known  that  there  is  no  direct  connection  between 
the  vascular  system  of  the  mother  and  that  of  the  child.  The  circu- 
lation of  the  foetus  is  isolated.  The  umbilical  arteries  carry  the  blood 
rich  in  carbon  dioxide  and  poor  in  oxygen  from  the  fcetus  through  the 
umbilical  cord  to  the  placenta.  Here  these  arteries  break  down  into 
extremely  fine  branches.  They  change  into  the  form  of  chorionic  villi  in 
the  enlarged  capillaries  of  the  mucous  membrane,  in  the  intravillous 
spaces  of  the  decidua.  To  this  region  the  organism  of  the  mother  sends 
blood  rich  in  oxygen.  In  order  that  this  oxygen  may  enter  the  fcetal 
circulation  —  i.e.,  that  it  may  enter  into  the  umbilical  veins,  — it  must  first 
penetrate  the  epithelium  and  vascular  walls  of  the  chorionic  villi,  and 
conversely  the  venous  fcetal  blood  of  the  umbilical  arteries  gives  up  its 
carbon  dioxide  in  the  same  way. 

Another  proof  that  the  oxygen  passes  through  the  walls  of  the  blood 
capillaries  lies  in  the  fact  that  the  saliva  contains  a  constant  amount  of 
free  oxygen.  According  to  E.  Pfliiger,2  it  contains  0.5  per  cent  by  volume 

1  Cf.  E.  Pfliiger:  Pfliiger's  Arch.  6,  43  (1872);  Hoppe-Seyler:  ibid.  7,  407  (1873). 

2  Pfliiger's  Arch.  1,  686  (1868).     See  also  R.  Kiilz:  Z.  Biol.  23,  321  (1887).     J.  L. 
Bancroft:  Biochem.  J.  1,  1  (1906). 


OXYGEN.  411 

of  this  gas.  This  oxygen  must  come  from  the  circulation,  and  is  undoubt- 
edly to  be  regarded  as  oxygen  that  has  not  been  consumed  by  the  oxida- 
tion processes  taking  place  in  the  cells  of  the  salivary  glands. 

Paul  Ehrlich1  has  proposed  a  very  pretty  method  for  following  the 
course  of  the  oxidation  processes  taking  place  in  the  tissues.  If  a  dye- 
stuff  which  becomes  decolorized  on  reduction  and  again  resumes  its  color 
on  oxidation  is  injected  into  the  veins  of  an  animal,  it  is  easy  to  recognize 
the  presence  of  oxidizable  substances  in  the  tissues.  Methylene'  blue  is 
especially  suited  for  such  experiments.  If  this  has  been  injected  into  the 
veins,  it  will  be  found  that  a  f rashly- killed  animal  will  be  of  normal  color; 
but  after  being  exposed  to  the  air  for  some  time,  the  color  of  methylene 
blue  eventually  appears,  showing  that  the  tissues  have  contained  this 
dyestuff  in  a  reduced  form. 

The  assumption  that  the  consumption  of  oxygen  must  actually  take 
place  in  the  tissues  and  cells  has  been  based  frequently  upon  numerous 
observations  concerning  the  oxygen  supply  of  lower  organisms.  Thus 
the  observations  of  Kupffer  2  and  of  Max  Schultze  3  regarding  the  direct 
supply  of  oxygen  to  the  cells  of  the  body  are  a  good  example.  The  former 
showed  that  insects  which  had  no  real  vascular  system  conduct  the  atmos- 
pheric oxygen  directly  to  the  tissues  by  means  of  an  infinitely-fine  tracheal 
system.  The  finest  little  runners  of  the  tracheae  send  out  branches  to  the 
individual  cells,  so  that  the  latter  by  means  of  these  tiny  tubes  take  the 
oxygen  directly  from  the  air.  Again,  Schultze  showed  that  in  the  organs 
of  phosphorescence  of  Lampyris  splendidula,  the  finest  ends  of  the  tracheae 
lead  to  the  individual  cells,  which  cause  the  phosphorescence. 

Although  these  observations  undoubtedly  indicate  the  ability  of  highly 
organized  animals  to  take  up  and  utilize  directly  the  oxygen  of  the  air, 
yet  they  do  not  prove  conclusively  that  also  in  the  highest  organized 
animals  such  a  direct  introduction  of  the  oxygen  to  the  cells  actually 
takes  place.  In  the  ascending  series  of  animal  species,  with  the  division 
of  labor  and  specialization  of  the  separate  cell  groups  becoming  more  and 
more  complicated,  it  would  not  seem  impossible  that  perhaps  one  par- 
ticular cell  group  may  be  limited  to  quite  restricted  functions;  and  that, 
for  example,  the  cells  receive  their  energy,  in  the  more  highly  developed 
organisms,  from  certain  cleavage  processes,  while  the  energy  produced 
by  oxidation  serves  merely  as  the  source  of  heat  for  the  organism.  We 
have  already  seen  4  that  intestinal  parasites,  and  even  frogs,  can  live  for 


1  Med.  Zentrb.  1885,  113.     Das  Sauerstoffbedurfnis  des  Organismus,  Berlin,  1885. 
Cf.  C.  A.  Herter:  Z.  physiol.  Chem.  42,  493  (1904),  and  Am.  J.  Physiol.  12,  128  (1904). 
Herter  and  Richards:  ibid.  12,  207  (1904).     C.  A.  Herter:  ibid.  12,  457  (1905). 

2  Beitrage  zur  Anatomic  und  Physiologie  (1875).     Cf.  E.  Pfliiger:  Pfluger's  Arch. 
10,  251  and  270  (1875). 

3  Arch,  mikros.  Anat.  1,  124;  5,  186. 

4  Lecture  IV,  p.  74. 


412  LECTURE  XVIII. 

a  long  time  without  oxygen,  and  produce  carbon  dioxide;  and,  on  the  other 
hand,  we  have  cited  the  experiments  of  Fick  and  Wislicenus,1  who  showed 
that  the  energy  set  free  in  the  cleavage  processes  was  altogether  insuffi- 
cient to  account  for  the  work  which  these  authors  were  capable  of 
accomplishing.  We  came  to  the  conclusion  then,  that  under  some  circum- 
stances the  muscular  cells,  in  order  to  satisfy  the  demands  placed  upon 
them,  must  utilize  all  the  chemical  energy  available  from  the  food 
materials  it  receives. 

On  the  other  hand,  the  assumption  that  the  cells  in  general  are  satisfied 
to  accomplish  their  work  with  the  energy  resulting  from  cleavage  processes, 
is  supported  by  the  fact  that  there  are  unicellular  organisms  which  not 
only  do  not  require  oxygen,  but  on  which  in  fact  this  gas  even  acts  as  a 
poison.  These  are  the  anaerobic  bacteria.  All  sorts  of  varieties  of  bacteria 
are  known,  ranging  from  those  to  which  oxygen  is  indispensable  to  those 
which  get  along  best  without  it.  There  are,  in  fact,  bacteria  which  are 
temporarily  anaerobic;  i.e.,  they  can  get  along  without  oxygen  for  a  time. 
It  is  characteristic  of  all  these  bacteria  that  they  eliminate  carbon 
dioxide,  no  matter  whether  they  take  up  oxygen  directly  from  the  air  or 
not.  The  bacteria  which  are  wholly  anaerobic,  and  those  which  are  tem- 
porarily so,  must  be  able  to  obtain  oxygen  from  the  nutriment  upon  which 
they  subsist.  In  the  latter  case,  the  assumption  might  be  made  that  they 
store  up  compounds  rich  in  oxygen,  which  they  consume  during  the  anaero- 
bic period,  just  as  the  muscular  cells  are  evidently  capable  of  storing  up 
oxygen,  when  they  are  in  a  state  of  rest,  which  they  require  when  the 
muscles  are  being  used. 

We  shall  later  on  2  go  more  into  detail  concerning  the  significance  of 
this  progressive  breaking  down  by  stages  of  the  nutriment  on  the  part  of 
the  cells  in  our  body,  and  shall  find  that  by  means  of  this  alternate  simple 
decomposition  and  oxidation  it  is  possible  to  obtain  energy  from  the  food 
as  it  is  required.  At  all  events,  all  our  observations  indicate  that  each 
individual  cell  in  the  body  must  have  the  possibility  of  obtaining  oxygen 
for  oxidation  processes,  and  for  the  regulation  of  its  internal  economy. 
We  shall  soon  become  acquainted  with  facts  which  compel  us  to  accept 
this  assumption. 

Let  us  now  attempt  to  trace  the  course  of  the  oxygen  from  the  time  it 
is  taken  up  by  the  lungs  till  it  is  given  up  to  the  cells  of  the  individual 
tissues.  The  blood  plays  an  intermediate  part  in  the  process.  It  takes 
the  oxygen  from  the  lungs  and  gives  it  up  to  the  tissues.  The  first  gas- 
exchange  is  commonly  spoken  of  as  external  respiration,  and  the  latter  as 
internal  respiration.  The  question  that  interests  us  first  of  all  is  how  does 
the  oxygen  circulate  in  the  blood.  There  are  two  possibilities  to  be  con- 


1  Lecture  IV,  p.  69. 

2  See  Lecture  XIX. 


OXYGEN.  413 

sidered.  The  oxygen  may  be  simply  absorbed  by  the  blood,  or  it  may  be 
that  there  is  some  compound  in  the  blood  which  unites  with  this  oxygen. 
In  the  former  case  the  absorption  of  oxygen  must  follow  the  gas  laws,1  of 
which  we  shall  briefly  sketch  the  most  important  particulars. 

The  absorption  of  a  gas  by  a  liquid,  when  there  is  no  chemical  reaction 
between  the  two,  is  dependent  upon  the  nature,  the  temperature,  and  the 
pressure  of  the  gas;  and,  in  fact,  the  weight  of  gas  which  is  absorbed  by  a 
definite  liquid  is  proportional  to  the  pressure  under  which  the  gas  is  placed. 
Now  according  to  Boyle's  law,2  the  weight  of  a  definite  volume  of  a  gas  is 
directly  proportional  to  the  pressure,  so  that  evidently  the  volume  of  gas 
absorbed  is  independent  of  the  pressure.  Again,  if  instead  of  a  single  gas 
a  mixture  of  gases  stands  above  a  liquid,  then  each  individual  gas  will  be 
absorbed  independently  of  the  others,  and  the  amount  absorbed  is  gov- 
erned entirely  by  the  pressure  which  this  gas  exerts  (Dalton's  law). 
This  pressure  is  called  the  partial  pressure.  The  partial  pressure  can  be 
computed  as  soon  as  one  knows  the  total  pressure  exerted  by  all  of  the 
gases  present  in  the  mixture,  and  the  percentage  composition  of  the  mix- 
ture. The  partial  pressure  is  the  same  percentage  of  the  total  pressure 
that  the  gas  in  question  is  present  in  per  cent  by  volume  in  the  mixture.3 

If  a  liquid  is  allowed  to  remain  in  contact  with  a  definite  gas  mixture 
for  some  time,  the  liquid  will  become  saturated  with  gas.  When  this 
has  taken  place,  then  the  pressure  exerted  by  each  gas  in  the  liquid  is 
equal  to  the  partial  pressure  of  the  same  gas  in  the  mixture  above  the 
liquid.  There  is  a  state  of  equilibrium  between  the  gas  in  the  atmosphere 
and  that  in  the  liquid.  If  this  equilibrium  is  disturbed,  for  example,  by 
diminishing  the  amount  of  gas  in  question  in  the  gaseous  mixture,  then 
the  liquid  will  give  up  this  gas  until  once  more  the  pressure  in  the  mixture 
is  in  equilibrium  with  the  pressure  exerted  by  the  gas  in  the  liquid.  This 
fact  may  be  taken  advantage  of,  if  we  wish  to  determine  in  a  simple 
manner  what  pressure  is  exerted  by  a  gas  which  is  dissolved  in  a  liquid. 
The  liquid  is  placed  in  contact  with  a  gas  mixture  of  a  definitely  known 
composition  and  pressure  (whereby,  as  stated  above,  the  partial  pressure 

1  Cf.  Text-books  on  Physics.     For  comparative  purposes  the  volumes  of  gases  are 
reduced  to  0°  C.  and  760  millimeters,  barometric  pressure.      As  regards  the  methods 
used  for  examining  the  gases  in  blood,  see  E.  Pfliiger's  Untersuchungen  aus  dem  physi- 
ologischen  Laboratorium  zu  Bonn,  Berlin,  1865.  Alexander  Schmidt :  Verhandl.  Sachsi- 
schen  Gesellsch.  Wissensch.  19,  30  (1867).    A.  Kossel  and  A.  Raps:  Z.  Physiol.  Chem. 
17,  644  (1893).     Neesen:  ibid.  22,  478  (1897).     Muller:  Pfliiger's  Arch.  103,  541  (1904). 
J.   Geppert:   Die  Gas-analyse  und  ihre  physiologische  Anwendung  nach  verbesserten 
Methoden,  Berlin,  1886. 

2  The  name  Mariotte's  law  is  often  given  to  this  principle  (earlier  discovered  by 
Boyle),  that  at  any  given  temperature  the  volume  of   a  given  weight  of   gas  varies 
inversely  as  the  pressure  which  it  bears. 

3  The  partial  pressure  of  a  gas  in  a  mixture  is  the  same  pressure  that  the  gas  exerts 
when  present  by  itself  in  the  volume  occupied  by  the  mixture. 


414  LECTURE  XVIII. 

exerted  by  the  gas  in  question  may  be  accurately  computed),  and  the  liquid 
shaken  with  this  gas  mixture  for  some  time.  Now,  according  as  the  gas 
contained  in  the  liquid  exerts  a  less  pressure,  the  same  pressure,  or  a  greater 
pressure,  than  is  exerted  by  the  same  gas  in  the  gas  mixture,  there  will  be 
either  an  increase,  no  change,  or  a  diminution  in  the  amount  of  the  par- 
ticular gas  above  the  liquid. 

Let  us  now  come  back  to  the  question  of  the  condition  of  the  oxygen 
as  it  circulates  in  the  blood.  According  to  the  above  principles,  it  ought 
to  be  easy  to  decide  whether  there  is  any  chemical  combination  between 
the  oxygen  and  the  blood.  From  the  amount  of  oxygen  in  the  air  that  is 
breathed  into  the  lungs,  or,  what  is  the  same  thing,  from  the  partial  pressure 
of  the  oxygen  in  the  alveolar  air,  taking  into  consideration  the  temperature 
of  the  body  and  the  composition  of  the  blood,  we  can  compute  how  much 
oxygen  the  latter  could  take  up  by  simple  absorption. 
.  There  are  a  number  of  different  methods  which  are  derived  from  the 
above  principles  for  determining  the  gas  content  of  a  liquid.  Since  with 
rise  of  temperature  the  amount  of  gas  absorbed  diminishes,  it  is  evident 
that  the  gas  can  be  expelled  from  a  liquid  by  heating  it.  When  the  liquid 
begins  to  boil,  i.e.,  when  it  is  itself  being  converted  into  vapor,  all  of  the 
absorbed  gases  have  been  expelled.  The  pressure  of  the  gas  in  the  liquid 
is  now  equal  to  zero,  whether  it  is  due  to  the  fact  that  there  is  a  complete 
vacuum  above  the  liquid,  or  because  the  gas  which  was  absorbed  by  the 
liquid  has  been  replaced  by  some  other  gas  (e.g.,  water  vapor)  in  the 
atmosphere  directly  in  contact  with  the  liquid.  According  to  the  above 
description  of  the  behavior  of  gases,  the  effect  in  the  latter  case,  as  far  as 
the  absorption  of  the  gas  goes,  must  be  exactly  the  same  as  if  all  the  gases 
had  been  removed,  for  then  the  partial  pressure  of  the  given  gas  in  contact 
with  the  liquid  would  have  become  zero. 

The  air  that  is  breathed  into  the  lungs  contains  in  round  numbers  79 
per  cent  by  volume  of  nitrogen,  21  per  cent  oxygen,  0.03  per  cent  of  carbon 
dioxide,  and  varying  amounts  of  water  vapor.  If  we  compare  the  amount 
of  oxygen  taken  up  by  the  blood  in  the  lungs,  with  that  computed  to  be 
present  from  the  partial  pressure  of  the  oxygen  in  the  gas  mixture  that 
reaches  them,  it  is  found  that  far  too  much  oxygen  is  removed  by  the 
blood,  so  that  it  is  quite  out  of  the  question  to  consider  the  phenomenon 
as  one  of  simple  absorption.1  Nitrogen  and  argon,  which,  as  far  as  we 
know,  take  no  part  in  the  metabolism  of  the  living  animal  organism,  behave 
quite  differently  when  in  contact  with  the  blood.  They  are,  for  the  most 
part,  merely  absorbed  mechanically.  The  absorption  coefficient  for  nitro- 
gen amounts  at  the  body  temperature  to  about  0.013  to  0.02.  Oxygen, 
however,  in  its  absorption  by  the  blood,  in  no  way  follows  the  gas  laws. 
The  amounts  of  oxygen  absorbed  by  the  blood,  when  it  is  exposed  to  differ- 

1  Cf.  Hiifner:  Arch.  Anat.  Physiol.  1890,  1;  1895,  209. 


OXYGEN. 


415 


ent  partial  pressures  of  this  gas,  show,  within  certain  limits,  but  a  slight 
variation.  The  blood-plasma  is  able  to  take  up  only  0.65  per  cent  by 
volume  of  oxygen.1  As  a  matter  of  fact,  the  arterial  blood  contains  more 
than  70  times  as  much  oxygen.  Again,  if  blood  be  placed  under  an  air- 
pump,  the  oxygen  is  not  removed  from  it  at  all  in  proportion  to  the 
change  in  gas  pressure.  The  oxygen  does  not  leave  the  blood  to  any 
extent  until  the  pressure  has  been  reduced  to  358  millimeters  Hg. 

Since  the  blood-plasma  contains,  as  stated  above,  0.65  per  cent  by 
volume  of  absorbed  oxygen,  the  rest  of  the  oxygen  contained  in  blood 
must  be  held  in  some  sort  of  chemical  combination;  and,  obviously,  this 
union  is  effected  with  the  blood  corpuscles.  In  the  arterial  blood  of  a  dog, 
Pfluger 2  found,  on  an  average,  22  per  cent  of  oxygen  by  volume.  If  now  a 
solution  of  hemoglobin  is  employed,  containing  the  same  amount  of  hemo- 
globin as  the  blood,  it  will  be  found  that  this  solution,  within  narrow  limits, 
is  capable  of  absorbing  the  same  amount  of  oxygen  as  the  blood.  This 
shows  that  it  must  be  the  hemoglobin  which  combines  with  the  greater 
part  of  the  circulating  oxygen  in  the  blood.  When  hemoglobin 
absorbs  oxygen,  it  is  changed  into  oxyhemoglobin;  one  molecule  of 
hemoglobin  unites  with  one  molecule  of  oxygen,  or  for  one  gram  of  hemo- 
globin there  are  required  1.56  cubic  centimeters  of  gas  (measured  at  0°  C. 
and  760  millimeters  pressure) .  Dog's  blood  contains  approximately  14.5 
per  cent  of  hemoglobin.  From  this  it  is  evident  that  22.6  per  cent  by 
volume  (1.56  X  14.5)  of  oxygen  can  be  absorbed  by  the  blood  of  a  dog. 
This  agrees  well  with  the  amount  found  by  actual  experiment.  It  is,  how- 
ever, not  permissible  to  apply  the  results  obtained  by  working  with  hemo- 
globin solutions  directly  to  the  absorption  of  oxygen  by  the  blood  under 
different  conditions.  There  are  a  number  of  facts  known  which  show 
that  there  are  certain  differences  as  regards  the  behavior  of  the  two  liquids. 
This  may  be  accounted  for  in  different  ways.  It  is  conceivable  that  certain 
changes  may  have  taken  place  in  the  preparation  of  the  hemoglobin  solu- 
tion. On  the  other  hand,  the  possibility  exists  that  the  hemoglobin  in  the 
blood  is  influenced  by  the  way  it  is  contained  in  the  blood  corpuscles.  It  is, 

1  Christian  Bohr,  Skand.  Arch.  Physiol.  17,  104  (1905),  has  recently  computed  the 
absorption  coefficients  of  the  plasma  and  blood  for  different  gases: 


Oxygen. 

Nitrogen. 

Carbon  Dioxide. 

Water           

15°  C.      38°  C. 
0.0342     0.0257 

15°  C.      38°  C. 
0.0179     0.0122 

15°  C.    38°  C. 
1  019     0  555 

Plasma 

0  033       0  023 

0  017       0  012 

0  994     0  541 

Blood    .    .    .  '  
Blood  corpuscles  .... 

0.031       0.022 
0.028       0.019 

0.016       0.011 
0.014       0.009 

0.937     0.511 
0.825    0.450 

a  E  Pfluger:  Zentrb.  med.  Wiss.  1867,  722,  and  Pfliiger's  Arch.  1,  274,  288  (1868). 


416  LECTURE  XVIII. 

moreover,  very  questionable  whether  hemoglobin  itself  is  a  simple  substance. 
The  component  containing  iron  is  constant  in  its  composition,  but  the 
relation  between  this  and  the  globin  (the  protein  constituent) ,  or,  in  other 
words,  the  numberof  globin  molecules  which  unite  with  the  hemochromogen, 
varies  in  different  cases.  It  is  necessary  to  mention  this  fact  in  this  con- 
nection, because  it  is  unquestionably  true  that  differences  in  the  results 
obtained  by  investigators  are  due,  to  some  extent  at  least,  to  the  fact  that 
the  results  obtained  by  working  with  hemoglobin  solutions  have  been 
applied  directly  to  the  absorption  by  the  blood. 

Hemoglobin  itself  consists  of  a  protein,  globin,  and  another  constituent, 
hemochromogen,1  which  contains  iron;  it  is  the  hemochromogen  alone  that 
unites  with  oxygen.  This  is  shown  by  the  fact  that  hemochromogen  absorbs 
as  much  oxygen  from  the  air  as  an  equivalent  amount  of  hemoglobin. 
When  hemochromogen  is  oxidized  to  hematin,  the  hemoglobin  of  the  blood 
becomes  oxyhemoglobin.  Whereas  the  oxygen  combined  in  hematin  can- 
not be  removed  by  means  of  an  air-pump,  this  is  not  the  case  with  oxy- 
hemoglobin itself.  This  fact  is  of  great  importance  for  the  understanding 
of  the  transportation  of  oxygen  by  the  blood  and  its  giving  up  of  the  same 
to  the  tissues.  Oxyhemoglobin  belongs  to  the  class  of  compounds  which 
are  said  to  be  dissociable.  Before  we  go  into  further  particulars  concern- 
ing this  transportation  of  oxygen  by  the  blood  and  the  subject  of  internal 
respiration,  we  must  make  perfectly  clear  what  are  the  conditions  in  the 
animal  organism  upon  which  the  dissociation  of  the  oxyhemoglobin  de- 
pends. We  have  already  mentioned  the  fact  that  the  blood-plasma  contains 
absorbed  oxygen.  The  amount  present  is,  corresponding  to  the  gas  laws, 
relatively  small.  It  is  perfectly  clear  that  it  follows  the  laws  of  gas  absorp- 
tion. First  of  all,  the  amount  of  this  gas  must  be  in  equilibrium  with  the 
alveolar  air.  On  the  other  hand,  this  absorbed  oxygen,  in  its  transporta- 
tion to  the  various  tissues,  must  necessarily  constantly  seek  to  be  in 
equilibrium  with  the  pressure  of  the  oxygen  in  these  tissues,  and,  likewise, 
in  accordance  with  the  well-defined  gas  laws.  Now,  as  we  shall  soon  see, 
the  tissues  are  constantly  consuming  oxygen  and  forming  carbon  dioxide 
therefrom.  For  this  reason  the  pressure  of  oxygen  in  the  tissues  is  kept 
lower  than  that  of  the  absorbed  (or  dissolved)  oxygen  in  the  blood.  Hence 
oxygen  is  constantly  entering  these  tissues  from  the  blood.  There  is  no 
doubt  at  all  that,  in  the  first  place,  this  absorbed  oxygen  is  given  up.  Now 
in  proportion  as  this  absorbed  oxygen  is  given  up  by  the  blood,  oxyhemo- 
globin becomes  dissociated,  i.e.,  begins  to  give  up  its  oxygen  to  the  plasma. 
If  this  conception  be  correct,  it  must  be  possible  to  remove  eventually 
all  the  oxygen  from  the  blood  by  means  of  the  air-pump,  even  at 
low  temperatures,  i.e.,  without  the  aid  of  heat,  which  itself  tends 

1  Cf.  Lecture  VII,  p.  141. 


OXYGEN.  417 

to  dissociate  the  oxy hemoglobin.  This  has,  in  fact,  been  found  to 
be  the  case.1  For  the  cells  themselves,  therefore,  at  any  given 
moment,  only  the  uncombined  oxygen  is  available.  The  oxygen  con- 
tained in  the  oxyhemoglobin  serves,  as  it  were,  as  a  reserve  supply.  It 
is  only  the  merely  mechanically  absorbed  oxygen  which  determines  the 
pressure  of  the  oxygen  in  the  blood,  and  determines  thereby  the  gas 
exchange.  Naturally  the  extent  of  the  giving  up  of  oxygen  to  the  tissues 
depends  solely  upon  the  magnitude  of  this  pressure  exerted  by  the  absorbed 
oxygen  in  the  blood.  The  fact  that  the  oxygen  in  the  blood  is  not  merely 
absorbed,  but  for  the  most  part  held  in  a  state  of  loose  combination,  is  of 
great  significance  for  the  entire  metabolism.  The  animal  organism  is, 
within  fairly  wide  limits,  independent  of  the  partial  pressure  of  the  oxygen 
in  the  surrounding  atmosphere.  From  rarefied  air,  the  blood  removes 
the  oxygen  and  combines  it  with  hemoglobin.  We  can  imagine  that  the 
process  takes  place  in  somewhat  the  following  manner:  First  of  all  the 
oxygen  is  absorbed  by  the  blood-plasma  from  the  alveolar  air  in  accord- 
ance with  the  gas  laws;  but  inasmuch  as  this  dissolved  oxygen  constantly 
tends  to  combine  with  the  hemoglobin,  more  and  more  oxygen  is  taken  up 
from  the  air.  In  this  way  a  considerable  store  of  oxygen  is  laid  away  in 
the  organism,  by  means  of  which  it  is  able  to  satisfy,  at  any  time,  any 
unusual  and  unexpected  demands  for  this  important  gas. 

The  question  next  arises  as  to  how  the  amount  of  oxygen  that  is  taken 
up  by  arterial  blood  corresponds  to  the  quantity  absorbed  when  a  sample 
of  blood  is  thoroughly  shaken  with  air.  Experiment  has  shown  that 
normally  the  blood  is  nearly  saturated  with  oxygen,  for  but  little  more  is 
absorbed  when  it  is  shaken  with  air.  The  taking  up  of  oxygen  by  the 
blood  is  dependent  upon  certain  definite  conditions.  This  is  evidently  true 
of  a  small  amount  that  is  mechanically  absorbed  by  the  plasma.  The 
amount  of  oxygen  which  unites  with  the  hemoglobin,  on  the  other  hand, 
is  entirely  independent  of  the  laws  which  govern  the  absorption  of  gases 
in  cases  where  no  chemical  combination  takes  place.  Paul  Bert 2  studied 
the  influence  of  the  temperature.  At  higher  pressures  he  was  not  able  to 
detect  any  definite  influence,  but  with  lower  gas  pressures  there  was  less 
absorption  at  the  temperature  of  the  body  than  at,  say,  the  room  tempera- 
ture. The  fact  that  the  absorption  of  the  oxygen  depends  upon  the  pres- 
sure of  the  gas  is  clearly  shown  by  the  following  table  prepared  by  Krogh.3 
Krogh  examined  the  blood  from  horses  at  38°  C.,  and  determined  the 
amount  of  chemically  combined  oxygen;  i.e.,  from  the  total  amount  of 

1  Christian  Bohr:  Blutgase  und  respiratorischer  Gaswechsel,  Handbuch  der  Physio- 
logie  des  Menschen.     Vol.  I,  pp.  221,  222  (1905). 

2  La  pression  barometrique,  Paris,  687  (1878).    Cf.  also  A.  Lowy:  Zentr.  Physiol.  13, 
449  (1899);  Arch.  Physiol.  Anat.  1904,  231  and  565. 

3  Skand.  Arch.  Physiol.  16,  390  (1894). 


418 


LECTURE  XVIII. 


oxygen  absorbed,  the  small  amount  merely  absorbed  by  the  plasma  was 
deducted.  These  values  may  be  represented  graphically  by  plotting  the 
oxygen  pressures  as  abscissae,  and  the  amount  of  oxygen  absorbed  as 
ordinates.  Two  such  plotted  curves  representing  the  curves  of  oxygen 
tension,  as  Bohr  called  them,  are  shown  below  in  which  the  dotted  line 
represents  the  absorption  by  the  plasma,  the  other  that  quantity  which 
is  chemically  bound. 


Horse  Blood  at  38°  C. 

Pressure  of  Oxygen  in 

In  100  c.c.  Blood. 

Oxygen  Absorbed. 

Millimeters. 

Combined  Oxygen. 

Oxygen  Dissolved 
in  the  Plasma. 

Per  cent  Chemi- 
cally Combined. 

Dissolved  in  100 
c.c.  Plasma. 

10 

6.0 

0.020 

30.0 

0.030 

20 

12.9 

0.041 

64.7 

0.061 

30 

16.3 

0.061 

81.6 

0.091 

40 

18.1 

0.081 

90.4 

0.121 

50 

19.1 

0.101 

95.4 

0.152 

60 

19.5 

0.121 

97.6 

0.182 

70 

19.8 

0.141 

98.8 

0.212 

80 

19.9 

0.162 

99.5 

0.243 

90 

19.95 

0.182 

99.8 

0.273 

150 

20.0 

0.303 

100 

0.455 

In  the  above  table  column  4  shows  the  per  cent  of  chemically  combined 
oxygen,  placing  arbitrarily  that  absorbed  at  150  millimeters  pressure  at 
100  per  cent. 


10   20   30   40   50   60   70   80  90  100  110  120  130  140  ISO 

FIG.  3.     Absorption  of  Oxygen  at  Various  Pressures  by  Horse's  Blood  at  38°. 

These  two  curves  show  very  clearly  the  different  behavior  of  the  chemi- 
cally combined  oxygen,  and  that  which  is  nearly  absorbed.  The  amount 
of  the  latter  increases  regularly  in  proportion  to  the  pressure  as  it  should 


OXYGEN.  419 

in  accordance  with  the  gas  laws.     The  chemically  bound  oxygen,  on  the 
other  hand,  is  only  affected  materially  by  low  pressures. 

We  must  not  fail  to  mention  that  recently  Ch.  Bohr1  has  made  certain 
observations  which  tend  to  shatter  the  belief  that  the  oxygen  combination 
by  hemoglobin  is  a  constant  quantity.2  Bohr  speaks  of  a  specific  oxygen 
capacity  of  the  blood  in  different  animals  and  different  individuals.  The 
proportion  of  hemoglobin,  or  of  the  iron  contained  in  it,  to  the  amount  of 
oxygen  consumed,  varies.  In  order  to  explain  this  fact,  Bohr  makes  the 
assumption  that  the  pigment  in  the  blood  is  not  a  simple  substance,  but 
is  composed  of  different  components,  which  separately  combine  with  vary- 
ing amounts  of  oxygen.  It  is  conceivable  that  each  individual  blood 
corpuscle  originally  incloses  a  uniform  pigment,  the  specific  nature  of 
which  is  gradually  attained  in  various  ways.  This  would  account  for 
the  fact  that  iron  and  oxygen  are  often  found  in  unequal  atomic  propor- 
tions. It  must  be  emphasized,  however,  that  Bohr's  assumption  is  to  be 
regarded  merely  as  an  hypothesis.  It  is  by  no  means  satisfactorily  proved. 
We  have  mentioned  these  investigations  of  Bohr,  partly  because  they  open 
up  again  to  experimental  research  one  of  the  few  fields  which  had  appar- 
ently been  investigated  exhaustively.  Once  more  our  interest  is  aroused 
concerning  all  the  questions  regarding  the  transportation  of  oxygen, 
new  inquiries  are  suggested,  and  a  process  which  has  been  regarded  as 
simple,  is  perhaps  to  be  looked  upon  as  of  quite  complicated  mechanism. 

In  order  to  understand  correctly  the  transportation  of  oxygen  in  the 
blood,  the  process  by  which  it  is  taken  up  in  the  lungs  and  given  up  to 
the  tissues,  we  must  for  the  present  stop  attempting  to  trace  the  course 
of  the  oxygen,  but  concern  ourselves  with  one  of  the  end-products  which 
results  from  the  oxidation  (combustion)  of  the  organic  substances  in  the 
tissues;  namely,  carbon  dioxide.  This  is  necessary,  because,  according  to 
Bohr's  investigations,  it  is  evident  that  definite  relations  exist  between  the 
oxygen  content  of  the  red  corpuscles  and  the  carbon  dioxide  content  of 
the  blood.  The  carbon  dioxide  in  the  blood  comes,  as  we  have  said,  from 
the  tissues.  It  is  formed  everywhere  in  the  cells  as  one  of  the  end-products 
in  the  metabolism  of  oxygen.  There  must,  therefore,  be  developed  in  the 
separate  tissues  a  certain  carbon  dioxide  gas  pressure,  which  is  in  equilibrium 
with  the  pressure  exerted  by  this  gas  in  the  surrounding  cell-complex,  and 
also  with  that  in  the  blood.  When  the  arterial  blood,  freshly  laden  with 
oxygen,  passes  through  these  tissues,  which  are  rich  in  carbon  dioxide, 
then  gas  will  diffuse  into  the  blood,  for  the  pressure  exerted  by  the  carbon 
dioxide  in  the  blood  is  less  than  that  of  the  tissues.  The  amount  of  carbon 
dioxide  in  arterial  blood  has  been  found  to  average  40  per  cent  by  volume, 
but  this  varies  greatly.  In  venous  blood,  i.e.,  that  which  is  flowing  away 

1  Handbuch  der  Physiol.  loc.  ciL  p.  93. 

J  G.  Hiifner:  Arch.  Anat.  Physiol.  1894,  130. 


420 


LECTURE  XVIII. 


from  the  tissues,  there  is  more  of  this  gas.  The  following  table  will  give 
some  idea  of  the  amounts  of  the  separate  gases  in  arterial  and  venous 
blood.1 


• 

Oxygen. 

Carbon  Dioxide. 

Nitrogen. 

Arterial  blood        .    . 

20 

43  6 

1  2 

Venous  blood  

12 

50  0 

1  2 

The  venous  blood  from  different  vascular  regions  shows  an  extremely 
varying  content  of  the  different  gases.  The  carbon  dioxide  content  of  all 
the  venous  blood  taken  as  a  whole,  must  be  represented  by  that  of  the 
right  heart;  for  it  is  here  that  the  venous  blood  coming  from  the  whole 
vascular  system  is  mixed.  Schoffer,2  working  in  Ludwig's  laboratory  in 
1860,  compared  the  composition  of  arterial  blood  with  that  of  the  right 
heart.  The  following  table  gives  the  results  obtained  by  Bohr  and 
Henriques. 


Oxygen. 

Carbon  Dioxide. 

Nitrogen. 

Artery. 

Right  Heart. 

Artery. 

Right  Heart. 

Artery. 

Right 
Heart. 

I. 
II.  .  . 
III.  .  . 

Average 

25.6 
21.3 
20.3 

17.3 
11.9 
14.4 

44.0 
42.6 
45.9 

51.5 

48.5 
50.3 

1.23 
1.19 

1.18 

1.31 
1.06 
1.40 

22.4 

14.5 

44.2 

50.1 

1.20 

1.26 

If  we  compare  the  amount  of  carbon  dioxide  present  in  arterial  blood 
with  that  in  venous  blood,  it  is  at  once  apparent  that  it  cannot  be  a  case  of 
simple  absorption.  The  quantity  present  is  far  too  large.  Like  oxygen 
it  must  be  chemically  combined  for  the  most  part.  The  amount  of  carbon 
dioxide  absorbed  by  the  blood  does  in  fact  depend  upon  the  pressure  of  the 
gas,  with  which  it  is  in  equilibrium;  but  the  absorption  is  not  proportional 
to  this  pressure,  as  it  would  be  in  a  case  of  simple  absorption.  With  what 
substance  in  the  blood  is  this  gas  combined?  The  relations  here  are  far 
more  complicated  than  in  the  case  of  oxygen.  With  the  latter  there  is 
but  one  kind  of  combination,  —  that  with  hemoglobin.  Carbon  dioxide, 
however,  combines  with  different  substances  in  the  blood.  A  part  of 


1  Christian  Bohr:  Handbuch,  loc.  cit.  p.  83. 

2  Sitzungsberichte  d.  Wiener  Akad.  41,  613  (1860).     C.  Ludwig:  Mediz.  Jahrbucher, 
Wien,  1865.     N.  Zuntz  and  Hagemann:  Erganzungsband  III  zu  der  landwirtschaftl. 
Jahrb.  27  (1898). 


OXYGEN. 


421 


this  gas  is  merely  dissolved  both  by  the  plasma  and  by  the  red  corpuscles, 
following  the  laws  of  gas  absorption.  The  average  gas  pressure  of  the 
carbon  dioxide  in  the  organism  may  be  taken  as  30  millimeters.  Cor- 
responding to  this  pressure,  the  amount  of  carbon  dioxide  physically 
dissolved  in  100  cubic  centimeters  of  blood  amounts  to  2.01  cubic  centi- 
meters. Now  the  total  amount  of  carbon  dioxide  absorbed  under  these 
conditions  is  about  40  per  cent  by  volume,  so  that  approximately  only 
5  per  cent  of  the  total  carbon  dioxide  absorbed  is  merely  held  in  solution. 

It  is  of  interest  to  know  how  the  carbon  dioxide  is  distributed  between 
the  blood-corpuscles  and  the  plasma.  According  to  Setschenow,1  about 
two-thirds  of  the  carbon  dioxide  in  dog's  blood  is  held  by  the  plasma,  and 
one-third  by  the  blood  corpuscles.  Kraus  2  found  similar  values  with  the 
blood  of  oxen.  In  blood  from  horses,  however,  Fre*de*ricq  3  found  only 
one-fourth  with  the  corpuscles  and  three-fourths  with  the  plasma. 

A.  Jaquet 4  studied  the  influence  of  the  carbon  dioxide  gas  pressure  upon 
the  absorption  of  the  gas  by  the  plasma  at  37.5°  C.  The  absolute  values 
of  this  absorption  vary  greatly.  They  depend  upon  the  alkalinity  of  the 
plasma.  Although  the  values  given  in  the  following  table  are,  therefore, 
only  relatively  true,  still  they  show  how  the  amount  absorbed  depends 
upon  the  pressure  exerted  by  the  gas. 

CARBON  DIOXIDE  ABSORPTION  BY  THE  SERUM. 


Pressure  of  CO2 
in  mm. 

CO2  chemically  com- 
bined in  100  cc. 

Pressure  of  CO2 
in  mm. 

CO2  chemically  com- 
bined in  100  cc. 

14.8 
16.5 
17.0 

45.8 
57.4 
58.5 

26.6 
42.7 

61.7 
63.7 

It  is  evident  from  the  above  figures  that  with  low  pressures  there  is  a 
marked  increase  in  the  absorption  with  increasing  pressure.  With  pres- 
sures above  20  millimeters,  however,  this  increase  is  not  so  marked. 

Let  us  now  see  what  the  nature  of  the  chemical  combination  is  between 
the  carbon  dioxide  and  the  plasma.  First  to  be  considered  are  the  salts 
of  the  alkalies,  especially  carbonates.  The  amount  of  these  present  in  the 
plasma  is  quite  large,  the  sodium  salts  predominating.  Now  we  know  that 
monocarbonates  are  changed  to  bicarbonates  by  the  absorption  of  carbon 
dioxide,  and  conversely  that  loss  of  the  same  gas  gives  rise  to  the  form- 
ation of  monocarbonates  again.  It  would  thus  be  very  easy  to  account 
for  the  transportation  of  the  carbon  dioxide  by  the  blood.  In  reality, 


1  Memoires  de  1'Acad.  de  St.  Petersburg,  26,  59  (1879). 
3  Festschrift  Graz.  p.  19  (1898). 

3  Compt.  rend.  84,  661  (1877);  85,  48  (1878). 

4  Arch,  exper.  Path.  Pharm.  30,  311  (1892). 


422  LECTURE  XVIII. 

however,  the  relations  are  by  no  means  so  simple.  The  dissociation  of  the 
bicarbonate  in  solutions  of  the  same  concentration  as  the  serum  at  37°  C., 
becomes  noticeable  only  when  the  pressure  of  the  gas  upon  the  solution  is 
less  than  a  few  millimeters.  With  a  pressure  of  0.2  millimeter  about 
three-fifths  of  the  total  dissociable  carbonic  acid  still  remains  chemically 
combined.  According  to  the  observations  of  Jaquet,  cited  above,  the  car- 
bonic acid  of  the  plasma  behaves  quite  differently.  Complete  saturation 
is  not  effected  with  15  millimeters  of  carbon  dioxide  pressure.  The  behavior 
of  the  carbonic  acid  loosely  combined  in  the  plasma,  therefore,  cannot  be 
explained  by  its  relations  to  bicarbonates  and  monocarbonates.  The  fact 
that  by  means  of  the  air-pump  more  than  half  of  this  carbonic  acid  may 
be  expelled  from  the  plasma,  speaks,  more  than  anything  else,  against  any 
such  assumption.  Inasmuch  as  we  know  of  no  other  compounds  in  the 
plasma  which  would  be  capable  of  uniting  with  carbon  dioxide  to  any 
considerable  extent,  we  are  forced  to  believe  that  other  weak  acids  are 
present  in  the  plasma  which  are  constantly  striving  to  unite  with  the 
alkali.  Sertoli 1  long  ago  looked  for  such  acids,  and  considered  as  such 
the  protein  substances  of  the  plasma,  especially  the  globulins.  To-day 
there  is  no  longer  any  doubt  that  these  protein  substances  are  actually 
present  in  the  form  of  alkali  salts  in  serum.  They  are  driven  out  of  these 
compounds  if  there  is  an  excess  of  carbonic  acid  present.  N.  Zuntz  and 
A.  Lowy2  have  shown  this  assumption  to  be  true  in  a  very  convincing 
manner.  They  found  that  the  amount  of  diffusible  alkali  in  the  serum 
increased  by  conducting  carbon  dioxide  into  it.  This  is  to  be  attributed 
to  the  fact  that  as  the  carbonic  acid  is  forced  into  the  serum,  the  alkali 
albuminates  which  are  not  diffusible  are  decomposed,  and  alkali  carbonates 
which  are  capable  of  passing  through  the  membrane  are  formed  in  their 
place. 

The  next  point  to  be  decided  is  whether  the  alkali  contained  in  the 
serum  is  entirely  combined  with  albumin  when  the  partial  pressure  of  the 
carbon  dioxide  gas  is  equal  to  0,  or  whether  an  excess  of  alkali  is  present  ? 
If,  other  than  alkali  albuminates,  there  were  no  other  alkali  salts  of  weak 
acids  present  in  the  serum,  then  it  would  be  expected  that  if  the  alkali 
were  completely  combined  with  the  protein  (i.e.,  when  the  partial  pressure 
of  the  carbonic  acid  gas  was  zero),  all  of  the  carbon  dioxide  would 
have  been  driven  out  of  the  plasma.  This  is  not  the  case,  as  E.  Pfliiger3  has 
shown.  In  one  experiment  he  found  4.9  per  cent  by  volume,  and  in 
another  9 . 3  per  cent  of  carbon  dioxide  which  remained  in  the  plasma,  and 


1  Sertoli:   Hoppe-Seyler,   Medizin-chem.   Untersuch.  Berlin,    1868,  p.   350.     Cf.  N. 
Zuntz:  Hermann's  Handbuch  der  Physiol.  Bd.  4,  64  (1882).     Torup:  Die  Kohlensaure- 
spannung  des  Blutes,  Kopenhagen,  p.  36  (1887).     Kurt  Brandenburg:  Z.  klin.  Med.  45, 
H.  3  and  4. 

2  Pfliiger's  Arch.  58,  511  (1894). 

3  Die  Kohlensaure  des  Blutes,  p.  11,  Bonn.  1864. 


OXYGEN.  423 

could  not  be  removed  by  the  air-pump.  Pfliiger  proved  this  amount  of 
carbonic  acid  to  be  present  by  adding  acid  to  the  plasma.  In  other  words, 
Pfluger  assisted  the  action  of  the  protein,  which  was  insufficient  to  take 
the  place  of  all  the  carbonic  acids  in  the  blood,  by  the  artificial  addition  of 
a  stronger  acid,  which  expelled  the  remainder  of  the  carbonic  acid  that  was 
combined  with  the  alkali. 

From  these  experimental  results,  we  can  describe  the  combination  of 
the  carbonic  acid  in  the  plasma,  somewhat  as  follows:  A  part  of  the 
carbon  dioxide  is  evidently  present,  even  with  low  pressures  of  gas,  as 
bicarbonate.  With  increasing  carbon  dioxide  pressures,  a  part  of  the  gas 
replaces  the  protein  in  its  combinations  with  the  alkali.  In  this  way  we 
are  able  to  understand  much  better  how  the  carbon  dioxide  gas  exchange 
takes  place,  although  it  cannot  yet  be  said  that  the  entire  process  has  been 
satisfactorily  explained. 

The  reason  that  we  do  not  at  present  understand  clearly  the  exact  way 
in  which  the  carbon  dioxide  is  combined  in  the  plasma,  and  have  no  exact 
data  concerning  the  dissociation  of  the  separate  compounds,  is  because 
the  plasma  itself  is  a  complicated  mixture  of  unlike  substances,  which 
mutually  influence  one  another  in  a  number  of  different  ways.  The  study 
of  the  behavior  of  the  bicarbonates  alone,  or,  on  the  other  hand,  of  the 
albuminates,  does  not  lead  to  results  which  can  be  applied  directly  to 
the  plasma,  for  it  is  at  present  impossible  for  us  to  imitate  precisely 
the  conditions  prevailing  in  this  fluid. 

There  is  no  doubt  that  alkali  phosphates  which  are  always  present  in 
the  plasma,  even  although  in  small  amounts,  also  have  an  effect  upon 
the  combination  with  carbonic  acid.  When  exposed  to  the  action  of  car- 
bon dioxide,  Na2HP04  is  attacked  with  the  formation  of  NaH2PO4  and 
NaHCO3. 

According  to  the  results  obtained  by  Setschenow,1  the  removal  of  the 
alkali  from  alkali  albuminates  takes  place  only  with  carbon  dioxide  pressures 
which  are  greater  than  those  ordinarily  prevailing  in  the  living  organism. 
Thus  we  may  have  in  these  compounds  a  regulating  mechanism  which 
prevents  the  carbon  dioxide  pressures  from  exceeding  a  certain  maximum. 
If  the  pressure  of  the  gas  exceeds  this  normal  value,  the  alkali  albuminates 
then  serve  to  unite  with  the  excess  of  the  carbonic  acid,  and  thus  prevent 
any  considerable  pressure  being  exerted  by  the  gas. 

Carbonic  acid  is  likewise  contained  in  the  blood  corpuscles,  partly  free, 
and  partly  in  a  state  of  chemical  combination.  At  38°  C.,  and  30  milli- 
meters gas  pressure,  there  is  present  in  the  blood  corpuscles  corresponding 
to  100  cubic  centimeters  of  blood,  about  0.6  cubic  centimeter  of  the  gas, 
which  is  simply  physically  dissolved.  The  greater  part  of  the  carbon 
dioxide  absorbed  by  the  red  corpuscles  does  not  follow  the  laws  for  gas 


1  Memoires  de  TAcad.  de  St.  Petersburg,  26,  60  (1879). 


424  LECTURE  XVIII. 

absorption.  This  part  is  chemically  combined,  and  in  fact,  chiefly  with 
the  pigment,  hemoglobin.  This  may  effect  the  absorption  of  carbon 
dioxide  in  two  ways.  In  the  first  place,  the  globin  in  it  and  the  remaining 
proteins  of  the  blood,  may  strive  to  combine  with  the  alkali,  as  does  the  car- 
bonic acid.  On  the  other  hand,  the  hemoglobin  itself  may  unite  directly 
with  the  carbon  dioxide.  The  first  way  in  which  the  hemoglobin  influences 
the  absorption  of  the  carbon  dioxide  is  perfectly  analogous  to  what  we 
have  just  been  discussing  with  regard  to  the  plasma.  Here,  also,  the  union 
between  the  hemoglobin  and  the  alkali  will  not  be  dissolved  until  the  pres- 
sure of  the  carbon  dioxide  has  reached  a  certain  value.  Thus  N.  Zuntz  1 
found  the  compound  between  the  hemoglobin  and  alkali  was  not  decom- 
posed appreciably,  until  the  pressure  of  the  carbon  dioxide  was  greater 
than  70  millimeters.  This  benefits  the  organism  only  in  time  of  excep- 
tional need. 

We  shall  now  consider  the  nature  of  the  chemical  union  between  the 
carbonic  acid  and  the  hemoglobin  itself.  We  have  seen  that  hemoglobin 
combines  with  oxygen,  and  that  this  property  is  peculiar  to  that  part  of 
the  molecule  which  contains  the  iron,  while  the  globin  participates  indi- 
rectly in  the  reaction  only  in  as  much  as  the  union  of  the  globin  with  the 
hematin  brings  forth  relations  which  change  the  firm  state  of  combination 
between  oxygen  and  hematin  into  one  which  is  more  readily  dissociable. 
It  is  conceivable  that  the  carbon  dioxide  unites  with  the  same  part  of 
the  hemoglobin  molecule  that  oxygen  does.  We  do  in  fact  know  of  gases 
of  which  this  is  true,  as,  for  example,  carbonic  oxide  (carbon  monoxide) . 
One  volume  of  the  latter  gas  replaces  one  volume  of  oxygen.2  This  car- 
bonic oxide  compound  with  hemoglobin  is  also  dissociable.  The  carbon 
monoxide  may  be  replaced  by  oxygen  again.  This  takes  place  when  the 
partial  pressure  exerted  by  the  oxygen  exceeds  that  of  the  carbonic  oxide.3 
The  fact  that  the  carbonic  oxide  actually  combines  at  the  same  place  as 
the  oxygen  was  shown  to  be  very  probable  by  Hoppe-Seyler,4  who  showed 
that  it  was  combined  in  the  iron-containing  radicle  of  the  molecule. 
Now  it  is  well  known  that  carbonic  oxide  has  a  poisonous  effect;  and  appar- 
ently this  is  due  to  the  fact  that  it  replaces  the  oxygen  in  its  combination 
with  the  hemoglobin,  so  that  it  seriously  affects  the  supply  of  oxygen  for 
the  tissues.  Such  an  action  is  unknown  in  the  case  of  carbon  dioxide.  It 
is  also  a  priori  hardly  probable  that  oxygen  and  carbonic  acid  should  each 
strive  for  possession  of  the  hemoglobin  molecule.  It  has  also  been  shown 

1  Zentr.  med.  Wiss.  6,  529  (1867). 

2  G.  Hiifner:  Arch.  Anat.  Physiol.  1895,  209.     Hiifner  and  Kiilz:  J.  pr.  Chem.  28, 
256  (1883) ;  and  Hiifner:  ibid.  30,  68  (1884). 

3  Recently  Hiifner  and  Kiister  have  undertaken  experiments  to  determine  the  rela- 
tions by  weight  in  which  hemochromogen  combines  with  carbonic  oxide.     Arch.  Anat. 
Physiol.  1904,  387. 

*  Z.  Physiol.  Chem.  13,  477  and  493  (1889). 


OXYGEN. 


425 


that  the  carbon  dioxide  is  taken  up  quite  independently  of  the  union  of 
hemoglobin  with  oxygen. 

This  is  made  very  clear  by  the  experiments  of  Bohr.1  He  showed  that 
the  presence  of  oxygen  had  no  apparent  effect  upon  the  amount  of  carbonic 
acid  absorbed  under  different  pressures.  The  hypothesis  is  also  supported 
by  the  fact  that  the  transformation  of  hemoglobin  into  methemoglobin2 
does  not  in  any  way  affect  its  combination  with  carbon  dioxide,3  while  that 
with  oxygen  is  disturbed.  It  seems  probable  that  the  carbon  dioxide  is 
not  combined  with  the  hematin  part  of  the  molecule,  but  rather  with  the 
globin.  This  appears  the  more  probable  since  M.  Siegfried  4  has  recently 
shown  that  carbonic  acid  is  associated  (i.e.,  chemically  bound)  by  the 
action  of  amino  acids  and  protein  substances.  From  such  compounds  it 
is  very  easy  to  set  the  carbonic  acid  free  again;  i.e.,  dissociate  it.  From 
glycocoll,  for  example,  a  carbaminoacetic  acid  is  formed.  From  the 
amphoteric  amino  acid  a  relatively  strong  dibasic  acid  results.5  The 
carbamino  acids  correspond  to  the  general  type : 

H 

R— N 

|       XCOOH. 
COOH 

The  union  of  carbonic  acid  with  globin  is  also  dependent  upon  the  pres- 
sure of  the  gas,  especially  when  this  is  low.  This  is  shown  by  the  following 
table.  It  gives  the  amount  of  carbonic  acid  chemically  combined  per  gram 
of  hemoglobin  at  different  gas  pressures  of  carbonic  acid.  The  concentra- 
tion of  the  hemoglobin  solutions  amounted  to  2.69  per  cent;  the  temper- 
ature was  38°  C. 


Tension  of  CO2  in 
Millimeters. 

CO2  Absorption  per 
Gram  of  Hemoglobin. 

Tension  of  CO2  in 
Millimeters. 

CO2  Absorption  per 
Gram  of  Hemoglobin. 

10 

1.260 

60 

2.363 

20 

1.647 

100 

2.701 

30 

1.902 

200 

3.113 

40 

2.091 

300 

3.312 

50 

2.240 

3.990 

1  Zentr.  Physiol.  4, 49  and  253  (1890);  and  Skand.  Arch.  Physiol.  3,  47  and  64  (1892). 

2  See  Lecture  XXIV. 

8  Skand.  Arch.  Physiol.  8,  363  (1898). 

4  Z.  Physiol.  Chem.  44,  85  (1905) ;  46,  490  (1905).     See  Lecture  XI,  p.  235. 

6  It  is  evident  that  such  compounds  may  be  formed  in  the  tissues,  and  that  in  this 
way  any  momentary  excess  of  carbonic  acid  can  be  combated.  Thus,  the  cells  can 
assist  the  oxidation  processes.  It  is  also  possible  that  the  carbonic  acid  assimilation 
on  the  part  of  plants,  as  Siegfried  has  suggested,  may  also  take  place  through  the  for- 
mation of  carbaminic  acids,  and  that  the  latter,  and  not  the  carbonic  acid,  are  reduced. 


426 


LECTURE  XVIII. 


The  concentration  of  hemoglobin  in  the  blood  amounts  to  15  per  cent  on 
an  average.  Bohr  1  computed  from  the  above  values  that  with  a  carbon 
dioxide  pressure  of  30  millimeters,  about  8 . 1  cubic  centimeters  would  be 
held  in  combination  in  100  cubic  centimeters  of  blood.  Allowing  for  the 
0 . 6  cubic  centimeter  of  the  gas  which  is  held  in  merely  physical  solution 
by  the  red  corpuscles,  then,  as  the  total  amount  of  carbon  dioxide  absorbed 
by  the  corpuscles  at  that  pressure  amounts  to  about  14  cubic  centimeters, 
there  remains  unaccounted  for  somewhat  over  5  cubic  centimeters  of 
carbon  dioxide.  This  must  be  combined  with  other  substances  in  the 
blood  corpuscle.  These  other  substances  are  evidently  the  alkalies  present 
which  can  form  bicarbonates. 

We  have  now  considered  the  absorption  of  carbon  dioxide  by  the  plasma 
and  by  the  corpuscles,  each  acting  independently,  and  it  remains  to  decide 
whether  such  a  mixture  as  is  present  in  the  blood  has  any  reciprocal  effect 
upon  such  absorption.  N.  Zuntz  2  has  shown  that  if  an  equilibrium  has 
been  established,  at  a  definite  carbon  dioxide  pressure,  in  the  exchange  of 
the  dissociable  substances  between  the  plasma  and  blood  corpuscles,  that 
a  change  in  the  pressure  of  the  carbon  dioxide  will  disturb  this  equilibrium. 
Thus  an  increased  pressure  of  the  gas  makes  the  serum  more  alkaline,  while 
the  chlorine  content  simultaneously  diminishes,  as  the  following  table 
shows.  It  demonstrates  likewise  the  reversibility  of  the  entire  process.3 


INFLUENCE  OF  CARBON  DIOXIDE  UPON  THE  COMPOSITION  OF  THE 
BLOOD  IN  CORPUSCLES  AND  SERUM. 


(6)    Blood  a, 

(c)    Blood  6, 

(a)    Blood  a, 

exposed  to  ac- 

after conducting 

shaken  with  air. 

tion  of  CO2  for 

air  through  it 

30  rain. 

for  two  hours. 

Specific  gravity  of  serum  
Total  solids  in  50  cc.  serum  .... 

1.026 
4.157 

1.030 
4.532 

1.026 
4.122 

N 
Volume  of  —  AgNO3  solution  corre- 

sponding to  the  chlorine  in  100  cc. 

serum                                      .... 

99  4 

90  7 

102  4 

This  increased  alkalinity  of  the  serum  is  explained  by  assuming  a  migra- 
tion of  the  alkali  carbonates  to  take  place  from  the  corpuscles  to  the 
plasma.  There  is,  however,  no  experimental  evidence  in  support  of  this 
assumption.  Giirber  4  has  shown  that  the  potash  is  not  driven  from  the 


1  Handbuch  f.  Physiol.  loc.  cit.  p.  115. 

2  Beitrage  zur  Physiol.  des  Blutes,  Inaug.  Diss.  Bonn,  1868. 

3  H.  J.  Hamburger:  Osmotischer  Druck  und  lonlehre  in  den  mediz.  Wissensch. 
I,  p.  263,  Weisbaden,  1902. 

4  Sitzb.  physikal.  med.  Ges.  Wiirzburg,  1896,  28. 


Vol. 


OXYGEN. 


427 


corpuscles  by  the  increased  pressure  of  the  carbon  dioxide  gas.  This 
author  believes  that  the  carbon  dioxide  expels  the  hydrochloric  acid  from 
sodium  chloride  by  virtue  of  its  mass-action.  Sodium  carbonate  is  formed, 
while  the  hydrochloric  acid,  set  free,  migrates  to  the  blood  corpuscles. 
The  reciprocal  relation  of  the  plasma  and  blood  corpuscles  has  not,  how- 
ever, been  explained  satisfactorily  up  to  date. 

Then,  again,  has  the  carbon  dioxide  tension  of  the  blood  any  influence 
upon  the  absorption  of  oxygen?  We  have  already  seen  that  the  converse 
is  not  true,  because  the  carbonic  acid  and  oxygen  are  combined  at  different 
places  in  the  hemoglobin  molecule.  It  has  been  believed  for  a  long  time 
that  the  pressure  exerted  by  carbon  dioxide  in  the  blood  does  effect  the 
absorption  of  oxygen.  From  the  above  facts,  however,  it  would  seem 
hardly  probable  a  priori.  Bohr,  Hasselbach,  and  Krogh,1  nevertheless,  have 
shown  that  as  a  matter  of  fact  the  absorption  of  oxygen  is  affected  by 
carbon  dioxide  pressures,  which  are  not  above  the  physiological  values. 
With  increasing  carbon  dioxide  pressures  the  absorption  of  oxygen  becomes 
less.  A  few  figures  will  show  how  great  this  effect  is: 


Oxygen  absorbed  at  CO2  pressures  of  — 

Oxygen  pressure 

in  mm. 

5  mm. 

10  mm. 

20  mm. 

40  mm. 

80  mm. 

5 

11 

7.5 

5 

3 

1.5 

10 

28.5 

20.5 

14 

9 

4 

15 

51 

36 

27 

18.5 

8 

20 

67.5 

54 

41 

29.5 

14 

40 

89 

84 

77 

66.5 

49 

60 

95 

93.5 

19.5 

86 

73 

80 

98 

97 

96 

94.5 

87 

100 

99 

98.5 

98 

97 

95 

150 

100 

100 

100 

99.8 

99.5 

Bohr  explains  this  by  assuming  that  the  entrance  of  carbonic  acid  into 
the  globin  molecule  changes  the  affinity  of  the  globin  for  hematin,  and 
thereby  influences  the  absorption  of  oxygen  by  hematin  at  low  oxygen 
pressures.  The  biological  significance  of  these  discoveries  may  be  ex- 
plained perhaps  as  follows :  We  have  already  seen  that,  as  regards  the  gas- 
exchange  with  the  tissues,  it  is  not  the  total  oxygen  contained  in  the  blood 
which  is  effective,  but  chiefly  that  which  is  contained  dissolved  in  the 
plasma;  it  is  this  that  causes  the  oxygen  pressure  of  the  blood.  If  now 
an  increased  amount  of  carbon  dioxide  be  produced,  then  as  the  hemo- 
globin cannot  hold  as  much  oxygen  in  combination  as  before,  there  will  be 
more  oxygen  in  the  dissolved  state,  so  that  the  oxygen  pressure  of  the 


Zentr.  Physiol.  17,  661  (1904),  and  Skand.  Arch.  Physiol.  16,  402  (1904). 


428  LECTURE   XVIII. 

blood  becomes  greater,  and  there  is  a  more  lively  gas-exchange  between 
the  tissues  and  the  blood. 

We  shall  now  attempt  to  trace  the  gas-exchange  of  the  blood  with  the 
alveolar  air  on  the  one  hand,  and  with  the  tissues  on  the  other.  In  the 
lungs,  two  processes  are  continually  taking  place  side  by  side.  Blood 
laden  with  carbon  dioxide  constantly  reaches  these  organs,  there  to  dis- 
charge this  gas  and  take  up  a  fresh  supply  of  oxygen.  The  dark-colored 
venous  blood  is  hereby  changed  into  bright-red  arterial  blood,  and  this 
reenters,  through  the  veins  of  the  lungs,  the  general  circulation.  In  order 
to  understand  the  entire  gas-exchange  in  the  lungs,  we  must  remember 
that  the  blood-vessels  of  the  lungs  (the  region  where  the  pulmonary  arteries 
end,  and  the  veins  begin)  represents  an  infinitely-fine,  capillary  network, 
spun  round  the  alveoli.  In  this  way  an  enormous  amount  of  surface  is 
exposed,  which  enables  us  to  comprehend  how,  in  spite  of  the  relatively 
quick  passage  of  the  blood  through  the  lungs,  a  complete  gas-exchange 
takes  place.  The  size  of  the  respiratory  surface  has  been  variously  esti- 
mated. Aeby  *  found  that  the  lung  surface  in  an  adult  with  quiet  breath- 
ing, amounted  to  80  square  meters.  N.  Zuntz,2  assuming  the  alveolar 
diameter  of  0.2  millimeter,  and  the  air  volume  of  the  lungs  to  be  3000 
cubic  centimeters,  estimated  the  alveolar  surface  to  be  90  square 
meters. 

If  we  compare,  first  of  all,  the  expired  and  inspired  air,  we  shall  find  that 
the  former  is  poor  in  oxygen  and  rich  in  carbon  dioxide,  in  comparison 
with  the  latter.  The  outer  air  does  not  reach  the  alveoli  in  an  unchanged 
condition.  It  is  first  saturated  with  water  vapor,  and  warmed  to  the 
temperature  of  the  body.  It  originally  contains,  on  an  average,  20.96 
per  cent  oxygen,  78  per  cent  nitrogen,  1  per  cent  argon,  and  0.04  per  cent 
carbon  dioxide  by  volume.  We  cannot,  however,  apply  these  values 
directly  to  the  gas-exchange  in  the  alveoli.  For  the  absorption  of  oxygen, 
on  the  one  hand,  and  the  giving  up  of  carbon  dioxide,  on  the  other,  it  is 
the  composition  of  the  alveolar  air  which  alone  comes  into  consideration. 
The  latter  is  poorer  in  oxygen,  and  richer  in  carbon  dioxide,  than  the 
expired  air,  which  contains  16.4  per  cent  oxygen  and  4.1  per  cent  carbon 
dioxide  by  volume.  This  is  because  only  a  part  of  the  inspired  air  reaches 
the  alveoli.  A  part  of  it  remains  unused  in  the  air-passages,  where  it  is 
mixed  there  with  the  alveolar  air  and  expired.  The  carbon  dioxide  and 
oxygen  content  of  the  alveolar  air  at  the  moment  it  leaves  the  alveoli 
may  be  computed,  if  we  know  the  volume  of  a  single  inspiration,  and  the 
size  of  the  air-passages  which  contain  the  unchanged  inspired  air  (nose, 
pharynx,  trachse,  and  bronchi).  Such  computations,  it  is  true,  are  not 
accurate,  partly  because  this  latter  value  is  not  known  closely  enough,  and 

1  Der  Bronchialbaum  der  Saugetiere  und  der  Menschen,  p.  90,  Leipzig,  1880. 

2  In  Hermann's  Handbuch  der  Physiologic,  4,  90  (1887). 


OXYGEN.  429 

because  the  composition  of  the  expired  air  varies  according  to  the  depth 
of  the  inspiration.  In  this  way  average  values  of  14.6  per  cent  oxygen 
and  5.6  carbon  dioxide,  by  volume,  have  been  found  for  the  alveolar  air 
when  it  leaves  the  alveoli.  During  inspiration,  its  composition  tends  to 
approach  that  of  the  inspired  air.  Some  idea  as  to  the  extent  of  the 
changes  in  the  composition  of  the  air  in  the  alveoli,  during  inspiration,  may 
be  obtained  by  comparing  the  amount  of  inspired  air  with  that  remaining 
in  the  lungs  at  the  end  of  respiration.  In  ordinary  breathing  there  remain 
2800  cubic  centimeters  of  air  (1200  cubic  centimeters  residual  and  1600 
cubic  centimeters  of  reserve  air).  As  the  average  inspiration  amounts 
to  only  500  cubic  centimeters,  of  which  about  360  cubic  centimeters 
reach  the  alveoli,  it  is  evident  that  the  changes  in  the  decomposition  of 
the  alveolar  air  as  a  result  of  inspiration  are  not  very  great.  The  necessity 
of  knowing  the  composition  of  the  alveolar  air,  in  each  case,  has  been 
realized  only  as  a  result  of  recent  investigation.  Upon  this  knowledge 
depends  our  judgment  as  to  whether  the  gas-exchange  in  the  alveoli, 
between  the  blood  and  alveolar  air,  follows  simply  the  laws  of  gas  absorp- 
tion, or  whether  other  forces  must  come  into  play.  It  is,  to-day,  still 
believed  by  many  that  the  first  explanation  of  the  gas-exchange  in  the 
lungs  is  entirely  satisfactory.  Blood  reaches  the  lungs,  through  the  pulmon- 
ary arteries,  having  a  greater  carbon  dioxide  tension  than  does  the  alveolar 
air.  An  equilibrium  must  be  established  between  these  two  gas-pressures, 
and  as  a  result  carbon  dioxide  diffuses  from  the  blood  into  the  alveoli. 
Similarly,  on  account  of  its  greater  tension  in  the  alveolar  air,  oxygen  passes, 
into  the  blood.  The  hemoglobin  in  this  way  becomes  saturated  with 
oxygen,  and  is  ready  once  more  to  enter  the  general  circulation.  This 
assumption  is  supported  by  the  work  of  Wolffberg1  and  of  Nussbaum.2 
If,  namely,  the  gas-exchange  in  the  alveoli  of  the  lungs  follows  exactly 
the  laws  of  gas  diffusion,  then,  in  a  lobule,  which  is  cut  off  by  the 
closing  of  the  bronchial  tube  leading  to  it,  the  alveolar  air  must  be: 
in  equilibrium  with  the  carbon  dioxide  tension  of  the  blood.  Similarly 
the  arterial  blood,  flowing  from  this  lobule,  must  have  the  same  carbon 
dioxide  tension  as  that  of  the  alveolar  air.  Wolffberg  and  Nussbaum 
found,  as  a  matter  of  fact,  that  the  carbon  dioxide  tension  in  the  alveoli 
was  the  same  as  that  of  the  venous  blood  which  flows  to  them.  They 
introduced  a  double-walled  elastic  catheter  into  a  branch  of  the  bronchus; 
of  a  tracheotomized  dog,  in  which  this  portion  of  the  lungs  was  shut  off, 
by  inflating  a  rubber  enlargement  of  the  catheter.  After  a  short  time 
a  sample  of  the  alveolar  air  was  withdrawn  through  a  tube  in  the  catheter 
and  its  chemical  composition  determined.  They  found  on  an  average  that 
this  isolated  alveolar  air  showed  a  carbon  dioxide  tension  of  3.84  per  cent 

1  Pfliiger's  Arch.  4,  465  (1871);  6,  23  (1872) 

2  Ibid.  7.  296  (1873). 


430 


LECTURE  XVIII. 


of  an  atmosphere.     The  corresponding  value  for  the  blood  of  the  right 
heart  was  3.81  per  cent. 

According  to  the  results  of  this  experiment,  it  would  seem  that  we  were 
unquestionably  justified  in  assuming  that  the  gas-exchange  in  the  alveoli 
of  the  lungs  takes  place  in  accordance  with  the  well-known  laws  of  gas- 
diffusion.  Quite  recently,  however,  and  especially  by  the  extended  experi- 
ments of  Bohr,1  facts  have  become  known  which  cannot  be  explained  on 
this  basis.  Bohr  desired,  in  each  experiment,  to  know  the  composition  of 
the  alveolar  air.  A  good  idea  of  this  can  be  obtained  by  analyzing  the 
out-going  air,  obtained  at  the  moment  it  passes  the  bifurcation  of  the 
trachea.  Such  air  contains  more  oxygen  and  less  carbon  dioxide  than 
does  alveolar  air,  but,  on  the  other  hand,  it  contains  less  oxygen  and  more 
carbon  dioxide  than  the  expired  air;  it  represents  a  mean  between  the  two. 
It  is  essential  in  such  experiments  that  the  gas  tension  of  the  arterial 
blood  should  be  ascertained  at  the  same  time  and  with  the  same  individual. 
Bohr  experimented  with  large  dogs  which  he  compelled  to  breathe  through 
easily  movable  valves.  A  gas-meter  measured  the  amount  of  the  expired 
air,  from  which  a  sample  was  taken  for  analysis.  Bohr  noted  the  depth 
of  each  inspiration  and  determined,  after  the  death  of  the  animal,  the 
volume  of  the  trachea  and  the  bronchial  tubes.  From  these  values  he 
computed  the  composition  of  the  air  at  the  bifurcation.  The  partial  pressure 
of  the  oxygen  and  carbon  dioxide  in  this  gas  was  thereby  known.  Simul- 
taneously, the  gas-pressure  from  the  blood  of  an  artery  was  measured,  in 
order  to  establish  normal  relations  as  far  as  possible.  Bohr  prevented 
coagulation  of  the  blood  by  injecting  peptone  solution,  or  leech  extract, 
and  carried  the  blood  back  through  a  vein  into  the  general  circulation, 
so  that  the  result  of  the  experiment  was  not  influenced  by  loss  of 
blood. 


Carbon  Dioxide  Tension. 

, 

Difference  between 
a  and  b. 

Nature  of  Air  breathed. 

(a)   Air  at  the 

Bifurcation. 

(6)  Arterial  Blood. 

16.6 

10.1 

-    6.5 

Atmospheric  Air. 

14.3 

16.7 

+    2.4 

<•                ii 

34.6 

17.4 

-  17.2 

..                it 

14.8 

27.6 

+  12.8 

ii                ii 

40.0 

29.7 

-  10.9 

4.9%C02,  18.8%02 

28.5 

0.9 

-  27.6 

3.2%CO2,  20.0%  O2 

The  results  of  these  experiments  showed,  on  the  one  hand,  that  the 
oxygen  tension  of  the  arterial  blood  flowing  out  of  the  lungs  is  frequently 
more  than  that  of  the  air  at  the  bifurcation  and,  on  the  other  hand,  in 

1  Skand.  Arch.  Physiol.  2,  236  (1891). 


OXYGEN. 


431 


several  cases  the  tension  of  the  carbon  dioxide  in  the  blood  was  Jess  than 
that  of  the  air  at  the  bifurcation.  The  following  table  gives  an  idea  of 
the  results  obtained  :  * 


Oxygen  Tension. 

Weight  of 

O2  absorbed  per  Kil- 

Difference 

Animal. 

ogram  in  1  minute. 

(a)  Air  at  the 

(6)    Arterial 

between 
a  and  b. 

Bifurcation. 

Blood. 

Kilograms. 

14.1 

9.8 

127 

144 

+  17 

15.5 

10.6 

131 

105 

-  26 

18.9 

14.1 

95 

101 

+    6 

41.5 

14.7 

110 

122 

+  12 

26.0 

13.6 

116 

106 

-  10 

14.7 

7.1 

130 

144 

+  14 

These  results  indicate  that  neither  the  passage  of  oxygen  from  the  alveo- 
lar air  to  the  blood,  nor  of  the  carbon  dioxide  from  the  blood  to  the  alveolar 
air,  can  be  accounted  for  by  diffusion  alone.  Some  forces  must  be  at 
work  which  tend  to  make  the  oxygen  more  active  towards  its  absorption 
by  the  blood  than  can  be  accounted  for  by  the  partial  pressures  of  the 
oxygen  gas,  and  at  the  same  time  these  forces  enable  the  blood  to  give  up 
its  carbon  dioxide  even  when  the  pressure  of  this  gas  is  greater  in  the 
alveoli  than  it  is  in  the  blood  itself.  Bohr  compares  the  lung  with  a  gland, 
and  conceives  of  its  activity  as  that  of  a  secretion.  He  assumes  that 
the  lung-cells  have  the  power  of  temporarily  uniting  with  oxygen  and  with 
carbonic  acid.  In  fact,  P.  Ehrlich  2  has  proved  that  the  lungs  possess  an 
extraordinarily  strong  reducing  power.  He  injected  alizarin-blue  into 
animals,  this  being  a  dyestuff  which  becomes  colorless  on  reduction.  The 
lungs  of  an  animal  freshly-killed  were  then  found  to  be  colorless,  the  blue 
color  being  apparent  only  after  exposure  to  the  air  for  some  time.  Now 
the  lung  tissue,  like  all  other  tissue,  has  its  own  metabolism.  It  con- 
sumes oxygen  and  evolves  carbon  dioxide.  Its  reduction  power,  according 
to  Ehrlich's  results,  however,  is  so  pronounced  that  it  seems  perfectly 
plausible  to  speak  of  an  oxygen-secretion  in  the  sense  meant  by  Bohr. 

Bohr  and  Henriques  3  also  made  the  discovery,  which  is  of  itself  very 
remarkable,  that  the  lungs  take  an  uncommonly  large  part  in  the  general 


1  Cf.  Bohr:  Handbuch  der  Physiol.  p.  146.     Bohr  measured  directly  the  oxygen  ten- 
sion at  the  lung  surface  and  compared  this  with  the  oxygen  tension  of  the  arterial  blood. 
There  was  in  this  case  a  more  considerable  excess  of  pressure  in  favor  of  the  blood. 
Cf.  L.  Fre-de-rfcq:  Zentr.  Physiol.  7,  33  (1893);  8,  34  (1897).      Haldane  and  J.  Lorrain 
Smith:  J.  Physiol.  20,  497  (1896);  and  22,  231  (1899). 

2  Sauerstoffbediirfnis  des  Organismus,  Berlin,  1885. 

8  Oversigt.  kgl.  Danske  Videnskabs-Selskabs  forhandl.     No.  1,  1897,  Arch,  physiol. 
9,  590  and  710  (1897). 


432  LECTURE  XVIII. 

metabolism.  They  estimate  that  about  one-third  of  the  total  metabolism 
takes  place  in  this  organ.  We  can  understand  this  active  metabolism,  by 
assuming  that  it  is  capable  of  performing  a  particularly  intense  kind  of 
work,  and  it  is  indeed  possible  that  it  is  here  that  the  work  of  secretion 
comes  into  play. 

It  must  be  admitted  that  the  views  of  Bohr  have  been  vigorously  chal- 
lenged. His  results  have  been  attributed  to  an  insufficient  equilibrium 
being  established  between  the  blood  and  the  alveolar  air.  Bohr  himself 
would  not  admit  this;  and  now  that  fifteen  years  have  passed  since  his  first 
important  results  were  published,  without  the  appearance  of  any  data 
which  conclusively  disputes  it,  we  are  compelled  to  place  his  opinions  in 
the  foreground  in  our  discussion  of  the  gas-exchange  which  takes  place  in 
the  lungs;  although  the  older  assumption  that  the  laws  of  gas  diffusion  are 
sufficient  to  explain  this  phenomenon  is,  on  account  of  its  greater  sim- 
plicity, very  attractive.  It  is,  of  course,  not  impossible,  but  on  the  other 
hand  extremely  probable,  that  diffusion  does  in  part  account  for  some  of 
this  exchange  of  carbon  dioxide  between  the  blood  and  the  alveolar  air. 
Other  factors  are  probably  active  at  the  same  time,  so  that  there  is  a  very 
active  penetration  of  oxygen  into  the  blood  and  removal  of  carbonic  acid 
from  the  latter. 

Bohr  calls  attention  to  the  following  observations  in  support  of  his 
assumption.  In  the  Amphibia  it  is  well  known  that,  besides  the  lungs, 
the  skin  serves  as  an  important  organ  of  respiration.  In  the  case  of  frogs, 
simultaneous  determinations  of  the  gas-exchange  of  skin  and  lungs  showed 
that  the  taking  up  of  oxygen  by  the  skin  is  independent  of  the  total  extent 
of  the  metabolism.  It  is  almost  constant,  and  amounts  to  43  to  60  cubic 
centimeters  per  kilogram  of  body  weight  in  an  hour.  The  carbon  dioxide 
elimination  on  the  other  hand  showed  variations  of  from  92  to  179  cubic 
centimeters  per  kilogram  in  an  hour.  The  gas-exchange  taking  place  in 
the  lungs  is  different.  Much  more  oxygen  is  absorbed  through  the  lungs 
than  by  the  skin,  and  the  variations  are  much  greater  (51  to  390  cubic 
centimeters  per  kilogram  in  an  hour) .  The  elimination  of  carbon  dioxide 
may,  in  winter  when  there  is  a  considerable  absorption  of  oxygen,  sink 
nearly  to  zero.  Krogh,1  who  first  mentioned  these  facts,  found  further 
that  a  carbon  dioxide  tension  of  but  a  few  per  cent,  in  the  atmosphere 
surrounding  the  skin,  caused  a  considerable  increase  in  the  amount  of 
©xygen  taken  up  by  the  lungs  alone,  while  at  the  same  time  the  amount 
taken  up  by  the  skin  might  be  diminished.  This  action  of  the  lungs  does 
not  take  place,  however,  if  the  cutaneous  branch  of  the  vagus  nerve  is  cut. 
The  respiration  by  the  skin  is,  on  the  other  hand,  apparently  indifferent 
to  the  nervous  system.  Evidently  the  gas-exchange  by  the  skin  takes  place 
by  diffusion,  while  pulmonary  respiration  is  more  in  the  nature  of  a  secretion. 


Skand.  Arch.  Physiol.  16,  378  (1904). 


OXYGEN.  433 

A  very  considerable  secretion  of  gases  takes  place  in  the  swimming- 
bladder  of  fishes.  Biot,1  who  examined  the  gases  in  fishes  which  live  at 
great  depths,  found  sometimes  as  much  as  80  per  cent  of  oxygen.  Whereas 
the  oxygen  tension  of  water  at  a  depth  of,  say,  1500  meters,  amounts  to 
only  about  one-fifth  of  an  atmosphere,  the  partial  pressure  of  this  gas  in 
the  swimming-bladder  is  equivalent  to  that  of  90  atmospheres.  Moreau  2 
has  shown,  moreover,  that  the  oxygen  content  of  these  gases  in  the  swim- 
ming-bladders of  fish  depends  upon  the  depth  at  which  the  fish  lives. 
Those  living  near  the  top  of  the  water  often  contain  a  lower  oxygen  pressure 
than  that  of  the  atmosphere.  If  the  same  fish  be  placed  at  a  greater  depth, 
it  is  no  longer  in  equilibrium  with  its  surroundings.  Equilibrium  is 
restored,  however,  by  more  oxygen  being  secreted  in  the  swimming-bladder. 
If  the  bladder  is  emptied  by  means  of  a  trocar,  it  refills  with  oxygen  after 
a  time.  This  secretion,  furthermore,  is  under  the  influence  of  the  nervous 
system.  On  severing  the  pneumogastric  (vagus)  nerve,  the  gas  secretion 
entirely  ceases.  Then,  on  artificially  emptying  the  swimming-bladder, 
it  does  not  refill  with  oxygen.  The  epithelium  of  the  bladder  itself  is 
impermeable  to  oxygen.  The  oxygen  passes  out  through  the  so-called 
oval. 

These  observations  are  sufficient  to  prove  beyond  question  that  the 
animal  organism  possesses  cells  whose  function  it  is  to  secrete  gases.  It  is 
true  that  these  results  cannot  be  applied  immediately  to  higher  organisms, 
but  it  gives  undoubted  support  to  Bohr's  opinions.3  By  means  of  this 
active  taking  up  of  oxygen,  the  animal  organism  obtains  a  certain  supply 
of  this  important  gas,  so  that  air  containing  but  little  oxygen  suffices  for 
its  support  within  certain  limits.  Thus,  for  example,  muscular  effort 
requires  an  increased  oxygen  supply  by  an  increase  in  the  blood  circula- 
tion. In  a  unit  of  time  more  blood  passes  through  the  lungs.  If,  by  an 
artificial  restriction  of  one  of  the  pulmonary  branches,  more  blood  is  made 
to  pass  through  one  lung  than  through  the  other,  there  is  more  oxygen 
taken  up  in  the  lung  with  the  more  blood,  although  the  effect  upon  the 
elimination  of  carbon  dioxide  is  not  so  marked.4 

An  interesting  question,  but  one  not  so  easy  to  answer,  is  whether  the 
lungs  of  mammals  are  dependent  upon  certain  nervous  influences.  This 
is  known  to  be  true  in  the  case  of  the  tortoise.  With  the  Testudo  grceca, 
the  trachea  divides  so  high  up  in  the  neck  that,  without  fear  of  injuring 
the  important  nerves,  cannulas  may  be  placed  in  the  bronchi,  and  thus 
either  lung  be  observed  independently.  If  the  vagus  branches  to  one  lung 
are  cut,  the  absorption  of  oxygen  by  that  lung  is  lessened,  while  that  of 


1  Me"moires  de  la  societe  d'Arcueil,  1807. 

2  Memoires  de  Physiologie.     Paris,  1877. 
8  C.  Bohr:  J.  Physiol.  15,  494  (1894). 

4  V.  Maar:  Skand.  Arch.  Physiol.  15,  1  (1903);  16,  358  (1904). 


434 


LECTURE  XVIII. 


the  other  lung  is  increased.1     The  carbon  dioxide  elimination  is  similarly 
affected. 


Oxygen  Absorption  in  — 

Right  Lung. 

Left  Lung. 

Total. 

Effect  of  severing  the  right  vagus  

j  15.4 
I  30.0 
j  29.1 
1  21.4 

17.1 
5.3 
5.2 
14.9 

32.5 
35.3 
34.3 
36.1 

Effect  of  severing  the  left  vagus 

Stimulation  of  the  vagus  leads  to  the  opposite  effect.  It  is  not  so  easy 
to  decide  how  much  these  results  are  due  to  an  influence  upon  the  lungs, 
and  how  much  is  due  to  the  influence  of  the  vasomotor  fibres.  Apparently 
the  latter  is  not  sufficient  to  account  for  the  whole  phenomenon.  The 
influence  of  the  vagus  nerve  has  also  been  observed  with  mammals.  Stim- 
ulation of  this  nerve  tends  to  make  the  respiratory  quotient  approach  the 
value  1. 

Now  if  we  consider  once  more  the  gas-exchange  in  the  lungs,  we  see  that 
two  processes  are  taking  place  side  by  side.  Oxygen  diffuses  from  the 
alveolar  air,  which  is  relatively  rich  in  this  gas,  and  saturates  the  venous 
blood  with  this  element  that  is  so  important  for  the  whole  metabolism. 
Simultaneously,  the  blood  laden  with  carbon  dioxide  gives  up  the  latter 
to  the  alveolar  air,  which  contains  relatively  less  of  it,  and  this  takes  place 
until  the  partial  pressure  of  the  carbon  dioxide  in  the  alveoli  is  equal  to 
that  of  the  blood,  i.e.,  until  equilibrium  has  been  established.  Now  begins, 
without  doubt,  the  activity  of  the  epithelium  of  the  lungs  by  means  of 
which  oxygen  from  the  alveolar  air  is  secreted  in  the  blood-vessels,  and  has 
the  effect  of  overbalancing  the  equilibrium  between  the  oxygen  tension  of 
the  blood  and  that  of  the  alveolar  air,  in  favor  of  the  former.  The  carbon 
dioxide  is  eliminated  with  equal  avidity,  and  given  up  to  the  alveolar  air. 

Oxygen  now  circulates  anew  with  the  blood  to  the  tissues  whose  oxygen 
content  is  relatively  less  than  that  of  the  blood,  so  that  oxygen  is  con- 
stantly diffusing  from  the  blood,  and  first  of  all  the  oxygen  is  lost,  which 
is  merely  dissolved  in  the  blood.  When  this  dissolved  oxygen  is  lost,  the 
reserve  supply,  i.e.,  that  combined  with  the  oxyhemoglobin,  comes  into 
play.  The  oxyhemoglobin  now  dissociates  and  oxygen  is  given  up  to  the 
plasma,  in  order  to  keep  the  oxygen  tension  of  the  blood  up  to  a  cer- 
tain value.  Now  the  question  arises  whether  this  internal  respiration 
takes  place  in  accordance  with  the  gas  diffusion  laws,  or  whether  we  must 
assume  that  here  also  a  secretion,  i.e.,  an  active  giving  up  of  oxygen, 

1  V.  Maar:  Skand.  Arch.  Physiol.  13,  269  (1902). 


OXYGEN.  435 

comes  into  play.  At  this  point  we  meet  with  great  difficulties  in  our 
search  for  knowledge.  To  answer  this  question  we  must  know,  in  the  first 
place,  exactly  how  great  the  gas  tension  in  the  tissues  is.  We  know,  from 
the  experiments  of  Strassburg,1  what  the  oxygen  tension  of  the  lymph  is, 
and  as  this  surrounds  all  tissues  and  cells  of  the  body,  we  get  some  idea  as 
to  the  gas-pressure  prevailing  there.  Strassburg  found  the  oxygen  ten- 
sion of  the  lymph  greater  than  one  atmosphere.  According  to  the  general 
conception,  the  oxygen  tension  in  blood  is  less  than  one  atmosphere. 
If  this  be  true,  it  is  necessary  to  assume  some  special  activity  as  the 
cause  of  the  giving  up  of  oxygen  to  the  tissues.  On  the  other  hand,  Strass- 
burg found  that  the  tension  of  carbon  dioxide  in  the  lymph  was  less  than 
that  of  venous  blood.  From  this  fact  we  should  speak  of  gas  secretions 
in  the  tissues.  Some  idea  of  the  consumption  of  oxygen  by  the  tissues 
is  obtained  by  tracing  the  oxygen  tension  of  the  blood  in  its  transformation 
from  the  arterial  to  the  venous  condition.2 

The  oxygen  supply  of  the  tissues  may  be  regulated  in  quite  a  number  of 
different  ways.  The  rate  of  the  blood  flow  has  an  effect  and  again  the 
change  of  the  content  of  the  blood  in  hemoglobin,  whether  it  be  due  to  the 
formation  of  new  hemoglobin,  or  a  relative  increase  by  elimination  of 
plasma.  By  means  of  such  changes  combined  with  variations  in  the 
intensity  of  work  of  the  organs  of  respiration,  -the  animal  organism  is, 
within  certain  limits,  independent  of  quite  considerable  variations  in 
oxygen  and  carbon  dioxide  tensions.  It  is  highly  interesting  that  each 
lung  has  its  own  independent  gas-exchange,  and  yet  is  able  to  mutually 
compensate  the  other.  If  there  is  a  greater  oxygen  tension  in  the  air 
supply  of  one  lung,  then  a  greater  absorption  of  oxygen  takes  place  in 
this  lung  than  in  the  other.  At  the  same  time,  the  other  lung  absorbs 
less. than  the  customary  amount  of  oxygen,  so  that  the  total  absorption 
of  oxygen  by  the  two  lungs  remains  about  the  same. 

If  the  partial  pressure  of  the  oxygen  in  the  inspired  air  becomes  lower,3 
then  naturally  that  of  the  alveolar  air  becomes  similarly  affected.  The 
degree  of  change  in  the  composition  of  the  latter  depends  materially  upon 
the  amount  of  oxygen  absorption  and  the  ventilation  of  the  lungs.  This 
is  an  extremely  important  fact.  It  is  for  this  reason  that  with  the  same 
oxygen  partial  pressure,  the  alveolar  air  of  two  different  individuals  may 
have  a  quite  different  composition,  according  as  to  whether  one  breathes 
more  deeply  than  the  other,  so  that  the  lungs  have  a  greater  ventilation. 

1  Pfliiger's  Arch.  6,. 65  (1872). 

2  Cf.  Ch.  Bohr:  Handbuch  d.  Physiol.  p.  196.     Loewy  and  von  Schrotter,  Z.  exper. 
Path.  u.  Ther.  1,  197  (1905). 

3  Cf.  Paul  Bert:  La  pression  barome'trique.     Paris,  1878.     Frankel  and    Geppert: 
Ueber  die  Wirkungen  der  verdiinnten  Luft  auf  den  Organismus,  Berlin  (1883).      A. 
Loewy:  Untersuchen  iiber  die  Respiration  und  Zirkulation  bei  Aenderung  des  Druckes 
und  des  Sauerstoffgehaltes  der  Luft,  Berlin,  1895. 


436  LECTURE  XVIII. 

The  lower  limit  for  oxygen  tension  in  the  alveolar  air  lies  a  little  above 
30  millimeters.  This  corresponds  to  an  oxygen  content  of  about  4.5  per 
cent,  assuming  a  total  pressure  of  710  millimetres  (=  1  atmosphere  at  the 
body  temperature) .  Moreover,  this  is  true  only  for  a  period  of  rest,  and 
not  for  one  of  active  work.  In  the  latter  case  an  oxygen  pressure  of 
30  millimeters  is  not  sufficient. 

Paul  Bert,  Frankel,  and  Geppert  have  shown  that  the  amount  of  oxygen 
absorbed  by  the  blood  becomes  equal  to  one-half  the  normal  amount, 
only  when  the  total  pressure  of  the  surrounding  atmospheric  air  is  less  than 
300  millimeters.  This  is  interesting,  because  it  gives  us  some  conception 
as  to  the  nature  of  the  behavior  of  the  gas-exchange  during  passage  into  a 
more  rarefied  atmosphere,  i.e.,  in  balloon  ascensions,  or  in  mountain  climb- 
ing. In  these  two  examples  naturally  the  requirements  upon  the  blood- 
gases  are  quite  different.  In  the  former  case,  there  is  practically  no  work 
to  be  performed,  so  that  aeronauts  reach  a  much  higher  altitude  than  do 
mountain  climbers,  before  they  experience  difficulty  in  breathing.  The 
fact  that  different  individuals  are  affected  differently  at  one  and  the  same 
height  is  explained,  first,  by  the  fact  that  the  lung  ventilation  and  amount 
of  air  breathed  is,  as  already  mentioned,  quite  different,  so  that,  in  one 
case,  the  blood  has  more  oxygen  at  its  disposal  than  in  another.  It  has 
been  found,  moreover,  that  the  animal  organism  possesses  an  extremely 
delicate  mechanism  of  regulation,  which  energetically  opposes  any  defi- 
ciency of  oxygen  in  the  system.  To  this  belongs  the  increase  in  the  number 
of  red  corpuscles,  and  thereby  of  hemoglobin,  which  unquestionably  takes 
place  when  men  and  animals  pass  from  a  locality  into  one  of  higher  altitude. 
The  increase  disappears  as  soon  as  the  original  level  is  again  reached.1 
The  object  of  this  is  plain.  No  matter  whether  we  assume  that  the  abso- 
lute amount  of  these  red  corpuscles  is  increased,  or  that  the  increase  is 
merely  relative,  brought  about  perhaps  by  the  passing  out  of  plasma, 
there  is  in  a  unit  of  blood  more  hemoglobin  passing  through  the  lungs  in 
a  unit  of  time  than  is  normally  the  case.  The  way  this  increase  in  the  red 
corpuscles  caused  by  ascending  high  mountains  is  effected,  has  not  been 
satisfactorily  explained.  It  is  remarkable  that  the  change  takes  place 
suddenly,  and  in  fact  without  any  indication  of  there  being  any  new  forma- 
tion of  blood  (red  corpuscles  with  nuclei,  etc.),  and  that  on  reaching  a  low 
level  again,  the  reverse  change  takes  place  without  any  of  the  usual  indi- 


1  Cf.  Paul  Bert:  loc.  cit.  Die  histiochemischen  und  physiologischen  Arbeiten  von 
Fr.  Miescher,  Vol.  II,  p.  328,  Leipzig,  1897.  Abderhalden:  Z.  Biol.  43,  125  and  443 
(1902) ;  Medizin,  Klinik,  No.  G  (1905);  Pfluger's  Arch.  110,  195  (1905).  von  Schrotter 
and  Zuntz:  ibid.  92,  479  (1902).  van  Voornveld:  ibid.  92,  1  (1902).  Otto  Cohnheim: 
Ergeb.  Physiol.  (Asher  and  Spiro)  II,  612  (1902).  Durig  and  Zuntz:  Arch.  Anat. 
Physiol.  Suppl.  1904,  p.  417.  Jaquet:  Ueber  die  physiologische  Wirkung  des  Hohenkli- 
mas,  Basel,  1904.  Zuntz,  Loewy,  Miiller,  and  Caspari :  Hohenklima  und  Bergwanderungen 
in  ihrer  Wirkung  auf  den  Menschen,  Bong  et  Cie,  1906. 


OXYGEN. 


437 


cations  of  a  diminution  in  the  number  of  red  corpuscles.  There  is  abso- 
lutely no  doubt  that  after  staying  at  a  mountain  height  for  some  time,  an 
acclimatization  takes  place  in  the  sense  that  a  new  formation  of  hemo- 
globin results.  It  remains  undecided  how  much  this  is  due  to  an  abso- 
lute increase  in  the  number  of  red  corpuscles,  and  how  much  to  a  merely 
relative  increase.  It  seems  reasonable  to  believe  that  this  may  be  brought 
about  by  the  adjustment  of  the  vascular  tonicity  to  definite  pressures 
of  the  atmosphere.1 

It  remains  for  us  to  decide  whether,  besides  the  lungs,  other  organs  of 
the  body  take  part  in  the  gas-exchange.  We  have  already  seen  that  with 
Amphibia  respiration  on  the  part  of  the  skin  plays  quite  an  important  part. 
In  higher  vertebrates  this  cutaneous  respiration  does  not  seem  to  be 
hardly  worth  considering.  Schierbeck  2  estimated  that  in  man  there  is 
an  elimination  of  carbon  dioxide  amounting  to  9  grams  per  24  hours, 
or  somewhat  less  than  1  per  cent  of  the  total  gas-exchange.  If  there 
is  an  increased  secretion  of  sweat,  it  may  rise  as  high  as  30  grams  in 
24  hours.  The  absorption  of  oxygen  is  much  less.  The  following  table 
prepared  by  Krogh  3  gives  a  good  idea  as  to  the  extent  of  this  cutaneous 
respiration  on  the  part  of  man  and  certain  animals: 


0 

2 

C< 

32 

Maximum. 

Average. 

Maximum. 

Average. 

Man  

0  50 

1    IS 

Man  
Pigeon 

0  92 

0  47 

3.1 
1   l 

0.94 
0  60 

Tortoise 

0  1 

0  15 

Rana  fusca     

1  8 

1  51 

5  3 

3  0 

Rana  esculenta      
Eel 

2.1 
1  05 

1.62 
0  74 

4.4 

3.1 

The  above  values  refer  to  the  amount  per  hour  and  per  square  decimeter 
of  the  skin.  The  volumes  of  the  gas  are  given  in  cubic  centimeters. 

It  was  for  a  long  time  believed  that  the  skin  took  part  in  the  elimination 
of  the  gaseous  products  of  metabolism.  It  had  been  observed,  for  example, 
that  if  the  skin  of  an  animal  were  varnished  over  it  soon  died.  This, 
however,  has  more  recently  been  found  to  be  caused  not  so  much  by  the 
retention  of  waste  gases,  as  by  the  greatly  increased  amount  of  heat, 
caused  by  the  crippling  of  the  means  for  regulating  the  body  tempera- 


1  Mountain  sickness  has  been  attributed  to  various  causes,  one  of  which  is  undoubt- 
edly a  faulty  regulation  of  the  vascular  tone. 

2  Arch.  Anat.  Physiol.  1893,  116.     Cf.  Aubert:  Pfliiger's  Arch.  6,  539  (1872). 

3  Skand.  Arch.  Physiol.  16,  378  (1904). 


438  LECTURE  XVIII. 

ture.  If  this  increase  in  temperature  be  prevented,  the  animal  will  not 
die.1 

We  recognize  certain  kinds  of  fish,  especially  the  loach,  Cobitis  fossilis, 
in  which  there  is  a  peculiar  intestinal  respiration.  The  middle  intestine 
of  the  Cobitis  contains  an  abundant  supply  of  capillary  blood-vessels  and  a 
peculiarly  transformed  epithelium.  These  fish  swallow  air,  and  discharge 
gases  through  the  rectum.  The  gas  which  leaves  the  body  contains  less 
oxygen  and  more  carbon  dioxide  than  that  entering.2 

With  the  remaining  members  of  the  animal  kingdom,  the  intestine  plays 
no  part  in  the  gas-exchange.  To  be  sure,  the  alimentary  canal  contains 
gas,  resulting,  in  part,  from  swallowed  air,  which  with  the  food,  the  saliva, 
and  drink,  is  constantly  being  introduced,  and  largely  from  bacterial 
decomposition,  fermentation,  etc.  Furthermore,  carbonic  acid  is  set  free 
in  the  neutralization  of  the  carbonates  of  sodium  in  the  intestinal  secretions 
by  the  hydrochloric  acid  from  the  stomach.  The  oxygen  of  the  swallowed 
air  is  taken  up  little  by  little  by  the  intestinal  walls;  and  similarly,  on 
account  of  its  partial  pressure,  the  carbon  dioxide  diffuses  to  some  extent 
into  the  intestinal  walls  and  into  the  blood-vessels,  and  in  other  cases 
these  gases  are  given  up  from  the  vascular  system,  if  the  amount  present 
in  the  intestine  is  slight.  Likewise  other  gases,  such  as  hydrogen,  methane, 
sulphureted  hydrogen,  and  nitrogen,  are  absorbed  according  to  the  laws 
of  gas  absorption,  and  can  be  eliminated  by  the  lungs. 


1  Cf.  Laschkewitsch:  Arch.  Anat.  Physiol.  1868,  61.     R.  Winternitz:  Arch,  exper. 
Path.  Pharm.  33,  286  (1895).     E.  Babak:  Pfliiger's  Arch.  108,  389  (1905). 

2  Baumert:    Chemische  Untersuchungen    der    Respiration  des  Schlammenpeizgers, 
Breslau,  1855.     D.  Calugareanu:  Pfluger's  Arch.  118,  42;  120,  425  (1907). 


LECTURE   XIX. 
ANIMAL  OXIDATIONS. 

IN  the  last  lecture  we  attempted  to  trace  the  path  of  oxygen  on  its  way 
through  the  animal  organism  from  the  time  of  its  being  acquired  from  the 
alveolar  air  to  its  being  given  up  to  the  tissues  and  their  cells,  and,  on  the 
other  hand,  we  found  that  carbon  dioxide  is  to  be  regarded  as  the  end- 
product  in  the  action  of  oxygen  upon  the  nutriment.  Meanwhile,  we  have 
failed  to  touch  upon  one  point  of  greatest  moment,  namely,  why  the  oxygen 
attacks  and  consumes  this  cell-nutriment.  Outside  the  animal  organism, 
if  we  expose  albumin,  fats,  or  carbohydrates  to  the  action  of  oxygen  at 
the  body  temperature,  even  for  a  long  time,  there  is  no  perceptible  oxida- 
tion of  these  materials.  Within  the  animal  organism,  on  the  contrary, 
these  substances  are  oxidized  in  a  short  time,  and  the  chief  products  of  the 
oxidation  are  carbon  dioxide,  water,  and  urea.  Consequently,  conditions 
must  prevail  within  the  organism  which  facilitate  the  action  of  oxygen 
upon  the  material  exposed  to  its  action. 

We  are  acquainted  with  quite  a  number  of  facts  which  compel  us  to 
assume  that,  even  within  the  animal  tissues,  oxygen  as  such  is  not  able  to 
act  upon  the  unchanged  food.  Under  no  circumstances  should  we  imagine 
for  a  -moment,  that  the  oxygen  supplied  to  the  tissues,  at  once  of  its  own 
accord,  begins  to  oxidize  the  different  substances  present  in  the  cells.  If 
this  were  the  case,  it  would  be  absolutely  impossible  for  us  to  account  for 
quite  a  number  of  processes  taking  place  in  the  animal  organism.  Above 
all,  it  would  then  be  unintelligible,  why  oxygen  is  brought  to  the  cells, 
together  with  the  newly  absorbed  nourishment,  without  any  oxidation 
taking  place  until  the  cells  are  reached.  The  fact  that  the  blood  contains 
the  greater  part  of  its  oxygen  chemically  united  with  the  hemoglobin,  does 
not  suffice  to  explain  this  fact ;  for  it  would  be  expected  that  the  oxygen, 
which  was  merely  dissolved  in  the  plasma,  would  be  replaced,  as  soon  as 
consumed,  by  the  oxygen  in  the  hemoglobin.  Again,  it  would  be  inex- 
plicable why,  in  the  combustions  taking  place  in  the  cells,  it  is  only  the  fuel 
that  is  consumed,  and  not  the  cell-substance  itself.  On  the  other  hand,  we 
have  seen  that  the  organism  can  lose  the  power  of  oxidizing  certain  sub- 
stances, such  as  carbohydrates,  for  example,  which  are  ordinarily  consumed 
easily,  while  other  oxidation  processes  are  not  affected  in  the  slightest. 
We  know  now  that  in  diabetes  substances  hard  to  oxidize  are  consumed 
without  difficulty;  whereas,  unchanged  d-glucose  alone  has  ceased  to  be  a 

439 


440  LECTURE  XIX. 

food,  because  the  organism  has  lost  the  power  of  being  able  to  utilize  the 
energy  stored  up  in  it.  If,  on  the  other  hand,  the  grape-sugar  is  slightly 
changed  before  its  introduction  into  the  organism  of  the  diabetic,  then  the 
tissues  are  capable  of  completely  oxidizing  it. 

If  the  animal  oxidation  took  place  merely  as  a  result  of  the  coming 
together  of  oxygen  and  nutriment,  it  would  be  expected  that  when  an 
increased  amount  of  the  reacting  substances  was  present,  a  more  vigorous 
oxidation  would  ensue.  This  is,  however,  not  the  case.  Under  normal 
conditions,  it  is  not  possible  to  increase  the  amount  of  oxidation  taking 
place  in  the  tissues  by  increasing  the  supply  of  oxygen  and  the  amount 
taken  up  by  the  blood.1  Similarly,  we  are  not  able  to  increase  the  total 
consumption  of  material  very  much  by  increasing  the  supply  of  carbo- 
hydrate or  fat.  Only  of  albumin  do  we  know  that  the  amount  present 
governs  somewhat  the  extent  of  the  transformation. 

We  know,  to  be  sure,  of  compounds  which  are  not  attacked  by  oxygen 
in  neutral  solutions,  but  are  attacked  in  the  presence  of  alkali.  Pyrogallol 
absorbs  oxygen  in  alkaline  solutions  so  vigorously  that  it  is  used  for  the 
detection  of  small  quantities  of  this  gas.  To  be  sure,  we  do  not  have  free 
alkali  present  in  our  tissues,  but  merely  alkali  carbonates.  These  also  favor 
such  oxidations.  Thus  it  is  known  that  a  solution  of  glucose  and  soda 
absorbs  oxygen  from  the  air,2  although  the  amount  taken  up  is  but  slight. 
Schmiedeberg  3  has  shown,  moreover,  that  benzyl  alcohol  in  the  presence 
of  water  is  not  attacked  by  atmospheric  oxygen,  but  is  transformed  to 
benzoic  acid  when  it  is  in  a  sodium  carbonate  solution  exposed  to  the  oxy- 
gen of  the  air.  This  compound  is  also  oxidized  by  the  oxygen  in  the  blood. 
If  benzyl  alcohol  is  conducted,  with  blood  containing  oxygen,  through  the 
kidneys  or  lungs  of  dogs  or  pigs,  benzoic  acid  is  formed;  while  if  salicylic 
aldehyde  is  employed  in  the  above  experiment,  salicylic  acid  is  formed  to 
some  extent.  The  amount  of  acid  obtained  in  each  case  is  very  small.  It 
is  necessary  to  state  in  this  connection  that  these  experiments  are  by  no 
means  sufficient  to  account  for  the  combustion  of  the  nutriment.  They 
merely  show  us  that  easily  oxidizable  substances  are  more  readily  acted 
upon  by  oxygen,  when  contained  in  alkaline  solutions,  than  in  neutral  or 
even  acid  ones.  They  in  no  way  refer  to  the  oxidation  of  the  more  diffi- 
cultly oxidizable  foodstuffs. 

We  are  compelled  to  assume  that  either  the  oxygen  is  changed  in  the 
tissues  to  a  form  in  which  it  is  more  active  than  usual,  or  that  the  nutriment 
is  in  some  way  changed  by  the  activity  of  the  cell,  so  that  it  is  more  readily 
acted  upon  by  oxygen.  Or  these  two  processes  may  take  place  side  by 
side  in  the  cell. 


1  See  Schaternikoff:  Arch.  Anat.  Physiol.  1904,  Suppl.  135. 

2  M.  Nencki  and  N.  Sieber:  J.  pr.  Chem.  26,  1  (1882). 

3  Arch,  exper.  Path.  Pharm.  14,  288  (1881). 


ANIMAL  OXIDATIONS.  441 

The  fact  that  the  oxygen  in  the  condition  in  which  it  is  given  up  to  the 
tissues  is  not  capable  of  consuming  the  unchanged  nutriment,  enables  the 
cell  to  adjust  the  metabolism  to  its  requirements.  Above  all,  this  fact 
enables  the  cell  to  utilize  a  certain  particular  material  for  definite  functions 
when  it  so  desires.  We  should  also  not  forget  that  we  know  altogether  too 
little  concerning  the  relations  of  the  separate  organs  to  one  another,  and 
of  the  different  kinds  of  cells  in  one  and  the  same  organ,  to  be  able  to 
judge  whether  under  all  conditions,  the  combustion  of  the  fuel  is  entirely 
effected  by  the  cell  that  begins  the  work,  or  whether  one  cell  merely 
carries  the  oxidation  to  a  certain  stage,  and  another  cell  carries  the  com- 
bustion farther,  until  finally  the  material  is  completely  oxidized.  Such 
an  assumption  seems  extremely  probable  from  the  observations  of  Bohr 
and  Henriques,1  who  found  that  extensive  oxidations  take  place  in  the 
lungs.  Oxygen  is  consumed  there  and  carbon  dioxide  evolved  to  an  extent 
sufficient  to  lead  one  to  presume  that  incompletely  oxidized,  metabolic 
products  reach  the  lungs  together  with  the  blood,  and  that  the  combustion 
is  completed  by  the  lungs.  On  the  other  hand,  according  to  the  assump- 
tion that  the  respiratory  exchange  takes  place  as  a  sort  of  secretion  process, 
it  is  probable  that  the  lungs  have  a  certain  amount  of  work  to  do  which 
requires  the  expenditure  of  energy,  so  that  this  supply  of  fuel  is  necessary 
for  its  function.  Bohr  and  Henriques  found  that  about  one-third  of  the 
total  metabolism  taking  place  in  the  body  was  effected  in  the  lungs.  The 
separate  observations  varied  from  0  to  66  per  cent.2 

We  must  emphasize  the  fact  at  the  start  that  we  are  not  yet  able  to  give 
a  perfectly  clear  explanation  as  to  the  nature  of  animal  oxidation  processes. 
At  present,  we  recognize  merely  the  initial  products,  food  and  oxygen,  and 
the  final  products  of  the  combustion.  We  are  therefore  forced  to  rely 
upon  assumptions.  In  fact,  the  great  number  of  hypotheses  which  have 
been  brought  forward,  show  clearly  upon  what  an  insecure  foundation  they 
all  rest.  Here  we  will  only  attempt  to  mention  only  the  more  important 
theories,  and  emphasize  only  those  which  rest,  to  some  extent,  upon 
experimental  observations. 

The  question  to  interest  us  first  of  all  is  this:  Is  the  oxygen  changed 
in  form  so  that  it  attacks  the  nutriment  more  readily?  The  formation 
of  ozone  has  been  suggested.  We  know  that  ozone  is  a  stronger  oxidizing 
agent  than  ordinary  oxygen,  and  oxidizes  compounds  which  are  not 
affected  by  the  latter.  Schonbein3  carried  his  studies  on  ozone  to  the 
phenomena  of  cell  life.  He  attributed  numerous  oxidations  taking 
place  in  the  plant  organism  to  the  primary  formation  of  ozone.  The  plant 
tissues,  he  assumed,  contain  some  substance  which  possesses  the  power  of 

1  Arch,  de  Physiol.  1897,  590.     See  Lecture  XVIII,  p.  432. 

2  These  high  figures  have  not  been  generally  accepted.  —  Translator. 

3  Poggendorff's  Annalen,  65,  171  (1845). 


442  LECTURE  XIX. 

ozonizing  atmospheric  oxygen.  The  cells  take  up  the  ozone,  and  then  as 
the  latter  breaks  down  to  ordinary  oxygen,  the  extra  atom  of  oxygen 
attacks  some  oxidizable  substance.  The  assumption  that  as  a  matter 
of  fact  there  is  an  ozone  formation  in  the  tissues,  meets  with  certain  diffi- 
culties. Relatively  small  amounts  of  ozone  are  poisonous  to  the  cells.  It 
has  never  been  possible  to  detect  the  presence  of  ozone  in  either  plant  or 
animal  organisms.  So  this  hypothesis  was  soon  abandoned.  The  assump- 
tion that  active  oxygen  is  present  in  the  tissues,  is  far  more  probable. 
Hoppe-Seyler,1  who  suggested  this  hypothesis,  based  it  upon  the  fact, 
that  in  the  animal  tissues  energetic  reduction  processes  take  place,  side  by 
side  with  the  oxidations.  In  this  way,  reducing  substances  are  formed 
which  unite  with  one  atom  in  the  oxygen  molecule,  setting  the  other  atom 
free  in  an  active  condition.  The  butyric  acid  fermentation  of  sugar  is  an 
example  of  such  a  reduction  process.  Hydrogen  is  set  free: 

C6H1206  =  C3H7COOH  +  2  C02  +  2  H2. 

A  support  for  the  assumption  that  active  oxygen  causes  the  animal 
oxidations,  is  furnished  by  the  theory  of  nitrification.  In  this  case  also, 
it  is  assumed  that  the  organism,  to  whose  activity  the  formation  of  nitrate 
is  due,  first  of  all  produces  readily  oxidizable  substances,  which  then  decom- 
pose the  atmospheric  oxygen  molecule,  and  thus  form  active  (nascent) 
oxygen  for  the  oxidation  of  the  nitrogen. 

The  formation  of  such  readily  oxidizable  substances  which  under  normal 
conditions  are  immediately  oxidized  further,  is  likewise  indicated  by  the 
so-called  "  spontaneous  combustion  "  of  hay.  In  this  case,  on  account 
of  insufficient  ventilation,  such  readily  oxidizable  substances  collect  in 
considerable  amount,  and  are  suddenly  oxidized  as  soon  as  fresh  air 
enters. 

If  we  are  to  believe  that  the  oxidations  in  the  animal  organism  take 
place  in  this  way,  we  must  assume  that  first  of  all  the  food  is  hydrolyzed, 
and  that  easily  oxidizable  compounds  are  formed  which  are  oxidized  by 
the  oxygen,  received  by  the  tissues  from  the  blood,  and  at  the  same  time 
a  part  of  this  oxygen  is  activated.  This  nascent  oxygen  unites  with  the 
more  difficultly  oxidizable  substances.  The  first  stage  in  the  oxidation 
of  the  food  is,  therefore,  a  hydrolysis;  and  inasmuch  as  the  last-mentioned 
process  is  brought  about  by  means  of  ferments,  these  play  a  part  in  the 
entire  phenomenon  of  oxidation.  This  assumption  has  much  in  its  favor, 
and  corresponds  to  certain  discoveries.  With  its  help  we  are  able  to  under- 
stand, for  example,  why  the  diabetic  cannot  oxidize  d-glucose,  and  only 
this  one  substance.  We  have  simply  to  assume  that  the  ferment  is  absent 
which  hydrolyzes  this  sugar  so  that  oxygen  does  not  come  in  contact  with 


1  Pfliiger's  Arch.  12,  16  (1876). 


ANIMAL  OXIDATIONS.  443 

the  cleavage-products  of  this  substance.  To  be  sure,  this  does  not  explain 
why  the  nascent  oxygen  set  free  in  the  combustion  of  other  foodstuffs, 
is  not  able  to  act  upon  d-glucose.  At  all  events,  the  assumption  that  oxi- 
dation is  preceded  by  a  hydrolysis,  gives  to  the  cell  the  power  of  utilizing 
its  nutriment  at  the  time  it  is  needed.  We  know  that  the  action  of  the 
ferments  is  specific,  i.e.,  that  they  are  able  to  act  only  upon  certain  definite 
compounds.  If  it  be  assumed  that  the  cells  do  not  contain  the  ferment 
in  an  active  condition,  but  that  the  ferment  is  activated  only  when  its 
action  is  needed,  we  are  able  to  understand  very  clearly  much  about  the 
economy  of  the  cells.  We  begin  to  understand  how  the  cell  can  have 
the  food,  the  ferment,  and  oxygen  all  present  together  without  any  com- 
bustion taking  place,  until  at  a  given  moment  the  ferment  becomes 
activated.  The  following  phenomenon  harmonizes  well  with  such  an 
assumption. 

The  animal  organism  consumes  without  difficulty  the  cleavage-products 
of  the  food  which  it  obtains  as  such.  Thus  the  decomposition  products  of 
albumin,  such  as  glycocoll,  alanine,  etc.,  are  readily  oxidized  to  urea.1  This 
is  true,  however,  only  of  those  amino  acids  which  are  present  in  albumin, 
i.e.,  those  having  the  same  configuration.  If,  for  example,  instead  of  feed- 
ing a  rabbit  with  /-leucine,  we  administer  the  racemic  form,  d-/-leucine, 
only  a  part  of  the  molecule,  namely  the  /-leucine,  is  oxidized,  while  the 
other  half  of  the  racemic  substance  molecule,  the  right-rotating  leucine, 
appears  unchanged  in  the  urine.  This  is  evidently  because  the  animal 
cells  are  not  adapted  to  the  combustion  of  d-leucine,  which  under  ordinary 
conditions  is  foreign  to  it,  so  that  it  possesses  no  ferment  to  attack  it. 
The  oxygen,  therefore,  is  not  able  to  attack  it.  Furthermore,  it  is  not 
strange  that  when  the  combustion  is  very  vigorous  a  part  of  this  substance 
is  actually  oxidized.  We  may  indeed  assume  that  oxygen  activated  by 
some  other  decomposition  process  can  cause  such  oxidation. 

Interesting  as  this  hypothesis  appears,  we  must  not  forget  to  state  that 
in  this  simple  form  it  does  not  suffice  to  explain  all  the  phenomena  pertain- 
ing to  animal  oxidation.  The  actual  relations  are  far  more  complicated 
than  we  have  indicated.  Above  all,  we  would  expect  that  in  the  absence 
of  oxygen  there  would  tend  to  be  a  piling-up  of  these  readily  oxidizable  sub- 
stances, and  to  a  considerable  degree,  particularly  as  now  the  entire  energy 
required  by  the  organism  must  be  furnished  by  the  hydrolytic  decomposi- 
tions. We  have  already  mentioned  experiments  performed  in  this  direc- 
tion.2 G.  von  Bunge3  has  shown  that  ascarids  are  able  to  exist  for 
several  days  without  any  oxygen  supply.  During  this  time  they  move 
about  quite  actively.  The  energy  necessary  in  such  cases  must  be  pro- 

1  Cf.  Lecture  XI,  p.  228. 

2  Lecture  IV,  p.  74. 

3  Z.  physiol.  Chem.  14,  318  (1890). 


444  LECTURE  XIX. 

duced  by  means  of  partial  decompositions.  We  should  expect,  therefore, 
that  hydrogen  and  other  easily  oxidizable  substances  would  be  formed. 

This  was,  however,  not  the  case.  The  presence  of  hydrogen  could  not  be 
detected,  nor  did  oxygen  disappear,  if  oxygen  was  supplied  after  the  worms 
had  existed  for  a  day  without  it.  Now  we  have  no  right  to  apply  the 
results  of  such  experiments  to  human  beings,  or  to  other  animal  organ- 
isms. The  parasites  of  the  intestine  are  accustomed  to  get  along  with  a 
very  limited  supply  of  oxygen.  It  is  perfectly  possible  that  their  metabo- 
lism takes  place  entirely  differently  than  is  the  case  with  the  remaining 
animal  organisms.  Perhaps  hydrolytic  decompositions  take  place  in 
them  without  forming  any  easily  oxidizable  substances.  Furthermore, 
it  is  conceivable  that  these  little  worms  normally  have  active  oxygen  at 
their  disposal,  formed,  at  least  to  some  extent,  by  the  energetic  reduction 
processes  which  take  place  in  the  alimentary  canal.  On  the  other  hand, 
we  must  remember  that  the  assumption  of  an  activation  of  oxygen,  by 
means  of  the  formation  of  reducing  substances  in  the  tissues,  has  never 
gotten  beyond  the  hypothetical  stage.  It  is  remarkable  too  that  the 
animal  organism  itself  is  able  to  keep  easily  oxidizable  substances  in  its 
tissues,  such  as  phosphorus,  for  example,  in  an  unchanged  condition  for 
a  considerable  length  of  time.  It  is  not  easy  to  understand  how  such  a 
substance  as  this  escapes  the  active  oxygen  unless  it  be  assumed  that 
during  its  transport  through  the  animal  tissues,  it  never  actually 
comes  in  contact  with  nascent  oxygen.  Such  an  assumption  seems 
strained,  for  we  know  of  countless  examples  in  which  the  animal  organism 
is  protected  from  poisons  by  their  being  oxidized.  The  oxidation  does  not 
always  take  place  to  such  an  extent,  but  frequently  it  serves  to  prepare  a 
new  substance  which  can  become  harmless  by  conjugation  with  something 
else,  whether  it  be  glycocoll,  sulphuric  acid,  glucuronic  acid,  or  urea.  On 
the  other  hand,  it  is  a  fact  that  a  reduction  process  may  facilitate  the 
combination  of  the  poison  with  one  of  the  above  compounds.  At  all 
events,  it  is  extremely  interesting  to  find  that  these  oxidations  are  quite 
different  in  various  cases.  At  one  time  the  compound  may  be  completely 
oxidized,  whereas,  in  another  case,  merely  an  atom  of  oxygen  may  be 
added  to  its  composition.  We  can,  indeed,  believe  that  the  cells,  as 
already  mentioned,  may  regulate  their  decompositions  by  means  of  their 
ferments;  but  it  remains  an  enigma,  according  to  the  assumption  of  the 
presence  of  active  oxygen,  why  the  oxidation  should  stop  at  a  certain 
stage  in  the  case  of  readily  oxidizable  substances,  whereas  in  other  cases 
a  total  oxidation  takes  place. 

Unquestionably,  we  would  prefer  an  hypothesis  which  in  itself  includes 
this  regulation  of  the  extent  of  oxidation.  The  first  suggestion  of  such  an 
hypothesis  was  made  by  Moritz  Traube.1  He  pointed  out  the  important 


1  Theorie  der  Fermentwirkungen.     Berlin,  1858. 


ANIMAL  OXIDATIONS.  445 

of  oxygen  carriers.  In  the  study  of  inorganic  chemistry,  we  know  of 
various  processes  which  take  place  in  the  presence  of  a  carrier  of  oxygen, 
but  will  not  take  place  from  direct  contact  with  oxygen.  An  example  of 
such  a  process  is  in  the  oxidation  of  glucose  by  potassium  indigo  sul- 
phonate,  or  by  copper  oxide.  If  a  solution  of  glucose  is  warmed  with 
alkali  carbonate  in  the  air  for  some  time,  practically  no  oxygen  is  taken 
up.  As  far  as  we  can  see,  the  glucose  remains  unaffected.  Now  if  we  add 
a  little  potassium  indigo  sulphonate  to  the  solution,  in  the  course  of  a 
short  time  the  blue  solution  becomes  decolorized,  and  the  amount  of 
unchanged  glucose  remaining  in  the  solution  gradually  becomes  smaller 
and  smaller.  The  glucose  has  become  oxidized.  If  now  we  shake  the 
solution,  it  soon  turns  blue  again,  but  again  on  standing  it  becomes  color- 
less. At  the  same  time,  more  of  the  glucose  becomes  oxidized.  This 
process  may  be  repeated  again  and  again,  until  finally  no  more  glucose 
remains.  A  very  small  amount  of  potassium  indigo  sulphonate  suffices 
to  cause  the  oxidation  of  a  large  amount  of  glucose.  Copper  oxide  exerts 
a  perfectly  similar  effect.  An  ammoniacal  solution  of  cupric  oxide 
becomes  decolorized  on  warming  it  with  glucose.  The  cupric  oxide  is 
converted  into  cuprous  oxide,  or,  in  other  words,  the  copper  is  reduced. 
Oxygen  has  been  furnished  to  the  glucose  molecule.  If  the  decolorized 
solution  is  exposed  to  the  air  for  some  time,  gradually,  and  first  at  the 
places  where  the  solution  is  in  direct  contact  with  the  air,  it  turns  blue 
again.  Oxygen  is  thus  being  taken  up  by  the  cuprous  oxide,  which  may- 
be given  up  subsequently  to  more  glucose.  The  whole  process  can  be 
accelerated  considerably  by  shaking  the  liquid  with  air. 

It  is  not  difficult  to  conceive  that  substances  are  present  in  the  animal 
tissues  which  act  as  carriers  of  oxygen  for  the  more  difficultly  oxidizable 
substances.  As  we  have  said,  a  very  small  amount  of  such  substances 
suffices  to  accomplish  an  indefinite  amount  of  oxidation.  The  carrier 
itself  is  in  the  same  condition  at  the  end  of  the  process  that  it  was  at  the 
beginning.  Now  we  know  that  ferments  play  an  important  part  both  in 
the  animal  and  vegetable  kingdoms.  The  thought  naturally  arises  that 
perhaps  certain  of  these  ferments  may  act  as  carriers  of  oxygen.  Traube 
speaks  of  oxidizing  ferments.  Recently  Schmiedeberg l  has  mentioned 
the  possibility  of  certain  definite  oxygen-carrying  ferments;  while  Jaquet 2 
has  followed  up  this  suggestion  and  succeeded  in  proving  that  extracts 
of  the  organs  serve  as  carriers  of  oxygen,  and  that  in  fact  the  principle 
which  causes  this  action  may  be  precipitated  by  means  of  alcohol  without 
its  losing  any  of  its  power  of  causing  oxidation.  Heating  to  100°  C., 
however,  destroys  it. 

To-day,  no  one  doubts  that  a  great  many  such  ferments  are  actually 

1  Arch,  exper.  Path.  Pharm.  14,  288  (1881). 
3  Ibid.  29,  386  (1892). 


446  LECTURE  XIX. 

present,  both  in  the  animal  and  vegetable  kingdoms.  It  is  easy  to  detect 
their  presence  by  means  of  certain  chemical  reagents.  If,  for  example, 
an  organ  extract  is  shaken  with  an  alkaline  solution  of  a-naphthol  plus 
p-phenylenediamine,  the  formation  of  blue  indophenol  is  soon  apparent.1 
Without  the  addition  of  the  organ  extract,  the  formation  of  this  color 
takes  place  very  much  more  slowly.  A  reaction  made  use  of  by  Schonbein 
is  the  blue  color  obtained  with  tincture  of  guaiacum.  Its  indication  of  the 
presence  of  oxidizing  ferments  is,  however,  not  altogether  reliable.  The 
guaiacum  reaction  is  also  brought  about  by  the  presence  of  numerous  other 
oxidizing  agents,  such  as  ferric  chloride,  chromic  acid,  chlorine,  bromine, 
etc.  By  means  of  these  organ  extracts  salicylic  acid  may  be  converted 
into  benzoic  acid,  and  benzyl  alcohol  into  benzoic  acid.2  Formaldehyde 
is  similarly  converted  into  formic  acid,3  and  arsenious  acid  into  arsenic 
acid.4  a-naphtylamine  is  changed  into  violet-blue  oxynaphtylamine,  and 
benzidine  into  a  brownish-violet  substance.5  Likewise  phenolphtalin  is 
changed  to  phenolphthalein.6  These  are  a  few  examples  of  the  oxida- 
tions which  may  be  brought  about  readily  by  means  of  organ-decoction  or 
organ-extract;  and,  in  fact,  with  plants  the  oxidizing  action  of  certain  of 
their  organs,  the  roots  for  example,  may  be  demonstrated  directly  by 
allowing  them  to  grow  upon  strips  of  paper  moistened  with  solutions  of 
the  above-mentioned  reagents. 

By  means  of  these  discoveries,  the  whole  question  of  animal  and  vege- 
table oxidations,  the  latter  not  differing  from  the  former  in  its  essential 
particulars,  has  been  turned  in  an  entirely  new  direction.  Although, 
at  the  present  stage  of  its  development,  it  is  perhaps  going  too  far  to  speak 
of  a  perfect  explanation  of  the  oxidation  processes  in  the  tissues,  still,  on 
the  other  hand,  it  is  true  that  numerous  processes  which  would  be  other- 
wise beyond  our  comprehension,  are  now  better  understood.  As  we  shall 
see  later,  we  have  every  reason  to  believe  that  a  given  ferment  always  acts 
upon  only  quite  definite  compounds.  Thus  the  proteolytic  ferment,  tryp- 
sin,  attacks  only  proteins,  and  not  carbohydrates.  It  might  have  been 
assumed  a  priori,  that  the  oxidizing  ferments  are  exceptions  in  this  respect, 
and  are  in  general  capable  of  serving  as  carriers  of  oxygen.  This  is,  as  a 
matter  of  fact,  not  the  case,  as  we  know  from  numerous  observations. 
Thus  it  is  only  certain  definite  oxidizing  ferments  which  are  capable  of 
causing  the  above-mentioned  oxidation  of  a-naphthol  and  p-phenylene- 
diamine  to  indophenol  in  alkaline  solution.  In  the  liver,  for  example, 

F.  Rohmann  und  W.  Spitzer:  Ber.  28,  567  (1895). 

Jaquet:  Arch,  exper.  Path.  Pharm.  29,  386  (1892). 

Pohl:  ibid,  38,  65  (1896). 

W.  Spitzer:  Pfliiger's  Arch.  71,  596  (1898). 

M.  Raciborski:  Anzeiger  der  akad.  der  Wissensch.  zu  Kraukau,  1905,  338. 

Kastle  and  Shedd:  Am.  Chem.  J.  26,  527  (1901). 


ANIMAL  OXIDATIONS.  447 

the  ferments  belonging  to  this  organ  are  capable  of  converting  aldehydes 
(e.g.,  salicylic  aldehyde)  into  the  corresponding  acid,  but  they  are  inca- 
pable of  effecting  the  indophenol  synthesis.  Jacoby l  was  unable  to  effect 
the  oxidation  of  such  compounds  as  acetic  acid,  stearic  acid,  etc.,  by 
means  of  the  ferment  which  changes  salicylic  aldehyde  into  salicylic  acid. 
Again,  ferments  are  known  which  will  turn  tincture  of  guaiacum  blue,  but 
have  no  action  upon  salicylic  aldehyde.2 

Particularly  in  the  vegetable  kingdom  we  meet  with  these  ferments 
possessing  a  quite  specific  oxidation  power,  which  are  designated  with 
particular  names  according  to  the  work  that  they  perform.  In  the 
sap  of  plants  we  often  find  the  so-called  tyrosinase?  i.e.,  a  ferment 
which  transforms  tyrosine  into  colored  products.  The  same,  or  at 
least  a  very  similar  ferment,  also  occurs  in  animal  organisms.  Thus 
the  stomach  juices  of  starved  meal-worms  act  upon  tyrosine.4  A 
similar  action  explains  an  old  observation.  As  is  well  known,  the  blood 
of  insects  is  nearly  colorless,  but  becomes  dark  as  soon  as  it  leaves  the 
body.  Von  Fiirth  and  Schneider 5  have  found  that  this  so-called  melanosis 
is  the  result  of  the  action  of  an  oxidizing  ferment.  They  proved  this  in 
the  following  manner:  They  obtained,  by  piercing  the  pupaB  of  DeilephUia 
elepenor  and  euphorbia,  a  greenish-colored  liquid,  from  which  they  obtained 
a  precipitate  upon  the  addition  of  ammonium  sulphate.  This  precipitate, 
on  being  dissolved  in  0 . 05  per  cent  soda  solution,  and  added  to  a  solution 
of  tyrosine,  soon  caused  a  violet  coloration,  which  gradually  turned  black. 
Eventually  dark  flocks  of  a  precipitate  were  thrown  down.  The  tyro- 
sinase  thus  obtained  acts  upon  other  aromatic  compounds,  containing 
hydroxyl  groups,  such  as  catechol,  chinol,  etc.  In  the  insect  blood  itself, 
tyrosine  is  not  present,  but  a  chromogen,  which  is  evidently  closely  related 
to  it.  It  may  be  assumed  safely,  that  tyrosinase  is  very  abundant  in 
nature,  and  undoubtedly  plays  an  important  part  in  the  formation  of  pig- 
ments. In  the  blood  of  the  river-crab  and  in  the  ink-glands  of  the  cepha- 
lopoda a  tyrosinase  is  found. 

Tyrosinase  is  much  more  widely  distributed  in  the  vegetable  kingdom 
in  which  it  was  discovered,  Bertrand  6  has  found  besides  the  tyrosinase 
a  second  ferment,  laccase,  which  acts  upon  only  quinol  and  pyrogallol. 

Closely  related  to  these  ferments  is  the  glucolytic  ferment,  which  we 
have  already  discussed,7  but  whose  existence,  however,  has  not  been  posi- 

1  Virchow's  Arch.  157,  235  (1899). 

2  Abelous  et  Biarnes:  Compt.  rend.  soc.  biol.  49,  175,  285,  493,  559,  596;  50,  495. 

3  E  Bourquelot  and  G.  Bertrand:  J.  pharm.  chim.  (6)  3,  177  (1896);  Bull.  soc.  mycol. 
France,  1896,  18  and  27. 

*  W.  Biedermann:  Pfliiger's  Arch.  72,  105  (1898). 
••     *  Hofmeister's  Beitrage:   1,  229   (1901). 

•  Compt.  rend.  122,  1132,  1215  (1895);  123,  463  (1896). 
'  See  Lecture  IV,  p.  73,  and  V,  p.  87. 


448  LECTURE  XIX. 

lively  established.     The  oxydase  which  takes  part  in  breaking  down  the 
nucleins  also  belongs  here.1 

In  this  class  of  oxidizing  ferments  we  must  also  reckon  the  ferment  of 
the  acetic  acid  bacteria,  discovered  by  E.  Buchner  and  J.  Meisenheimer.2 
Quite  independently  of  the  other  activity  of  these  microbes,  this  ferment 
changes  alcohol  into  acetic  acid: 

CH3  .  CH2OH  +  O2  =  CH3  .  COOH  +  H20. 

Unquestionably,  a  great  many  other  oxidations  are  to  be  traced  to  the 
action  of  oxidizing  ferments,  and  we  find  in  the  literature  numerous  other 
ferments  described  under  particular  names.  We  must  not  forget,  how- 
ever, that  the  identification  of  ferments  is  an  extremely  difficult  task,  and 
it  is  very  seldom  that  in  any  case  it  is  absolutely  proven  a  new  one  is  at 
hand.  Thus  we  know  from  the  investigations  of  Bertrand  3  that  in  the 
juice  of  the  berries  of  mountain  ash  a  hexatomic  alcohol,  sorbitol,  is  present 
which  under  certain  conditions  is  changed  to  the  hexose,  sorbose.  It  would 
be  unjustifiable  from  this  fact  alone  to  assume  that  this  evident  oxidation 
is  to  be  attributed  to  the  presence  of  a  ferment.  It  has  been,  in  fact, 
established  that  a  certain  species  of  bacteria,  Bacterium  xylinum,  which 
is  introduced  into  the  berries  by  means  of  a  tiny  red  flea,  Drosophila 
Junebris,  causes  this  transformation.  This  bacterium  will  likewise  oxidize 
mannitol  to  fructose,  xylose  to  xylonic  acid,  etc.  Although  it  is  indeed 
very  likely  that  these  bacteria  act  side  by  side  with  oxidizing  ferments, 
still,  on  the  other  hand,  it  is  not  right  to  assume  their  presence  until  the 
ferment  itself  has  been  isolated. 

We  have  intentionally  made  this  digression  in  order  that  we  may  gain 
some  idea  as  to  the  way  in  which  such  oxidations  are  effected,  and  as  to 
the  abundance  of  such  ferments.  Of  course  this  has  not  told  us  much 
concerning  the  "  oxidative  "  breaking  down  of  the  most  important  food- 
stuffs. At  present  we  do  not  know  exactly  how  and  when  the  oxidation 
takes  place  in  the  case  of  protein,  fat,  or  carbohydrate.  We  can  make 
assumptions,  but  we  know  nothing  with  certainty. 

We  have  up  to  now  concerned  ourselves  merely  with  the  empirical 
knowledge,  and  have  not  said  anything  as  regards  the  way  in  which  these 
ferments  act.  Perhaps  a  glance  at  the  mechanism  of  their  action  may 
give  us  some  idea  of  the  oxidation  as  it  takes  place  in  the  tissues.  Unfor- 


1  See  Lecture  XIII,  p.  293. 

2  Ber.  36,  634  (1903). 

3  Compt.  rend.  122,  900  (1896);  126,  842,  984  (1898);  127,  124,  758  (1898).     Con- 
cerning the  oxidation  of  glucose  to  gluconic  acid,  and  of  gluconic  acid  to  oxygluconic 
acid,  see  Bontroux:  Ann.  Pasteur,  2,  308  (1887);  Compt.  rend.  127,  1224  (1898).     Oxi-_ 
dation  of  quinic  acid  to  protocatechuic.       Emmerling  and  Abderhalden:  Zentr.  Bac- 
teriol.  Parasitenkunde  und  Infectionskrankheiten,  10,  Abt.  II,  p.  337  (1903). 


ANIMAL  OXIDATIONS.  449 

Innately,  we  must  again  state  that  we  are  now  dealing  entirely  with 
hypotheses,  and  that  we  are  not  yet  in  position  to  explain  with  certainty 
the  exact  nature  of  the  processes  which  are  brought  about  by  the  action 
of  oxidizing  ferments. 

Traube  *  suspected  the  formation  of  hydrogen  peroxide.  In  the  oxida- 
tion of  readily  oxidizable  substances,  instead  of  the  oxygen  molecule  being 
merely  split  and  active  oxygen  set  free,  he  imagined  that  water  is  first  split 
off.  The  hydroxyl  group  in  the  latter  then  combines  with  the  oxidizable 
substance,  R,  and  the  free  hydrogen  atom  combines  with  neutral  oxygen, 
forming  hydrogen  peroxide: 

R  +  2  H20  +  O2  =  R(OH)2  +  H2O2. 

Hydrogen  peroxide  is  a  strong  oxidizing  agent,  and  will  attack  the  diffi- 
cultly oxidizable  substances. 

The  above  process  may  be  supposed  to  take  place  somewhat  differently. 
Perhaps  the  readily  oxidizable  substance  (R)  combines  with  the  oxygen, 
and  forms  itself  a  peroxide.  The  latter  can  then  give  up  its  extra  atom 
of  oxygen  to  some  difficultly  oxidizable  substance  (Ri).2 

R  -f  02  =  R02.  RO2  -f  RI  =  RO  +  RiO. 

In  this  case  the  peroxide  takes  the  place  of  the  hydrogen  peroxide,  and 
has  the  same  effect.  According  to  this  theory  it  is  not  that  we  have  active 
oxygen  present,  but  rather  that  the  oxygen  in  the  peroxide  is  held  in  a 
loosely  combined  condition  from  which  it  is  easily  set  free. 

The  question  now  arises,  What  connection  do  the  ferments  have  with  this 
peroxide  formation?  We  can  imagine  that  the  ferment  itself  combines 
with  oxygen,  and  by  forming  a  peroxide  thus  acts  as  a  carrier.  In 
fact,  such  an  action  has  been  assumed,  and  A.  Bach  with  R.  Chodat 3  has 
supported  the  assumption  by  quite  a  number  of  experimental  observa- 
tions. These  authors  carried  out  their  investigations  with  plants.  They 
separated  the  ferments  which  take  part  in  oxidations  into  three  classes. 
First,  there  are  albumin-like  substances  which  form  peroxides  from  the 
oxygen  that  is  brought  to  the  tissues  by  the  blood.  Such  ferments  they 
designate  as  oxygenases.  Then  Bach  and  Chodat  identified  peroxydases, 
ferments  which  have  the  power  of  increasing  the  peroxidation  power  of 
the  former.  Finally,  in  each  cell  there  are  present,  according  to  these 
authors,  catalases,  which  decompose  hydrogen  peroxide  catalytically  with 
evolution  of  oxygen. 

1  Ber,  10,  1111   (1886);  10,  1115;  22,  1496  and  3057  (1889);  26,  1471  and  1476 
(1893). 

2  C.  Engler  and  W.  Wild:  Ber.  30,  1669  (1897). 

3  Biochem.  Zentr.  1,  417  and  457  (1903).     A.  Bach:  Berichte,  38,  1878  (1905);  37, 
3785  (1904).     Bourquelot:  Compt.  rend,  de  la  soc.  biol.  49,  402  (1897).     Batelli  and 
Stern:  Compt.  rend.  140,  1197  and  1352  (1905);  141,  139  (1905). 


450  LECTURE  XIX. 

Substances  which  act  catalytically  upon  hydrogen  peroxide  have  been 
known  in  nature  for  a  long  time.  It  was  even  known  to  Thenard  *  that 
fibrin  and  the  tissue  of  the  kidneys  and  lungs  were  capable  of  decom- 
posing hydrogen  peroxide  into  water  and  oxygen  just  as  energetically 
as  is  done  by  platinum,  gold,  and  silver.  In  milk2  also,  and  in  blood,3 
there  is  a  hydrogen-peroxide-catalase.  The  catalases  are  evidently  of 
quite  common  occurrence.4  Their  significance  is  differently  explained. 
It  is  held  that  they  tend  to  prevent  the  appearance  of  active  oxygen.  It 
may  be  shown,  for  example,  that  urea  and  xanthine  cannot  be  oxidized 
by  hydrogen  peroxide  in  the  presence  of  a  catalase.  They  decompose 
hydrogen  peroxide  with  the  formation  of  molecular  oxygen.5  In  fact,  the 
catalases  are  not  oxidizing  ferments  at  all.  They  are  not  of  themselves 
able  to  turn  tincture  of  guaiacum  blue,  nor  in  the  presence  of  hydrogen 
peroxide.  Thus  the  cells  evidently  possess  a  means  of  restricting  and 
regulating  the  activity  of  the  oxidation  processes  taking  place  within 
them. 

The  action  of  the  oxygenases  appeared  to  have  a  very  simple  explana- 
tion, when  it  was  found  that  their  ash  contained  substances  which  of 
themselves  could  act  as  carriers  of  oxygen.  Thus  Bertrand  6  found  2 . 5 
per  cent  of  manganese  in  the  ash  from  laccase.  Manganese  salts  are 
very  active  carriers  of  oxygen.  In  other  oxidases  iron  is  present.  Ber- 
trand compared  0 . 1  gram  of  ferment  in  50  cubic  centimeters  of  quinol 
solution  in  its  action  first  with  manganese  alone  and  then  with  a  man- 
ganous  salt  plus  the  ferment. 

Manganous  salt  alone 0.3  c.c.  oxygen  absorbed 

Laccase,  from  Lucerne,  alone    ....   0.2  c.c.  oxygen  absorbed 
Laccase  plus  manganous  salt     .    .    .    .6.3  c.c.  oxygen  absorbed 

These  inorganic  constituents  have  been  assumed  to  combine  with  albu- 
min, and  form  a  dissociable  compound.  The  metal  constituent  serves  to 
carry  the  oxygen  and  in  much  the  same  way  as  we  described  for  the 
oxidation  of  sugar  in  alkaline  solution  by  means  of  copper  oxide.  The 
manganese  is,  according  to  this  view,  originally  present  in  the  divalent  or 
manganous  form,  which  takes  up  oxygen  from  the  tissues  with  the  forma- 
tion of  tetravalent  manganese  (corresponding  to  the  manganese  dioxide 
type) ,  and  the  other  atom  in  the  oxygen  molecule  is  carried  to  the  oxidizable 

Ann.  chim.  et  physiol.  (2)  11,  85  (1819). 

P.  Raudnitz:  Zentr.  Physiol.  12,  790  (1899);  Z.  Biol.  42,  91  (1901). 
George  Senter:  Z.  physikal.  Chem.  44,  257  (1903),  and  51,  673  (1895);  Proc.  of  the 
Roy.  Soc.  74,  201  (1894). 

O.  Loew:  Z.  Biol.  43,  256  (1902). 

Philip  Shaffer:  Am.  J.  Physiol.  14,  299  (1905). 

Compt.  rend.  124,  1032,  1055  (1897). 


ANIMAL  OXIDATIONS.  451 

substance.  Again,  the  manganese  dioxide  decomposes  with  loss  of  oxygen, 
and  in  this  way  the  splitting  off  of  oxygen  by  the  ferment  containing  the 
manganese  is  effected.  Such  views  are,  however,  very  improbable,  because, 
according  to  the  researches  of  Chodat  and  Bach,  the  oxidases  containing 
manganese  obtained  from  plants  are  inactive  in  the  absence  of  peroxidases. 
The  peroxidases  themselves  have  the  function  of  activating  the  oxidases, 
for  in  the  great  dilution  in  which  they  are  present  in  the  juices  and  cells, 
the  latter  do  not  readily  give  up  their  oxygen  from  the  peroxide  formation. 
The  action  of  the  peroxidases  may  be  compared  with  the  decomposition 
of  peroxides  by  means  of  ferrous  salts. 

With  the  help  of  these  hypothetical  representations  we  are  able  to  see 
how  the  cells  are  not  only  able  to  regulate  carefully  the  hydrolytic  decom- 
positions caused  by  ferments,  but  also  the  oxidations  as  well.  The  latter 
are  directly  dependent  upon  the  formation  of  the  peroxidases.  Now  the 
observations  upon  which  this  line  of  reasoning  is  advanced  have  been, 
made  upon  plants,  but  there  is  little  doubt  that  the  animal  cells  conduct 
their  oxidations  in  much  the  same  way.  All  this,  however,  is  purely 
hypothetical.  It  should  always  be  taken  into  consideration  that  all 
experiments  conducted  in  the  study  of  the  action  of  oxidases  have  been 
with  substances  which  are  oxidized  without  much  difficulty.  The  com- 
bustion of  such  important  foodstuffs  as  albumin,  fat,  and  carbohydrate 
is  still  an  obscure  process.  We  do  not  know  definitely  in  what  manner  the 
oxidizing  destruction  takes  place.  It  is  clear  to  us,  from  this  discussion, 
that  the  metabolism  which  takes  place  within  the  cells  is  infinitely  com- 
plicated, and  that  in  the  establishment  of  the  fact  that  oxygen  is  taken 
up  and  carbon  dioxide  eliminated,  nothing  whatever  was  determined  as  to 
the  real  root  of  the  matter.  We  are  now  beginning  to  understand  at  how 
many  places  the  mechanism  concerned  in  the  cell-decompositions  may  be 
disturbed  and  how  diverse  these  disturbances  may  be. 

In  the  light  of  our  present  information  concerning  the  breaking  down 
and  combustion  of  the  separate  foodstuffs  in  the  animal  organism,  we 
may  safely  assume  that  the  preliminary  stage  of  practically  all  decompo- 
sitions is  a  hydrolysis.  First  of  all  the  foodstuffs  are  subjected  to  hydro- 
lytic cleavage.  According  to  all  our  present  knowledge,  amino  acids  are 
formed  from  albumin,  glucose  from  glycogen,  and  glycerol  and  fatty  acids 
from  the  fats.  We  must  assume  that  the  other  substances  which  play  a 
part  in  the  metabolism  of  the  organism  are  prepared  for  combustion  in  an 
entirely  analogous  manner.  We  know  that  the  nucleins  are  decomposed 
into  albumin  and  nucleic  acid,  and  that  these  are  again  broken  down  into 
their  simpler  components.  Purine  bodies  are  thus  formed,1  which  we 
believe  first  lose  their  nitrogen  group  and  are  then  prepared  for  oxidation. 
In  this  case  we  can  establish  very  accurately  the  moment  at  which  oxygen 

1  See  Lecture  XIII,  p.  292. 


452  LECTURE  XIX. 

attacks  the  molecule.  Lecithin  is  also  decomposed  into  its  separate 
constituents.  In  short,  an  intermediate  metabolism  takes  place  in  the 
tissues,  which  is  caused  by  processes  perfectly  similar  to  those  taking  place 
in  the  alimentary  canal.  There  the  decomposition  serves  the  purpose  of 
converting  substances  which  are  naturally  foreign  to  the  organism,  but 
are  contained  in  the  food,  into  substances  which  the  tissues  can  assimilate 
and  incorporate.  Hydrolysis  is  in  all  cases  the  preliminary  stage  to  com- 
bustion. The  fact  that  oxygen  itself  in  any  form  is  not  capable  of  acting 
directly  upon  the  cell-nutriment,  i.e.,  that  it  cannot  directly  ignite  this 
fuel,  makes  it  possible  for  the  cells  to  satisfy  the  demands  for  energy  within 
quite  wide  limits  without  regard  to  external  conditions.  The  cells  are 
able  at  all  times  to  utilize  certain  cleavage-products  for  building  up  new 
cell-material  while  they  make  use  of  other  less  valuable  substances  merely 
as  fuel.  They  can  adjust  their  own  economy  according  to  their  indi- 
vidual requirements.  The  breaking  down  of  the  nutriment  can  take 
place  from  time  to  time  along  different  lines,  as  we  explained  in  the  case 
of  sugar.  Only  at  a  certain  given  moment  does  oxidation  ensue.  Again, 
it  is  remarkable  that-,  as  far  as  we  know  at  present,  we  meet  with  specific 
actions.  Not  every  oxidase  is  capable  of  oxidizing  tyrosine.  Here  cer- 
tain doubts  arise  as  to  whether  the  oxidation  takes  place  exactly  as  we 
have  represented,  or  whether,  for  example,  the  oxygen  given  up  by  the 
activated  oxygenase  actually  of  its  own  accord  attacks  the  difficultly 
oxidizable  substances  without  further  assistance  and  consumes  it.  We 
meet  with  objections  to  such  an  assumption,  especially  as  there  are  many 
classes  of  compounds  known  of  which  only  one  optical  isomer  is  oxidized, 
while  the  other  is  not.  We  have  already  indicated  the  behavior  of  the 
amino  acids.  If  a  rabbit  is  fed  with  leucine  it  is  chiefly  the  /Meucine  which 
is  oxidized,  while  the  greater  part  of  the  d-leucine  which  does  not  occur  in 
albumin  is  eliminated  as  such.1  A  great  many  similar  examples  are 
known.  We  need  merely  refer  to  the  observations  made  with  carbo- 
hydrates. C.  Neuberg  and  J.  Wohlgemuth 2  injected  d-,  1-,  and  dl- 
arabinose  into  rabbits,  and  found  that  7 . 1  per  cent  of  the  Z-arabinose,  36 
per  cent  of  the  d-arabinose,  and  of  the  dZ-arabinose  31  per  cent  of  dl- 
arabinose  plus  9.6  per  cent  of  d-arabinose  were  eliminated  unchanged. 
The  remander  of  the  material  was  oxidized.  On  the  other  hand,  A.  Brion  3 
found  that  of  levo-  and  mesotartaric  acid  93.6  to  97.3  per  cent  were  oxi- 
dized, of  racemic  acid  only  58 . 1  to  75 . 3  per  cent,  and  of  dextrotartaric 
acid  70.7  to  74.4  per  cent.  We  will  discuss  these  facts  later.  Here  they 

1  J.   Wohlgemuth:  Ber.,  38,  2064  (1905).      Schittenhelm  and  Katzenstein:  Z.  exper. 
Path.     Ther.  2,   560  (1906).     Abderhalden  and  Samuely:  Z.  physiol.    Chem.  47,  346 
(1906). 

2  Ber.,  34,  1745  (1901),  and  Z.  physiol.  Chem.  35,  41  (1902);  37,  530  (1903). 

3  Z.  physiol.  Chem.  25,  283  (1898). 


ANIMAL  OXIDATIONS.  453 

are  merely  cited  to  show  that  the  oxidation  processes  taking  place  in  the 
animal  organism  are  by  no  means  to  be  considered  as  direct  in  nature,  i.e., 
the  cleavage-products  as  such  (the  amino  acids,  dextrose  and  the  fatty 
acids),  are  of  themselves  not  susceptible  to  oxidation  in  the  tissues  under 
the  prevailing  conditions,  unless  it  be  assumed  that,  for  example,  d-leucine 
does  not  enter  into  the  metabolism  of  the  cells  and  does  not  come  in  con- 
tact with  the  carriers  of  oxygen.  There  is,  however,  no  support  to  such 
an  assumption.  On  the  contrary,  we  know  that  the  muscular  cells  of  the 
diabetic  are  constantly  being  offered  d-glucose.  The  cells  consume  albu- 
min and  fat,  or  rather  their  decomposition  products,  just  as  well  as  ever. 
Glucose  alone  they  allow  to  pass  on  unchanged.  The  key  is  lost  which 
can  unlock  the  energy  stored  up  in  the  glucose  molecule.  Now  of  course 
an  assumption  that  the  oxydase  which  is  capable  of  offering  oxygen  to  the 
dextrose  is  absent,  helps  us  here.  The  fact  that  the  diabetic  can  complete 
the  oxidation  without  difficulty,  if  the  glucose  is  previously  converted 
into  a  more  readily  oxidizable  form,  does  not  necessarily  prove,  however, 
that  the  glucose  molecule  must  be  opened  up  in  some  way  before  oxida- 
tion. It  is  indeed  possible  that  the  glucuronic  acid  and  saccharic  acid 
offered  to  the  diabetic  may  be  consumed  at  an  entirely  different  place  in 
the  organism,  and  not  utilized  at  all  for  the  work  of  the  muscular  cells. 1 
At  the  same  time  the  empirical  knowledge  that  we  possess,  indicates  that 
the  foodstuffs  as  such  are  not  at  once  suitable  for  oxidation.  Something 
must  be  taken  out  of  the  complex  molecule  before  the  oxygen  in  the  cells 
tissues  can  act  upon  it.  The  investigations  of  Schittenhelm  point  in  this 
direction.  Guanine,  a  cleavage-product  of  the  nucleic  acids,  is  first  of  alt 
changed  into  xanthine: 

HX— CO  HN— CO  HN— C 


NH2.C    C— NH  OC     C— NH  OC    C— NH 


\ 


CH- 


\ 


CH- 


\ 


CO 


// 

N— C— N  HN— C— N  HN— C— NH 

Guanine  Xanthine  Uric  acid 


This  transformation  takes  place  with  loss  of  ammonia;  a  hydrolytic 
ferment  is  active.  Now  for  the  first  time  the  molecule  is  ready  for  oxida- 
tion, and  uric  acid  is  formed  from  it.  The  latter  is  then  acted  upon  with 
the  aid  of  another  ferment  in  a  manner  unknown  to  us.  We  thus  see  that 
a  whole  chain  of  different  processes  is  necessary  in  order  to  completely 
consume  a  relatively  simple  substance,  a  purine  base. 

We  must  regard  the  breaking  down  of  the  amino  acids  as  taking  place 

1  See  Lecture  XIII,  p.  292. 


454  LECTURE  XIX. 

in  a  quite  similar  manner.  Here,  evidently,  first  of  all  the  NH2  group  is 
removed  by  the  action  of  a  hydrolytic  ferment,  and  then  combustion  takes 
place. 

The  fact  that  we  are  now  getting  closer  to  the  realization  of  the  actual 
conditions  is  shown  by  the  recent  investigations  of  Embden,  Salomon,  and 
Schmidt.1  They  conducted  through  the  liver  of  a  dog,  right  after  killing 
it,  blood  to  which  the  different  amino  acids  had  been  added,  and  found, 
for  example,  that  leucine  caused  a  considerable  increase  of  acetone  in  the 
circulation.  Shortly  previous  it  was  established  by  Embden  and  Kal- 
berlah  2  that  the  liver  normally  produced  acetone.  Now  all  of  the  amino 
acids  do  not  yield  acetone.  Thus,  for  example,  it  is  not  formed  from 
aminovaleric  acid,  although  a  glance  at  the  formulas  of  these  two  acids 
shows  they  are  closely  related  compounds: 

CH3      CH3  CH3    CH3 

\    /  \/ 

(r)    CH  (/?)  CH 

(/?)  CH2  (a)  CH  .  NH2 

(a)  CH  .  NH2  COOH 

COOH 

Leucine  Aminoisovaleric  acid 

Perhaps  the  different  behavior  of  these  two  amino  acids  gives  us  an 
indication  as  to  the  manner  in  which  at  least  a  part  of  the  decomposition 
products  of  albumin  is  acted  upon  in  the  tissues.  Embden  recalled  the 
observation  of  Knoop  3  that  aromatic  fatty  acids  were  decomposed  in  the 
animal  body  first,  so  that  there  was  a  cleavage  in  the  side-chain  between 
the  a  and  /?  carbon  atoms.  Thus  phenylbutyric  acid  was  first  changed 
into  phenylacetic  acid.  The  latter  then  appeared  as  phenaceturic  acid  in 
the  urine.  It  is  perfectly  possible  that  the  breaking  down  of  the  aliphatic 
fatty  acids  takes  place  in  the  same  way.  Thus  in  the  above  instance  we 
can  imagine  that  the  leucine  and  aminovaleric  acid  were  first  of  all  robbed 
of  the  amino  group.  From  the  former  isobutylacetic  acid  is  formed,  and 
from  the  latter  isovaleric  acid.  Then,  by  loss  of  carboxyl  and  oxidation, 
iso valeric  acid  is  formed  from  the  isobutylacetic  acid,  and  isobutyric 
acid  from  the  isovaleric  acid.  Next  cleavage  takes  place  between  the  a 
and  /?  carbon  atoms.  Now  if  these  ideas  are  correct,  we  must  expect  that 


1  Hofmeister's  Beitrage,  8,  Heft  3/4  (1906). 

2  Ibid. 

3  Der  Abbau  aromatischer  Fettsauren  im  Tierkorper.     Habil.-Schrift,  Freiburg  i.  B. 


1904. 


ANIMAL  OXIDATIONS.  455 

isobutyl  acetic  acid  itself  is  not  broken  down  into  acetone,  while  this  will 
be  the  case  with  iso valeric  acid,  as  the  following  formulas  show: 


CH3        CH3 


\    / 


H 


CH3      CH3 


CH3    CH3  \ 

§  \  /  CO 

(/?)  CH 


(a)  CH2  (a)  CH 


(a)  C] 


COOH 
Isobutylacetic  acid  Isovaleric  acid  Acetone 

Direct  experiment  confirms  this  explanation.  The  decomposition  of 
leucine,  therefore,  may  be  represented  as  taking  place  in  the  following 
stages : 

CH3   CH3         CH3  CH8 
\  /  \  /  CH3  CH3 

CH  CH  \  / 

| >    | >    CO 

CH2:  CH2 

CH  j  (NH2)       COOH 

COOH 

Leucine  Isovaleric   acid  Acetone 

In  place  of  the  isovaleric  acid,  naturally  the  corresponding  aldehyde  or 
alcohol  may  appear: 

CH3    CH3  CH3    CH3 

\    /  \    / 

CH  CH 

CH2  CH2 

I  I 

CHO  CH2OH 

Isovaleric  aldehyde  Isoamylalcohol 

We  have  intentionally  gone  into  this  hypothesis  at  length  in  order  to 
emphasize  the  complexity  of  such  a  process  in  contrast  to  the  simple  idea 
of  combustion  in  the  tissues  that  is  generally  assumed.  Many  observa- 
tions speak  for  the  above  conception  of  the  breaking  down  of  the  amino 
acids.  We  have  discussed  this  with  tyrosine  and  phenylalanine.  On  the 
other  hand,  we  must  admit  that  we  are  not  yet  able  to  understand  why 
the  animal  organism  can  split  off  a  carboxyl  group  from  leucine,  but  not 


456  LECTURE  XIX. 

from  isobutylacetic  acid.  There  seems  to  be  an  intimate  relation  to  the 
urea  formation.  The  NH2  and  CO  groups  leave  the  molecule  of  the  amino 
acid  at  one  time.  With  the  proof  of  the  acetone  formation  from  products 
obtained  from  albumin,  we  obtain  for  the  first  time  a  clear  idea  concerning 
the  utilization  of  the  carbon  chains  free  from  nitrogen  from  certain  amino 
acids.  We  learn  in  this  way  to  consider  the  formation  of  acetone  as  a 
normal  process,  it  being  an  intermediate  product  in  the  decomposition  of 
leucine.  One  source  of  acetone  is  thus  established.  Perhaps  from  this 
stage  in  the  breaking  down  of  the  amino  acids  we  can  trace  their  relation 
to  the  carbohydrates  and  fats. 

We  do  not  yet  know  how  the  preliminary  preparation  of  the  glucose 
molecule  for  oxidation  is  effected.  In  the  case  of  the  fatty  acids,  however, 
we  are  justified  in  assuming  that  oxidation  is  preceded  as  above  described 
by  a  cleavage  between  the  a  and  ft  carbon  atoms.  It  seems  probable  that 
the  eventual  oxidation  always  takes  place  with  products  having  but  few 
carbon  atoms  in  the  chain.  With  these  presumptions,  we  can  at  least 
draw  a  picture  of  the  oxidation  processes  in  the  animal  organism,  which 
will  at  least  not  contradict  any  known  facts.  The  cells  prepare  substances 
for  oxidation  as  they  require  energy.  They  cannot  effect  the  oxidation  of 
d-leucine,  for  example,  because  no  ferment  is  present  which  is  capable 
of  breaking  the  molecule  down  sufficiently  to  make  the  oxygen  accessible 
to  it.  The  cells  do  their  work  in  stages.  At  any  moment  the  decom- 
position may  be  stopped,  and  the  products  already  formed,  used  for  new 
syntheses.  They  do  not  decompose  suddenly.  We  cannot  by  any  means 
compare  the  oxidation  in  the  animal  organism  with  a  conflagration. 
Everything  is  regulated  to  the  most  minute  detail.  Cleavage  and  oxida- 
tion take  place  alternately,  so  that  the  cell  can  utilize  the  energy  it  obtains 
from  step  to  step,  and  only  in  this  way  is  it  possible  to  regulate  so  care- 
fully the  heat  supply. 

The  difficulties  which  are  met  with  in  attempting  to  explain  animal, 
as  well  as  vegetable,  oxidations,  have  led  to  various  hypotheses  which  depend 
upon  the  fact  that  the  difficultly  oxidizable  substances  are  made  capable 
of  taking  up  oxygen  directly  only  by  means  of  some  function  exerted  by 
the  protoplasm.  These  attempts  at  explanation,  however,  do  not  rest 
upon  any  experimental  basis.  They  are  far  in  advance  of  our  knowledge 
concerning  the  nature  of  the  cell-protoplasm.  It  is  for  this  reason  that  it- 
is  so  difficult  to  submit  them  to  experimental  proof.  O.  Loew  l  traces 
the  oxidation  to  the  unstable  condition  of  the  albuminoid  in  protoplasm. 
It  transfers  the  lively  movement  of  the  atoms  in  the  active  albumin  mole- 
cule to  the  oxygen  and  the  oxidizable  substance.  In  this  way  there  is  a 
loosening  up  of  the  molecule,  so  that  the  atom  of  oxygen  is  offered  a  point 


1  Ber.,  35,  2487  (1902). —  cf.  E.  Wolff:   Die  chemische  Energie  der  lebenden  Zellen. 
Munich,  1899. 


ANIMAL  OXIDATIONS.  457 

of  attack.  We  shall  not  enter  here  into  a  discussion  of  this  or  a  number  of 
similar  hypotheses.  It  may  be  merely  said  concerning  them  that  they 
are  not  very  helpful,  because  we  know  practically  nothing  concerning  the 
chemistry  of  the  protoplasm. 

Oxygen  has,  as  we  have  seen,  not  only  the  function  of  enabling  the 
organism  to  make  use  of  the  energy  stored  up  in  the  decomposition  products 
of  the  food,  but  it  also  serves  frequently  to  prevent  the  cells  from  suffering 
injury.  It  is  entirely  wrong  to  assume  that  oxygen,  after  it  once  enters 
into  reaction,  immediately  burns  up  the  substance  completely.  We  are 
certain  that  in  many  cases  only  a  partial  oxidation  takes  place;  i.e.,  the 
oxidation  takes  place  in  stages.  This  fact  also  precludes  any  simple 
explanation  of  animal  or  vegetable  oxidations.  The  cell  must  in  each 
individual  case  determine  the  degree  of  oxidation.  With  activating  of 
the  oxygen,  or  by  the  carrying  of  oxygen  by  means  of  a  peroxide  formation, 
the  course  of  oxidation  in  the  animal  tissues  is  by  no  means  explained. 
Exactly  as  the  chemist  may  choose  special  oxidizing  agents,  and,  by  estab- 
lishing the  conditions,  he  may  regulate  the  degree  of  oxidation,  so  in  the 
same  way  the  cell  is  capable  of  regulating  the  oxidation  according  to  its 
requirements.  Particularly  instructive  examples  are  shown  by  the 
behavior  of  certain  foreign  substances,  injurious  to  the  cells,  from  whose 
action  the  organism  protects  itself,  as  we  have  repeatedly  seen,  in  a  num- 
ber of  different  ways.  Rudolph  Cohn  l  has  shown  that  methylquinolin 
is  for  the  most  part  entirely  oxidized,  and  that  the  same  is  true  of 
o-nitrobenzaldehyde.2  With  santonin,3  Ci5Hi803,  on  the  other  hand,  the 
oxidation  is  not  carried  so  far  but  it  is  changed  into  oxysantonin,  CisHigO^ 
Ttie  animal  organism  prepares  a  large  number  of  such  substances  by 
coupling  them  with  certain  substances  such  as  sulphuric  acid,  glycocoll, 
glucuronic  acid,  and  urea.  The  first  two  of  these  substances  just  named 
come  from  albumin,  while  glucuronic  acid  results  from  carbohydrates. 
Sulphuric  acid  combines  with  a  great  many  substances  of  a  phenolic 
nature;  thus,  ordinary  phenol  when  introduced  into  the  body  leaves  it  in 
the  form  of  potassium  phenyl  sulphate:4 

C6H5OH  +  HO  .  SO3K  =  C6H5  .  O  .  S03K  +  H20. 

In  this  case,  which  was  first  noticed  and  is  the  simplest  of  all,  the 
coupling  takes  place  directly.  Sometimes,  however,  the  phenol  is  first 
oxidized.  In  this  way  quinol  is  formed,  which  then  unites  with  the 
sulphuric  acid:5 

HO  .  C6H5  +  0  =  HO  .  C6H4  .  OH 

HO  .  C6H4  .  OH  +  HO  .  S03K  =  HO  .  C6H4  .  O  .  SO3K  +  H20 

Z.  physiol.  Chem.  20,  210  (1895). 

Ibid.  17,  274  (1893). 

M.  Jafite:  ibid.  22,  538  (1896-97). 

Baumann  and  Herter:  ibid.  1,  244  (1877-78). 

Baumann  and  Preusse:  Z.  physiol.  Chem.  3,  156  (1879). 


458  LECTURE  XIX. 

Here,  the  object  of  the  oxidation  is  not  so  apparent,  because  the  combina- 
tion with  sulphuric  acid  takes  place  just  as  easily  before  as  after.  In  other 
cases  it  is  necessary  for  the  poisonous  substance  to  be  oxidized  first,  in 
order  to  make  it  possible  for  the  combination  with  sulphuric  acid  to  take 
place.  Thus  we  know  that  benzene  is  first  changed  into  phenol,1  indole 
to  indoxyl,  and  skatole  to  skatoxyl.2  Acetanilide  appears  in  the  urine  as 
p-aminophenol,  as  p-acetylaminophenol,  and  as  the  anhydride  of  hydroxy- 
phenylcarbamic  acid  partly  united  with  sulphuric  acid  and  in  part  with 
glucuronic  acid.3  In  the  group  of  glycocoll  conjugates  we  have  xylene 
converted  to  toluic  acid : 4 

CH3  .  C6H4  .  CH3  +  3  O  =  CH3  .  C6H4  .  COOH  +  H2O. 

Mesitylene  is  changed  into  mesitylenic  acid,5  and  cymene  to  cumic  acid.8 
For  conjugation  with  glucuronic  acid,  similarly,  the  cells  act  upon  poi- 
sonous substances  in  various  ways.     Thus,  for  example,   o-nitrotoluene 
is  changed  to  nitrobenzyl  alcohol,  which  then  unites  with  glucuronic  acid : 7 

N02  .  C6H4  .  CH3  +  0  =  N02  .  C6H4  .  CH2OH 
N02  .  C6H4  .  CH2OH  +  C6H1007  =  NO2  .  C6H4  .  CH2O  .  C6H906  +  H2O 8 

We  have  distinguished  in  the  case  of  all  the  organic  foodstuffs  two 
different  functions  which  they  have  in  the  cells  of  the  animal  organism. 
On  the  one  hand  they  may  serve  as  sources  of  energy,  while  on  the  other 
hand  they  may  serve  as  material  for  the  construction  of  new  tissue.  Like- 
wise it  is  possible  for  the  inorganic  salts  to  develop  energy  by  physical 
methods;  but  their  chief  use,  however,  is  in  the  formation  of  new  material, 
whether  it  be  due  to  an  intimate  union  with  organic  material,  or  whether 
the  unchanged  inorganic  salt  is  in  an  indispensable  constituent  of  the  cells 
and  that  their  activity  only  results  from  its  presence.  Of  oxygen  we 
have  spoken  of  but  one  function,  that  of  making  energy  available.  The 
question  naturally  arises  whether  oxygen  itself  is  not  used  as  building 
material  in  the  construction  of  new  cells?  There  are,  as  a  matter  of  fact, 
certain  observations  which  seem  to  indicate  that  the  entrance  of  oxygen 
into  the  contents  of  the  cell,  the  protoplasm,  plays  an  important  part  in  the 
excitability  of  the  cell.  Kuhne  recognized  the  fact  that  the  protoplasm 
of  Amcebce,  Myxomycetes,  and  the  filament  hairs  of  Tradescantia,  lost  its 

1  Schultzen,  Naunyn,  and  Munk:  Du  Bois'  Arch.  1876,  340,  and  I.  Munk:  Pfliiger's 
Arch.  12,  142  and  148  (1876). 

3  Baumann  and  Brieger:  Z.  physiol.  Chem.  3,  254  (1879). 

3  Jaffe"  and  Hilbert:  Z.  physiol.  Chem.  12,  295  (1888).     Morner:  ibid.  13,  12  (1889). 

4  Schultzen  and  Naunyn:  Du  Bois'  Arch.  1876,  353. 

5  Nencki:  Arch,  exper.  Path.  Pharm.  1,  420  (1873). 
0  Nencki  and  Ziegler:  Ber.  5,  749  (1872). 

'  Jaffe":  Z.  physiol.  Chem.  2,  47  (1878-79). 

8  Cf.  Fromm:  Die  chemischen  Schutzmittel  des  Tierkorpers  bei  Vergiftungen.  Strass- 
burg,  1903. 


ANIMAL  OXIDATIONS.  459 

motion  and  excitability  when  in  hydrogen,  but  became  active  when  placed 
in  oxygen  again.1  Max  Verworn  2  confirmed  these  observations  on  Rhizo- 
poda  of  the  Red  Sea.  It  is  difficult  to  perform  such  experiments  upon 
the  cells  of  more  highly  organized  forms,  because  they  contain  combined 
oxygen,  which  enables  the  muscles,  for  example,  to  work  for  some  time 
with  production  of  carbon  dioxide  in  an  atmosphere  devoid  of  oxygen.3 
If,  however,  a  muscle  is  allowed  to  act  until  exhausted,  it  is  found  that  it 
becomes  active  again,  only  when  provided  with  a  new  supply  of  oxygen. 
Such  relations  have  been  established  for  the  muscles  of  the  heart.  Finally, 
as  is  well  known,  E.  Pfluger  4  has  shown  that  frogs  which  were  kept  at  low 
temperatures  in  pure  nitrogen  gradually  lost  their  excitability,  but  regained 
it  again,  even  after  remaining  twenty-four  hours  in  this  atmosphere,  on 
being  placed  in  the  air  once  more.  We  have  to  thank  Max  Verworn  5  for 
a  very  interesting  experiment  in  this  direction.  He  replaced  all  the  blood 
in  a  frog  with  a  physiological  salt  solution,  containing  0 . 6  to  0 . 8  per  cent. 
The  salt  solution  was  free  from  oxygen.  If  now  by  injection  of  strychnine 
the  ganglion  cells  of  the  spinal  medulla  were  excited,  as  much  as  possible, 
then  the  neurons  worked  (under  the  constant  streaming  of  salt  solution) 
until  finally  all  the  oxygen  stores  had  been  exhausted.  In  less  than  an 
hour  the  reflex  excitability  is  lost.  After  this  the  strongest  irritation 
produces  no  reflex  action.  If  now  a  salt  solution  containing  dissolved 
oxygen  is  caused  to  circulate  through  the  blood-vessels,  the  frog  revives 
within  a  few  minutes,  and  again  shows  the  increased  excitability  caused  by 
the  strychnine.  Every  time  the  circulation  of  the  salt  solution  containing 
the  dissolved  oxygen  is  stopped,  the  ganglion  cells  at  once  become  unex- 
citable.  The  experiment  may  be  repeated  over  and  over  again,  with  the 
same  frog.  Since  in  this  experiment  the  ganglion  cells  are  not  provided 
with  fresh  nutriment,  it  is  not  possible  to  explain  the  action  of  oxygen  by 
the  simple  assumption  that  its  absence  prevents  the  complete  combustion 
of  the  decomposition  products,  while  at  the  moment  oxygen  enters  the 
energy  becomes  available  to  the  cells.  To  be  sure,  we  are  quite  ignorant 
concerning  the  work  of  the  ganglion  cells.  We  do  not  know  what  their 
expenditure  of  energy  is.  It  may  be  very  small.  If  we  remember  that 
the  oxygen  of  itself  is  not  able  to  attack  the  decomposition  products  from 
the  food,  but  requires  assistance  on  the  part  of  the  cell  before  the  oxygen 
can  find  a  point  of  attack,  then  it  is  not  perfectly  clear  why  the  oxygen 

1  Untersuchungen  iiber  das  Protoplasma  und  die  Kontraktilitat,  Leipsic,  1864.     Z. 
Biol:  36,  425  (1898). 

2  Die  Bewegung  der  lebenden  Substanz.     Jena,  1892.     Cf .  also  Die  Biogenhypothese. 
Jena,  1903. 

3  Kronecker:    Ueber   die   Ermiidung   und   Erholung    der   quergestreiften   Muskeln 
(1871).     Joteyko:  La  fatigue  et  la  respiration  e'le'mentaire  du  muscle.     Paris,  1896. 

4  Pfliiger's  Arch.  10,  251  (1875). 

•  Arch.  Anat.  Physiol.   1900,  Suppl.   152. 


460  LECTURE  XIX. 

should  nevertheless  revive  the  excitability  as  shown  by  the  oxidation  and 
development  of  energy.  It  is  not  necessary  in  every  case  that  all  of  the 
hydrolytic  products  should  be  consumed.  The  cell  is  able  to  be  very  eco- 
nomical with  its  fuel.  On  the  other  hand,  it  is  perfectly  possible  that 
oxygen  under  these  conditions  may  play  an  unusual  part  in  the  mechanism 
of  the  cell  work.  We  cannot  work  out  such  problems  successfully  until  we 
have  a  more  accurate  insight  into  the  oxidations  of  the  cells  and  tissues, 
and  as  long  as  our  physical  and  chemical  conceptions  of  the  proto- 
plasm are  still  vague.  We-  meet  here  with  a  great  many  riddles,  which 
for  the  present  are  unanswerable  —  for  the  present,  we  say,  because 
we  can  scarcely  doubt  that  before  long  the  rapid  progress  of  biological 
chemistry  will  bring  clearness  to  our  conception  of  these  complicated 
processes.  An  advance  in  the  science  is  only  possible,  however,  when  it 
is  clearly  and  sharply  recognized  where  the  facts  end  and  the  hypotheses 
begin.  We  can  only  build  upon  the  former,  and  the  latter  serve  merely 
as  a  framework  which  is  of  value  only  when  it  is  possible  to  replace  the 
fantasies  of  the  brain  little  by  little  with  facts  verified  by  experimentation. 


LECTURE  XX. 
FERMENTS.1 

WE  have  repeatedly  encountered  the  conception  ferment  in  our  discussion 
of  the  transformations  of  our  organic  foodstuffs  in  the  alimentary  tract  and 
in  the  tissues.  We  have  seen  that  the  proteins  are  subjected  to  the  action 
of  pepsin-hydrochloric  acid  in  the  stomach,  and  to  trypsin  in  the  intestine, 
and  that  the  ferment  diastase  decomposes  almost  completely  the  compli- 
cated carbohydrates  in  the  mouth,  and  to  a  much  greater  extent  in  the 
intestine,  while  the  ferment  lipase  hydrolyzes  the  fats  in  the  stomach  and 
in  the  intestine.  The  ferments  also  participate  largely  in  tissue-metabolism. 
We  meet  them  wherever  life  processes  occur.  They  are  distributed  as. 
widely  in  the  vegetable  world  as  in  the  animal  kingdom.  Fermentation 
phenomena  are  so  striking  that  they  were  recognized  in  very  early  times, 
alcoholic  fermentation  first  attracting  attention.  Spallanzani,2  in  1785, 
showed  the  solvent  action  of  the  gastric  juice  on  protein,  while  Kirchhoff,8 
a  few  years  later,  called  attention  to  the  fact  that  fresh  gluten  will  saccharify 
starch.  Liebig  and  Wohler  4  discovered  emulsin,  which  splits  amygdalin, 
and  Bussy  identified  myrosin.  If  to  these  we  add  the  discovery  of  the 
oxidases  by  Schonbein,  and  the  preparation  by  Berthelot  of  yeast  invertin, 
the  action  of  which  upon  cane-sugar  was  known  even  to  Mitscherlich,  we 
shall  include  practically  all  of  the  most  important  fermentation  phenomena 
known  at  the  end  of  the  nineteenth  century.  It  is  only  during  the  last 
few  decades  that  we  have  really  made  any  great  progress  in  our  knowledge 
concerning  the  various  kinds  of  ferments. 

Before  discussing  the  nature  of  the  ferments  and  their  action,  we  must 
state  in  advance  that  we  have  not  yet  succeeded  in  characterizing  the 
ferments  as  chemical  individuals.  We  know  practically  nothing  concern- 


1  In  order  to  avoid  confusion,  we  shall  employ  the  term  "ferment"  in  its  original  sense, 
—  something  which  causes  fermentation.    It  has  been  customary  to  distinguish  between 
organized  ferments  and  unorganized  ferments,  or  enzymes;  but  it  will  be  shown  in  the 
following  pages  that  such  a  distinction  was  based  upon  a  misapprehension.     For  a  more 
complete   orientation   concerning  ferments   and   fermentations,    consult   J.    Reynolds 
Green:  The  Enzymes;  and  Carl  Oppenheimer:   Die  Fermente  und  ihre  Wirkungen, 
Leipzig,  1903. 

2  Lazz.  Spallanzani:  Versuche  iiber  d.  Verdauungsgeschaft.     Leipzig  (1785). 

3  Schweiger's  Journal,  14,  389  (1815).     Dubrunfaut:  Soc.  Agricult.  Paris  (1823.) 

4  Poggendorff's  Ann.  41,  345  (1837). 

461 


462  LECTURE  XX. 

ing  their  constitution;  in  fact,  we  do  not  even  know  to  what  class  of  com- 
pounds they  belong,  or  whether  they  form  a  class  of  their  own.  It  has 
always  been  customary  to  classify  the  ferments  with  the  proteins.  There 
were  various  reasons  for  this  assumption.  .Until  recently,  the  composition 
and  structure  of  the  proteins  were  as  little  understood  as  that  of  the  fer- 
ments themselves,  while  the  fats  and  carbohydrates  had  been  thoroughly 
investigated.  Our  knowledge  concerning  the  compositions  of  the  latter 
compounds  makes  it  seem  improbable  that  the  ferments  belong  to  either 
of  these  two  classes.  The  proteins,  on  the  other  hand,  with  their  compli- 
cated structure  and  their  various  elementary  components,  are  far  more 
likely  to  include  the  ferments,  endowed  as  they  are  with  such  numerous 
and  finely  differentiated  functions.  We  are,  however,  at  present  unable 
with  our  limited  knowledge  of  the  proteins  to  draw  any  conclusions  regard- 
ing the  structure  of  the  ferments.  It  is  often  stated,  in  order  to  show  their 
albuminous  nature,  that  the  pure  ferments  give  the  reactions  of  the  proteins. 
Unfortunately,  we  have  not  yet  succeeded  in  isolating  any  ferment  in  a 
pure  state.  In  the  first  place,  we  have  absolutely  no  criterion  of  purity. 
Pekelharing  1  and  M.  Nencki  and  N.  Sieber 2  have  recently  attempted  to 
purify  the  pepsin  of  the  stomach,  the  former  claiming  to  have  accomplished 
the  feat.  Until  we  have  some  clear  conception  of  the  composition  of  the 
ferments,  it  is  of  little  avail  to  discuss  their  nature.  We  are  not  even  jus- 
tified in  assuming  that  the  ferments  belong  to  a  single  class  of  compounds. 
It  is  possible  that  the  fats  and  carbohydrates  also  take  part  in  their  com- 
position. For  the  present  we  are  unable  to  state  that  the  identification 
of  this  or  that  compound  actually  indicates  that  it  belongs  to  the  ferment. 
Such  substance  may  simply  be  dragged  down  mechanically  in  the  process 
of  isolating  the  ferment.  All  of  our  methods  for  the  preparation  of  the 
ferments  are  such  that  this  assumption  is  justified. 

The  ferments  are  unquestionably  closely  related  to  the  life-processes  of 
the  cells.  They  are  to  be  directly  looked  upon  as  their  secretion  products. 
The  ferments,  until  recently,  were  sharply  divided  into  two  groups,  the 
organized  ferments,  or  simply  ferments,  and  the  unorganized  ferments,  or 
enzymes.  Those  which  were  only  active  in  the  presence  of  the  living  cell 
were  included  with  the  former,  while  those  which  acted  independently 
of  the  cells,  such  as  diastase,  pepsin,  trypsin,  etc.,  were  placed  in  the 
latter  class.  The  designation  organized  or  unorganized,  was  to  give  the 
impression  that,  in  the  first  case,  the  protoplasm  of  the  cell  was  absolutely 
necessary  for  performing  the  function  of  the  ferment,  while  the  unorgan- 
ized ferments  were  capable  of  accomplishing  their  work  without  any 
further  assistance.  It  is  true,  however,  that  we  are  not  at  all  acquainted 

1  Z.  physiol.  Chem.  22,  233  (1896/97);  36,  8  (1902). 
3  Ibid.  32,  291  (1901). 


FERMENTS.  463 

with  the  ferments  as  such.  We  only  recognize  their  presence  by  their 
activity,  which  alone  distinguishes  them.  This,  in  principle,  is  the  same 
for  the  organized  as  the  unorganized  ferments.  The  cell  produces  fer- 
ments, which  it  requires  for  its  own  economy,  and  others,  which  it 
sends  out,  to  produce  results  that  will  directly  or  indirectly  benefit 
it.  The  assumption  that  the  ferments  which  were  active  when  away 
from  the  cells  had  other  powers  than  those  remaining  in  the  cell  was 
entirely  arbitrary.  Especially,  as  it  had  never  been  found  possible  to 
isolate  such  a  ferment,  i.e.,  an  organized  one,  from  the  cell,  and  bring 
it  into  activity  in  its  isolated  form,  there  was  no  logical  ground  for 
sharply  differentiating  between  organized  and  unorganized  ferments.  We 
know  that  all  ferments  are  more  or  less  subject  to  external  influences. 
Definite  conditions  must  be  fulfilled  to  develop  their  action.  Thus,  for 
most  ferments  the  optimum  temperature  lies  between  35°  and  45°  C.  The 
reaction  of  the  medium  in  which  the  development  occurs  is  also  of  con- 
siderable importance.  Pepsin,  for  instance,  requires  a  hydrochloric  acid 
solution,  while  trypsin  acts  in  a  neutral  or  faintly  alkaline  medium.  When 
we  find,  furthermore,  that  the  formation  of  ferments  by  the  cells  and  their 
activation  has  recently  been  recognized  as  a  complicated  process  dependent 
upon  certain  influences,  we  can  readily  understand  why  a  definite  ferment 
ceases  to  act  when  it  has  been  torn  away  from  its  original  sphere  of  activity. 
We  do  not  know  how  many  ferments  the  individual  cell  contains.  It  is  very 
probable  that  the  ferments  are  first  produced  in  an  inactive  form,  as  zymo- 
gens,  and  only  activated  by  the  cells  when  they  are  needed.  It  is  also 
possible  that  the  individual  ferments  are  very  closely  related  in  their  work, 
i.e.,  they  act  together,  and  assist  one  another.  We  also  know  that  many 
ferments  have  their  action  restricted  by  the  decomposition  products  which 
they  themselves  produce.  Such  an  accumulation  of  cleavage-products 
would  hardly  occur  in  the  cell  itself,  for  they  are  quickly  acted  upon  by 
other  ferments.  If,  however,  such  a  cell-ferment  were  forced  to  develop 
its  activity  outside  of  the  cell,  we  can  easily  see  how  it  might  soon  cease 
to  be  efficient. 

The  discovery  by  E.  Buchner,1  that  it  is  possible  to  isolate  and  separate 
from  the  cell  structure,  the  ferment  from  yeast  which  converts  sugar  into 
carbon  dioxide  and  alcohol,  proved  for  the  first  time  that  the  similar  effects 
of  ferment  and  cell  activities  are  evidently  due  to  the  fact  that  the  same 
agents  are  at  work  in  each  case.  This  discovery,  which  does  away  with 
our  previous  distinction  of  ferment  and  enzyme,  was  carried  out  in  the 
following  manner:  Buchner 2  ground  a  kilogram  of  yeast  with  a  kilogram  of 
quartz-sand  and  2.3  kilograms  of  infusorial  earth.  His  purpose  was  to 

1  E.  Buchner,  H.  Buchner  and  M.  Hahn:   Die  Zymasegarung.     Miinchen  &  Berlin 
(1903). 

2  Albert  and  Buchner:  Ber.  33,  266,  971  (1900) 


464  LECTURE  XX. 

destroy  the  cell  walls  and  permit  the  release  of  the  cell  protoplasm.  The 
whole  mass  was  then  subjected  to  a  pressure  of  from  400  to  500  atmospheres. 
The  expressed  liquor  had  a  slightly  acid  reaction,  it  was  weakly  opalescent, 
and  contained  albuminous  material.  It  contained  the  active  principle 
which  converts  sugar  into  carbon  dioxide  and  alcohol.  Buchner  calls  it 
zymase.  It  is  very  unstable,  the  filtered  juice  losing  its  activity  after  a 
few  days.  The  zymase  is  destroyed  at  40-50  degrees.  It  can  be  dried, 
and  in  this  form  keeps  much  better.  It  can  also  be  precipitated  from  its 
solution  by  the  addition  of  alcohol  or  ether,1  by  which  we  obtain  a  white 
powder,  only  partially  soluble  in  water,  but  more  so  in  glycerol.2  The  glycerol 
extract  is  very  active.  Zymase  has  recently  been  obtained  directly  from 
the  yeast  cell,  by  first  killing  the  cell  by  contact  with  ether-alcohol  or  ether- 
acetone.  The  zymase  remains  active  after  this  treatment.  Such  prepa- 
rations, which  may  be  kept  for  a  considerable  time,  are  called  preserved 
yeasts. 

A  vigorous  objection  was  quickly  raised  against  classifying  zymase  with 
the  unorganized  ferments.  Special  attention  was  called  to  the  fact  that 
the  zymase  in  the  expressed  liquor  was  active  only  for  a  short  time.  This 
was  explained  on  the  assumption  that  the  zymase  must  be  looked  upon  as 
a  part  of  the  protoplasm,  which,  on  being  separated  from  the  remainder 
of  the  cell  contents,  possessed  only  a  short  period  of  activity.  Quite  aside 
from  the  fact  that  it  is  now  possible  to  prepare  zymase  with  better  keep- 
ing qualities,  this  objection  is  met  by  what  has  been  said  above  con- 
cerning the  cell  ferments  and  their  dependence  upon  their  environment 
and  other  ferments,  etc.  The  expressed  liquor  contains  not  only  zymase, 
but  also  other  ferments,  of  which  one,  the  so-called  endotryptase,  quickly 
destroys  zymase.  Zymase  is,  in  fact,  very  susceptible  towards  proteolytic 
ferments.  It  is  also  perfectly  clear,  that  those  ferments  contained  within 
the  cells  would  naturally  be  much  more  susceptible  to  unusual  conditions 
than  those  other  ferments  which  are  given  off  by  the  cells,  and  are  undoubt- 
edly better  equipped  for  battle  with  the  outer  world. 

That,  moreover,  fermentation  is  not  necessarily  dependent  upon  living 
cells,  was  already  indicated  by  an  observation  of  Fiechter,3  who  showed 
that  hydrocyanic  acid  completely  arrests  the  vital  processes  of  yeast,  but 
does  not  at  once  stop  the  fermentation. 

The  tracing  of  the  conversion  of  glucose  to  alcohol  to  a  fermentation 
process  is  not  the  only  case  where  a  so-called  "  life-process  "  has  been 
proved  to  take  place  independently  of  the  living  organism.  Zymase,  like 
all  other  ferments,  must  be  regarded  as  a  product  resulting  from  the  life- 
processes  of  the  cells.  The  enigma  of  their  formation  and  existence  still 

1  R.  Albert:  Ibid.  33,  2775  (1900). 

2  R.  Albert:  Ibid.  35,  2375  (1902). 

3  Wirkung  der  Blausaure.     Diss.  Basel  (1875). 


FERMENTS.  465 

remains  even  after  they  have  been  isolated.  E.  Buchner  and  J.  Meisen- 
heimer 1  have  recently  succeeded,  by  using  the  acetone  method  of  procedure, 
in  obtaining  a  preparation  from  Bacillus  Delbrilcki  (Leichmann)  which 
produced  lactic  acid  from  grape-sugar  in  the  same  manner  as  the  bacillus 
itself.  They  also  obtained  preserved  preparations  from  beer-acetic-acid 
bacteria,  using  the  acetone  method,  which  converted  alcohol  into  acetic 
acid. 

There  is  evidently  no  sharp  dividing  line  between  the  individual  cell- 
ferments  and  the  free,  unorganized  ferments.  There  are  some  which  are 
undoubtedly  closely  related  to  the  cell  contents,  and  others  which  are  more 
loosely  united  to  the  cell  contents  than  is  the  case  with  yeast  zymase,  and 
can  consequently  be  more  easily  isolated  from  the  cells.  Finally,  there 
are  those  ferments  which  are  given  off  by  the  cells  themselves. 

The  secretion  by  the  gland  cells  can  be  followed  directly  by  histological 
methods,  and  it  is  quite  possible  that  certain  visible  changes  of  the  gland 
cells  may  be  related  to  the  formation  of  ferments.  The  morphological 
changes  in  the  cells  of  the  pancreas  have  been  studied  in  particular. 
Although  the  cells  of  the  resting  gland  are  but  slightly  distinguishable 
from  one  another,  we  observe  sharp,  generally  double,  boundary  lines,  at 
the  instant  when  activity  begins.  The  cells,  and  likewise  the  gland  itself, 
change  their  form.  They  become  filled  out.  We  observe  kernels,  which 
belong  to  the  inner  zone  of  the  cells,  migrate  towards  the  lumen  of  the 
gland,  become  smaller,  and  finally  disappear.  The  cell-changes  in  the 
salivary  glands,  especially  the  parotid,  have  been  very  carefully  studied 
during  their  activity.  The  cells  decrease  in  size  during  secretion.  The 
nucleus,  usually  angular,  becomes  rounded,  and  shows  granules  very 
distinctly.  The  clear,  homogeneous  substance,  predominating  when  at 
rest,  decreases  in  amount,  while  the  granular  substance  increases.  It  is 
difficult  to  say  whether  the  gland  cells  give  up  a  part  of  their  protoplasm 
during  the  secretion,  or  if,  as  seems  more  probable,  products  are  formed 
which  then  go  over  into  the  secretion.  It  is  possible  that  the  granules 
mentioned  possess  some  relation  to  the  formation  of  ferments. 

The  fact  that  a  great  many  ferments  are  not  secreted  as  such,  but  in  an 
inactive  form,  must  be  looked  upon  as  of  the  greatest  significance  for  the 
conception  of  fermentation  processes.  The  activation  results  from  the 
influence  of  another  substance  which  is  often  produced  at  another  place, 
and  does  not  necessarily  form  a  part  of  the  ferment,  and  may  even  be  of 
simpler  composition.  We  call  the  secreted  inactive  ferment  a  zymogen  or 
proferment.  Thus,  we  know  that  the  pepsin  zymogen  is  activated  by 
hydrochloric  acid,  while  the  trypsin  zymogen  requires  the  enterokinase. 
Undoubtedly  there  are  innumerable  other  ferments  which  are  secreted  in 

1  Ber.  36,  634  (1903). 


466  LECTURE  XX. 

an  inactive  form,  both  in  the  animal  and  the  vegetable  organisms.  The 
cell  is  thus  enabled  to  regulate  its  entire  metabolism.  It  only  activates 
the  ferments  when  it  needs  them.  The  way  this  activating  process  is 
brought  about  is  still  unknown.  We  can  imagine  that  the  activating  agent 
splits  the  zymogen,  perhaps  forming  a  smaller  molecule,  or  possibly  it 
breaks  open  an  anhydride  or  lactone  formation,  thus  permitting  those 
groups  to  act  which  are  able  to  force  an  entrance  into  the  material  to  be 
acted  upon. 

Although  the  discovery  of  the  wide  distribution  of  ferments  and  their 
action,  and  the  knowledge  that  the  cell-functions  in  a  narrow  sense 
correspond  to  such  processes,  opens  up  new  paths  and  points  of  view  for 
Biology,  although  on  the  other  hand  we  must  not  forget  that  the  great 
mystery  of  cell-life  remains  unsolved.  The  living  cell  produces  the  fer- 
ment; of  this  there  is  no  doubt.  At  this  point  we  encounter  the  most 
important  problems  of  the  whole  subject  of  biology.  We  should  be  mak- 
ing a  great  mistake  if  we  were  to  say  that  the  knowledge  of  fermen- 
tation reactions  has  solved  the  mystery  of  life.  It  has,  to  be  sure,  cleared 
up  many  processes  which  were  previously  obscure,  and  has  given  us  a 
very  much  clearer  conception  of  the  whole  subject  of  metabolism.  If, 
however,  we  turn  from  fermentation  to  the  ferments  themselves,  we  imme- 
diately touch  the  unknown.  The  ferments  point  to  the  cells  and  their 
metabolism  and  functions.  It  would  be  equally  short-sighted,  and  lead  to 
a  complete  misunderstanding  of  biological  chemistry,  if  we  were  to  consider 
a  solution  of  this  mystery  as  impossible,  and  content  ourselves  with  an 
undefinable  conception  of  "  the  vital  force."  There  can  be  no  doubt  that 
the  rapidly  advancing  biological  science  will  attack  the  problem  of  the 
chemistry  of  the  ferments  as  soon  as  the  time  is  ripe.  The  mystery  of 
the  ferments  will  disappear  as  soon  as  we  are  able  to  replace  our  conception 
with  a  chemical  representation.  In  the  attempt  to  explain  biological 
processes  more  and  more  in  accordance  with  the  laws  governing  the  exact 
sciences,  it  is  never  advisable  to  wipe  away  the  boundary  between  the 
knowledge  gained  by  exact  methods  and  what  has  been  established  by 
mere  hypotheses.  The  more  sharply  we  separate  the  known  from  the 
unknown,  the  freer  will  be  the  development  of  our  further  investi- 
gations, and  the  more  independently  will  the  facts,  as  such,  speak  for 
themselves. 

Let  us  review  what  we  know  about  the  nature  of  fermentation  from  this 
point  of  view.  As  a  result  of  our  unfamiliarity  with  the  chemical  nature 
of  the  ferments,  we  are  deprived  of  one  of  the  most  important  supports 
in  any  exact  study  concerning  them,  and  are  temporarily  restricted  to 
hypotheses  in  explaining  their  manner  of  action.  The  number  of  ferments 
is  very  large.  We  can  here  only  refer  to  such  as  are  in  harmony  with  experi- 
mental facts. 


FERMENTS.  467 

Let  us,  at  the  start,  ascertain  what  are  the  characteristics  of  the  ferments 
themselves. 

The  first  remarkable  fact  is  that  they  are  never  found  as  end-products 
of  the  reactions.  They  remain  unchanged.  The  smallest  amounts 
suffice  to  repeat  the  same  reaction  a  countless  number  of  times.  Thus, 
invertase  is  capable  of  inverting  at  least  200,000  times  its  own  weight  of 
cane-sugar,1  rennin  at  least  400,000  parts  of  casein. 

The  action  of  the  ferments  should,  theoretically,  be  an  unlimited  one. 
There  is,  however,  as  has  been  shown  in  the  case  of  rennin,2  a  gradual  loss 
of  efficiency.  This  is  not,  however,  caused  by  the  reaction  itself.  We  also 
know,  as  we  shall  see  more  in  detail  later,  that  the  ferments  have  a  specific 
action,  i.e.,  trypsin,  for  instance,  only  attacks  protein,  and  never  the  car- 
bohydrates or  fats;  while  diastase  never  acts  on  albumin,  nor  does  lipase 
ever  have  any  effect  upon  carbohydrates  or  albumins.  We  know,  further- 
more, that  the  ferments  are  produced  by  living  cells,  some  of  them  being 
given  up  by  the  cells,  while  others  are  retained  in  the  cell  itself.  Finally, 
we  are,  in  most  cases,  acquainted  with  the  end-products,  and  are  thus  able 
to  draw  conclusions  regarding  the  nature  of  most  reactions  which  they 
cause  to  take  place. 

Now  there  are  in  inorganic  chemistry  a  great  many  facts  known,  which 
remind  us  very  much  of  the  behavior  of  ferments.  We  refer  to  those 
chemical  processes  in  which  the  presence  of  a  minimum  amount  of  a 
given  substance  is  sufficient  to  produce  a  marked  acceleration.  We 
speak  in  such  cases  of  catalyzers,  and  call  the  whole  process  catalysis,  or 
one  of  contact  action.  Ostwald 3  defines  catalysis  as  an  acceleration  of  a 
slow  chemical  change  brought  about  by  the  aid  of  a  foreign  substance.  Accord- 
ing to  this  definition,  the  reaction  in  question  is  not  started  by  the  cata- 
lyzer, but  whereas  it  takes  place  very  slowly  of  itself  —  perhaps  even  to 
an  imperceptible  extent  —  the  rate  of  change  is  accelerated  by  the  presence 
of  a  specific  substance.  In  support  of  this  assumption  we  have  the  fact 
that  increasing  the  amount  of  the  catalyzer  causes  further  acceleration  of 
the  catalysis.  If  the  process  served  merely  to  start  the  chemical  change, 
we  should  hardly  expect  that  the  amount  of  catalyzer  present  would  have 
any  influence,  and  at  all  events  the  speed  of  the  reaction  would  be  inde- 
pendent of  the  amount  of  contact  substance  present.  We  shall  subse- 
quently come  back  to  this  definition.  We  are  interested  here  in  the  simi- 
larity between  these  contact  substances  and  the  ferments.  One  of  the 
chief  common  characteristics  is  the  fact  that  neither  appears  among  the 


1  J.  Chem.  Soc.  Trans.  57,  834  (1890). 

2  Reichel  and  Spiro:  Hofmeister's  Beitrage,  6,  68  (1904),  and  7,  479  (1905). 

3  Grundriss  der  allgemeinen  Chemie,  3d  ed.  (1889),  p.  514.  Ueber  Katalyse.  Lecture. 
Hirzel.  Leipzig  (1902).    Compare  also,  G.  Bredig:  Die  Elemente  der  chemischen  Kinetik, 
etc.,  Ergeb.  Physiol.  (Asher  and  Spiro)  1,  134  (1902). 


468  LECTURE  XX. 

end-products  of  the  reaction,  and  both  are  effective  when  present  in  very 
minute  quantities.  Thus,  a  very  small  amount  of  nitrous  acid  is  sufficient 
to  convert  relatively  large  quantities  of  sulphur  dioxide  and  atmospheric 
oxygen  into  sulphuric  acid.  To.^znr  to  ^o^tfuo  milligram  of  colloidal 
platinum  or  manganese  dioxide,  or  ^.TTOO  milligram  of  gold,  will  cause 
the  decomposition  of  more  than  one  million  times  as  much  hydrogen 
peroxide.  Ernst 1  has  shown  that  TV  milligram  of  colloidal  platinum 
will  catalyze  50,000  times  as  much  oxyhydrogen  gas  without  losing  any 
of'  its  efficiency.  It  is  of  great  significance  for  the  conception  of  the 
action  of  catalyzers  to  know  that  there  are  substances  which  have  the 
opposite  effect,  and  retard  reactions  which  are  already  in  progress.  Bredig  2 
calls  these  negative  catalyzers.  Thus,  we  know  that  traces  of  ethylene, 
alcohol,  ether,  oil  of  turpentine,  and  ethyl  iodide  will  tend  to  prevent  the 
oxidation  of  phosphorus.3  Bigelow4  for  instance,  has  shown  that  the 
presence  of  0.000,0014  gram  of  mannitol  per  cubic  centimeter  will  reduce 
the  rate  of  the  oxidation  of  800  times  as  much  sodium  sulphite  in  aqueous 
solution  to  one-half  its  former  value.  On  the  other  hand,  we  also  know  of 
substances  which  will  directly  prevent  catalysis.  These  are  known  as 
anti-catalyzers  or  paralyzers.  As  an  example  of  this  may  be  mentioned, 
that  0.000,000,001  gram  of  hydrocyanic  acid  per  cubic  centimeter 
will  reduce  the  catalytic  effect  of  0.000,006  gram  of  colloidal  plati- 
num in  the  decomposition  of  hydrogen  peroxide  to  one-half  its  original 
value. 

Not  only  do  we  have  the  above  analogies  between  the  ferments  and 
catalyzers,  but  there  are  other  similarities,  such  as  the  effect  of  external 
conditions  upon  their  activity,  e.g.  temperature,  etc.  Certain  laws  have 
also  been  worked  out  showing  how  the  rate  of  the  reaction  depends  upon 
the  amount  of  ferment  present  and  upon  the  temperature,  etc.,  and  these 
relations  illustrate  the  analogy  between  the  ferments  and  the  above- 
mentioned  catalyzers.  It  would  be  beyond  the  scope  of  these  lectures  to 
dwell  longer  upon  these  interesting  observations.  We  can  abandon  the 
subject  the  more  readily  because  if  we  were  to  attempt  to  apply  these 
principles  to  the  processes  in  the  animal  and  vegetable  organisms,  it  would 
further  our  insight  into  the  cell  processes  but  little.  We  must  not  be 
deceived  by  the  little  knowledge  we  have  gained  regarding  catalysis,  for, 
generally  speaking,  we  know  nothing  at  all  concerning  the  way  in  which 
the  catalyzers  act.  We  know  merely  that  their  presence  is  necessary. 
We  must  admit  that  the  relations  between  catalyzers  and  ferments  are 
to  be  regarded  only  as  analogies,  there  being  no  proof  that  their  actions 

1  Z.  physikal.  Chem.  37,  448,  454  (1901). 

2  Bredig  and  v.  Berneck:  Ibid.  31,  324  (1899);  Bredig  and  Ikeda,  37,  1,  63  (1901). 

3  Centnerszwer:  Ibid.  26,  1  (1898). 

4  Ibid.  26,  493,  503  (1898). 


FERMENTS.  469 

are  identical.  Even  the  application  of  the  definition  of  catalysis  to 
fermentation  requires  reflection.  The  ferment  in  such  a  case  would 
merely  serve  to  accelerate  reactions  which  were  already  in  progress.  We 
would  have  to  assume,  for  example,  that  albumin  would  be  decomposed 
hydrolytically  at  37  degrees  in  an  aqueous  solution  or  suspension,  although 
the  hydrolysis  proceeds  so  slowly  that  we  are  unable  to  detect  its  progress. 
The  addition  of  pepsin-hydrochloric  acid,  or  of  trypsin,  accelerates  the 
reaction  to  such  an  extent  that  we  are  able  to  recognize  the  hydrolysis  in  a 
short  time,  on  account  of  the  appearance  of  cleavage-products.  We  can- 
not deny  that  such  an  explanation  is  hardly  satisfactory.  It  is  not  sus- 
ceptible to  direct  proof,  and  leads  to  a  forced  assumption.  It  is  not  at 
all  clear  why  pepsin-hydrochloric  acid  should  hydrolyze  the  albumin 
molecule  so  much  less  and  possibly  in  an  entirely  different  manner  than 
trypsin  does,  or  why  the  latter  should  split  off  definite  amino  acids  so 
much  quicker  than  others,  and  furthermore  leave  certain  complexes  en- 
tirely unaltered.  We  know,  furthermore,  that  grape-sugar  may  be  decom- 
posed in  various  ways,  which  must  be  regarded  as  fermentation  processes. 
In  butyric  acid  fermentation,  it  yields  butyric  acid,  carbon  dioxide,  and 
hydrogen  : 

C6Hi2O6  =  C4H8O2  +  2  CO2  +  2  H2. 
In  lactic  acid  fermentation,  it  is  decomposed  as  follows: 

O    =  2  CHO. 


Finally,  we  know,  that  zymase  splits  it  into  ethyl  alcohol  and  carbon 
dioxide: 

C6H1206  =  2  C2H5OH  +  2  CO2. 

The  two  latter  processes  are  unquestionably  pure  fermentations.  In  these 
cases,  the  ferment  not  only  accelerates  reaction  already  existing,  but  it 
also  determines  the  direction  and  progress  of  the  same.  The  fact  that  the 
ferments  act  in  such  a  specific  manner,  i.e.,  only  attack  substances  of 
definite  configuration,  leaving  other  closely  related  compounds  entirely 
untouched,  indicates  very  clearly  that  we  cannot  be  satisfied  with  the 
definition  of  Ostwald,  at  least  as  far  as  fermentation  processes  are  con- 
cerned. We  cannot  expect  to  understand  perfectly  the  action  of  fer- 
ments until  we  have  become  better  acquainted  with  their  chemical 
composition.  As  long  as  we  deal  with  them  only  as  conceptions,  we  can 
hardly  expect  to  make  any  progress  regarding  the  nature  of  their  action. 
We  do  not  wish  to  underestimate  the  value  of  physical  chemistry  in  this 
direction;  we  merely  wish  to  differentiate  between  those  facts  which  we 
can  consider  as  proved,  out  of  the  numerous  investigations  of  recent  years, 
and  those  results  which  are  only  based  upon  hypotheses. 


470  LECTURE  XX. 

One  of  the  most  interesting  properties  of  the  ferments  is  their  specific 
action.  The  animal,  and  also  the  plant  organism,  as  we  have  mentioned 
many  times,  works  almost  exclusively  with  optically  active  carbon  com- 
pounds, i.e.,  with  compounds  which  have  at  least  one  asymmetric  carbon 
atom.  The  asymmetry  of  the  elementary  constituents  of  the  cells  begins 
at  the  moment  of  the  assimilation  of  carbon-dioxide 1  by  the  parts  of  the 
plants  containing  chromophyll,  and  is  transferred  directly  by  the  herbivora, 
indirectly  by  the  carnivora,  into  the  animal  organism.  From  a  compound 
containing  only  one  asymmetric  carbon  atom  we  can  imagine  two  optical 
isomers  and  one  racemic  compound  formed  by  a  union  of  the  two.2  Even 
Pasteur  3  was  acquainted  with  the  fact  that  if  we  inoculate  a  solution  of 
ammonium  tartrate,  containing  a  small  amount  of  nutrient  salts,  with 
traces  of  Penicillium  glaucum,  a  peculiar  change  takes  place.  The  solu- 
tion, which  was  at  first  entirely  inactive,  becomes  optically  active  during 
the  development  of  this  mold,  rotating  towards  the  left.  The  laevo- 
rotation  continues  to  increase,  and  only  assumes  a  constant  value  when 
the  dextrotartaric  acid,  the  optical  isomer  of  the  laevotartaric  acid,  has 
been  entirely  consumed  by  the  mold.  This  interesting  phenomenon  can 
be  explained  on  the  assumption  that  the  mold  evidently  only  utilizes  one 
of  the  optical  modifications  of  tartaric  acid,  while  laevotartaric  acid  remains 
unchanged.  After  this  observation  of  Pasteur,  which  was  attributed  to 
the  action  of  an  organized  ferment,  others  followed.  Thus,  by  the  aid  of 
Penicillium  glaucum,  the  following  optically  active  forms  were  obtained  from 
the  racemic  compounds:  d-mandelic  acid, d-aspartic  acid, d-leucine, Z-tartaric 
acid,  Z-mannonic  acid  lactone,  Z-glutamic  acid,  and  Z-glyceric  acid.4 

Felix  Ehrlich  5  has  made  an  interesting  discovery  in  this  direction.  He 
permitted  a  pure  culture  yeast  to  act  upon  synthetically  prepared,  racemic 
leucine,  in  the  presence  of  cane-sugar.  After  a  time  a  distinct  odor  of 
fusel  oil  was  noticed.  Isoamyl  alcohol  was  separated  from  the  liquid  by 
fractional  distillation.  All  the  leucine  present  was  not  used  up  in  this  pro- 
cess, but  only  the  Z-leucine.  The  d-leucine  could  be  recovered  unchanged 
from  the  liquid.  The  same  experiment,  using  d-isoleucine,  resulted  in  the 
formation  of  d-amyl  alcohol.  The  splitting  of  racemic  bodies  into  the 
optically  active  components  by  means  of  lower  organisms  has  become  an 
important  method  for  the  preparation  of  such  compounds,  and  has  become 
of  great  significance  in  identifying  synthetically  produced  substances 
with  those  which  occur  naturally.  As  different  organisms  decompose 
different  parts  of  the  racemic  bodies,  it  is  possible  for  us  to  obtain  in  this 

1  Compare  Lecture  IV,  p.  54. 

2  Compare  Lecture  II,  p.  15. 

3  Compt.  rend.  51,  298  (1860). 

4  Compare  C.  Winther:  Ber.  28,  3000  (1895). 

5  Z.  Vereines  Deut.  Zuckerind.  56,  592  (1905X 


FERMENTS.  471 

way  either  one  of  the  optical  isomers,  by  selecting  the  proper  organism. 
Emil  Fischer,1  who  early  recognized  the  significance  of  stereo-chemical 
influences  in  biological  processes,  studied  the  alcoholic  fermentation  from 
this  point  of  view.  He  found  that,  of  two  isomers,  yeast  will  ferment  only 
one;  in  fact,  the  following: 

Ferments  Does  not  Ferment 2 
d-Glucose  Z-Glucose 

d-Mannose  Z-Mannose 

d-Galactose  Z-Galactose 

d-Fructose  Z-Fructose 

The  configuration  of  these  compounds  has  been  explained  by  the 
researches  of  Emil  Fischer,3  and  it  is  possible  from  the  structural  formulae 
at  hand  to  determine  the  influence  of  the  configuration  upon  the  attack 
by  yeasts.  The  formulae  of  the  four  fermentable  sugars  are  as  follows: 

COH 

H  .  C  .  OH 
HO  .  C . H 
H  .  C . OH 
H  .  C  .  OH 

CH2OH 
d-Glucose 

It  is  clear  from  these  formulae  that  d-fructose,  d-glucose,  and  d-mannose 
closely  resemble  one  another  in  their  stereo-structure.  The  OH  and 
H  groups  are  arranged  alike  in  three  of  the  four  asymmetric  carbon  atoms. 
It  is  interesting  to  note  that  these  three  sugars  also  possess  close  chemical 
relations,  as  is  indicated  by  many  of  their  transformations,  and  especially 
by  the  fact  that  they  go  over  into  one  another,  simply  on  heating  with 
alkali.  The  d-galactose,  in  its  configuration,  does  not  stand  so  close  to  the 
sugars  mentioned.  The  same  also  applies  to  its  behavior.  It  is  more 
slowly  fermented;  in  fact,  some  varieties  of  yeast,  such  as  Saccharomyces 
apicidatus  and  productivis,  do  not  act  upon  it  at  all.  All  of  the  other 
known  aldose  and  ketose  sugars  remain  unacted  upon  by  yeasts.  The 


COH 

COH 

CH2OH 

HO  .  C  .  H 

H  .  C  .  OH 

io 

HO  .  C  .  H 

HO  .  C  .  H 

HO  .  C  .  H 

H  .  C  .  OH 

HO  .  C  .  H 

H  .  C  .  OH 

H  .  C  .  OH 

H  .  C  .  OH 

H  .  C  .  OH 

CH2  .  OH 

CH2  .  OH 

CH2.0 

d-Mannose 

d-Galactose 

d-Fructose 

1  Z.  physiol.  Chem.  26,  60  (1898-99). 

2  Ber.  23,  382,  2620;  25,  1259;  27,  2031;  27,  2985;  27,  3479;  28,  1429;  27,  2035 
(1894). 

3  Compare  Lecture  II,  p.  17. 


472 


LECTURE  XX. 


following  formula  of  a  non-fermentable  sugar,  d-talose,  will  show  what 
a  slight  difference  in  the  configuration  in  the  molecule  may  prevent  the 
action  of  the  yeast : 

COH 

HO  .  C . H 
HO . C . H 
HO . C . H 
H  .  C . OH 

CH2  .  OH 

d-Talose 

Although,  from  what  was  said  about  zymase,  we  can  conceive  of  the 
selective  behavior  of  the  cells  of  Penicillium  glaucum,  yeasts,  etc.,  as  due 
to  the  action  of  ferments,  it  is  nevertheless  desirable  to  perform  such 
experiments  with  the  individual  ferments  themselves.  In  many  cases  the 
cell,  with  its  ferments,  may  conceal  such  a  specific  action  on  account  of 
the  acting  together  of  ferments  of  different  kinds.  Emil  Fischer  has  suc- 
ceeded in  showing  that  the  specific  activity  of  the  cells  is  dependent  upon 
the  ferments  contained  therein.  If  aldoses  are  heated  with  very  weak, 
alcoholic  hydrochloric  acid,  we  obtain  two  isomeric  glucosides,  which  are 
designated  as  the  a-  and  /^-compounds.  Emil  Fischer  has  assigned  the 
following  formulas  to  these  methyl  derivatives  of  d-glucose : 


OH 


OH 


Only  one  of  these  two  compounds,  in  fact  the  /?-form,  is  hydrolyzed  by 
emulsin  into  methyl  alcohol  and  grape-sugar;  the  a-form  remains  unacted 
upon  by  this  ferment.  On  the  other  hand,  ferments  obtained  from  yeast 
do  not  attack  the  /?-glucoside,  but  hydrolyze  the  a-form.  The  stereo- 
isomers  of  the  above  compounds,  a-methyl-Z-glucoside  and  /?-methyl- 
Z-glucoside,  are  not  attacked  by  either  emulsin  or  the  yeast  ferments. 


FERMENTS.  473 

Moreover,  the  ferments  are  so  sensitive  that  they  can  detect  differences 
in  chemical  compounds  which  are,  as  far  as  our  present  knowledge  of 
structure  and  stereo-chemistry  shows,  perfectly  analogous.  This  is  clearly 
shown  by  comparing  the  a-  and  /?-methyl-d-glucosides  with  the  a-  and  /?- 
methylxylosides. 


H  .  C^OCH3  CH3O  . 

H  .  C  .  OI^  H  .  C  .  GET 

lxo  i           r> 

HO  .  C  .  H  ,  HO  .  C  .  H 

H  .  C/  H  .  C/ 

H  .  C  .  OH  H  .  C  .  OH 


CH2 


2  .  OH  CH2  .  OH 

a-  and  /?-methyl-d-glucosides 

H  .  C  .  OCH3  CH3O  .  C^H 

H  .  C  .  OEt\  H  .  C  . 

HO  .  C . H 


H.A. 


CH2  .  OH  C 

a-  and  ^5-methylxylosides 

While  the  former  are  split  by  either  emulsin  or  the  yeast  ferments,  the 
xylosides  are  not  acted  upon  by  either  of  them. 

Emil  Fischer  made  analogous  observations  with  the  polysaccharides. 
Some  of  these  are  also  unfermentable,  and  their  different  behavior  is 
undoubtedly  due  to  differences  in  the  configuration  of  the  molecules.1 

For  investigating  the  relations  of  the  action  of  ferments  to  the  con- 
figuration of  the  individual  compounds,  Emil  Fischer  by  his  extensive 
syntheses  in  the  protein  group  has  opened  up  recently  a  new  field  which 
in  its  diversity  far  exceeds  the  relations  with  the  carbohydrates.  This 
scientist  has,  as  we  have  already  seen,  made  the  cleavage-products  of  the 
proteins  unite  together  in  various  anhydride-like  combinations.  The 
number  of  chains  which  it  is  possible  to  unite  in  this  manner  is  very  large. 
The  number  of  possible  isomers  which  can  be  obtained  by  using  different 
amino  acids  and  in  different  sequence,  and  also  by  employing  the  racemic 
amino  acids,  is  greatly  increased  on  account  of  the  fact  that  all  of  the  known 
cleavage-products  of  albumin,  with  the  exception  of  glycocoll,  contain  at 

1  Compare  also  A.  Kalanthar :  Z.  physiol.  Chem.  26,  89  (1898). 


474  LECTURE  XX. 

least  one  asymmetric  carbon  atom.  Now  it  was  of  great  interest  to  trace 
the  behavior  of  the  synthetic  polypeptides  in  the  presence  of  proteolytic 
ferments,  in  order  to  ascertain  whether  the  fine  distinctions  which  were 
noticed  with  the  carbohydrates  would  also  apply  here.  The  synthetic 
polypeptids  do,  in  fact,  show  a  decidedly  different  behavior  toward  the 
pancreatic  juice,  as  is  shown  by  the  following  table:  1 

The  Pancreatic  Juice 

Hy  droly  zes :  Does  not  hy drolyze : 

*  Alanyl-glycine  Glycyl-alanine 
*Alanyl-alanine  Glycyl-glycine 

*  Alanyl-leucine  A  Alanyl-leucine  B 
*Leucyl-isoserine  A  Leucyl-alanine 

Glycyl-Z-tyrosine  Leucyl-glycine 

Leucyl-Z-tyrosine  Leucyl-leucine 

*Alanyl-glycyl-glycine  Aminobutyryl-glycine 

*Leucyl-glycyl-glycine  Aminobutyryl-aminobutyric  acid  A 

*Glycyl-leucyl-alanine  Aminobutyryl-aminobutyric  acid  B 

*Alanyl-leucyl-glycine  Ammoisovaleryl-glycine 

Dialanyl-cystine  Glycyl-phenylalanine 

Dileucyl-cystine  Leucyl-proline 

Tetraglycyl-glycine  Diglycyl-glycine 

Triglycyl-glycine-ester  Triglycyl-glycine 

(=Curtius>  Biuret-base.)  Dileucyl-glycyl-glycine 

If  we  examine  these  two  columns,  we  observe  that  the  pancreatic  fer- 
ment has  various  points  of  attack.  In  the  first  place,  the  structure  of  the 
individual  compounds  must  be  taken  into  consideration.  A  good  example 
here  is  the  behavior  of  alanyl-glycine: 

CH3  .  CH(NH2)  .  CO  .  NH  .  CH2  .  COOH, 
and  its  isomer,  glycyl-alanine : 

NH2  .  CH2  .  CO  .  NH  .  CH(CH3)  .  COOH. 

The  former  is  hydrolyzed,  the  latter  is  not.  The  nature  of  the  individual 
amino  acid  is  also  important.  Thus,  those  dipeptides  are  susceptible  to 
hydrolysis  in  which  the  alanine  acts  as  acyl,  examples  being:  alanyl- 
glycine,  alanyl-alanine,  alanyl-leucine.  The  hydroxy  acids,  tyrosine  and 
isoserine,  have  a  similar  effect  when  they  are  at  the  end  of  the  chain.  It  is 

1  Emil  Fischer  and  Emil  Abderhalden:  Z.  physiol.  Chem.  46,  52  (1905).  Compare 
also,  Sitzber.  Kgl.  Preuss.  Akad.  Wiss.  10  (1905),  and  Emil  Fischer  and  Peter  Bergell: 
Ber.  36,  2592  (1903);  37,  3103  (1904). 


FERMENTS.  475 

possible  that  the  electro-negative  character  of  these  compounds  plays  a 
part.  It  has  not  yet  been  decided  whether  the  easy  cleavage  of  the  two 
cystine  derivatives  is  due  to  this  cause,  or  that  the  length  of  the  chain  is  a 
factor.  It  is  very  noteworthy  that  the  dipeptides,  which  contain  a-amino- 
butyric  acid,  and  leucine  as  acyl,  offer  great  resistance. 

The  influence  of  configuration  is  also  clearly  indicated  in  this  case.  The 
polypeptides  in  the  above  table  which  are  designated  by  an  asterisk,  are 
racemic  compounds.  In  all  of  these  cases,  the  hydrolysis  is  an  asym- 
metric one,  i.e.,  only  half  of  the  racemic  body  is  attacked.  The  products 
resulting  from  the  hydrolysis  were  the  same  as  those  active  amino  acids 
which  are  contained  in  the  natural  protein-substances.  A  special  case  is 
shown  by  the  contrast  between  the  alanyl-leucine  A.  and  alanyl-leucine  B. 
In  these  two  racemic  compounds  are  present  all  four  combinations  of  the 
four  active  amino  acids.  One  racemic  compound  is  d-alanyl-d-leucine  + 
Z-alanyl-Z-leucine;  the  other,  d-alanyl-Z-leucine  +  Z-alanyl-d-leucine.  Of 
these  four  combinations,  the  pancreatic  juice  will  attack  only  that  corre- 
sponding to  d-alanyl-Z-leucine.  This  fact  is  of  great  significance.  It 
supplies  us  with  a  means  for  determining  directly  the  configuration  of  the 
synthetic  polypeptides. 

The  number  of  the  amino  acids  contained  in  the  complex  molecule  is 
also  of  influence.  The  glycine  chains  give  us  a  distinct  example  of  this. 
Glycyl-glycine,  diglycyl-glycine,  and  triglycyl-glycine  are  not  hydrolyzed, 
while  tetra-glycyl-glycine  is  acted  upon.  Leucyl-glycine,  also,  is  not 
decomposed,  although  leucyl-glycyl-glycine  is.  The  reason  that  dileucyl- 
glycyl-glycine  is  not  decomposed,  lies  probably  in  the  configuration  of  the 
dileucyl  group. 

If  the  cleavage  takes  place  along  asymmetric  lines,  the  beginning  of 
hydrolysis  in  the  previously  inactive  digesting  liquid  is  established  by  the 
appearance  of  optical  activity. 

We  may  here  include  the  observation  of  O.  Warburg,1  who  showed  that 
the  ester  of  racemic  leucine  is  saponified  asymmetrically  by  the  pancreatic 
juice.  We  do  not  know  what  ferment  produces  this  result.  Lipase  may 
be  the  active  principle,  as  is  suggested  by  an  analogous  observation  of 
H.  D.  Dakin.2 

Closely  related  to  these  discoveries,  is  the  fact  previously  mentioned,3 
that  the  animal  organism  utilizes  only  one-half  of  certain  racemic  sub- 
stances, the  other  optical  isomer  being  eliminated  unchanged.  These 
discoveries  show  very  clearly  the  similarity  of  "  organized  "  and  unor- 
ganized ferments,  and  justify  us  in  concluding  that  all  ferments  must  be 
considered  from  the  same  point  of  view. 


1  Ber.  38,  187  (1905). 

3  Proc.  Chem.  Soc.  19,  161  (1903);  J.  Physiol.  32,  199  (1905). 

3  Compare  Lecture  XIX,  p.  452. 


476  LECTURE  XX. 

The  fact  that  the  ferments  act  asymmetrically  leads  to  the  assumption 
that  they  themselves  are  asymmetrically  constituted.  The  ferment  must 
be  exactly  fitted  to  act  on  the  compound  which  is  to  undergo  cleavage. 
Possibly  the  assumption,  so  often  made,  that  the  ferment  temporarily 
combines  with  the  substance  to  be  hydrolyzed,  will  account  for  the  specific 
behavior  of  every  individual  ferment.  If  this  be  true,  we  can  easily 
understand  that  only  a  definite  ferment  can  act  upon  a  given  compound. 
This  assumption  is  supported  by  the  observation,  that  pepsin  and  papain, 
for  example,  form  such  strong  combinations  with  fibrin  that  they  cannot 
be  removed  by  washing.  It  has  also  been  found  that  the  inversion  of 
cane-sugar  by  ferments  is,  as  a  rule,  the  same  during  equal  intervals 
of  time. 

Further  light  has  been  thrown  upon  this  problem  by  tracing  the  optical 
behavior  of  solutions  containing  optically-active  polypeptides  after  the 
addition  of  a  solution  containing  ferments.1  -All  results  indicate  that  the 
ferment  temporarily  unites  with  the  substance  which  it  splits.  It  is 
important  that  the  cleavage  products  tend  to  prevent  the  further  cleavage 
of  the  substance,  in  accordance  with  the  mass-action  law. 

A  peculiar  significance  of  the  ferments  has  recently  been  indicated  by 
certain  observations.  Morgenroth 2  found  that,  after  subcutaneous 
injection  of  rennin  in  small  doses,  the  serum  of  the  animal  so  treated, 
contained  a  substance  which  prevented  the  curdling  of  milk.  This  phe- 
nomenon is  analogous  to  the  production  of  anti-toxin  by  the  animal 
organism  after  the  injection  of  a  toxin.  In  one  case  we  obtain  an  anti- 
toxin, in  the  other  an  anti-rennin.  Two  per  cent  of  the  strongest  immu- 
nizing-serum  which  Morgenroth  obtained,  added  to  milk,  prevented  its 
curdling  even  when  the  ferment  was  present  to  the  extent  of  1:20,000. 
Without  the  addition  of  anti-rennin,  the  curdling  took  place  when  the 
ratio  was  as  low  as  1 : 3,000,000.  Even  normal  serum  is  supposed  to  con- 
tain some  anti-rennin.  Such  anti-ferments  have  also  been  prepared  which 
act  against  pepsin,  trypsin,  fibrin-ferment,  tyrosinase,  lactase,  and  urease. 
These  experiments  are  of  great  importance  in  two  directions  if  they  can  be 
confirmed.  In  the  first  place,  this  discovery  will  serve  to  unite  a  purely 
biological  process  with  another  which,  up  to  the  present  time,  has  not 
been  studied  by  itself.  The  acquirement  of  immunity  and  the  formation 
of  anti-ferments  may  prove  to  be  analogous  phenomena;  and  the  toxins, 
which  resemble  the  ferments  in  many  respects,  may  belong  to  the  same 
class  of  substances.  A  further  analogy  lies  in  the  fact  that  the  ferments 

1  Abderhalden  and  Koelker:  Z.  physiol.  Chem.  51,  294  (1907);  Abderhalden  and 
Michaelis:  ibid.  52,  326  (1907);  Abderhalden   and  Gigon:  ibid.  53,  251  (1907);  Abder- 
halden and  Koelker:  ibid.  54,  363  (1908). 

2  Zentr.  Bact.  26,  349  (1889);  27,  721  (1900). 


FERMENTS.  477 

have  a  toxic  effect  when  injected  subcutaneously.  Hildebrandt1  found 
that  the  lethal  dose  for  a  medium-sized  rabbit  was  0 . 1  gram  for  pepsin, 
invertase,  and  diastase;  0.05  gram  for  emulsin  and  myrosin;  and  2  grams 
for  rennin.  All  of  the  injected  ferments  caused  rise  of  temperature. 
Dogs,  which  had  had  ferments  injected,  would  not  eat,  showed  thirst,  trem- 
bling, restlessness,  an  unsteady  gait,  and  eventually  coma.  Rabbits 
showed  principally  emaciation,  weakness,  and  sometimes  extensor  con- 
vulsions. Such  observations  necessarily  have  only  a  relative  value, 
owing  to  the  fact  that  the  nature  of  the  ferments  is  still  unknown,  so  that 
their  purity  cannot  be  estimated. 

On  the  other  hand,  the  formation  of  the  anti-ferments  and  the  observed 
normal  occurrence  of  these,  gives  us  an  indication  of  the  role  which,  for 
example,  the  ferments  absorbed  by  the  intestines  perform  in  their  circu- 
lation through  the  body.  We  can  easily  imagine  that  the  organism  par- 
alyzes the  activity  of  the  absorbed  ferments  by  the  production  of  the  anti- 
ferments.  The  presence  of  such  substances  also  suggests  an  explanation 
of  how  the  living  tissue  is  protected  against  self-digestion.2  We  can  also 
imagine  that  this  protection  is  obtained  by  the  cells  altering  the  material 
which  they  require  for  constructive  purposes,  and  do  not  wish  to  consume, 
so  that  the  ferments  are  unable  to  find  any  point  of  attack.  It  is  certainly 
not  without  significance  that  the  connective  tissue,  e.g.,  elastin  and 
substances  like  spongin  and  silk-fibroin,  which  are  not  considered  as 
nutrient  materials,  contain  in  large  quantities  just  those  amino  acids 
which  make  hydrolysis  difficult.  The  substances  are,  as  a  matter ,  of 
fact,  hardly  attacked  by  pepsin-hydrochloric  acid  or  by  trypsin.  The 
cell  has  only  to  cause  a  slight  rearrangement  of  the  atoms  in  the  mole- 
cules of  the  assimilated  products  to  form  modifications  which  the  fer- 
ments are  not  able  to  attack,  or  it  may  cause  them  to  combine  with  other 
cell-components. 

An  unsolved  problem  is  the  origin  of  the  ferments.  It  has  often  been 
suggested  that  they  bear  a  definite  relation  to  the  food.  In  fact,  many 
observations  indicate  a  close  connection  between  the  production  of  fer- 
ments and  the  assimilation  of  the  food.  We  merely  do  not  understand 
the  more  intimate  relations  existing  between  the  two  processes.  Brown 
and  Morris  3  have  shown  that  the  leaves  of  many  plants  contain  the  most 
diastase  in  the  morning,  the  amount  decreasing  during  the  day.  If  the 
assimilation  is  carried  out  in  the  sunlight,  the  formation  of  diastase  ceases 


'  Virchow's  Arch.  121,  1  (1890);  131,  26  (1893). 

2  E.  Weinland,  Z.  Biol.  43,   86   (1902),  has  found  such  anti-ferments  in  cell-free 
extracts  of  parasitical  worms.     Extracts  from  the  mucous  membranes  of  the  stomach 
and  intestine,  as  well  as  erythrozytes,  are  credited  with  retarding  the  solution  of  fibrin. 
Z.  Biol.  41,  1,  146  (1902). 

3  J.  Chem.  Soc.  62,  604  (1893);  57,  493  (1890). 


478  LECTURE  XX. 

entirely.  The  dormant  seeds  do  not  contain  any  ferments,  i.e.,  not  in  an 
active  form;  they  do  not  become  active  until  the  beginning  of  germina- 
tion. The  barley  embryo  does  not  produce  diastase  when  absorbable  sugar 
is  available  for  it. 

The  formation  of  ferments  among  the  molds  is  likewise  influenced  by 
the  nature  of  the  nourishment.  If  they  are  provided  with  albumin,  they 
will  produce  proteolytic  ferments;  if  they  are  cultivated  upon  starch,  they 
will  form  diastase.  Furthermore,  it  is  known  that  yeast,  for  example, 
which  has  been  cultivated  for  a  long  time  on  a  specific  substratum,  can 
be  "  taught "  to  utilize  definite  compounds  if  we  gradually  withdraw  the 
other  nutriment. 

Closely  related  to  these  observations  is  the  fact  that  the  plant  cells,  in 
the  presence  of  definite  products,  also  produce  the  ferments  which  will 
decompose  them.  This  is  usually  true  of  the  glucoside-splitting  ferments. 
Thus  we  find  amygdalin  together  with  the  ferment  emulsin  in  bitter 
almonds;  while  the  glucoside,  sinigrin,  is  accompanied  by  the  ferment 
myrosin  in  black  pepper. 

There  are  numerous  analogous  observations  in  the  animal  kingdom.  It 
was  known  to  Claude  Bernard  *  that  the  larvae  of  Musca  lucilia,  a  kind  of 
fly,  possessed  large  stores  of  glycogen,  but  did  not  produce  any  diastase. 
The  latter  appears  only  when  these  stores  are  required  by  the  pupa. 

Numerous  relations  between  the  kind  of  food  and  the  amount  and 
nature  of  the  secreted  digestive  fluids  have  become  known  by  the  extensive 
researches  of  Pawlow.  Nervous  influences  dominate  the  production  of  the 
ferments.  This  was  evident  long  ago  from  the  investigations  of  Claude 
Bernard  on  the  decomposition  of  glycogen  in  the  liver.  Pawlow  has 
studied  this  subject  more  carefully,  as  we  shall  see  later. 

From  all  of  these  statements,  we  involuntarily  obtain  the  impression 
that  fermentation  processes  play  a  large  part  in  the  whole  economy  of  the 
individual  cell,  the  tissues,  and  finally  the  entire  organism.  This  view  is 
supported  by  the  common  occurrence  of  such  processes  throughout  the 
whole  plant  and  animal  kingdoms.  The  fact  that  their  activity  begins  as 
soon  as  the  life  processes  start  indicates  their  importance.  The  ferments 
are  found  in  very  early  stages  of  human  and  animal  embryos.  Langen- 
dorff  2  detected  trypsin  especially  early.  Pepsin  is  entirely  absent  among 
the  carnivora  just  after  birth,  but  is  found  in  the  herbivora.  Diastase  is 
absent  from  human  beings  and  rabbits  previous  to  birth.  The  ferments, 
evidently,  play  a  part  not  only  in  physiological  relations,  but  also  in  patho- 
logical ones.  Thus,  we  observe  that  fibrin  from  the  bronchial  tubes 
during  croupous-pneumonia  is  gradually  dissolved  and  finally  disappears.3 

1  Revue  scientifique  (1873),  p.  515. 

a  Arch.  Anat.  Physiol.  1879,  95. 

3  F.  Miiller:  Verhandl.  XX.  Kongresses  in.  Med.  zu  Weisbaden  (1902). 


FERMENTS.  479 

In  this  case,  apparently  the  migrant  leucocytes  which  are  present  in  large 
numbers  furnish  the  ferment  and  cause  a  normal  digestion  in  the  lungs. 
Some  insight  into  the  cell  processes,  and  the  ferments  which  come  into 
action  thereby,  was  believed  to  be  obtained  from  Salkowski's  discovery 
that  organs,  even  when  kept  perfectly  sterile,  gradually  dissolve  of  them- 
selves.1 Cleavage-products  are  formed  at  the  same  time  which  suggest 
the  presence  of  trypsin-like  ferments.  To  be  sure,  it  is  generally  stated 
that  the  disintegration  of  the  cell  contents  and  especially  of  the  albumin, 
in  this  process  which  is  known  as  autolysis,  is  not  the  same  as  that  which 
takes  place  in  a  true  trypsin  digestion.  It  is  true  that  the  same  end- 
products  (amino  acids,  purine  bases,  etc.)  are  formed,  but  we  do  not  know 
whether  the  decomposition  takes  place  in  the  same  way,  and  with  the 
formation  of  the  same  intermediate  products.  It  is  questionable  whether 
we  are  justified  at  present  in  making  deductions  regarding  normal  cell 
metabolism  from  the  autolytic  processes  which  result  several  days  after 
death.2 

Thus  far  we  have  considered  cell-metabolism  and  fermentation  from 
only  one  point  of  view.  We  have  mentioned  only  the  splitting  ferments. 
Now  we  know  that  extensive  syntheses  take  place  in  the  animal  organism. 
Since  Wohler,  in  1824,  proved  that  benzoic  acid  administered  to  the  animal 
organism  was  neither  consumed  nor  excreted  as  such,  but  that  a  nitro- 
genous acid,  richer  in  carbon,  appeared  in  the  urine,  namely  hippuric  acid, 
which  is  composed  of  glycocoll  and  benzoic  acid,  a  great  many  other  syn- 
theses have  been  proved  to  take  place.  We  need  only  to  recall  the  fact 
that  fats  are  split  into  glycerol  and  fatty  acid  in  the  alimentary  tract, 
only  to  reappear  on  the  other  side  of  the  intestine  as  fats,  and  also  that  the 
albumins  and  complicated  carbohydrates  are  disintegrated  into  simple 
components  only  to  be  reconstructed,  to  realize  that  synthesis  is  another 
established  function  of  the  animal  cell.  Although,  as  far  as  our  present 
knowledge  shows,  these  syntheses  are  for  the  most  part  simple  ones,  and 
usually  consist  of  the  union  of  two  or  more  molecules  with  elimination  of 
water,  we  must  not  conclude  that  the  animal  cell  is  incapable  of  effecting 
complicated  syntheses.  Certain  recent  results  lead  us  to  suspect  that  the 
animal  organism  is  capable  of  building  up  complicated  structures.  The 
synthetic  processes  of  the  plant  and  animal  organisms  were  for  a  long  time 
hidden  in  obscurity.  Indeed,  on  purely  theoretical  grounds,  by  comparing 
ferments  with  catalyzers,  the  conclusion  was  drawn  that  fermentations 
must  be  reversible  processes,  and  that  they  may  be  endothermic  as  well  as 
exothermic  reactions.  As  a  matter  of  fact,  a  whole  series  of  syntheses  has 
been  carried  out  by  the  aid  of  ferments.  Thus  we  may  refer  to  the  for- 
mation of  isomaltose  from  concentrated  d-glucose  solutions  by  means  of 

1  Z.  Klin.  Med.  17,  Suppl.  77  (1890). 

2  Cf.  Lecture  XII,  p.  265. 


480  LECTURE   XX. 

yeast  maltase,  and  to  the  production  of  isolactose  from  glucose  and  galac- 
tose  by  kephir-lactase,  and  to  the  synthesis  of  amygdalin  from  mandelo- 
nitrile  glucoside  and  grape-sugar  with  the  aid  of  yeast  maltase.1  From  these 
observations  there  can  be  no  doubt  that  fermentations  are  reversible  pro- 
cesses. This  does  not  prove,  however,  that  the  conditions  in  the  tissues  and 
cells  are  such  that  the  known  ferments  are  active  in  this  direction  to  any 
great  extent.  It  is  very  tempting  to  refer  all  metabolic  processes  to  fer- 
mentation. At  one  place  there  is  a  decomposition,  at  another,  construction, 
according  to  the  requirements  of  the  cells.  The  ferment  acts  as  an  inter- 
mediary. Many  enigmas  would  thus  be  solved  at  one  stroke,  and  many 
apparently  different  processes  referred  to  one  simple  basis.  It  is  certainly 
possible  that  such  a  significance  really  belongs  to  the  ferments,  and  that 
they  dominate  the  entire  metabolism.  We  must,  however,  confine  our- 
selves to  the  facts,  and  build  on  them  alone  as  foundation.  We  are,  in  the 
first  place,  impressed  with  the  fact  that  all  the  fermentation  syntheses  so 
far  carried  out  satisfactorily  do  not  give  rise  to  products  to  which  the  fer- 
ment is  accustomed,  with  the  possible  exception  of  the  amygdalin  synthesis. 
We  do  not  obtain  maltose  from  grape-sugar,  but  an  isomer,  isomaltose; 
nor  do  we  obtain  lactose  from  glucose  and  galactose,  but  only  isolactose. 
These  facts  are  certainly  not  without  significance.  Can  the  maltase  again 
decompose  isomaltose,  or  kephir-lactase  hydrolyze  isolactose?  These 
were  unsolved  problems  until  recently.  Thanks  are  due  E.  F.  Armstrong  2 
for  thoroughly  studying  these  fermentation  syntheses,  and  especially 
the  formation  of  maltose  and  isomaltose.  Armstrong  started  with  the 
fact  which  we  have  not  previously  mentioned,  that  d-glucose  can  exist  in 
stereo-isomeric  forms.  If  we  crystallize  grape-sugar  from  alcohol,  we  only 
obtain  the  a-form.  If  this  is  kept  for  several  days  at  105  degrees,  it  goes 
over  into  the  /?  form.  The  two  modifications  have  different  optical 
behaviors.  It  has  been  attempted  to  represent  this  type  of  stereo-isomer- 
ism  by  means  of  formulae,  although  a  satisfactory  explanation  is  still  lack- 
ing. If  glucose  is  dissolved  in  methyl  alcohol,  containing  hydrochloric 
acid,  glucosides  corresponding  to  both  forms  are  produced.  As  we  have 
already  seen,  only  one  of  these  varieties  is  split  by  maltase,  the  other  only 
by  emulsin.  The  variety  hydrolyzed  by  maltase  is  the  a  form.  If  we 
apply  these  observations  to  maltose  and  isomaltose,  we  can  regard  the 
former  as  glucose-a-glucoside,  and  the  latter  as  glucose-/?-glucoside.  In 
this  case  also,  the  maltase  is  only  capable  of  splitting  the  a  form,  while 
the  /?-glucoside  remains  unattacked.  Now  maltase  produces  synthetically 
/9-glucoside,  i.e.,  the  glucoside  which  it  cannot  decompose.  The  following 
experiments  completely  cleared  up  these  relations.  If  glucose  was  treated 

1  Cf.  Lecture  III,  pp.  37,  38. 

2  Pro.  Roy.  Soc.  76  (B),  592  (1905);  19,  209   (1903);  Jour.  Chem.  Soc.  83,  1305 
(1903). 


FERMENTS.  481 

with  concentrated  hydrochloric  acid,  and  hydrochloric  gas  acid  passed 
into  the  liquid  at  0  degrees,  it  was  shown,  after  long  standing  at  10 
degrees,  that  the  fluid  contained  both  glucosides,  maltose  and  isomaltose, 
as  well  as  unchanged  glucose.  The  hydrochloric  acid  makes  no  distinction; 
it  works  with  the  a  as  well  as  the  /?  form  of  glucose.  That  both  bioses 
had,  in  fact,  been  formed,  was  proved  by  the  circumstance  that  maltase 
as  well  as  emulsin  produced  glucose  from  it.  If  glucose  was  kept  at  25 
degrees  for  two  or  three  months  in  the  presence  of  yeast  maltase,  it  was 
shown  after  removing  the  unchanged  glucose  by  means  of  Saccharomyces 
intermedians,  that  isomaltose  was  present.  Emulsin  produced  d-glucose 
from  it,  but  maltase  was  unable  to  do  so.  When  glucose,  on  the  other 
hand,  was  acted  upon  by  emulsin,  maltose  was  produced.  These  relations 
may  be  summarized  as  follows: 


a-glucose 

i 

glucose-a-glucoside  (maltose) 

i 

a-glucose 
/?-glucose 

i 


synthesized  by  emulsin. 


hydrolyzed  by  maltase. 


synthesized  by  maltase. 


glucose-/3-glucoside  (iso-maltose) 

hydrolyzed  by  emulsin. 
^-glucose 

Each  of  these  ferments,  emulsin  and  maltase,  builds  up  that  biose  which 
it  cannot  itself  decompose.  This  synthesis  by  ferments  is,  therefore, 
different  as  far  as  our  present  knowledge  goes  from  that  produced  by 
true  catalyzer. 

We  have  gone  into  these  relations  in  detail  in  order  to  show  that  we  are 
at  present  not  justified  in  concluding  that  a  single  ferment  in  the  cells  can 
effect  decomposition  or  synthesis  according  to  the  outer  conditions.  We 
have  no  reason  for  believing  this.  This  does  not,  of  course,  exclude  the 
possibility  that  these  processes  may  be  carried  out  differently  in  the  cells 
and  tissues.  We  are,  however,  not  justified  in  regarding  all  processes  of 
metabolism  in  the  tissues  and  cells  as  being  due  to  fermentation.  It  is 
absolutely  necessary  right  at  this  point  to  confine  ourselves  to  the  facts, 
and  not  follow  a  plausible  hypothesis,  the  value  of  which  is  especially 
problematical  here,  for  there  is  a  vast  amount  of  research  to  be  made. 
Although  our  knowledge  of  fermentation  reactions  constantly  broadens, 
the  great  mystery  regarding  the  origin  and  formation  of  the  ferments 
remains,  and  the  important  question  relating  to  their  chemical  structure 
is  still  unsolved. 

Let  us  now  turn  to  the  classification  of  the  ferments.     We  have  often 


482  LECTURE  XX. 

encountered  them  in  tracing  the  course  of  the  organic  nutrient  materials 
in  their  passage  from  the  alimentary  canal  to  the  tissues.  It  remains 
only  to  classify  them  in  a  comprehensive  manner.  We  may  divide  the 
ferments  into  two  main  groups:  (1)  the  hydrolytic,  and  (2)  the  oxidizing 
ferments.  The  former  may  be  further  subdivided  according  to  the  material 
to  be  attacked,  e.g.  (a)  ferments  which  effect  the  decomposition  of  the 
carbohydrates,  (6)  the  proteolytic  ferments  which  act  upon  the  proteins, 
and  (c)  the  fat-splitting  ferments.  The  diastatic  ferments  belong  to  class 
(a).  They  hydrolyze  starch  into  dextrins  and  maltose.  The  decompo- 
sition of  maltose  into  two  molecules  of  dextrose  is  effected  by  maltase. 
Invertase  splits  cane-sugar  into  one  molecule  of  dextrose  (d-glucose)  and 
one  of  Isevulose  (d-f ructose) .  To  this  group  belong  a  series  of  ferments 
whose  characteristics  have  been  less  carefully  studied,  such  as  cellulase, 
which  is  supposed  to  decompose  cellulose;  inulinase,  which  acts  on  inu- 
lin;  seminase,  which  disintegrates  mannans  and  galactans;  and  finally 
pectinase,  which  is  responsible  for  the  hydrolysis  of  pectin.  We  might 
also  mention  trehalase,  melibiase,  and  la,ctase,  which  decompose  the  sugars 
corresponding  to  their  names.  Special  ferments  are  also  known  which 
hydrolyze  the  glucosides,  as  well  as  a  urease  that  changes  urea  into 
ammonium  carbonate.  To  class  (6),  the  proteolytic  ferments,  belong 
pepsin,  trypsin,  rennin,  the  fibrin-ferment,  and  pectase  which  hydrolyzes 
pectin  substances.  The  fat-splitting  ferments  form  a  class  by  them- 
selves. Then  there  is  lactic-acid  ferment,  which  produces  lactic  acid 
from  sugar.  It  attacks  all  of  the  simple  hexoses,  and  some  pentoses,  but 
not  cane-sugar  or  milk-sugar.  It  produces  chiefly  the  a-hydroxypropionic 
acid,  CH3  .  CHOH  .  COOH.  It  is  still  a  question  whether  the  lactic 
acid  fermentation  is  to  be  looked  upon  as  an  independent  process. 

The  second  main  group  comprises  the  oxidizing  ferments  which  have 
already  been  discussed.  They  obtain  their  oxygen  either  from  the  air  or 
from  decomposed  hydrogen  peroxide.  To  the  former  class  belong  the 
true  oxidases,  acting  as  oxygen  carriers  to  the  cells  and  tissues.  Atmos- 
pheric oxygen  is  also  utilized  during  the  acetic  acid  fermentation  of 
ethyl  alcohol. 

Alcoholic  fermentation  is  quite  a  special  process.  It  is  a  complicated 
affair,  and  the  ferments  producing  it  cannot,  at  present,  be  assigned  to 
any  of  the  above  groups.  As  we  have  already  shown,1  alcoholic  fermenta- 
tion plays  a  part  of  which  we  cannot  at  present  estimate  the  extent  in 
plant  and  animal  tissues,  and  inasmuch  as  an  inspection  of  this  process 
will  give  us  some  idea  of  the  progress  of  a  fermentation  reaction,  we  will 
briefly  discuss  it.  The  reaction  takes  place  according  to  the  following 
general  equation: 

C6H12O6  =  2  C2H5OH  +  2  CO2. 

1  Cf.  Lecture  IV,  p.  74. 


FERMENTS. 


483 


Until  recently  the  whole  process  of  alcoholic  fermentation  was  sur- 
rounded with  great  obscurity.  E.  Buchner  and  J.  Meisenheimer l  have 
succeeded  at  least  in  indicating  the  way  in  which  the  decomposi- 
tion proceeds.  Thus,  in  their  cell-free  fermentations,  they  invariably 
found  inactive  lactic  acid.  They  concluded  that  this  must  be  a  normal 
intermediate  product,  and  formulated  the  alcoholic  fermentation  to  take 
place  as  follows: 


CHO 

OH 

CHOH 

OH 

| 

H 

CHOH 

H 

CHOH 

OH 

CHOH 

OH 

CH2OH 

H 
H 

COOH 


COOH 

CH  .OH          CH  .  OH 

CH2  H    Cl 

'co 


H  CH3 

OH  COOH 

I  I 

CH  .OH  CH  .  OH 


OH 
H 


OH 
H 


CO2 
CH2OH 


CH; 


CH3 


CO2 
CH2OH 


Glucose  Hypothetical 

intermediate  product 
+  5H20 


1-3 

2  molecules 
lactic  acid 


Ethyl  alcohol 
+  CO2 


At  all  events,  alcoholic  fermentation  is  a  very  complicated  process, 
and  the  question  has  now  arisen,  whether  it  is  to  be  looked  upon  as  brought 
about  by  one  or  by  several  ferments.  One  ferment  may  convert  the  sugar 
into  lactic  acid,  while  a  second  transforms  this  into  alcohol.  There  are 
also  by-products  in  the  alcoholic  fermentations.  Glycerol,  succinic  acid, 
and  acetic  acid  have  been  noticed  among  these.  If  we  employ  zymase, 
such  products  are  not  formed  to  any  extent.  They  are  evidently  not  a 
part  of  the  alcoholic  fermentation  itself,  but  are  due  to  other  metabolic 
changes  of  the  yeast.2 


1  Ber.  37,  417  (1904). 

2  For  the  older  conception  of  alcoholic  fermentation,  cf.  C.  v.  Nageli;  Theorie  der 
Canning.  Miinchen  (1879), 


LECTURE  XXI. 
THE    FUNCTIONS    OF    THE    DIGESTIVE    ORGANS. 

I. 

WE  have  up  to  now  considered  the  transformation  of  each  separate 
substance  in  the  alimentary  canal  by  itself,  as  well  as  its  absorption,  assimi- 
lation, and  subsequent  destination  until  the  final  products  of  metabolism 
were  reached.  Such  a  method  of  presentation  has  the  advantage  that  it 
gives  us  a  clear  idea  concerning  the  behavior  of  any  given  foodstuff  in 
the  animal  organism,  and  makes  it  easier  for  us  to  trace  the  relations  of 
the  separate  organs  to  the  remaining  groups  of  foodstuffs  and  to  their 
functions.  On  the  other  hand,  in  order  to  avoid  repetition,  it  was  necessary 
for  us  to  touch  only  briefly  upon  certain  very  essential  points,  and,  further- 
more, there  were  certain  important  observations  which  we  could  not  dis- 
cuss at  all.  We  shall  now  in  the  following  lectures  consider  each  individual 
organ  of  the  animal  organism  by  itself,  and  in  this  way  find  opportunity 
to  mention  what  we  have  omitted,  and,  at  the  same  time,  to  bind  together 
certain  apparently  isolated  facts  with  other  analogous  ones  to  a  single  unit. 
It  is  extremely  difficult,  and  in  fact  impossible,  to  draw  a  sharp  line  between 
pure  physiology  and  physiological  chemistry.  The  time  has  long  since 
passed  when  the  latter  branch  of  biological  science  could  be  considered  as 
concerned  chiefly  with  the  investigation  of  the  composition  of  the  separate 
organs,  the  fluids  of  the  body,  and  the  excretions  and  secretions.  It  has 
been  recognized  for  some  time  that  the  tracing  of  the  relations  of  the  differ- 
ent groups  of  foodstuffs  to  one  another  and  their  transformations  in  the 
organism,  has  introduced  new  problems  into  the  field  of  physiological 
chemistry.  With  the  solution  of  these  problems,  which  are  fundamentally 
important  for  the  understanding  of  the  entire  metabolism,  the  limits  of  the 
working  field  of  the  physiological  chemist  are  by  no  means  reached,  as  we 
shall  see.  Physiological  chemistry  takes  part  more  and  more  in  explaining 
the  functions  of  the  various  organs.  Certain  of  the  apparently- very-com- 
plicated processes  have  been  brought  nearer  to  our  comprehension  by  the 
more  recent  investigations;  and  for  some  functions  of  which  it  was  not 
supposed  that  there  was  any  relation  to  chemical  processes,  newer  obser- 
vations have  opened  up  entirely  new  perspectives,  especially  from  a  chem- 
ical point  of  view.  Undoubtedly  physiological  chemistry  must  become 
more  closely  united  with  pure  physiology  in  order  that  the  fruits  obtained 
in  both  fields  may  become  fully  ripe. 

484 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.        485 

Such  a  point  of  view  is  particularly  advantageous  now  that  we  come  to 
consider  the  functions  of  the  various  organs  in  the  digestive  canal.  They 
are  of  most  diverse  nature  according  to  the  part  of  the  digestive  stratum 
in  which  they  are  found.  Let  us  begin  with  the  functions  of  the  upper  end 
of  the  alimentary  canal,  the  mouth.  In  it  the  food  which  has  been  pre- 
pared in  various  ways,  is  chewed  up  into  small  pieces  and  intimately  mixed 
with  the  saliva.  In  this  way  the  morsels  are  prepared  for  digestion.  The 
saliva  comes  from  the  salivary  glands  and  from  the  mucous  membrane  of 
the  mouth.  There  are  three  pairs  of  the  former,  which  may  be  dis- 
tinguished chiefly  by  the  nature  of  the  fluids  they  secrete.  The  parotid 
(near  the  ear)  gland  produces  a  thin  watery  fluid  containing  chiefly  albumin 
and  salts.  It  is  spoken  of  in  general  as  an  albuminous  gland.  Small  glands 
of  this  nature  are  found  as  well  in  the  mucous  membrane  of  the  nose  and 
mouth.  The  other  glands  are  the  so-called  mucous  glands.  They,  in  con- 
trast to  the  former,  furnish  a  glairy,  or  more  ropy  secretion,  due  to  the 
mucin  which  it  contains.  To  this  class  of  glands  belong,  in  the  case  of  most 
animals,  the  submaxillary  and  sublingual  glands.  Small  mucous  glands 
are  found  distributed  in  the  mouth,  throat,  and  oesophagus.  This  distinc- 
tion between  two  kinds  of  glands  is  not  a  sharp  one.  Thus  the  lower  jaw 
of  man  contains  glands  which  yield  a  thin  secretion  rich  in  albumin  as  well 
as  one  of  a  more  mucous  nature. 

The  secretion  from  each  separate  gland  may  be  examined  by  construct- 
ing fistulas  in  the  exit  ducts,  or  more  simply  by  introducing  a  canula  into 
the  mouth  of  the  duct  from  where  it  discharges  outward.  Normally  a 
mixture  of  the  secretions  from  all  of  the  glands  comes  into  action.  The 
extent  to  which  the  different  glands  take  part  in  the  formation  of  the 
saliva  varies.  The  secretion  of  the  glands  is  dependent  upon  quite  a 
number  of  outside  influences,  as  J.  P.  Pawlow  1  has  quite  recently  called 
to  our  attention.  In  the  exercise  of  their  function,  they  are  dependent 
upon  nervous  influences.  The  innervation  of  each  gland  is  twofold. 
Cerebral  and  sympathetic  fibers  lead  to  each.  The  submaxillary  gland 
contains  fibers  from  the  chorda  tympani,  and,  on  the  other  hand,  fibers 
enter  the  blood-vessels  of  the  gland  from  the  sympathetic  system.  This 
double  innervation  also  corresponds  to  the  nature  of  the  secretion. 
By  stimulating  the  cerebral  fibres,  in  other  words,  those  of  the  chorda 
tympani,  an  abundant  secretion  of  a  thin  liquid  is  produced;  whereas,  by 
stimulating  the  sympathetic  nerve,  only  a  few  drops  of  a  viscid  liquid  rich 
in  mucin  are  obtained.  The  sublingual  gland  behaves  quite  similarly.  The 
parotid  gland  is  also  partly  dependent  upon  the  cerebral  nervous  system 
(in  this  case  the  glossopharyngeal  nerve)  and  partly  on  the  sympathetic. 

For  some  time  it  was  believed  that  the  influence  of  the  nerves  which 
reach  these  glands  could  be  explained  by  an  action  upon  the  blood-vessels. 


Ergeb.  Physiol.  (Asher  and  Spiro)  Jahrg.  III.,  Abt.  I,  p.  177  (1904). 


486  LECTURE  XXI. 

If  the  lingual  nerve,  which  carries  the  cerebral  fibers  to  the  sub- 
maxillary  gland,  is  cut,  and  then  the  peripheral  stump  stimulated,  the 
blood-vessels  in  the  gland  become  dilated.  The  blood  streams  from  the 
veins  with  a  bright  red  color  similar  to  that  of  the  arterial  blood.  At  the 
same  time  there  is  an  increased  secretion  of  saliva.  On  the  other  hand, 
by  stimulating  the  fibers  of  the  sympatheticus,  the  blood-vessels  are  con- 
tracted. The  blood  passes  more  slowly,  and  the  flow  from  the  veins  is 
small  in  amount  and  of  a  dark  blue  color.  The  activity  of  the  secretion 
is  diminished.1  That,  on  the  other  hand,  the  innervation  of  the  blood- 
vessels is  not  the  sole  function  of  the  above-mentioned  nerves,  is  shown 
by  the  experiments  of  Heidenhain.2  He  found  that  with  the  lingual  nerve 
two  kinds  of  nerve  fibers  enter  the  gland.  If  a  dog  was  poisoned  with 
atropin,  then  stimulation  of  the  facial  nerve  fibers  caused  as  before  an 
acceleration  of  the  blood-stream,  while,  on  the  other  hand,  there  was  no 
increase  in  the  secretion  of  saliva.  From  this  it  is  clear  that  the  facial 
nerve,  as  well  as  the  sympathetic,  carries  fibers  to  the  submaxillary  gland 
which  have  a  specific  action  upon  the  individual  cells  of  the  gland.  For 
the  present  we  know  but  little  concerning  the  details  by  which  this  stim- 
ulation is  effected.  It  has  not  yet  been  found  possible  to  establish 
beyond  reasonable  doubt  the  anatomical  relations  of  the  nerve  fibers  to 
the  cells  of  the  gland. 

C.  Ludwig  and  A.  Spiess  3  have  shown  that  with  the  activity  of  the  cells 
the  temperature  also  rises.  They  introduced  a  thermometer  in  the  large 
vein  of  the  submaxillary  gland  of  a  dog,  a  second  in  the  exit  duct  from  this 
gland,  and  a  third  in  the  carotid  artery.  If  now  the  facial  fibers  were 
stimulated,  then  from  the  time  of  beginning  of  the  activity  of  the  glands 
the  thermometers  in  the  saliva  and  in  the  vein  registered  higher  tempera- 
tures than  that  of  the  carotid. 

It  was  at  one  time  believed  that  the  formation  of  the  saliva  could  be 
regarded  as  a  filtration  process.  It  was  soon  found,  however,  that  the 
separation  of  this  liquid  was  evidently  due  to  a  specific  activity  on  the  part 
of  the  gland-cells.  Even  the  chemical  composition  of  the  saliva  indicates 
this.  It  is  entirely  different  from  the  blood  and  lymph,  and  must  have  been 
formed  only  by  means  of  a  specific  choice  of  the  individual  constituents 
of  these  liquids  on  the  part  of  the  gland-cells.  In  fact,  it  is  even  necessary 
for  these  last  to  produce  for  themselves  certain  substances.  Here,  we 
cannot  treat  in  detail  of  all  the  evidence  which  has  been  brought  forward 
against  the  assumption  that  the  separating  of  the  saliva  is  a  result  of  a 
filtration  process.  We  can  only  briefly  touch  upon  it.  Thus  it  has 


1  Claude  Bernard:  Compt.  rend.  47,  245  (1858). 

2  Pfliiger's  Arch.  5,  309  (1872);  17  (1878).     See  also  Barbara:  Bull,  scienze  med. 
di  Bologna  (8),  2,  1  (1902). 

3  Sitzber.  Wiener  Akad.  25,  548  (1857). 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.        487 

been  found  that  if  a  mercury  manometer  be  introduced  into  the  exit  duct, 
then  after  stimulating  the  cerebral  secretory  nerves,  the  mercury  will  in  a 
short  time  rise  100  millimeters  or  more  higher  in  this  manometer  than  in 
another  one  that  is  placed  in  the  carotid  artery.  There  is,  therefore,  a 
considerable  increase  of  pressure  during  the  secretion  of  saliva.1  It  is  also 
an  important  fact  that  stimulation  of  the  secretory  nerves  has  an  effect 
even  in  animals  from  which  the  blood  has  been  removed  completely. 
That  the  cells  of  the  gland  are  active  during  the  preparation  of  saliva,  is 
evident  from  a  microscopic  examination  during  a  period  of  rest  and  one 
of  action.2  We  have  to  thank  Heidenhain3  for  this  interesting  information. 
He  described  the  contents  of  the  albuminous  glands  at  rest  and  after 
secretion  had  taken  place,  using  alcoholic-carmine  preparations.  In  the 
first  instance,  a  shrunken,  finely  granular  substance  is  seen  in  a  clear, 
uncolored  background.  The  nucleus  itself  appears  as  an  irregular,  serrated 
structure  without  any  distinct  nucleolus.  On  making  preparations  in  the 
same  way  of  glands  which  have  been  in  marked  activity  for  some 
time,  under  nervous  stimulation,  there  is  a  quite  different  appear- 
ance. The  size  of  the  cells  has  increased  to  a  greater  or  less  extent.  The 
nucleus  no  longer  appears  serrated,  but  round.  The  nucleolus  is  now 
much  more  sharply  outlined,  and  there  is  a  considerable  increase  in  the 
amount  of  substance  in  the  vicinity  of  the  nucleus  so  that  the  cells  appear 
opaque.  The  glands  themselves  show  similar  changes.  During  a  period 
of  rest  its  gland-cells  are  large  and  clear.  Their  nuclei  are  flattened  and 
parietal.  The  protoplasm  is  small  in  amount.  The  chief  constituent 
in  the  composition  of  the  cells  is  a  clear  substance  which  represents  the 
secretion  material  of  the  gland-cells.  When  the  gland  becomes  active  the 
nuclei  become  round.  The  nucleoli  become  more  distinct,  and  at  the  same 
time  the  nuclei  are  pressed  more  and  more  to  the  center  of  the  cells.  The 
cells  themselves  become  smaller  on  account  of  loss  of  the  above-mentioned 
clear  substance.  At  the  same  time,  there  is  an  increase  in  the  amount 
of  protoplasm,  evidently  the  beginning  of  the  production  of  a  new  secretion. 
If  we  examine  fresh  material,  instead  of  hardened  preparations,  we  will 


1  We  might  mention  in  this  connection  the  formation  of  retention  cysts  which  often 
take  place  in  the  parotid  gland  when  the  duct  from  a  lobule  becomes  stopped  up  for 
any  reason ;  for  example,  in  case  of  inflammation.     If  the  secretion  of  saliva  were  to  be 
regarded  as  a  mere  filtration  process,  it  would  be  expected  that  the  activity  in  the  region 
cut  off  would  soon  cease.     The  secretion,  however,  continues.     The  amount  of  pressure 
developed  in  consequence  is  indicated  by  the  swelling  produced.     Even  if,  later  on, 
secondary  changes  appear,  creating  new  conditions,  still  for  the  beginning  of  the  forma- 
tion of  cysts  our  observation  holds  true. 

2  Cf.  A.  Noll:  Die  Sekretion  der  Driisenzelle,  Ergeb.  Physiol.   (Asher  and  Spiro)  Jg. 
IV.  p.  84  (1905). 

3  Zentr.  med.  Wissensch.  9,   130  (1866).     Hermann's  Handbuch  der  Physiol.  5,  L 
64  (1883). 


488  LECTURE  XXI. 

obtain  quite  corresponding  results.  Thus  in  place  of  the  above  clear  sub- 
stance, little  granules  are  noticed  which  represent  the  secretion  material 
produced  by  the  cells.  During  rest  these  granules  are  being  formed  con- 
stantly to  be  given  off  during  activity.  There  has  been  a  great  deal  of 
discussion  as  to  whether,  in  the  secretion  of  the  glands,  the  cells  themselves 
are  destroyed,  or  whether  it  is  to  be  assumed  that  the  cell,  as  such,  retains 
its  protoplasm  and  nucleus  intact,  and  merely  gives  up  the  specific  secre- 
tion produced  by  it.  According  to  all  known  observations,  the  latter 
conception  appears  to  be  the  correct  one,  for  if  the  cells  of  the  gland  them- 
selves should  undergo  breaking  down,  then  there  should  be  considerable 
evidence  in  the  active  gland  of  a  renewal  of  cell  material.  As  a  matter 
of  fact,  there  is  but  little  sign  of  any  such  cell  division  taking  place. 

The  cells  of  the  various  glands  in  the  animal  organism  do  not,  to  be  sure, 
show  any  marked  difference  from  the  cells  of  the  other  tissues.  We 
know  that  all  sorts  of  different  cells  are  constantly  producing  definite 
products  which  take  part  in  metabolism  and  in  the  exercise  of  particular 
functions.  We  know,  for  example,  that  many  cells  give  up  ferments, 
while  others  produce  compounds  of  simple  constitution;  for  example,  the 
cells  of  the  suprarenal  bodies  produce  adrenalin,  and  those  of  the  intestine 
form  secretin.  The  formation  of  such  products  as  an  immediate  con- 
sequence of  the  activity  of  the  cells  escapes  our  observation  only  because 
the  amount  formed  is  so  small,  and  partly,  as  is  the  case  with  the 
digestive  ferments,  because  it  is  not  these  alone  that  are  given  up 
by  the  cells,  but  there  is  a  much  larger  amount  of  other  material  set  free 
simultaneously. 

We  may  consider  the  formation  of  the  secretion  by  the  gland-cells  in  the 
same  light,  and  trace  it  to  the  activity  of  the  cells,  and  in  a  narrower  sense 
to  the  protoplasm  and  cell-nuclei.  We  do  not  wish  to  speak  —  in  order 
to  avoid  misconceptions  —  of  a  transformation  of  protoplasm  into  secretion, 
as  is  often  done,  but  rather  of  the  production  of  the  latter  by  cell  activity. 
We  must  remember  that  the  gland-cells  are  constantly  being  supplied  with 
new  material  by  the  blood,  from  which  the  secretion  can  be  formed.  This 
is  taken  up  according  as  the  cell  requires  such  material,  and  by  means  of 
complicated  processes  the  cell  manufactures  the  secretion  from  it.  The 
protoplasm  itself  remains  behind  in  the  cell  together  with  the  nucleus; 
both  are  preserved  for  a  new  formation  of  secretion.  If  we  were  to 
assume  that  the  cells  themselves  were  passing  over  into  the  secretion,  it 
would  be  much  more  difficult  to  explain  the  process.  There  is  no  doubt 
that  ferments  play  an  important  part  in  the  formation  of  this  secretion. 
Thus  the  cells  of  the  gland  have  to  break  down  to  some  extent  the  protein 
substance  in  the  serum  in  order  to  construct  the  mucin  which  is  contained 
in  the  secretion.  The  fact  that  evidently  quite  extensive  transformations 
take  place  is  shown  by  the  fact  that  mucin  contains  a  large  amount  of 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.         489 

glucosamine,  while  in  the  protein  bodies  present  in  serum  there  is  but  a 
small  amount  of  this  aminohexose.  It  is  conceivable  that  the  albuminous 
substances  in  blood-serum  contain  perhaps  unknown  preliminary  stages 
in  the  glucosamine  formation,  but  it  is,  however,  also  possible  that  we  have 
here  one  stage  in  the  process  of  the  conversion  of  an  amino  acid  into  a 
sugar.  At  all  events,  the  formation  of  mucin  with  its  peculiar  composition 
deserves  considerable  attention. 

It  is  not  to  be  assumed  that  during  the  activity  of  the  gland,  the  cells 
must  be  entirely  built  up  as  well  as  the  secretion  formed.  At  the  same 
time  we  should  not  think  for  a  moment  that  these  cells  are  permanent 
structures.  We  do  not  doubt  that  they  are  constantly  being  renewed  like 
all  other  cells  of  the  body,  and  that  here  and  there  a  cell  disappears  to 
be  replaced  by  a  new  one. 

The  decrease  in  the  volume  of  the  individual  cells  during  their  activity 
also  has  an  effect  upon  the  weight  of  the  gland.  If  the  submaxillary 
gland  is  brought  into  activity  by  stimulating  the  fibers  of  the  facial  nerve, 
it  is  found  that  the  active  gland  decreases  in  weight. 

Some  attention  is  due  to  the  question  as  to  the  manner  in  which  inner- 
vation  of  the  salivary  glands  is  normally  produced.  The  Russian  physi- 
ologist Pawlow  deserves  great  credit  not  only  for  having  developed  the 
operative  technique  so  that  it  is  possible  under  purely  physiological  con- 
ditions to  trace  the  functions  of  the  various  digestive  glands,  but  also  for 
having  shown  in  an  entirely  original  way  how  the  activity  of  the  same  is 
dependent  upon  definite  external  conditions.  We  have  known  for  a  long 
time  that  the  activity  of  the  salivary  glands  is  influenced  by  sensations 
of  taste  and  smell,  and  even  by  certain  imaginations.  Pawlow,  however, 
deserves  the  credit  for  clearly  demonstrating  by  experiment  the  remark- 
able ability  that  the  salivary  glands  have  for  adapting  themselves  to  their 
work.  Among  other  things  he  called  attention  to  the  following  observa- 
tions :  If  a  dog  is  fed  with  dry,  solid  nourishment,  there  at  once  takes  place 
a  considerable  flow  of  saliva;  while  on  the  other  hand,  if  the  nourishment 
is  liquid,  there  results  but  a  slight  flow.  Chemicals  which  act  as  irritants, 
such  as  acids  and  alkalies,  increase  the  flow  of  saliva  in  proportion  to  the 
irritation  produced.  The  organism  attempts  in  this  way  to  protect  itself 
from  the  action  of  such  substances.  It  dilutes  them  and  washes  them  out 
from  the  mouth  as  much  as  possible.  If  small  quartz  pebbles  are  placed 
in  the  mouth  of  a  dog,  the  animal  permits  them  to  drop  out  gradually 
from  his  mouth,  but  without  any  flow  of  saliva.  If,  on  the  other  hand,  the 
same  material  is  placed  in  the  dog's  mouth  in  the  form  of  a  powder,  there 
is  a  considerable  flow  of  saliva.  The  purpose  of  this  is  clear,  —  in  this  way 
the  sand  is  washed  out  of  the  mouth,  while  in  the  case  of  the  little  stones 
the  tongue  alone  can  accomplish  their  removal.  In  all  such  cases  we  are 
struck  with  the  utility  of  the  whole  mechanism.  This  is  still  more  marked 


490  LECTURE   XXI. 

when  we  find  not  only  that  the  amount  of  saliva  is  regulated  according  to 
the  requirements,  but  likewise  its  composition.  At  one  time  it  contains 
considerable  mucin,  at  another  time  relatively  little,  according  to  the  con- 
ditions. Apparently  the  irritation,  whether  it  be  chemical,  thermal,  or 
mechanical,  stimulates  the  apparatus  at  the  end  of  the  afferent  nerves 
in  the  mucous  membrane  of  the  mouth.  From  here  the  impulses  are 
transmitted  to  the  central  organ  of  the  nervous  system,  and  now  by 
means  of  the  efferent  nerves  the  individual  salivary  glands  are  called 
into  action.  We  speak  of  such  a  process  in  general  as  a  reflex  action. 

It  is  of  chief  interest  to  us  that  it  is  possible  by  various  outward  effects 
to  influence  the  activity  of  the  glands  in  such  a  way  that  the  composition 
of  the  saliva  secreted  is  adjusted  to  the  prevailing  conditions.  At 
present  we  can  only  imagine  how  this  adjustment  may  be  effected. 
The  saliva  itself  always  contains  besides  inorganic  salts  and  water  a  certain 
amount  of  organic  material,  as  we  have  seen.  We  also  repeat  that 
the  saliva  contains  a  ferment  capable  of  hydrolyzing  starch,  the  diastase. 
It  is  remarkable  too  that  it  always  contains  small  amounts  of  alkali 
thiocyanate.  We  are  wholly  in  the  dark  concerning  the  formation  of  this 
last  compound,  or  as  regards  its  use. 

In  this  connection  it  seems  fitting  to  mention  some  observations  con- 
cerning secretions  in  the  mouths  of  certain  invertebrates.  They  are  of 
particular  value  because  they  make  it  easier  for  us  to  understand  the  most 
important  work  of  the  gland-cells.  Here  we  meet  with  the  preparation 
of  strong  acids  by  means  of  cell  activity  from  material  which  could  not 
have  contained  the  acid  already  formed.  Long  ago  Troschel  *  noted,  in 
examining  a  kind  of  snail,  Dolium  galea,  that  the  animal  squirted 
from  its  mouth  a  stream  of  liquid  clear  as  water.  The  liquid  showed  a 
strongly  acid  reaction,  and  caused  effervescence  on  coming  in  contact  with 
the  limestone  lying  on  the  ground.  The  secretion  was  produced  from  two 
large  gland-like  organs  lying  near  the  stomach.  The  ducts  from  it  ascend 
on  each  side  of  the  gullet  and  empty  into  the  mouth.  The  secretion  con- 
tains sulphuric  acid,  and,  in  fact,  as  much  as  4.1  per  cent  of  the  free  acid  is 
present.  Besides  this,  there  is  0.4  to  0.6  per  cent  of  hydrochloric  acid. 
Other  varieties  of  snails  similarly  produce  acids.  •  Some  of  these  "  acid 
snails  "  have  been  quite  recently  studied  by  Fr.  N.  Schulz.2  He  followed 
particularly  closely  the  acid  production  on  the  part  of  the  naked  snail, 
Pleurobranchia  Meckelii  of  the  order  Opisthdbranchi.  On  being  touched, 
the  snail  rolls  itself  up.  If  the  animal  is  squeezed  a  little,  its  external 
surface  after  a  short  time  becomes  covered  with  a  slimy  secretion  of  acid 
reaction.  This  comes  from  glands  which  are  very  numerous  in  the  skin. 

1  Poggendorf  Js  Ann.  93,  614  (1854) ;  J.  pr.  Chem.  63,  170  (1854) ;  see  also  de  Luca  and 
Panceri,  Compt.  rend.  65,  577  and  712  (1867). 

2  Z.  allgem.  Physiol.  6,  206  (1905). 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.        491 

Besides  this  secretion  the  animal  empties  from  its  pharynx  a  very  strongly- 
acid-reacting  juice.  This  comes  from  a  gland-like  structure  consisting  of 
long  coils  enveloped  in  a  highly  complicated,  contractile  network.  The 
chief  constituent  of  the  individual  cells  is  a  liquid,  while  the  amount  of  pro- 
toplasm itself  is  relatively  small.  If  the  gland  is  stimulated,  the  above- 
mentioned  network  contracts;  and  the  liquid  secretion  of  the  gland-cells, 
which  is  contained  in  larger  or  smaller  vacuoles,  is  emptied  into  the 
exit  duct.  Evidently  in  this  case  the  secretion  is  merely  mechanically 
removed  from  the  cells.  After  the  relaxation  of  the  contracted  cell-coil, 
there  remain  in  the  cells  at  first  only  the  shrunken  protoplasm  and  the 
cell-nuclei,  and  then  begins  anew  the  formation  of  secretion.  Several 
things  indicate  that  the  nucleus  itself  plays  an  important  part  in  this 
process.  The  secretion  contains  free  sulphuric  acid.  What  is  the  source 
of  this  acid?  It  might  come  from  sulphates,  or  from  organic  compounds 
containing  sulphur,  such  as,  for  example,  albumin.  The  latter  is  hardly 
to  be  considered  as  a  possible  source  of  sulphuric  acid.  It  seems  certain 
that  most  of  the  acid  must  be  formed  from  sulphates,  for  the  amount  of 
acid  produced  is  too  large,  and  the  amount  of  sulphur  present  in  albumin 
too  small,  to  account  for  the  formation  by  the  assumption  of  an  oxidizing 
decomposition,  as,  for  example,  of  cystine.  It  has  been  found  that  the 
secretion  continues  during  starvation.  If  the  albumin  itself  were  the 
source  of  the  sulphur,  we  would  expect  that  the  formation  of  sulphuric  acid 
would  soon  cease  in  the  starved  organism.  It  has  never  been  explained 
how  the  cells  in  the  gland  are  able  to  produce  the  free  acid.  When  we  come 
to  discuss  the  formation  of  hydrochloric  acid  in  the  human  stomach,  we 
shall  find  likewise  that  we  are  again  in  the  dark.  It  has  been  attempted 
to  explain  the  formation  of  the  strong  acid  as  a  result  of  the  mass-action 
law.  We  know  that  from  salts  of  the  mineral  acids  a  small  amount  of 
acid  may  be  set  free  by  the  action  of  large  amounts  of  carbonic  acid,  for 
example.  We  also  know  that  as  a  result  of  ionization  a  small  amount  of 
acid  ions  are  probably  set  free  in  the  organism.  We  shall  not  deny  that 
perhaps  a  part  of  the  acid  in  the  secretion  may  be  formed  in  some  such 
way,  and  it  is  indeed  conceivable  that  eventually  all  of  the  acid  may  be 
produced  in  such  manner,  if  we  assume  that  as  soon  as  a  little  acid  is  set 
free,  it  is  in  some  manner  carried  out  of  the  range  of  chemical  reaction,  so 
that  constantly  more  and  more  of  the  acid  will  be  formed.  But  even  such 
an  hypothesis,  which  necessitates  the  further  assumption  of  some  means 
of  removing  the  acid  as  fast  as  it  may  be  formed,  does  not  enable  us  to 
explain  satisfactorily  the  whole  process.  At  all  events,  the  cells  themselves 
must  exert  a  specific  action.  In  this  case,  the  cells  of  the  gland  form  sul- 
phuric acid  alone,  while  in  the  stomach  only  hydrochloric  acid  results.  It 
might  be  assumed  that  the  membrane  of  the  cells  is  only  permeable  to  certain 
ions.  It  has,  for  example,  been  asserted  that  the  walls  of  the  stomach  axe 


492  LECTURE   XXI. 

impermeable  to  chlorine  ions,  and  in  this  way  the  formation  of  hydrochloric 
acid  in  the  stomach  was  explained.1  It  was  soon  apparent,  however,  that 
such  a  theory  was  untenable.  If  we  stop  considering  the  production  of 
the  acid  by  itself,  but  remember  that  the  formation  of  the  remaining 
products  of  secretion  point  to  a  specific  and  extensive  activity  on  the 
part  of  the  gland-cells,  then  evidently  the  formation  of  the  free  acid  repre- 
sents only  one  link  in  the  chain  of  the  entire  secretion  process.  It  is  not 
any  more  remarkable  than,  for  example,  the  formation  of  mucin  in  the 
cells  of  the  salivary  glands.  Just  as  little  as  we  are  unable  to  account  for 
the  formation  of  the  latter  as  a  result  of  purely  physical  or  chemical 
processes,  is  it  possible  for  us  to  understand  clearly  the  production  of  acid 
on  the  part  of  the  cells. 

The  question  next  arises  concerning  the  biological  significance  of  the 
acid  secretion  in  snails.  Troschel,  the  discoverer  of  the  presence  of  the 
acid,  was  inclined  to  believe  that  it  was  a  means  of  protection  against 
enemies.  This  is  hardly  correct  in  the  sense  meant.  Although  the 
Dolium  galea  is  able  to  throw  out  this  secretion  when  on  land,  the  irritating 
effect  of  the  acid  would  be  lost  when  the  animal  is  in  the  water,  and, 
moreover,  the  water  itself  offers  so  much  resistance  that  obviously  the 
animal  would  not  be  able  to  send  out  a  stream  of  secretion  at  any  desired 
moment.  On  the  other  hand,  it  is  possible  that  the  acid  formation,  espe- 
cially on  the  part  of  the  glands  in  the  skin  of  the  Pleurobranchi,  may  serve 
indirectly  as  a  means  of  protection  in  the  sense  that  by  reason  of  it  these 
snails  will  be  avoided  as  food  by  other  animals.  Unquestionably,  the 
secretion  of  the  large  glands  in  the  gullet  must  have  some  other  significance. 
It  has  been  suggested  that  they  play  a  role  in  digestion.  Careful  investi- 
gation, however,  has  proved  that  this  is  not  the  case.  Semon2  believed 
that  the  sulphuric  acid  acts  upon  the  lime  skeletons  of  other  animals  upon 
which  these  snails  feed.  Thus  calcium  sulphate  would  be  produced. 
The  effect  of  this  decomposition  Semon  studied  on  the  skeleton  of  the 
star-fish.  He  found  that  the  latter,  after  it  had  lain  for  some  time  in 
water  containing  sulphuric  acid,  could  be  broken  up  by  means  of  the 
fingers.  The  direct  examination  of  the  intestinal  contents  of  these  snails 
did  not  lend  any  support,  however,  to  the  assumption  of  any  such  action. 
It  is,  therefore,  improbable  that  the  sulphuric  acid  is  produced  for  the 
purpose  suggested  by  Semon.  Now  we  find  in  the  animal  kingdom 
repeated  examples  of  contrivances  by  means  of  which  one  animal  which 
eats  another  species  for  its  nourishment  is  able  to  cripple  its  prey.  This 
is  the  case  with  the  poison  glands  of  snakes.  Perhaps  in  the  case  of  the 
snails  the  acid  forms  a  weapon  of  attack.3  Many  sea  animals  are  extremely 

1  Cf.  Koppe,  Pfliiger's  Arch.  62, 567  (1892),andLandislaus  v.  Rohrer:  ibid.  110,416  (1905). 

2Biol.  Zentr.  9,  80  (1890). 

8  W.  Preyer:     Naturwissensch.  Wochschr.  Berlin  6,  481  (1890). 


THE    FUNCTIONS   OF  THE   DIGESTIVE    ORGANS.         493 

sensitive  to  acid.  Thus  the  Echinoderms  draw  in  their  suckers  when 
exposed  to  acid.  They  are  then  easily  removed  from  the  place  to  which 
they  had  attached  themselves. 

Let  us  now  return  to  the  saliva.  We  have  already  mentioned  its  most 
important  functions.  They  are  chiefly  of  a  mechanical  nature,  —  the 
food  is  surrounded  by  saliva  and  thus  made  easy  to  swallow.  The  saliva 
also  is  an  important  means  of  keeping  the  teeth  clean.  In  this  case  also 
it  exerts  first  of  all  a  mechanical  action,  and,  on  the  other  hand,  when  of 
normal  composition,  it  also  tends  to  prevent  decomposition  by  the  bacterial 
flora  of  the  mouth.  It  is  probable  that  in  many  cases  the  formation  of 
caries  in  teeth  is  due  to  an  abnormal  composition  of  the  saliva.  Tooth 
decay,  moreover,  usually  results  from  a  faulty  formation  of  the  tooth  itself. 
The  tissue  composing  the  teeth  is  closely  related  to  that  of  the  bones. 
Three  tissues  are  known  to  take  part  in  the  formation  of  teeth,  of  which  one, 
the  cement,  corresponds  to  the  bony  tissue.  Dentine  also  has  a  similar 
composition.  We  find  that  bones  contain:  calcium  phosphate,  magnesium 
phosphate,  calcium  fluoride,  calcium  chloride,  calcium  carbonate,  ferric  oxide, 
and  an  organic  basal  substance,  which  on  boiling  yields  gelatin.  Enamel, 
the  third  tissue  of  teeth,  is  characterized  by  its  containing  the  least  water 
and  the  most  mineral  matter  of  any  substance  in  the  human  body.  Under 
normal  conditions  it  exerts  great  resistance  to  external  influences,  and,  as 
long  as  it  is  intact,  prevents  infection  by  bacteria.1  The  enamel  contains 
lime  salts  chiefly.  At  this  place  we  need  hardly  mention  the  importance 
of  the  food  being  well  chewed.  It  is  perfectly  clear  that  the  subdivision 
of  the  food  is  of  great  benefit  as  regards  the  rapidity  with  which  it  is  acted 
upon  by  the  digestive  ferments.  By  means  of  the  teeth  the  food  is  changed 
into  such  a  state  that  it  can  be  acted  upon  readily  by  the  digestive  juices. 
It  might  be  thought  that  on  feeding  with  broth,  the  function  of  the  teeth 
would  be  replaced.  We  shall  see  later  on,  however,  that  the  manner  in 
which  the  food  is  prepared  has  a  great  influence  upon  the  function 
of  the  secretions  in  the  digestive  tract,  especially  that  of  the  stomach. 
A  uniform  diet  could  not  possibly  stimulate  our  senses  permanently. 

In  many  cases  the  saliva  acts  as  a  solvent,  and  in  this  way  the  sensation 
of  taste  is  obtained,  for  we  can  only  taste  substances  which  are  in  solution. 
The  peripheral  organs  of  the  sense  of  taste  are  distributed  throughout  the 
whole  of  the  mouth.  We  find  them  on  the  upper  surface  of  the  tongue, 
on  the  under  surface  at  the  tip  of  the  tongue,  in  the  mucous  membrane  of 


1  We  should  not  fail  to  mention  in  this  case  the  remarkable  readiness  with  which 
wounds  in  the  mucous  membrane  of  the  mouth,  or  indeed  of  the  entire  alimentary 
canal,  are  healed;  and  how  seldom  there  is  any  infection  here  in  spite  of  frequent  ex- 
posure. We  may  perhaps  speak  of  the  immunity  of  cells  in  the  mucous  membrane 
and  surrounding  tissue.  This  immunity  may  be  acquired  by  the  fact  that  metabolic 
products  of  bacteria  in  the  mouth  are  absorbed  from  the  dilute  solution  there,  and  this 
creates  immunity. 


494  LECTURE  XXI. 

the  soft  and  hard  palate,  the  anterior  pillar,  the  tonsils,  the  posterior  pillar, 
the  uvula,  the  epiglottis,  and  even  the  throat,  itself.  This  wide  distribution 
of  the  organs  for  taste  perception  is  only  noticeable  during  youth.  In 
adults  the  sensation  is  more  localized,  although  it  varies  greatly  with  indi- 
viduals. The  mucous  membrane  of  the  cheeks,  the  uvula,  tonsils,  and 
the  middle  of  the  tongue,  are  almost  always  incapable  of  taste  perception 
in  adults.  The  end-apparatus  of  the  taste-nerves  form  the  so-called  taste- 
buds  or  taste-goblets.  In  man  the  glossopharyngeal  and  trigeminal  nerves 
have  been  recognized  as  taste-nerves.  The  former  innervate  the  back 
.part  of  the  tongue,  the  latter  the  front  part.  Individual  peculiarities  are 
noticed  here,  and  sometimes  one  of  these  nerves  alone  provides  for  the  whole 
region.  The  different  sensations  of  taste  may  in  general  be  attributed 
to  four  different  qualities;  namely,  sweet,  sour,  bitter,  and  salt.  We  also 
speak  of  alkaline  and  metallic  tastes.  There  is  hardly  room  for  doubt  that 
these  different  sensations  of  taste  are  produced  by  the  aid  of  different 
nerves,  so  that  for  the  taste-nerves  the  law  of  specific  sense  energy  l  applies. 
According  to  this  law,  one  and  the  same  excitant  when  acting  upon  different 
nerves  will  always  produce  different  sensations,  while,  on  the  other  hand, 
all  sorts  of  different  excitants  always  produce  the  same  sensation  when 
acting  upon  the  same  nerve.  The  different  quality  of  the  sensation  is 
therefore  merely  caused  by  the  different  nature  of  the  end-apparatus  in 
the  central  nervous  system.  Moreover,  the  peripheral  reception  appara- 
tus is  so  specialized  that  it  is  only  affected  by  certain  definite  excitants. 
It  might  be  thought,  and  especially  in  the  study  of  the  sensation  of  taste, 
that  the  chemical  constitution  of  a  substance  having  a  definite  quality  of 
taste  might  give  us  some  idea  of  the  way  in  which  the  definite  end-apparatus 
is  excited.  Numerous  experiments  have  been  performed  with  this  idea 
in  mind,  but  without  success.2  Thus,  for  example,  a  great  many  amino 
acids  taste  sweet,  while  others  are  bitter.  Glycocoll,  alanine,  and  a-amino- 
valeric  acid  are  sweet,  while  Z-leucine,  which  occurs  in  nature,  is  bitter. 
It  is  remarkable  that  c£-leucine  has  a  sweet  taste.3  In  cW-leucine  the  sweet 
taste  predominates.  The  sense  of  smell  is  closely  related  to  that  of  taste, 
and  frequently  they  are  confused  with  one  another.  It  is,  furthermore, 
interesting  that  both  these  sensations  of  taste  and  of  smell  may  be  pro- 
duced by  means  of  a  very  small  amount  of  material.  The  organ  of  smell 
is  in  some  cases  especially  sensitive.  Emil  Fischer  and  Penzoldt  found, 
for  example,  that  as  little  as  0.000,000,04  milligram  of  mercaptan  in  a 

1  Johannes   Miiller:    Zur   vergleichenden   Physiologic   des   Gesichtssinnes.     Leipzig 
(1826).     Cf.  R.  Weinmann:  Die  Lehre  von  den  specifischen  Sinnesenergien,  Hamburg 
and  Leipzig  (1895). 

2  Cf.  Wilhelm  Sternberg:  Arch.  Anat.  Phys.  1903,  538;  1904,  483;  1905,  201;  Ber. 
15,  36  (1905). 

3  Emil  Fischer  and  Otto  Warburg:  Ber.  35,  3997,  4005  (1905). 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.         495 

liter  of  air  is  perceptible.  We  shall  repeatedly  come  back  to  the  influence 
of  the  sensatory  impressions  upon  the  functions  of  the  digestive  glands. 
The  nerves  of  smell  and  of  taste  are  important  protective  organs.  They 
call  attention  to  processes  of  decomposition,  to  decay  in  our  food,  and  allow 
us  to  recognize  the  presence  of  many  injurious  substances. 

From  the  mouth,  the  food  is  carried  by  the  process  of  swallowing  into 
the  oesophagus,  and  from  here  directly  into  the  stomach  through  the  cardia. 
With  the  exception  of  a  slight  transformation  of  starch  into  sugar,  the 
real  process  of  digestion  does  not  begin  until  the  food  reaches  the  stomach, 
where  it  proceeds  energetically.  We  repeat  that  the  diastase  from  the 
saliva  can  under  certain  conditions  continue  its  action  for  some  time,  but, 
on  the  other  hand,  the  stomach  itself  has  its  own  ferments.  As  has  been 
recently  shown,  it  possesses,  for  one  thing,  a  lipolytic  ferment,  although  we 
have  at  present  no  means  of  estimating  the  extent  of  its  activity.  Its  sig- 
nificance has  been  quite  variously  estimated  and,  in  fact,  its  very  presence 
has  been  doubted  by  some.  Besides  lipase,  there  are  ferments  present  in 
the  stomach  which  are  capable  of  acting  upon  the  protein  of  the  foods. 
These  are  pepsin  and  rennin.  We  have  already  stated  that  the  existence 
of  the  latter  ferment  has  been  quite  recently  questioned,  and  it  has  been 
assumed  that  the  two  properties  of  coagulating  milk  and  dissolving  albu- 
min are  due  to  the  action  of  a  single  ferment.  We  can  adopt  this  assump- 
tion that  the  action  of  rennin  corresponds  to  that  of  pepsin,  only  when 
it  has  been  verified  by  further  investigation.  Until  this  has  been  done, 
we  will  content  ourselves  with  the  older  conception  of  the  presence  of  both 
pepsin  and  rennin,  although,  we  have  already  seen,  there  are  a  number  of 
facts  which  speak  in  favor  of  Pawlow's  hypothesis. 

These  ferments  are  produced  by  certain  glands  in  the  mucous  membrane 
of  the  stomach.  The  stomach  itself  is  not  a  physiological  unit.  Even 
the  outer  appearance  shows  a  marked  difference  between  the  pyloric  and 
fundus  (or  cardiac)  portions  of  the  mucous  membrane.  That  of  the 
former  is  pale  and  has  a  few  deep  folds,  while  the  latter  is  of  a  reddish- 
yellow  or  reddish-gray  color,  and  has  numerous  folds  which  are  connected 
with  one  another  by  a  sort  of  network.  In  these  net-like  little  hollows 
between  the  folds  end  the  stomach  glands.  There  are  two  types  of  these 
glands,  one  of  which  contains  but  a  single  kind  of  cell,  while  the  other 
contains  two.  In  the  pyloric  end  there  is  found  but  one  cell  form,  while 
in  the  cardiac  or  fundus  end  the  glands  are  of  the  latter  type.  There  is 
no  sharp  distinction  between  them,  however.  These  two  types  of  glands, 
both  of  which  are  tubular  in  shape,  are  named  according  to  the  locality 
in  which  they  are  found,  and  are  known  respectively  as  pyloric  and  cardiac 
or  fundus  glands.  The  former  contain  a  cylindrical  epithelium,  and  the 
latter  contain,  in  addition,  other  smaller  cells  irregularly  distributed 
between  the  larger  cells  and  the  basement  membrane.  The  first  kind  of 


496  LECTURE  XXI. 

cells  are  designated  in  the  cardiac  glands  as  chief,  central,  principal,  or 
adelomorphous  cells,  while  the  latter  are  called  either  border,  parietal, 
or  delomorphous  cells.  Between  the  gland-cells  there  are  fine  secretion 
capillaries  which  surround  the  border  cells  like  a  basket.  For  a  long 
time  it  was  believed  that  this  histological  distinction  of  two  kinds  of  cells 
also  corresponded  to  a  physiological  distinction.  The  fundus  glands  were 
supposed  to  secrete  only  pepsin,  while  the  pyloric  glands  merely  formed 
mucous.  That  this  is  not  the  case  is  shown  by  the  fact  that  the  secretion 
carefully  collected  from  the  latter  portion  of  the  stomach  does  actually 
contain  pepsin.  The  pyloric  and  cardiac  parts  can  easily  be  isolated,,  and 
in  this  way  " small  stomachs"  are  formed  in  the  Pawlow  sense,  and  by 
means  of  fistulas  the  contents  of  each  may  be  studied  by  itself.  At 
present  we  are  still  undecided  as  to  the  especial  significance  of  the  chief 
cells  and  of  the  border  cells.  It  has  been  established  that  the  former 
take  part  in  the  formation  of  pepsin  and  rennin,  but  the  function  of  the 
border  cells  remains  vague.  From  the  fact  that  the  pyloric  part  of  the 
stomach  produces  little  or  no  hydrochloric  acid,  it  has  been  suggested  that 
the  border  cells  produce  the  acid,  but  there  has  never  been  any  direct 
proof  of  this. 

Whatever  the  functions  of  the  cells  may  be,  it  is  to  be  said  that  much 
the  same  changes  take  place  in  them  during  activity  as  in  the  cells  of 
the  salivary  glands.  During  a  period  of  rest  the  secretion  is  formed 
which  is  given  up  during  the  period  of  work. 

All  the  secretions  of  the  mucous  membrane  of  the  stomach  and  its 
glands  taken  together  form  the  so-called  gastric  juice.  It  consists  in  part 
of  mucous  which  is  given  off  chiefly  from  the  superficial  surface  of  the 
mucous  coat,  together  with  the  ferments,  hydrochloric  acid,  inorganic 
salts,  and  small  amounts  of  other  organic  substances.  Exact  studies 
concerning  the  formation  of  the  gastric  juice  and  of  its  dependence  upon 
outward  influences  were  first  made  possible  by  the  operative  skill  of 
Pawlow  and  his  pupils.  His  methods  and  his  investigations  gave  us  the 
first  insight  into  the  relation  between  the  secretions  of  the  stomach 
and  physiological  conditions.  Pure  gastric  juice  may  be  obtained  by  the 
establishment  of  a  fistula,  best  in  combination  with  one  in  the  oesophagus. 
Thus  the  food  swallowed  by  the  animal  may  be  removed  before  it  reaches 
the  stomach.  In  this  way  a  fictitious  feeding  is  obtained,  and  the  gastric 
juice  is  not  contaminated  with  the  food,  nor  with  the  intestinal  products. 
It  was  found  advisable  also  to  isolate  a  portion  of  the  stomach,  forming 
a  little  stomach,  or  blind  sack,  in  which  the  secretion  process  could  be 
studied  by  means  of  a  fistula  while  digestion  was  going  on  in  the  rest  of 
the  organ.  The  gastric  juice  flowing  out  of  such  a  fistula  is,  after  filtering 
off  the  mucous,  clear  as  water,  odorless,  and  of  an  acid  taste.  This  taste 
is  due,  as  has  been  stated,  to  the  presence  of  free  hydrochloric  acid.  In 


THE    FUNCTIONS    OF   THE   DIGESTIVE   ORGANS.         497 

dogs  there  is  from  0.46  to  0.6  per  cent  acid  present,  while  in  man  the 
values  vary  greatly.  Thus  the  amount  present  has  been  variously  stated 
in  the  literature  as  from  0.05  to  0.57  per  cent.  We  have  already  said 
that  it  now  seems  impossible  to  regard  this  free  acid  as  taken  directly 
from  the  blood,  for  the  blood  may  be  considered  as  of  neutral  reaction. 
A  great  number  of  experiments  have  been  undertaken  without  definitely 
settling  this  question  of  the  acid  formation.  We  must  rest  content  with 
the  hypothesis  that  it  is  due  to  a  specific  activity  on  the  part  of  the  cells, 
and  will  state  once  more  that  it  does  not  imply  a  process  any  more  com- 
plicated than  that  of  the  formation  of  other  substances  which  result  from 
the  specific  activity  of  the  cells  in  every  gland.  There  is  no  justifiable 
ground  for  giving  a  peculiar  position  to  the  acid  secretion. 

The  individual  ferments  are  not  found  in  a  finished  state  in  the  mucous 
coat  of  the  stomach;  i.e.,  they  are  not  given  up  by  it  in  an  active  condi- 
tion. This  preliminary  condition  of  the  ferment  is  spoken  of  in  general 
as  that  of  a  zymogen,  and  in  the  case  of  pepsin  itself  we  have  pepsinogen. 
The  presence  of  such  a  substance  may  be  shown  by  the  following  experi- 
ment: Pepsin  itself  is  extremely  sensitive  to  a  solution  of  soda,  by 
means  of  which  it  is  soon  destroyed.  Pepsinogen,  on  the  other  hand, 
resists  the  action  of  soda  much  more  strongly.  If  the  mucous  membrane 
of  the  stomach  is  cut  up  into  small  pieces  and  extracted  with  a  dilute 
soda  solution,  there  is  obtained  after  filtering  a  liquid  which  of  itself  exerts 
no  digestive  action  upon  albumin,  but  does  so  on  being  acidified  with 
hydrochloric  acid.  The  acid  serves  to  convert  pepsinogen  into  pepsin. 
If,  now,  after  the  digestion  has  proceeded  for  a  short  time,  the  liquid  is 
again  made  alkaline,  a  further  addition  of  acid  will  no  longer  bring  forth 
the  digestive  action  of  pepsin.  The  pepsin  has  been  destroyed  by  the 
soda.  We  are  at  present  unable  to  explain  how  the  acid  activates  the 
zymogen,  and,  in  fact,  such  processes  will  remain  obscure  until  we  know 
more  about  the  chemical  nature  of  the  ferments  themselves.  We  can 
indeed  assume  that  the  hydrochloric  acid  in  some  way  causes  a  rearrange- 
ment of  the  atoms  in  the  ferment  molecule,  possibly  by  the  formation  of 
an  anhydride  or  something  similar,  and  that  in  the  new  state  the  ferment 
is  capable  of  exerting  its  characteristic  action. 

Rennin  likewise  is  not  present  in  the  mucous  membrane  as  such,  but  in 
the  form  of  a  zymogen.  It  is  activated  in  precisely  the  same  manner  as 
pepsinogen,  and  in  fact  these  two  ferments  are  very  similar  in  their  entire 
behavior. 

It  is  highly  significant  that  the  function  of  the  mucous  membrane  and 
its  glands  is  dependent  upon  definite  kinds  of  stimulation.  These  can  be  ef- 
fected in  part  in  the  stomach  itself,  or  the  stimuli  may  be  transmitted  to  the 
stomach  from  other  organs.  The  secretion  of  .the  gastric  juice  is  brought 
about  by  reflex  action.  This  may  be  demonstrated  very  prettily  by  making 


498  LECTURE  XXI. 

oesophageal  and  gastric  fistulas  in  a  dog.  Before  the  animal  is  fed,  no 
gastric  juice  flows  out  of  the  latter.  When  the  animal  is  offered  food, 
first  of  all  the  dog  chews  it;  on  swallowing,  instead  of  reaching  the  stomach, 
the  food  passes  out  through  the  fistula  in  the  oesophagus.  Thus  there 
is  no  chemical,  thermal,  or  mechanical  stimulation  produced  upon  the 
mucous  membrane  of  the  stomach.  Notwithstanding,  five  or  six  minutes 
after  the  animal  is  offered  food,  there  takes  place  regularly  an  abundant 
secretion  of  gastric  juice.  Pawlow  and  Schumow-Simanowskaja  1  have 
also  succeeded  in  proving  that  the  vagus  nerve  carries  secretory  fibers. 
The  production  of  gastric  juice  is  not  entirely  dependent  upon  the  vagus 
as  is  evident  from  the  fact  that  it  continues  after  both  the  vagi  have  been 
severed,  although  the  quality  of  the  secretion  is  apparently  changed;  at 
least,  there  is  less  pepsin  in  it. 

Highly  important  is  the  observation  that  psychic  influences  have  the 
decisive  effect  upon  the  formation  of  gastric  juice.  It  may  be  shown  that 
the  action  of  the  nerves  of  taste  and  of  smell  alone  do  not  suffice  to  cause 
a  secretion  from  the  lining  of  the  stomach.  Similarly  the  act  of  chewing 
is  ineffective  of  itself.  The  reflex  secretion  of  the  stomach  juices  is  only 
effected  when  the  animal  has  the  desire  to  eat.  If,  after  the  latent 
period  of  about  five  minutes,  the  secretion  of  gastric  juice  has  once  begun, 
it  then  continues  for  two  or  three  hours.  This  secretion  produced  reflex- 
ively  ceases  immediately  on  cutting  the  two  vagi  nerves.  It  would  be 
wrong  to  assert  that  the  nerves  of  smell  and  of  taste  take  part  in  the  psy- 
chical stimulation  of  the  secretion.  To  be  sure,  they  may  aid  indirectly 
in  many  cases,  by  recalling  to  the  imagination  certain  impressions  which 
awaken  the  desires  to  eat.  Of  course  these  impressions  may  in  some  cases 
be  first  caused  by  the  momentary  stimulation  of  smell  or  taste. 

By  means  of  such  experiments  as  those  carried  out  by  Pawlow  in  many 
directions,  the  great  importance  of  the  appetite  has  been  clearly  estab- 
lished. It  is  by  no  means  a  matter  of  indifference  whether  one  eats  with 
pleasure  or  from  compulsion. 

The  importance  of  the  gastric  secretion  produced  reflexively  by  psy- 
chical influences  is  made  very  clear  by  the  following  experiment  performed 
by  Pawlow.  He  took  two  dogs,  each  having  fistulas  in  the  oesophagus  and 
in  the  stomach,  and  introduced  equal-sized  pieces  of  meat  through  the 
gastric  fistula  of  each  dog  in  such  a  way  that  the  animal  was  not  conscious 
of  the  operation.  One  of  the  dogs  was  then  given  a  piece  of  meat  to  devour. 
(In  such  cases,  where  the  food  devoured  does  not  reach  the  stomach  of  the 
animal,  we  speak  of  a  fictitious  meal.)  After  some  time  had  passed,  Pawlow 
compared  the  pieces  of  meat  in  the  stomachs  of  the  two  dogs.  It  was 
found  that  the  meat  in  the  stomach  of  the  dog  which  had  received  the 


Arch.  Anat.  Physiol.  1895,  53. 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.         499 

fictitious  meal  was  much  more  thoroughly  digested  than  the  meat  in  the 
stomach  of  the  other  dog.1 

It  is  an  old  experience  that  psychic  influences  may  destroy  the  appetite. 
In  this  case  there  are  great  individual  differences;  often  slight  anger  will 
suffice  to  destroy  the  appetite  completely.  These  experiences  can  be  shown 
experimentally  to  be  well  founded.  Thus,  among  others,  A.  Bickel 2  has 
found  that  the  gastric  secretion  stops  at  once  when  a  dog  is  confronted 
with  a  cat.  Undoubtedly  the  same  relations  exist  in  man.  Naturally, 
in  the  latter  case  we  do  not  possess  such  a  rich  field  for  observation.  In 
man  such  experiments  are  influenced  much  more  by  secondary  effects  than 
is  the  case  with  animals,  where  reactions  take  place  more  in  accordance  with 
sensatory  impressions.  Certain  imaginary  effects  are  not  so  prominent 
in  animals  as  in  man.  On  the  other  hand,  such  experiments  carried  out 
with  human  beings  are  less  valuable,  because,  when  there  is  a  gastric  fistula, 
there  is  usually  some  pathological  derangement  of  the  stomach  or  cesopha- 
gus.  Frequently  there  are  tumors,  especially  cancers,  to  be  considered. 
The  latter  are  especially  likely  to  cause  a  most  deep-seated  effect  upon  the 
whole  metabolism  of  the  cells  and  weaken  the  whole  body,  so  that  it  is  out 
of  the  question  to  speak  of  a  normal  function  of  the  lining  of  the  stomach 
and  of  its  glands,  even  although  the  carcinoma  may  not  have  attacked 
the  stomach  itself.  On  the  other  hand,  now  and  then  the  formation  of  a 
gastric  fistula  becomes  necessary  when  there  is  no  chance  for  the  food  to 
reach  the  stomach  through  the  oesophagus,  for  example,  as  a  result  of 
strictures  caused  by  injury  to  the  mucous  membrane.  In  such  cases  it  is 
possible  to  carry  out  observations  with  human  beings  which  are  similar  to 
those  of  Pawlow  with  dogs.  Thus,  Hornborg,3  who  studied  a  case  of  gas- 
tric fistula  with  oesophageal  stricture,  observed  that  it  was  not  possible  to 
detect  psychic  influences  in  all  cases.  The  chewing  of  substances  with 
pleasant  taste  produced  a  secretion,  while  chewing  of  indifferent  or  badly 
tasting  substances  had  no  effect.  Chewing  of  itself  appeared  to  act  favor- 
ably upon  the  gastric  secretion,  while  the  mere  sight  of  food  had  no  effect. 
On  the  other  hand,  the  secretion  stopped  if  the  boy  was  not  allowed  to  eat 
at  once  something  that  tasted  good;  this  evidently  made  the  boy  angry, 
and  this  feeling  was  indicated  by  a  flow  of  tears. 

The  secretion  of  the  gastric  juice  is  produced  not  merely  as  a  result  of  a 
reflex  action,  but  we  recognize  certain  other  influences  as  well,  which  may 
be  exerted  within  the  stomach  itself.  Mechanical  irritation  does  not 
suffice  to  start  the  flow  of  the  juice.  Chemical  influences  alone  are  to  be 


1  The  highly  interesting  studies  by  Pawlow  and  his  students  have  nearly  all  appeared 
in  Russian  only.  His  lectures  have  been  translated  into  German  by  A.  Walther,  and 
published  in  1898  by  Bergmann  of  Wiesbaden. 

3  Deut.  Med.  Wochschr.  31,  1829  (1905). 

3  Inaug.  Dissert.  Helsingfors  (1903). 


500  LECTURE  XXI. 

considered  in  this  connection.  Digestive  activity  is  especially  favored 
by  broths,  extracts,  juice  of  meats  and  milk,  and  is  somewhat  stimulated 
by  water  and  small  amounts  of  alcohol.  Fats,  on  the  other  hand,  restrain 
the  production  of  the  digestive  fluid,  and  also  influence  its  qualitative  and 
quantitative  composition.  These  effects  may  be  observed  to  best  advan- 
tage by  introducing  the  different  substances  into  the  stomach  of  an 
animal  without  its  knowledge.  The  secretion  under  such  conditions  does 
not  take  place  as  quickly,  usually  not  until  after  15  to  30  minutes, 
and  persists  for  various  lengths  of  time  according  to  the  nature  of  the 
food.  Experiments  of  this  nature  give  one  the  impression  that  such 
a  direct  stimulation  of  the  glands  is  incomplete  in  effect.  A  har- 
monious course  of  digestion  is  only  assured  when  the  secretion  is  strongly 
stimulated  reflexively.  We  can  indeed  imagine  that  by  means  of 
digestion  itself,  substances  are  formed  constantly  which  act  as  chemical 
irritants  upon  the  lining  of  the  stomach  and  the  glands,  so  that  after 
the  flow  of  the  juice  is  once  started,  it  continues  for  a  considerable 
length  of  time. 

Pawlow  and  his  students  obtained  very  interesting  results  when  they 
attempted  to  ascertain  the  effect  of  different  kinds  of  food.  It  was  found 
that  the  cells  of  the  stomach  did  not  produce  the  same  juice  in  all  cases. 
On  the  contrary,  the  composition  of  the  digestive  juice  was  suited  to  the 
nature  of  the  food.  First  of  all,  it  is  of  interest  to  know  that  the  acidity 
of  the  juice  remains  constant  in  the  secretion,  while  the  amount  of  ferment 
present  varies  greatly.  Now  it  is  a  well-known  clinical  fact  that  widely 
divergent  degrees  of  acidity  are  found  in  the  contents  of  the  stomach. 
Such  determinations,  however,  are  of  but  a  slight  value,  for  many  reasons; 
on  no  account  should  they  be  used  to  indicate  the  amount  of  hydrochloric 
acid  normally  present  in  the  gastric  juice.  As  we  have  already  men- 
tioned, it  is  not  right  to  regard  the  contents  of  the  stomach  as  a  uniform 
mixture  of  the  digestive  secretion  and  the  food.  As  Griitzner  *  has  recently 
proved,  the  newly-introduced  food  stands  in  the  midst  of  that  which  has 
been  in  the  stomach  for  some  time,  and  does  not  at  once  come  in  contact 
with  the  walls  of  the  stomach.  In  the  pars-splenica  of  the  stomach,  the 
food  may  remain  for  hours  without  coming  into  intimate  contact  with  the 
gastric  juice.  If  now  a  part  of  such  a  digesting  mixture  be  siphoned  out 
of  the  stomach,  it  is  obvious  that  a  determination  of  the  degree  of  its  acidity 
might  easily  give  rise  to  false  conclusions.  Quite  a  number  of  factors 
here  come  into  play  which  may  easily  conceal  the  fact  of  the  original 
uniformity  in  the  acid  content  of  the  juices.  It  has  been  observed, 
for  example,  that  with  dogs  in  which  there  was  a  vigorous  secretion,  there 
was  more  acid  in  the  gastric  juice  than  when  the  production  of  the  same 
took  place  more  slowly.  Similarly  a  higher  acidity  was  noted  if  the  juice 


Pfliiger's  Arch.  106,  463  (1905). 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.         501 

was  taken  directly  from  the  fistula  than  when  the  latter  was  closed  for  a 
time.  The  reason  for  this  can  be  explained.  The  gastric  juice  flows  over 
the  walls  of  the  stomach,  which  are  covered  with  alkaline  mucus,  before 
it  reaches  the  fistula.  When  there  is  a  considerable  amount  of  the  juice 
being  secreted,  it  is  obvious  that  proportionately  less  hydrochloric  acid 
will  be  neutralized  than  when  only  a  small  amount  of  juice  passes  over 
these  walls;  and  similarly  when  the  fistula  is  closed,  the  acid  is  more  com- 
pletely neutralized  by  the  alkaline  mucus  than  when  it  passes  off  freely. 
As  Pawlow  has  stated,  in  a  normal  stomach  as  much  as  25  per  cent  of  the 
original  acidity  may  be  neutralized  by  the  mucus.  There  are,  to  some 
extent,  very  complicated  processes  concerned  in  this  neutralization  the 
significance  of  which  cannot  be  entirely  disregarded.  It  is  indeed  possible 
that  certain  relations  exist  between  the  hydrochloric  acid  content  of  the 
stomach  juices  and  the  formation  of  the  mucus  by  the  membrane  of  the 
stomach,  and  that  here  again  there  is  an  adjustment  corresponding  to 
the  nature  of  the  different  foodstuffs.  Naturally  the  deviations  in  the 
acidity  of  the  stomach  juices  vary  much  more  greatly  after  the  food  has 
reached  the  stomach.  At  all  events,  any  values  obtained  in  this  case 
should  be  very  cautiously  applied  to  the  composition  of  the  juice  itself/ 
The  clinical  practitioner  must  always  have  in  mind  all  sorts  of  different 
relations,  and  should  determine  the  combined  hydrochloric  acid  as  well 
as  that  which  is  still  free.  The  careful  physician  should  never  be  satisfied 
with  a  single  observation,  but  should  base  his  judgment  upon  examina- 
tions carried  out  under  the  most  varied  conditions. 

Pawlow  calls  attention  to  the  adaptability  of  the  whole  work  of  the 
stomach,  and  especially  of  its  glands.  This  is  shown  in  a  number  of  little 
ways,  and  we  are  able  to  trace  the  functions  of  the  stomach  very  well 
because  we  know  the  condition  of  the  food  as  it  enters.  Such  relations 
are  much  more  difficult  to  establish  in  the  study  of  the  pancreas,  and  in 
some  cases  it  is  impossible,  because  its  juices  come  in  contact,  under 
normal  conditions,  with  an  inextricable  mixture  consisting  partly  of 
decomposition  products,  and  partly  of  unchanged  food.  Investigations 
have  shown  that  a  mixed  diet,  as  well  as  the  feeding  of  single  articles,  such 
as  milk,  bread,  meat,  etc.,  leads  to  a  perfectly  definite  formation 
of  the  gastric  juice.  This  is  true  not  only  of  the  composition  of  the  fluid, 
but  of  the  amount  secreted  and  the  duration  of  the  secretion.  First  of 
all  it  is  to  be  noted  that  the  amount  of  gastric  juice  secreted  is  practically 
proportional  to  the  amount  of  food.  Thus  100  grams  of  raw  meat  caused 
the  secretion  of  26.0  cubic  centimeters  of  juice;  200  grams  =  40.0  cubic 
centimeters;  400  grams  =  106.0  cubic  centimeters.  For  a  mixed  diet, 
composed  of  milk,  bread  and  meat,  the  following  values  were  obtained:  - 
100  cubic  centimeters  of  milk,  50  grams  meat,  and  50  grams  of  bread, 
correspond  to  42.0  cubic  centimeters  of  gastric  juice,  while  double  the 


502 


LECTURE  XXI. 


above  quantity  of  the  mixture  caused  the  secretion  of  83.2  cubic  centi- 
meters. 

The  digestive  power  of  the  gastric  juice  depends  greatly  upon  the  nature 
of  the  food.  Pawlow  and  his  students  studied  the  power  of  digesting 
albumin  on  the  part  of  both  the  gastric  and  pancreatic  juices  by  Mett's 
method.  This  consists  of  sucking  up  the  white  of  an  egg  into  glass  tubes 
of  1  to  2  millimeters  bore  and  then  coagulating  it  at  a  definite  temperature. 
These  tubes  are  inserted  under  entirely  corresponding  conditions  into  the 
digestive  liquids,  and  taken  out  at  the  end  of  a  definite  period.  Then, 
by  means  of  a  millimeter  rule  and  a  microscope,  the  amount  of  albumin 
that  has  become  digested  is  measured.  The  following  values  are  given 
as  examples  of  such  an  experiment : l 

At  8  o'clock  the  animal  experimented  upon  was  fed  200  grams  of  bread. 
It  secreted  the  following  amounts  of  gastric  juice  with  varying  digestive 
power: 


Time. 


Amount  of  Juice  per  Hour. 


Digestive  Power. 


8-9  o'clock 3.2c.c.  8.0mm. 

9-10  o'clock 4.5c.c.  7.0mm. 

10-11  o'clock l.Sc.c.  7.0mm. 

The  same  dog  was  then  fed  200  grams  of  raw  meat: 

Time.                                  Amount  of  Juice  per  Hour.  Digestive  Power. 

12  o'clock S.Oc.c.  5.37mm. 

1  o'clock 8.8c.c.  3.50mm. 

2  o'clock 8.6c.c.  3.75mm. 

Then  200  cubic  centimeters  of  milk  were  fed  to  it: 

Time.                                  Amount  of  Juice  per  Hour.  Digestive  Power. 

3  o'clock 9.2c.c.  3.75mm. 

4  o'clock    ,                                                            8.4c.c.  3.30mm. 


A  control  experiment  showed  that  the  values  given  were  in  no  way 
caused  by  the  order  in  which  the  food  was  eaten.  It  is  evident  from  these 
figures  that  the  juice  secreted  after  feeding  with  bread  possesses  the  greatest 
digestive  power.  Milk  produces  the  weakest  secretion  of  all. 

1  Cf.  J.  P.  Pawlow:  Die  Arbeit  der  Verdaungsdriisen,  p.  42.  P.  Chigin:  Arch,  des 
sciences  biol.  Ill  and  Inaug.  Diss.  St.  Petersburg  (1894). 


THE   FUNCTIONS   OF   THE   DIGESTIVE    ORGANS.         503 

The  total  acidity  likewise  varies  according  to  the  nature  of  the  food. 
It  is  greatest  with  meat  and  least  with  bread.  It  is  interesting  also  to 
note  that  the  duration  of  the  secretion  is  also  regulated  according  to  the 
nature  of  the  food;  and  in  fact  during  the  course  of  secretion,  from  hour 
to  hour,  the  composition  adjusts  itself  qualitatively  to  the  conditions. 
We  will  give  here  the  result  of  another  of  Pawlow's  experiments:1 

AMOUNT  AND  NATURE  OF  GASTRIC  JUICE  WITH  DIFFERENT 

NOURISHMENT. 


200  gms.  Meat,  200  gms.  Bread,  600  c.c.  Milk. 

Hours. 

Amount  of  Fluid  in  c.c. 

Digestive  Power  in  mm. 

Meat. 

Bread. 

Milk. 

Meat. 

Bread. 

Milk. 

1 

11.2 

10.6 

4.0 

4.94 

6.10 

4.21 

2 

11.3 

5.4 

8.6 

3.03 

7.97 

2.35 

3 

7.6 

4.0 

9.2 

3.01 

7.15 

2.35 

4 

5.1 

3.4 

7.7 

2.87 

6.19 

2.65 

5 

2.8 

3.3 

4.0 

3.20 

5.29 

4.63 

6 

2.2 

2.2 

0.5 

3.58 

5.72 

6.12 

7 

1.2 

2.6 

. 

3.25 

5.48 

8 

0.6 

2.2 

.  .  . 

3.87 

5.50 

. 

9 

0.9 

.  .  . 

5.75 

.  .  . 

10 

0.4 

... 

From  these  figures  it  is  evident  that  the  maximum  secretion  is  produced 
by  meat  during  the  first  or  second  hour.  In  the  case  of  bread,  the  max- 
imum secretion  is  reached  during  the  first  hour,  while  with  milk  it  is  the 
second  or  third  hour.  With  meat  the  juice  secreted  during  the  first  hour 
has  the  greatest  digestive  power,  in  bread  it  is  that  of  the  second  and 
third  hours,  while  with  milk  the  maximum  digestive  power  is  obtained 
much  later. 

These  values  do  not  merely  correspond  to  a  single  experiment.  They 
have  been  obtained  again  and  again.  At  present  we  cannot  say  anything 
concerning  the  significance  of  these  variations.  We  can  indeed  assume 
that  one  food  requires  more  ferment  for  its  hydrolysis  than  another,  in 
order  that  its  decomposition  may  take  place  to  an  equal  extent  within  a 
given  period.  We  must  admit,  however,  that  we  are  here  confronted 
with  many  problems  which  cannot  be  solved  until  we  know  more  concern- 
ing the  nature  of  the  ferments  themselves  and  of  the  fermentation  processes 
which  they  cause  to  take  place.  We  introduce  these  interesting  observa- 
tions here,  only  to  show  how  well  organized  are  the  functions  of  the  diges- 
tive glands.  In  this  way  it  is  easier  for  us  to  understand,  in  considering 


1  Loc.  cit.  p.  44. 


504  LECTURE  XXL 

physiological  processes,  how  great  an  effect  is  produced  by  any  disturbance 
in  the  functions  of  the  stomach.  It  is  now  clear  to  us  that  severe  gastric 
disturbances  may  be  brought  about  by  purely  nervous  influences  without 
there  being  organic  changes.  It  is  easy  for  us  to  believe  that  a  hyper- 
secretion  may  be  produced  by  a  condition  of  stimulation,  caused,  for 
example,  by  a  supersensitiveness  of  the  secretory  fibers  of  the  vagus.  On 
the  other  hand,  the  experience  of  Pawlow  and  his  school  indicates  the  possi- 
bilities of  conditions  of  restraint  with  a  limited  supply  of  secretion.  The 
fact  that  the  cells  of  the  stomach  glands  are  extremely  sensitive  to  chem- 
ical stimulation,  and  adjust  themselves  to  the  nature  of  the  nourishment 
with  regard  to  their  entire  activity,  enables  us  to  understand  that  under 
pathological  conditions  it  is  not  necessary  for  the  amount  of  secretion  to 
have  become  decreased  or  increased.  Disturbances  may  arise  which  affect 
the  production  of  some  particular  substance.  It  is  perfectly  clear  that 
under  such  conditions  the  entire  adjustment  of  the  secretion  to  the  nour- 
ishment would  be  affected.  Thus,  normally,  for  the  digestion  of  bread, 
but  little  hydrochloric  acid  is  present  in  the  stomach  during  the  entire 
duration  of  the  secretion.  There  is,  to  be  sure,  a  reason  for  this,  for  by  this 
means  the  digestion  of  starch  by  the  diastase  in  the  saliva  will  continue 
much  longer. 

It  is  absolutely  necessary  that  we  should  give  prominence  to  the  researches 
of  Pawlow  in  our  study  of  digestion  in  the  stomach.  By  means  of 
them,  all  the  observations  which  have  served  for  a  long  time  to  establish 
the  existence  of  characteristic  sense-nerves,  may  be  applied  likewise  to  the 
innervation  of  the  intestinal  canal  and  its  glands.  These  organs  also 
do  not  react  fully  by  means  of  a  single  stimulation.  Here  again  the  stim- 
ulation is  only  taken  up  by  certain  definite  cells  and  transmitted  in  a 
perfectly  definite  manner.  The  results  of  Pawlow's  experiments  are  not 
at  all  astonishing.  We  may  assume  that  purely  chemical  processes  play 
a  prominent  part  here.  We  may  imagine  that  a  certain  kind  of  cell  is 
adjusted  so  that  it  is  susceptible  to  a  given  chemical  stimulation,  while 
a  different  cell  is  affected  by  another  chemical  substance.  We  may  per- 
haps apply  the  facts  that  we  have  established  in  the  study  of  ferments 
directly  to  the  cells  as  a  whole.  The  ferments  are  likewise  products  of 
the  cells.  The  individual  cells  produce  them  in  such  a  way  that  they 
possess  certain  groups  which  can  react  only  with  definite  compounds 
corresponding  to  a  characteristic  grouping.  Conversely,  the  cells  may  be 
so  constructed  that  their  function  as  a  whole  only  appears  when  started 
by  the  action  of  certain  definite  substance. 

The  more  extensive  our  knowledge  becomes,  and  the  more  we  enter 
into  the  secrets  of  the  metabolism  of  cells,  the  better  we  become  con- 
vinced that  the  cells  themselves  act  by  means  of  ferments.  They  do  not 
part  with  such  ferments,  but  retain  them  for  their  own  use.  These  cell- 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.         505 

ferments  may  perhaps  have  a  zymogen  state  of  existence  which  requires 
an  activator  to  bring  its  action  into  play.  Every  cell  may  possess  several 
ferments.  One  substance  may  serve  to  activate  a  given  ferment,  while 
another  activates  a  different  one.  Again,  the  gland-cells  act  by  the  aid 
of  ferments.  They  are  broken  down  and  again  built  up  until  from  the 
building  material,  which  is  of  quite  different  composition,  the  specific 
secretion  is  produced.  Now  the  cells  of  the  glands  in  the  stomach  produce 
the  secretion  during  a  period  of  rest.  They  retain  it  until,  by  means  of 
some  sort  of  stimulation,  they  are  made  to  give  it  up.  We  must  not 
imagine  that  the  act  of  secretion  itself  is  a  purely  physical  process.  The 
material  of  which  the  secretion  is  composed  does  not  exist  in  the  cells  in 
a  condition  capable  of  exerting  the  characteristic  function.  Probably 
during  the  secretion  activity,  a  group  of  atoms  is  eliminated  here  and 
there  and  new  combinations  are  effected.  We  do  not  yet  know  whether 
all  these  cells  of  a  gland  contain  the  same  secretion,  or  not.  All  such 
assumptions  are  but  speculations,  without  any  experimental  foundation. 
We  mention  them  merely  because  the  first  glance  at  the  results  of  Paw- 
low's  investigations,  which  almost  lead  one  to  assume  that  the  digestive 
glands  are  furnished  with  intelligence,  must  give  one  the  impression  that 
we  are  meeting  with  conditions  here  which  are  infinitely  complicated,  and 
which  will  be,  apparently,  inaccessible  to  further  investigation.  This  is 
not  really  true.  We  have  no  doubt  that  from  these  experiments  of  Paw- 
low  the  first  light  will  be  shed  upon  the  great  obscurity  which  enshrouds 
the  functions  of  the  glands  and  their  dependence  upon  nervous  influences. 
To  be  sure,  we  are  still  far  from  the  goal.  Pawlow  deserves  our  thanks 
for  having  at  least  pointed  out  to  us  the  way  this  is  to  be  attained. 

We  have  up  to  now  been  concerned  chiefly  with  pepsin,  which  is  brought 
into  activity  by  acid,  and  which  is  extremely  sensitive  to  alkali.  Now  it 
is  known  that  the  pylorus  part  of  the  stomach  secretes  no  acid.  In  spite 
of  this  fact,  there  is  digestive  power  in  the  juice  produced  at  this  region 
of  the  stomach,  as  has  been  shown  by  experiments  with  an  isolated  blind 
sack  in  the  pylorus.  It  is  of  much  interest  to  find  by  the  experiments  of 
Pawlow  and  Parastschuk  *  that  the  proteolytic  ferment  of  the  pylorus 
digestive  juice  also  requires  hydrochloric  acid  to  activate  it.  The  acti- 
vated juice  shows  a  proteolytic  and  milk-coagulating  action.  It  has  been 
asserted  that  the  pylorus  portion  of  the  stomach  secretes  a  ferment  which 
is  active  in  alkaline  solution.2  If  this  be  true,  then  we  shall  be  forced  to 
assume  that  a  ferment  other  than  pepsin  is  produced  in  this  portion  of  the 
stomach.  At  present,  however,  we  do  not  have  sufficient  ground  for  believ- 
ing that  there  is  actually  a  different  ferment  here,  for  it  seems  far  more 
probable  that  the  mucous  membrane  of  the  pyloric  region,  or  the  glands 


1  Z.  physiol.  Chem.  42,  415  (1904). 

2  Karl  Glassner:  Hofmeister's  Beitr.  1,  24  (1904). 


506  LECTURE  XXI. 

there,  secrete  pepsinogen,  which  comes  into  action  only  when  brought  into 
contact  with  the  acid  juices  of  the  stomach.  We  do  not  yet  have  the  means 
at  our  command  for  arranging  the  proteolytic  ferments  into  classes  with 
satisfactory  exactness.  We  can,  however,  distinguish  between  ferments  of 
the  pepsin  class  and  those  similar  to  trypsin.  The  best  way  of  establish- 
ing the  class  to  which  a  ferment  belongs,  is,  in  this  case,  to  allow  it  to  act 
upon  a  polypeptide,  and  the  results  from  the  experiment  are  obtained  most 
readily  if  we  choose  a  polypeptide  in  the  formation  of  which  a  difficultly 
soluble  amino  acid,  e.g.  tyrosine  or  cystine,  takes  part.  Glycyl-Z-tyrosine 
is  decomposed  in  a  short  time  by  trypsin  and  similar  ferments,  but  this 
dipeptide  is  not  acted  upon  by  pepsin.  The  secretion  of  the  pyloric  region 
behaves  quite  like  the  latter  after  it  has  been  activated  by  hydrochloric 
acid.1  It  seems  certain,  therefore,  that  the  ferment  of  the  pylorus  cells 
belongs  to  the  pepsin  group,  as  was  assumed  by  Pawlow. 

Now  that  we  have  become  acquainted  with  the  influence  of  the  food, 
and  its  nature,  upon  the  secretory  relations  in  the  stomach,  it  is  time 
for  us  to  turn  to  the  action  of  the  gastric  juice  upon  the  food  itself.  We 
have  discussed  this  already  at  some  length  in  considering  the  different 
classes  of  foodstuffs.  Here  we  will  merely  repeat  that  pepsin,  with  the 
aid  of  hydrochloric  acid,  converts  the  albumins  chiefly  into  peptones  and 
in  part  to  simpler  cleavage-products;  but  on  the  other  hand,  a  breaking 
down  of  the  simplest  cleavage-products,  i.e.  amino  acids,  cannot  take 
place  here,  or  at  least  only  to  a  very  slight  extent.  Again,  the  lipase  causes 
the  hydrolysis  of  a  part  of  the  fat,  and  in  this  way  prevents,  to  some 
extent,  the  restraining  influence  which  the  fats  have  upon  the  gastric 
secretions.  The  carbohydrates,  furthermore,  may  be  decomposed  some- 
what while  they  remain  in  the  stomach,  but,  to  be  sure,  not  by  means 
of  the  ferment  obtained  from  the  gastric  glands,  but  rather  by  means  of 
the  diastase  from  the  saliva.  This  diastase,  however,  is  destroyed  on 
coming  in  contact  with  the  acid  of  the  stomach.  Its  period  of  action, 
therefore,  depends  upon  the  acidity  of  the  gastric  juice  and  the  nature  of  the 
food.  In  case  the  food  is  in  the  form  of  a  loose  mixture  which  is  easily  mois- 
tened, it  is  evident  that  the  action  of  the  diastase  cannot  long  continue. 

Under  the  influence  of  the  gastric  juice,  the  food  is  changed  into  a  pulpy 
mass  known  as  the  chyme.  This  consists,  in  part,  of  products  formed 
from  the  decomposition  of  the  food,  and  in  part  of  unchanged  food.  For- 
merly it  was  thought  that  the  muscular  activity  of  the  stomach  had  a 
great  deal  to  do  with  the  formation  of  this  chyme.  Doubtless  in  this  way 
the  contents  of  the  stomach  are  thoroughly  mixed  and  brought  into  inti- 
mate contact,  layer  by  layer,  with  the  gastric  juice,  but,  on  the  other 
hand,  this  process  takes  place  gradually,  and  not  by  means  of  violent 
muscular  contractions,  so  that  it  is  not  right  to  speak  of  the  food  being 


1  E.  Abderhalden  and  P.  Rona:  Z.  physiol.  Chem.  47,  359  (1906). 


THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.          507 

kneaded  in  the  true  sense  of  the  word.  The  innervation  of  the  musculature 
of  the  stomach  is  partly  provided  by  the  vagus  and  partly  by  the  sym- 
patheticus.  Since  even  the  extirpated  stomach  contracts  spontaneously, 
it  has  been  assumed  that  the  ganglion-cells  in  the  walls  of  the  stomach  can 
cause  this  action.1 

After  the  chyme  is  formed,  the  stomach  has  fulfilled  its  task.  The 
pylorus  then  opens  and  the  chyme  enters  the  duodenum.  This  trans- 
ference does  not  take  place  all  at  once.  The  time  that  the  food  remains 
in  the  stomach  depends  upon  a  number  of  factors.  Purely  physical 
conditions,  such  as  the  size  of  the  food  particles  and  the  chemical  nature 
of  the  contents  of  the  stomach,  both  have  an  effect.2 

Frequently  we  hear  of  a  foodstuff  being  easily  digestible  or  difficultly 
so  without  its  being  perfectly  clear  just  what  is  meant  by  the  term. 
As  a  matter  of  fact,  it  depends  upon  two  factors.  A  food  may  be  readily 
digestible,  i.e.,  it  can  be  readily  acted  upon  by  the  ferments  in  the  stomach, 
and  yet  appeal  to  us,  according  to  its  entire  behavior,  as  difficultly  diges- 
tible. This  is  due  to  the  fact  that  although  it  may  be  easy  for  the  ferments 
to  act  upon  a  food,  still  it  may  be  converted  into  chyme  only  with  consider- 
able difficulty.  The  readiness  with  which  a  food  may  be  converted  into 
chyme  should  always  be  considered  with  regard  to  its  digestibility.  Diges- 
tion experiments  in  a  test-tube  cannot  decide  this.  Many  contradictions 
in  theory  and  practice  are  to  be  traced  to  this  point.  Our  present  knowl- 
edge concerning  the  digestibility  of  various  foods  in  the  human  stomach  is 
still  very  vague. 

As  just  mentioned,  the  stomach  is  not  emptied  all  at  once.  It  begins 
to  be  emptied  very  soon  after  the  beginning  of  digestive  activity.  Thus 
when  a  dog  is  fed  with  meat,  the  first  products  of  digestion  appear  in  the 
duodenum  after  a  few  minutes.  The  stomach  is  emptied  intermit- 
tently.3 In  feeding  100  grams  of  meat  to  a  dog  weighing  7  to  8  kilograms, 
all  the  chyme  was  emptied  in  the  course  of  2J  hours.  It  is  difficult  to  get 
a  correct  idea  of  the  time  spent  by  the  food  in  the  stomach  from  such 
experiments.  They  are  often  very  contradictory.  We  shall  understand 
immediately  why  this  is  so,  when  we  are  told  that  Pawlow  has  proved 
that  normally  the  opening  and  closing  of  the  pylorus  are  regulated  by  the 
duodenum.  If  hydrochloric  acid,  or  gastric  juice,  is  constantly  intro- 
duced into  the  duodenum  through  a  fistula,  a  soda  solution  placed  in  the 
stomach  will  be  retained  during  the  whole  course  of  the  experiment.  The 
period  which  normally  follows  the  opening  and  closing  of  the  pylorus 


1  Concerning  the  literature,  see  E.  H.  Starling:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  I, 
Abt.  2,  446  (1902).  Extensive  studies  on  the  functions  of  the  muscles  of  birds  have 
been  made  by  Mangold:  Pfliiger's  Arch.  Ill,  163  (1906). 

3  Cf.  Moritz:  Z.  Biol.  42,  565  (1901).  von  Mering:  Kongress  f.  innere  Med.  Berlin, 
1877  and  Wiesbaden,  1893-.  A.  Hirsch:  Zentr.  klin.  Med.  47,  993  (1892). 

3  Cf.  Ludwig  Tobler:  Z.  physiol.  Chem.  45,  185  (1905). 


508  LECTURE  XXI. 

corresponds  evidently  to  the  time  required  by  the  alkaline  juices  of  the 
intestine  to  neutralize  the  hydrochloric  acid  in  the  chyme.  When  this 
has  been  effected,  then,  reflexively,  the  pylorus  is  opened  and  a  new 
portion  of  chyme  passes  out  of  the  stomach.  The  suitability  of  such 
an  arrangement  is  quite  obvious.  We  shall  see  that  the  ferments  of  the 
pancreas  can  act  only  in  neutral  or  alkaline  solutions.  If  now  the  entire 
acid  contents  of  the  stomach  were  to  be  suddenly  emptied  into  the  intes- 
tines, then  evidently  the  subsequent  digestion  would  suffer.1  In  fact,  only 
moderate  amounts  of  chyme  are  to  be  found  in  the  intestines  of  animals 
killed  at  various  times  after  an  abundant  feeding.  This  is  particularly 
remarkable  when  we  compare  the  contents  of  the  tightly  stretched  stomach 
at  the  beginning  of  digestion  with  that  of  the  duodenum.  The  small 
portions  of  chyme  as  they  leave  the  stomach  are  evidently  at  once  further 
digested  and  absorbed.  To  the  fat,  also,  has  been  ascribed  an  effect  on 
the  opening  and  closing  of  the  pylorus.  Enough  has  been  said  to  show 
that  the  emptying  of  the  stomach  may  take  place  with  different  degrees 
of  rapidity  according  to  the  prevailing  conditions.  On  the  other  hand,  it 
enables  us  to  understand  why  such  contradictory  statements  are  found 
in  the  literature  concerning  the  time  required.  Almost  all  of  the  early 
investigators  followed  the  course  of  the  stomach's  activity,  by  means  of  a 
fistula  in  the  duodenum,  in  such  a  way  that  the  chyme  on  leaving  the 
stomach,  in  part  at  least,  passed  at  once  through  the  fistula  opening, 
whereby  naturally  quite  unusual  conditions  were  created,  leading  to  quite 
uncontrollable  changes  in  the  natural  processes. 

A  question  which  has  been  much  discussed  is  whether  absorption 
begins  to  take  place  in  the  stomach.  At  present  we  can  only  answer  this 
question  in  so  far  as  we  know  that  it  is  certain  that  the  mucous  membrane 
of  the  stomach  does  take  up  certain  substances  from  the  chyme.  As  soon 
as  we  possess  further  information  concerning  the  amount  and  nature  of 
the  absorbed  substances,  we  shall  be  able  to  close  up  this  gap  in  our 
knowledge.  Pure  water  is  not  absorbed  perceptibly;  but,  on  the  other 
hand,  aqueous  solutions  of  sugar  and  peptone  and  of  salts  lose  part  of  the 
dissolved  substance,  and  part  of  the  water  while  they  are  in  the  stomach. 
The  absorption  of  digested  albumin  in  the  stomach  has  been  studied  par- 
ticularly carefully,  but  without  its  being  possible  to  get  any  clear  idea  as 
to  the  extent  that  this  takes  place.  We  shall  come  back  to  this  question 
of  absorption  when  we  speak  of  the  functions  of  the  remaining  parts  of  the 
alimentary  canal.  We  may,  however,  state  in  advance  that  it  has  not 
yet  been  found  possible  to  refer  these  processes  completely  to  physical  or 
chemical  laws. 


1  This  fact  must  be  considered  in  cases  where  there  is  an  excessive  secretion  of 
gastric  juice,  and  especially  of  hydrochloric  acid.  This  tends  to  increase  the  time 
required  by  the  stomach  to  empty  itself. 


THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.          509 

Thus  far  we  have  concerned  ourselves  entirely  with  the  stomachs  of 
man  and  the  carnivora;  but,  before  leaving  this  part  of  the  subject,  we 
must  pay  some  attention  to  a  class  of  animals  whose  stomachs  are  much 
more  complicated,  namely  the  ruminants.  The  stomachs  of  these  animals 
consist  of  four  separate  compartments  connected  with  one  another.  The 
food  at  first  passes  into  the  rumen,  or  paunch,  then  into  the  reticulum, 
which  is  connected  with  the  former  by  means  of  a  wide  opening.  The 
reticulum  itself  has  three  openings.  One,  as  just  mentioned,  leads  to 
the  paunch;  a  second  to  the  third  stomach,  which  is  variously  known 
as  the  omasum,  psalterium,  or  manyplies;  while  the  third  opening  connects 
the  reticulum,  also  called  the  honeycomb,  directly  with  the  gullet.  The 
psalterium  provides  the  connection  with  the  fourth  stomach,  the  so-called 
abomasum,  or  rennet-bag.  From  the  paunch  and  the  reticulum,  the  food, 
which  has  already  been  mixed  with  saliva  to  some  extent,  is  regurgitated, 
or  thrown  up  into  the  mouth,  in  from  20  to  70  minutes  after  it  has  been 
first  swallowed.  This  process  is  known  as  rumination,  or  chewing  the  cud. 
Each  time  only  certain  portions  of  the  food  are  given  up  by  the  stomach. 
In  the  mouth  the  food  is  ground  up  extremely  fine  and  kneaded  together 
with  saliva,  after  which  it  is  swallowed  again,  and  reaches,  if  it  is  already 
sufficiently  pasty,  the  psalterium,  through  the  so-called  cesophageal  groove. 
The  latter  leaves  one  side  of  the  gullet  at  almost  a  right  angle,  and  con- 
sists of  a  tube  formed  by  parallel  folds  communicating  directly  with  the 
psalterium.  Only  pasty  and  liquid  materials  can  pass  along  this  path. 
The  solid  and  semi-solid  constituents  of  the  food  fall  from  the  gullet 
directly  into  the  paunch  and  reticulum.  A  part  of  the  food  paste  also 
reaches  the  psalterium  through  the  narrow  passage  between  it  and  the 
reticulum.  In  the  psalterium  the  food  is  still  more  finely  subdivided  and 
intimately  mixed.  In  the  abomasum,  the  action  of  the  stomach  is  com- 
pleted, and,  on  the  whole,  the  entire  effect  is  similar  to  the  process  which 
takes  place  in  other  mammals.  The  first  two  divisions  correspond  to  the 
cardiac  portion  of  a  single  stomach,  and  the  two  latter  to  the  pyloric  end. 

Finally,  we  must  answer  the  question  whether  the  stomach  is  an  organ 
which  is  indispensable  to  life.  This  is  not  the  case.  The  entire  stomach 
has  been  completely  extirpated  from  a  number  of  dogs  and  the  oasophagus 
connected  directly  with  the  duodenum  without  causing  any  disturbance 
in  the  health  of  the  animal.1  Recently  the  stomach  has  been  successfully 
extirpated  from  human  beings  a  number  of  times.2  In  no  case  have  any 
symptoms  developed  which  would  indicate  that  the  stomach  is  an  organ 


1  Czerny:   Beitrage  zur  operativen  Chirurgie,  Stuttgart,  p.  141  (1878).     M.  Ogata: 
Arch.  Anat.    Physiol.    1883,    89.  Carvallo  and  Pachon:    Arch,  de  physiol.  5  s6rie  T. 
6,  p.  106  (1894). 

2  Langenbuch:  Deut.  Med.  Wochschr.  1894,  No.  52.  C.  Schlatter:  Korrespondenz- 
blatt  Schweizer  Aerzte  27,  705  (1897). 


510  LECTURE  XXI. 

indispensable  to  life,  but  these  operations  enable  us  to  understand  exactly 
what  the  duty  of  the  stomach  is  in  the  economy  of  the  whole  organism. 
The  stomach  enables  us  to  partake  of  our  daily  food  within  a  relatively 
short  time  and  at  considerable  intervals.  It  is  to  a  certain  extent  a 
store-room.  The  stomach  is  also  to  be  regarded  as  serving  to  protect  the 
intestines.  It  prevents  the  injurious  action  of  too  hot  or  too  cold  foods. 
If  the  stomach  has  been  removed,  it  is  necessary  to  eat  the  food  in  small 
portions  and  at  frequent  intervals.  The  food  must  then  be  in  a  pasty 
condition  before  it  is  swallowed.  It  is  interesting  to  find  that  if  but  a 
small  piece  of  the  walls  of  the  stomach  remain  in  the  system  after  the 
operation,  this  enlarges  and  develops  into  a  new  stomach,  which  performs 
the  functions,  to  some  extent  at  least,  of  the  original  stomach. 


LECTURE  XXII. 

THE   FUNCTIONS   OF  THE  DIGESTIVE   ORGANS. 

II. 

FROM  the  stomach  the  food  reaches  the  duodenum,  and  undergoes  an 
energetic  digestion.  Here,  as  we  have  already  repeatedly  stated,  the  food- 
stuffs which  in  their  composition  are  complex  and  unlike,  as  well  as  entirely 
unsuited  for  direct  absorption  by  the  tissues,  are  to  a  greater  or  less  extent 
broken  down  into  their  simpler  components.  Thus  complicated  carbo- 
hydrates are  transformed  into  the  simplest  sugar,  the  albumins  into 
amino  acids  and  polypeptides,  and  the  fats  eventually  into  fatty  acids 
and  glycerbl.  From  these  materials  the  body  is  able  to  construct  the 
components  of  its  tissues.  Digestion  serves  not  only  to  make  the  sub- 
stances suitable  for  absorption,  but,  above  all,  for  assimilation. 

By  means  of  this  breaking  down  of  the  foodstuffs,  the  animal  organism 
makes  the  cells  of  its  tissues  to  a  large  extent  independent  of  the  nature  of 
its  food.  It  is  to  the  cells  a  matter  of  indifference  whether  the  food  is  of 
animal  or  vegetable  origin;  they  will  in  all  cases  receive  the  same  carbo- 
hydrates, the  same  fats  and  proteins  from  the  blood.  We  may  state  in 
advance  that  evidently  the  walls  of  the  intestine  themselves  play  an 
important  part  in  effecting  the  transformation  of  the  separate  foodstuffs. 
Within  them  takes  place,  according  to  our  present  knowledge,  the  building 
up  of  albumin  and  fat  from  the  more  simple  components.  Absorption 
takes  place  without  doubt  in  proportion  as  this  synthesis  is  accomplished. 
This  fact  makes  it  difficult  to  trace  the  exact  relations  of  the  foodstuffs 
to  the  intestine.  Our  knowledge  ceases  essentially  with  the  taking  up  of 
the  food  by  it.  It  might  be  thought  that  some  idea  of  the  complicated 
processes  taking  place  in  the  intestine  could  be  gained  by  causing,  with 
suitable  methods,  an  accumulation  of  the  decomposition  and  synthetical 
products,  e.g.,  in  the  examination  of  a  surviving  intestine.  Up  to  the 
present  time,  however,  such  experiments  have  failed  to  give  satisfactory 
results.  The  absorption  of  fats  and  their  synthesis  from  the  simple  com- 
pounds has  alone  been  followed  to  a  certain  extent  by  means  of  the  micro- 
scope. With  the  proteins  the  relations  are  far  more  complicated.  The 
walls  of  the  intestine  themselves  consist  chiefly  of  albumin.  It  is  hard 
to  tell  what  is  new  and  what  was  originally  present.  As  long  as  we  are 
unable  to  differentiate  sharply  between  the  different  albumins,  there  is 
practically  no  prospect  of  our  being  able  to  get  direct  proofs  by  means  of 

511 


512  LECTURE  XXII. 

the  paths  already  trod.  We  must  not  forget,  moreover,  that  the  action  of 
the  ferments,  especially  those  of  the  cells,  is  extremely  sensitively  regulated. 
It  is  entirely  dependent  upon  certain  definite  external  conditions,  such 
as,  for  example,  the  concentration  relations.  Every  disturbance  in  this 
direction  must  force  the  entire  course  of  the  cell-work  into  other  channels 
and  quickly  bring  it  to  a  halt.  It  is  very  important  that  digestion  should 
be  considered,  at  present,  in  a  broad  sense  rather  than  to  attempt  to 
establish  its  significance  in  any  definite  direction.  Only  from  this 
standpoint  are  we  able  to  comprehend  the  nature  of  digestion  in  its  com- 
pleteness, and  from  thence  new  ways  and  new  goals  appear  for  future 
investigation  in  this  infinitely  complicated  field. 

In  the  duodenum,  the  chyme  first  comes  in  contact  with  the  alkaline 
intestinal  juices.  The  acid  in  the  food  mixture  begins  to  be  neutralized. 
This  juice  is  partly  obtained  from  glands  placed  in  the  mucous  membrane 
at  the  beginning  of  the  duodenum,  and  known  as  Brunner's  Glands;  but 
the  so-called  Lieberkuhn' s  Glands  are  more  important.  These  are  found 
in  the  mucous  membrane  of  the  entire  small  intestine.  Even  in  the  large 
intestine  similar  little  glands  are  found,  although  these  differ  in  the  nature 
of  the  epithelium  and  in  their  functions  from  the  corresponding  glands 
in  the  small  intestine. 

The  glands  of  Brunner  have  been  considered  by  some  as  small  pan- 
creatic glands,  while  others  have  regarded  them  as  similar  to  the  glands 
in  the  pyloric  region  of  the  stomach.  The  work  of  Pawlow  and  Parast- 
schuk  1  makes  it  seem  probable  that  these  glands  yield  a  ferment  which 
corresponds  to  pepsin.  These  investigators  have  shown,  moreover,  that, 
like  pepsin,  this  ferment  requires  hydrochloric,  or  some  other  acid,  to  acti- 
vate it.  The  secretion  from  these  glands  also  has  a  milk-coagulating  action. 
Here,  in  the  same  way  as  with  regard  to  the  juice  of  the  pyloric  region  of 
the  stomach,  it  is  possible  to  show  that  Pawlow's  assumption  is  correct.2 

The  secretion  from  the  glands  of  Lieberkuhn  has  been  the  object  of 
much  careful  investigation.  It  may  be  studied  by  the  aid  of  a  fistula, 
made  in  the  small  intestine.  It  has  been  shown  that  starving  dogs  pro- 
duce no  secretion,  or  at  least  but  very  little.  Secretion  sets  in  when  the 
intestine  is  in  any  way  irritated,  whether  by  mechanical,  chemical,  or  elec- 
trical means.  Ingestion  of  food  also  causes  the  secretion.  The  secretion 
varies  in  different  parts  of  the  intestine.  In  the  upper  part  it  is  less  abun- 
dant than  in  the -lower.  The  juice  of  the  intestine  reacts  alkaline,  and 
always  contains  sodium  chloride  and  carbonate  in  apparently  quite  con- 
stant proportions.  According  to  recent  investigations,  it  contains  a  fat- 
splitting  ferment,3  and  one  with  a  slight  amyolytic  action.  Furthermore, 


1  Z.  physiol.  Chem.  42,  415  (1904). 

2  Abderhalden  and  Rona:  Z.  physiol.  Chem.  47,  359  (1906). 

3  W.  Boldireff:  Zentr.  Physiol.  18,  460  (1905). 


THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.         513 

an  invertase,  a  maltase,  and,  in  mammals,  a  lactase,  have  been  found. 
Finally  there  is  erepsin,  already  described,  which  has  no  direct  action 
upon  native  proteins,  with  the  exception  of  casein,  but  does  act  upon 
their  hydrolytic  decomposition  products,  the  peptones. 

The  function  of  the  mucous  membrane  of  the  small  intestine  is  by  no 
means  restricted  to  the  production  of  the  intestinal  juice.  We  shall 
soon  see  that  substances  are  secreted  by  it  which  are  of  far-reaching 
importance  for  the  functions  of  the  pancreas  and  its  ferment,  trypsin. 

The  secretions  produced  by  the  Brunner  and  Lieberkuhn  cells  are  un- 
important compared  with  that  of  two  more  important  accessory  glands, 
the  liver  and  pancreas.  To  be  sure,  this  is  not  necessarily  true  of  the 
physiological  functions  themselves,  which  in  no  case  are  to  be  judged 
entirely  from  the  standpoint  of  quantity,  but  rather  from  that  of  quality. 
Particularly  the  more  recent  investigations  have  taught  us  that  no  matter 
how  insignificant  the  function  of  any  organ  may  appear,  it  must  not  be 
disregarded.  All  sorts  of  different  processes  are  closely  related  to  one 
another  and  influence  each  other  reciprocally.  Whether  the  particular 
link  in  the  chain  of  the  total  processes  is  long  or  short  is  immaterial. 
We  may  well  imagine  that  the  secretion  produced  by  the  glands  of  Brunner 
is  in  many  cases  highly  significant  for  the  digestion  of  proteins.  The 
pancreatic  juice  is  not  able,  or  at  least  only  imperfectly,  to  attack  con- 
nective tissue,  for  example,  while  pepsin  in  the  presence  of  hydrochloric 
acid  quickly  accomplishes  this.  Now  we  know  that  when  fat  is  present  in 
the  food  the  secretion  of  the  gastric  juice  becomes  considerably  diminished, 
and  it  is  very  probable  that  in  such  cases  the  secretion  from  these  intestinal 
glands  is  of  great  assistance. 

One  of  the  above  organs,  the  liver,  constantly  gives  up  a  peculiar  secre- 
tion, the  bile,  which  is  continually  passing  through  the  bile-duct  into  the 
intestine.  It  should  be  mentioned  at  once  that  the  formation  of  the  bile 
is  continuous,  although  the  amount  secreted  varies.  It  continues  during 
fasting,  though  in  diminished  amount.  After  eating,  the  secretion  in- 
creases in  amount;  and,  in  fact,  it  has  been  found  that  the  extent  of  the 
secretion  depends,  in  part,  upon  the  nature  of  the  food.  We  shall  soon 
come  back  to  these  relations.1 

The  bile,  as  it  reaches  the  intestine,  represents  a  mixture  of  the  secre- 
tions of  the  liver-cells,  the  glands  of  the  gall-bladder  and  the  biliary  pass- 
ages. The  latter  yield  mucous  chiefly.  The  bile  reacts  alkaline  to  litmus. 
Its  color  varies  in  different  animals  and  likewise  in  different  individuals 
of  the  same  species.  In  man  the  fresh  bile  is  usually  a  golden  yellow, 
but  sometimes  it  has  a  greenish  hue.  It  contains,  besides  salts,  mucin 
and  water,  its  own  specific  substances.  These  are  the  bile-acids,  which 
are  combined  with  alkali,  and  the  bile-pigments.  There  are  also  constitu- 


Barbera:  Bull,  della  szienz.  med.  di  Bologna  (7)  9,  (1898). 


514  LECTURE  XXII. 

ents  which  are  found  in  other  parts  of  the  body  as  well.  These  are  chole- 
sterol, lecithin,  soaps,  neutral  fats,  and  urea.  Conjugated  glucuronic  acids 
have  also  been  detected  in  the  bile.  The  salts  of  the  bile-acids  are  of 
chief  interest  to  us.  We  shall  come  back  to  the  bile-pigments  when  we 
come  to  consider  the  pigments  of  the  blood  from  which  the  former  result. 
That  the  bile-acids  owe  their  formation  unquestionably  to  the  activity  of 
the  liver,  is  evident  from  quite  a  number  of  observations.  If,  for  exam- 
ple, the  liver  be  entirely  extirpated  from  a  frog,  no  more  bile-acids  can  be 
detected  subsequently  in  its  tissues.  If  they  were  produced  by  other 
organs,  the  acids  would  be  formed  after  the  removal  of  the  liver,  unless 
it  is  to  be  assumed  that  the  liver  acts  in  conjunction  with  other  organs  in 
their  production,  and  that  it  produces  either  the  original  stages  or  at 
least  some  essential  stage  in  their  formation.  Although  we  are  compelled 
to  assume  the  existence  of  such  reciprocal  relations  in  a  great  many 
cases,  still  at  present  it  may  be  regarded  as  proven  that  the  liver  is  the 
sole  place-  in  which  these  bile-acids  are  formed.  Any  other  assumption 
would  appear  less  probable.  In  dogs  also,  it  may  be  shown  that  the 
preparation  of  the  bile  is  a  function  of  the  liver-cells.  If  the  bile  duct 
is  ligated,  there  is  first  of  all  an  accumulation  of  bile.  Certain  con- 
stituents of  the  latter  then  pass  into  the  lymph,  and  are  carried  by  means 
of  the  thoracic  duct  to  the  blood.  Now  if  the  thoracic  duct  be  ligated  as 
well  as  the  bile  duct,  no  more  bile-acid  can  be  detected  in  the  blood. 

The  bile-acids  belong  to  two  groups;  namely,  the  glycocholic  and  tauro- 
cholic  groups.  The  members  of  the  first  group  contain  carbon,  hydrogen, 
and  nitrogen,  and  by  their  hydrolysis  yield  glycocoll  and  a  non-nitroge- 
nous acid;  while  those  of  the  other  group  contain  sulphur  in  addition  to 
the  above  elements,  and  on  hydrolysis  they  yield  taurine,  and  similarly  a 
non-nitrogenous  acid.  The  constitution  of  the  nitrogen-free  acid  which  is 
contained  in  both  groups  of  bile-acids,  and  which,  moreover,  appears  to 
have  a  different  composition  in  different  bile-acids,  has  not  yet  been 
fully  explained.  In  general,  such  an  acid  is  known  as  cholic  or  cholalic 
acid.  We  will  merely  mention  the  fact  that  the  acid  has  been  assumed 
repeatedly  to  be  related  to  cholesterol,  but  this  relation  has  never  been 
established  satisfactorily. 

The  relative  amounts  of  these  two  groups  of  acids  vary  according  to 
the  species  of  animal,  and  in  fact  one  or  the  other  group  may  be  missing. 
Glycocholic  acid,  C26H43NO6,  is  always  present  in  human-  and  ox-bile. 
Besides  this  a  second  acid,  glycocholeic  acid,1  is  frequently  found  which 
differs  from  the  first  with  regard  to  the  "  cholalic  acid  "  which  it  yields; 
in  this  case  the  acid  is  known  as  choleic  acid.  The  solubility  relations  of 


1  V.  Wahlgren:  Z.  physiol.  Chem.  36,  656  (1902).  0.  Hammarsteii :  ibid.  43,  109 
(1904).  H.  P.  T.  Oerum:  Skandin.  Arch.  Physiol.  16,  273  (1904).  C.  Gimdelach  and  A. 
Strecker:  Ann.  62,  205  (1847). 


THE  FUNCTIONS  OF  THE  DIGESTIVE  ORGANS.          515 

this  last  acid  are  different  from  the  first  cholic  acid,  and  it  has  a  higher 
melting-point.  A  hijoglycocholic  acid1  has  been  isolated  from  the  bile  of 
pigs. 

Taurocholic  acid 2  is  found  in  the  bile  of  man,  carnivora,  oxen,  and  a  few 
other  herbivora,  and  yields,  on  being  boiled  with  acids  or  alkalies,  taurine 
and  cholic  acid.  It  has  the  empirical  formula  C^HisNSOy.  In  the  bile 
of  the  goose  the  so-called  cheno-taurocholic  acid  is  found.3 

In  the  bile  of  the  shark,  Scymnus  borealis,  Olof  Hammarsten,4  to 
whom  our  thanks  are  due  for  most  careful  investigations  concerning 
the  bile  of  different  species  of  animals,  found  in  place  of  the  usual 
bile-acids,  two  ethereal-sulphuric  acids  which  he  called  scy mud-sulphuric 
acids.  They  yield  on  hydrolysis,  besides  sulphuric  acid,  a  non-nitrogen- 
ous acid,  scymnol,  which  gives  the  characteristic  color  reactions  of  cholic 
acid. 

As  we  have  said,  only  one  constituent  of  the  bile-acids  is  understood 
in  each  case  as  regards  its  composition,  and  this  is  either  glycocoll  or 
taurine.  These  two  substances  originate,  as  we  have  already  discussed 
in  detail,  from  the  proteins,  and,  in  fact,  glycocoll  is  recognized  as  one  of 
the  direct  cleavage-products  of  albumin,  while  it  is  perfectly  evident  that 
taurine  is  formed  from  cystine. 

The  constitution  of  cholic  acid  is  not  yet  clearly  established.  Mylius  5 
has  succeeded  in  obtaining  from  it  a  monobasic  hydroxy-acid  with  one 
secondary  and  two  primary  alcoholic  groups.  By  oxidation  of  cholic 
acid,  the  so-called  dehydrocholic  acid  C24H3405  is  formed;  while  by  more 
energetic  oxidation  bilianic  acid  C24H3408  is  obtained,  perhaps  more 
correctly  a  mixture  of  bilianic  and  isobilianic  acids.  By  the  oxidation  of 
bilianic  acid,  the  so-called  cilianic  acid,  C2oH28O8,  is  formed.  On  reduc- 
tion, cholic  acid  yields  desoxycholic  acid,  C24H4oO4.  According  to  our 
present  knowledge,  we  can  give  to  cholic  acid  the  following  formula: 

fCH(OH) 
C20H31{(CH2OH)2 

ICOOH 


Severin  Jolin:  Z.  physiol.  Chem.  12,  512  (1888);  13,  205  (1889). 

Concerning  the  preparation  of  pure  taurocholic  acid,  see  0.  Hammarsten,  Z.  physiol. 
Ch  in.  43,  127  (1904),  and  Stefan  Tengstrom:  ibid.  41,  210  (1904). 

Heintz  and  Wislicenus:  Poggendorffs  Annal.  108,  547  (1859). 

Z.  physiol.  Chem.  24,  323  (1898). 

Cf.  Strecker:  Annal.  65,  1  and  130  (1848);  67,  1  (1848);  70,  149  (1849).  F.  Mylius: 
Ber.  19,  369  and  2000  (1886);  Z.  physiol.  Chem.  12,  262  (1888).  P.  T.  Cleve:  Compt. 
rend.  91,  1073  (1880).  Olof  Hammarsten:  Ber.  14,  71  (1881).  Lassar-Cohn:  ibid.  32, 
683  (1899).  Z.  physiol.  Chem.  17,  607  (1893).  Fritz  Pregl:  Pfluger's  Arch.  71,  303 
(1898);  72,  266  (1898) ;  Sitzber.  kaiserl.  Akad.  Wissensch.  in  Wien,  Math,  naturw.  Klasse, 
111,  Abt.  II  b.  October,  1902,  and  Z.  physiol.  Chem.  45,  166  (1905).  G.  Bulnheim: 
Z.  physiol.  Chem.  25,  296  (1898). 


516 


LECTURE  XXII. 


Choleic  acid  has  also  been  oxidized,  but  this  has  not  served. to  ex- 
plain its  constitution.  We  may  mention,  in  passing,  that  a  cholic  acid 
described  as  fellic  acid 1  C2sH4o04  has  been  obtained  from  human 
bile.  In  the  polar  bear  another  cholic  acid  has  been  isolated  by 
Hammarsten 2  which  he  designated  as  ursocholeic  acid,  Ci9H3o04  or 

CisH^gO^ 

Our  present  knowledge  does  not  tell  us  much  concerning  the  for- 
mation and  destiny  of  these  cholic  acids  in  the  animal  organism,  and 
we  are  forced  to  rely  upon  assumptions.  It  is  indeed  perfectly  possible 
that  they  are  related  to  cholesterol,  although  this  has  never  been  estab- 
lished positively. 

The  composition  of  the  bile  varies  not  only  in  amount  but  also  as  regards 
its  composition.  We  shall  give  a  few  figures  showing  the  relative  amounts 
of  the  different  constituents.  In  1000  parts  of  bile  from  the  hepatic  duct 
there  were  found  to  be  present : 3 


Solids    

25.20 

35.26 

25.40 

Water   

974.80 

964.74 

974.60 

Mucin  and  pigments    

5.29 

4.29 

5.15 

Alkali  bile-salts 

9  31 

18  24 

9  04 

Taurocholates        ...                      .... 

3  03 

2  08 

2  18 

Glycocholates     

6.28 

16.16 

6  86 

Fatty  acids  from  soaps  

1.23 

1  36 

1  01 

Cholesterol      

0.63 

1.60 

1.50 

Lecithin 

0  22 

0  57 

0  65 

Fats 

0  22 

0  96 

0  61 

Soluble  salts 

8  07 

6  76 

7  25 

Insoluble  salts 

0  25 

0  49 

0  21 

Of  the  inorganic  salts  present,  sodium  chloride  predominates.  Sulphates 
and  phosphates  are  present  only  in  small  amounts.  The  bile  from  the  gall- 
bladder shows  a  somewhat  different  composition  from  that  taken  directly 
from  the  bile-ducts.  This  is  due  to  the  fact  that  while  the  bile  remains 
in  the  bladder  it  becomes  thickened,  owing  to  the  absorption  of  some  of 
the  water,  while  at  the  same  time  mucin  and  other  substances  are  given  up 
by  the  mucous  membrane  of  the  bladder.  The  following  analyses  show 
the  difference  in  the  percentage  composition  of  the  bile  from  these  two 
sources: 4 


1  G.  Schotten:   Z.   physiol.   Chem.   11,  268  (1887).       Lassar-Cohn:  Ber.    27,   1339 
(1894). 

3  Z.  physiol.  Chem.  36,  625  (1902). 

3  Olof  Hammarsten:  A  Text  Book  of  Physiological  Chemistry  (Mandel),  1908,  p.  327. 
Cf.  also  Ergeb.  Physiol.  (Asher  and  Spiro)  4,  1  (1905),  and  Z.  physiol.   Chem.  32,  435 
(1901). 

4  Olof  Hammarsten:  Nova  acta.  Reg.  Soc.     Upsal,  Serie  III,  1894. 


THE    FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.        517 


Liver-bile. 

From  Gall- 
bladder. 

Solids 

2  06 

16  02 

Water                                             

97  94 

83.98 

Mucin  and  pigments      .           

0.28 

4.44 

Alkali  bile-salts      

0.85 

8.72 

Taurocholates      

0.11 

1.93 

Glycocholates 

0  74 

6  79 

Fatty  acids  from  soaps     .   .       

1.06 

Cholesterol                   

0.08 

0.87 

Lecithin             "1 

0.14 

Fats                                                                                               j 

0.03 

0  15 

Soluble  salts                ... 

0  80 

0  30 

Insoluble  salts                                   .       

0  02 

0.24 

The  part  played  by  bile  in  the  animal  organism  has  been  variously 
estimated  at  different  times.  Some  have  even  regarded  it  as  an  excre- 
tion. According  to  this  view,  the  bile  serves  merely  to  carry  away  the 
by-products  which  are  formed  as  a  result  of  the  activity  of  the  cells.  We 
know  that  the  liver  plays  an  important  part  in  the  metabolism  of  the 
animal  organism.  Important  decompositions  and  syntheses  are  con- 
stantly taking  place  in  its  cells.  Its  position  between  the  blood-vessels 
of  the  viscera  and  those  of  the  rest  of  the  body  make  it  easy  to  recognize 
its  numerous  important  functions.  We  have  spoken  of  the  position  it 
occupies  with  regard  to  carbohydrate  metabolism,  and  have  seen  that  at 
one  time  the  liver  cells  construct  glycogen  from  glucose  molecules,  while 
at  another  time  it  decomposes  the  latter  into  its  constituents.  Many 
discoveries  indicate  that  the  liver  plays  an  important  part  in  the  trans- 
formation of  fats  and  proteins  into  carbohydrates.  Even  in  the  metab- 
olism of  albumin  it  assumes  a  central  position.  In  it  is  effected  the 
formation  of  urea  and  of  uric  acid.  The  liver  captures  the  ammonia  set 
free  in  the  alimentary  canal  and  in  the  intestines  themselves  in  order  to 
make  use  of  it  in  various  ways,  partly  for  the  formation  of  urea,  and  partly 
for  the  neutralization  of  acid.  The  liver  also  stores  up  many  substances 
injurious  to  the  organism,  or  at  least  foreign  to  it.  This  is  shown  by  the 
large  amount  of  iron  which  accumulates  here  when  large  quantities  of 
this  element  are  taken  into  the  system,  and  by  the  fact  that  many  other 
substances  are  found  in  it  which  are  otherwise  foreign  to  the  organism. 
The  liver  also  effects  the  combination  of  many  substances  injurious  to  the 
system  with  sulphuric  acid  and  glucuronic  acid.  It  is  indeed  possible 
that  in  these  processes,  which  by  no  means  include  the  entire  functions 
of  the  liver,  waste  products  are  constantly  being  formed  which  the  cells 
of  the  liver  no  longer  have  any  use  for,  and  are  consequently  given  up  to 
the  outside.  This  idea  is  supported  by  the  fact  that  certain  substances 
found  in  the  bile  are  not  indifferent  to  the  organism.  Thus  we  know  that 


518  LECTURE  XXII. 

the  salts  of  the  bile-acids  lessen  the  frequency  of  the  pulse.  This  is  due  to 
their  action  upon  the  heart.  The  latter  is  first  of  all  stimulated,  and  for 
a  short  time  there  is  an  acceleration  of  the  heart  action,  which,  however, 
soon  becomes  retarded.  Respiration  also  becomes  less  frequent.  Thus 
we  found  in  describing  icterus,  which  results  from  the  restricted  discharge 
of  the  bile  into  the  intestines,  what  severe  pathological  conditions  appear 
if  the  secretions  of  the  liver-cells  are  compelled  to  be  eliminated  through 
the  kidneys,  being  carried  thither  by  means  of  the  lymph  and  blood-vessels. 
The  fact  that  the  bile  undoubtedly  plays  an  important  part  in  digestion 
does  not  necessarily  contradict  any  such  assumption.  There  may  be  some 
adaptation  here.  It  would  not  be  altogether  remarkable  if  we  should  find 
that  the  animal  organism  makes  use  of  a  definite  function  for  different  pur- 
poses. The  secretion  of  bile  does  not  necessarily  assume  a  peculiar  position 
because  it  has  not  yet  been  possible  to  find  secretory  nerves  which  govern 
the  secretion.  The  liver  behaves  in  this  respect  like  the  kidneys.  The 
secretion  of  bile,  according  to  this,  is  to  be  compared  to  the  formation  of 
the  urine.  In  the  case  of  all  the  other  glands  that  we  have  studied  up  to 
this  point,  we  have  found  secretory  nerves.  We  should  not,  however, 
lay  too  much  stress  upon  the  fact  that  we  have  never  found  any  nerves 
which  in  any  way  govern  the  secretion  of  the  liver,  for  it  was  but  a 
short  time  ago  that  such  nerves  were  positively  proved  to  exist  for  the 
stomach  and  pancreas.  It  is  not  altogether  impossible  that  such 
nerves  will  be  found  in  the  case  of  the  liver  and  possibly  for  the  kidneys 
as  well.  Certain  contradictory  observations,  and  much  that  is  not  in 
accordance  with  the  theory  at  present  accepted  concerning  the  secretion 
of  the  bile  and  urine,  will  at  once  become  explicable  if  nerves  can  be 
found  governing  the  action  of  these  organs. 

The  experiments  of  Pawlow  and  his  school  have  brought  forward  many 
observations  showing  the  close  relation  between  digestion  and  the  secre- 
tion of  bile,  so  that  we  are  obliged  to  regard  bile  in  the  light  of  a  specific 
secretion  of  the  liver-cells.  The  constituents  of  bile  are  by  no  means 
waste-products  of  cell-metabolism,  but  they  are  much  rather  to  be  regarded, 
according  to  their  formation  and  their  entire  functions,  as  true  secretion 
products.  It  is  indeed  possible  that  the  formation  of  the  bile  is  accom- 
plished by  means  of  definite  cells.  It  is  also  conceivable  that  their  for- 
mation is,  nevertheless,  bound  up  with  the  intermediate  metabolism  in 
the  liver  to  the  extent  that  the  cells  of  the  liver  utilize  in  a  specific  way 
certain  decomposition  products.  The  fact  that  the  flow  of  bile  is  con- 
tinuous is  not  contrary  to  any  such  hypothesis.  Our  knowledge  concern- 
ing the  destiny  of  the  bile  is  still  very  limited.  We  do  not  know  whether 
a  part  of  it  is  constantly  being  resorbed.  In  fact,  frequently  the  biliary 
cycle  has  been  spoken  of  under  the  assumption  that  bile  is  constantly 
being  resorbed  and  again  secreted.  It  has  also  been  observed  that  the 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.        519 

bile  and  its  constituents,  namely  the  bile-salts,  accelerate  the  secretion  of 
bile.  Experiments  carried  out  in  this  direction  leave  it  uncertain  for  the 
present  as  to  what  significance  we  shall  give  to  this  resorption  process. 

Since  it  was  not  known  precisely  what  role  the  bile  played  in  diges- 
tion, it  has  been  assumed  to  be  quite  different  by  different  scientists. 
Some  have  held  that  the  bile  had  an  antiseptic  action.  It  had  been 
observed  that  animals  with  a  biliary  fistula  showed  increased  putrefaction 
in  the  intestines.  Direct  experiments  upon  the  bile  itself  have  shown  that 
it  indeed  tends  to  restrain  the  action  of  certain  bacteria,  but  that  it  is  by 
no  means  a  good  antiseptic  agent.  Furthermore,  if  fat  be  entirely  excluded 
from  the  food,  or  only  a  limited  amount  of  it  given  to  animals  with  such 
a  fistula,  the  intestinal  putrefaction  is  not  greater  than  under  normal 
conditions.  It  was,  therefore,  not  so  much  the  absence  of  the  bile  that 
caused  the  observed  putrefaction,  but  rather  the  faulty  absorption  of  the 
fats. 

Bile  has,  further,  been  thought  to  have  an  influence  upon  the  peristalsis 
of  the  intestines.  The  extent  of  such  action,  under  normal  conditions,  is 
still  undecided.  It  has  also  been  observed  that  if  bile  is  added  to  a  peptic 
digesting  fluid  a  precipitate  will  be  formed  at  once.  Now  normally  the 
acid  chyme  passes  out  of  the  stomach  mixed  with  pepsin  into  the  duode- 
num. It  might  be  thought  that  the  action  of  the  pepsin,  which  is  no 
longer  desired  in  this  part  of  the  intestine,  is  stopped  by  the  bile  precipi- 
tating pepsin  with  the  albumin  and  its  higher  cleavage-products.  It  has, 
however,  never  been  possible  to  establish  satisfactorily  the  formation  of 
such  precipitates  in  the  intestines,  so  that  at  present  we  are  hardly  justi- 
fied in  assuming  that  this  test-tube  experiment  represents  the  normal 
condition.  At  the  same  time  it  does  seem  probable  that  the  bile  prevents 
the  further  action  of  the  pepsin. 

We  have  already  touched  upon  one  quite  essential  function  of  the  bile, 
namely  its  role  in  the  absorption  of  fats.  We  have  seen  that  a  large  part 
of  the  fats,  or  perhaps  even  all,  is  decomposed  into  its  components  the 
fatty  acids  and  glycerol.  The  "bile  is  an  excellent  solvent  for  these  fatty 
acids  and  the  soaps  (the  salts  of  these  acids),  and  on  account  of  this 
fact  a  great  importance  has  been  ascribed  to  the  bile  in  assisting  the  absorp- 
tion of  the  fats  and  their  cleavage-products.  Before  this  action  of  the  bile 
had  been  verified  by  direct  experiment,  it  had  been  observed  that  if,  for 
any  reason,  the  flow  of  bile  into  the  intestine  was  prevented,  the  fa3ces 
showed  a  pronounced  pale  color,  and  when  a  considerable  amount  of  fat 
was  present  in  the  food  it  was  at  once  obvious  that  undigested  fat  was 
present.  Other  facts  indicate  a  faulty  absorption  of  the  fats  in  such  cases. 
In  animals  with  biliary  fistula,  where  the  bile  was  taken  away,  animals 
decreased  rapidly  in  weight,  although  fed  with  the  same  nourishment 
that  had  previously  agreed  with  them.  It  is  clear  that  the  loss  of  a 


520  LECTURE  XXII. 

material  as  rich  in  caloric  power  as  the  fats  will  be  quickly  felt  through  the 
entire  organism.  If  the  nourishment  of  the  just-mentioned  animals  was 
so  chosen  that  they  obtained  sufficient  calories  from  albumin  or  carbo- 
hydrates, then  there  was  no  further  loss  in  weight.  The  absorption  of 
the  fat  in  such  cases  is  not  entirely  prevented,  but  merely  restricted. 
That  an  excessive  amount  of  fat  in  the  nourishment  can  act  injuriously 
upon  the  absorption  and  digestion  of  albumin  is  clear,  for  the  fat  particles, 
from  their  mechanical  action,  can  prevent,  or  make  more  difficult,  the 
action  of  the  digestive  juice  upon  the  proteins. 

The  bile  not  only  takes  part  in  the  solution  of  the  fatty  acids  and  their 
alkali  salts  in  the  absorption  of  the  fats,  but  its  significance  reaches  much 
farther.  We  must  remember  that  the  fat  is  hydrolyzed  by  the  aid  of  a 
particular  ferment,  called  steapsin  or  lipase.  This  ferment  is  not  present 
originally  in  the  pancreatic  juice  as  such,  but  in  the  form  of  a  zymogen. 
The  latter  is  activated  by  the  bile.  The  bile  also  increases  the  fat-splitting 
action  of  the  pancreas-lipase  in  a  way  which  has  never  been  satisfactorily 
explained.1  Furth  and  Schiitz2  have  proved  that  the  cholic  acid  com- 
ponent of  the  bile  salts  is  the  cause  of  this  marked  acceleration  in  the 
digestion  of  fats. 

An  exact  idea  concerning  the  conditions  governing  the  secretion  of  the 
bile  and  its  function  was  first  made  possible  when  Pawlow  3  instead  of 
making  use  of  a  biliary  fistula  placed  the  entrance  of  the  bile-duct 
into  the  duodenum  on  the  outside  of  the  body.  He  cut  out  the  mouth 
of  the  bile-duct  together  with  a  piece  of  the  intestinal  membrane  and 
sewed  it  into  the  wound  in  the  body.  He  was  then  able  to  study  the 
secretion  of  the  bile  under  normal  conditions.  The  observations  made 
upon  animals  in  which  the  bile  flowed  out  of  a  fistula  in  the  gall-bladder 
naturally  could  not  represent  normal  conditions,  for  the  bladder  repre- 
sents a  reservoir  for  the  bile,  so  that  when  it  is  constantly  being  emptied 
to  the  outside,  the  secretion  of  the  bile  must  take  place  abnormally. 

Pawlow  succeeded  in  showing  at  once  from  the  amount  of  bile  flowing 
through  this  normal  opening  that  the 'bile  secretion  depended  upon  the 
taking  of  food.  He  also  showed  the  influence  of  the  nature  of  the  food 
upon  the  secretion.  Thus  we  know  that  meat  causes  a  particularly  in- 
tense flow  of  bile,  while  for  the  carbohydrates  a  slight  amount  suffices. 
The  fats  stand  intermediate  between  meat  and  carbohydrates.  The 
nature  of  the  secretion  is  also  regulated  by  that  of  the  nourishment.  The 
maximum  flow  of  bile  does  not  correspond  to  the  maximum  amount  of 
food,  and  it  appears  that  there  are  specific  differences  here.  The  purpose 

1  M.  Nencki:  Arch,  exper.  Path.  Pharm.  20,  367  (1885). 

2  Zentr.  Physiol.  20,  47  (1906);  Hofmeister's  Beitr.  9,  28  (190G)  —  cf.  A.  S.  Loeven- 
hart  and  C.  G.  Soiiden:  J.  Biol.  Chem.  2,  415,  (1907). 

3  Pawlow:  Le  travail  des  glandes  digestive  (Pachon  et  Sabrazes).     Paris,  1901. 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.        521 

of  this  adjustment  to  the  different  foodstuffs  is  easy  to  understand, 
when  we  point  out  that  the  bile  assists  the  action  of  the  pancreatic  juice 
by  accelerating  the  action  of  the  ferments.  It  affects  the  fat-splitting 
ferments  most,  but  it  also  increases  the  action  of  trypsin  and  diastase. 
Bile,  consequently,  is  concerned  not  alone  with  the  digestion  of  fat,  but 
influences  considerably  that  of  the  other  foods.  It  assists  the  transference 
of  the  seat  of  digestion  from  the  stomach  to  the  intestines,  probably  by 
preventing  the  further  action  of  pepsin. 

The  functions  of  the  bile  are  not,  in  general,  considered  to  be  as  impor- 
tant as  would  seem  probable  from  the  researches  of  Pawlow.  It  has  been 
found,  in  fact,  that  the  bile  may  be  entirely  excluded  from  the  intestines 
without  any  serious  disturbance  taking  place,  provided  the  food  be  prop- 
erly chosen.  It  would  be  wrong  to  conclude  from  this  that  the  bile  is 
of  little  importance  in  the  digestive  process,  for  even  with  complete  extir- 
pation of  the  pancreas,  digestion  does  not  cease  entirely.  The  animal 
organism  possesses  ways  and  means  of  replacing,  to  some  extent  at  least, 
lost  functions.  The  ferments  of  the  pancreatic  juice  can  indeed  perform 
their  work  without  the  aid  of  the  bile,  but  it  requires  more  time.  Even 
then  a  part  of  the  fat  will  be  absorbed.  There  are  no  exact  experiments 
to  indicate  the  effect  of  the  loss  of  the  bile  upon  the  metabolism  as  a 
whole.  Its  absence  is  not  without  influence,  because  it  is  then  necessary 
to  choose  the  food  more  carefully.  Food  rich  in  fat  must  be  avoided. 
We  merely  wish  to  emphasize  the  fact  that  it  does  not  follow  because  an 
animal  is  able  to  exist  without  a  certain  function,  and  even  be  kept  in 
good  health,  that  the  function  is  perfectly  dispensable.  Thus  we  should 
make  a  serious  error  if  we  reasoned  that  because  a  man  could  live  without 
a  stomach  that  this  organ  occupies  physiologically  a  subordinate  posi- 
tion. We  must  accustom  ourselves  to  have  in  mind  the  working  together 
of  all  the  organs,  and  never  follow  the  functions  of  a  single  organ  only 
under  certain  special  conditions  but  under  as  many  different  conditions 
as  possible,  and  especially  under  those  which  occur  normally.  Only  in 
such  cases  are  we  able  to  form  a  proper  judgment  as  to  the  relative  value 
of  the  functions  of  a  given  organ. 

Now  that  we  have  traced  the  transition  between  the  digestion  of  the 
stomach  and  that  of  the  intestines,  we  must  turn  our  attention  especially 
to  the  functions  of  the  pancreatic  juice.  This  contains,  as  we  have  stated 
repeatedly,  three  ferments,  —  trypsin,  steapsin,  and  a  ferment  which  has 
a  diastatic  action.  While  it  has  not  yet  been  established  positively  that 
the  last  ferment  is  secreted  originally  in  a  zymogen  condition,  this  is  surely 
the  case  with  the  two  other  ferments,  trypsin  and  steapsin.  Trypsinogen 
is,  according  to  the  important  observations  of  Pawlow,  activated  by  a 
substance  which  occurs  in  the  intestinal  juices.  Pawlow  called  this 
substance  enterokinase.  It  is  very  likely  that  this  substance  itself  belongs 


522  LECTURE  XXII. 

to  the  group  of  ferments.  It  is  possible  to  activate,  by  means  of  very 
small  quantities  of  enterokinase,  large  amounts  of  trypsinogen.  It  is 
evidently  to  be  considered  as  a  secretion  of  the  intestinal  membrane. 
Intestinal  juice,  obtained  through  a  fistula,  may  be  added  directly  to 
the  inactive  pancreatic  juice.  A  preparation  of  enterokinase  may  also  be 
obtained  by  scraping  off  the  superficial  layers  of  the  intestinal  membrane 
and  preparing  an  extract  from  these  scrapings.  The  action  of  the  entero- 
kinase may  be  well  shown  by  taking  some  pancreatic  juice  which  has  never 
been  in  contact  with  the  walls  of  the  intestine,  so  that  the  ferments  con- 
tained in  it  are  inactive,1  and  placing  some  fibrin  in  it  which  will  not  dissolve. 
Now  if  we  add  to  another  portion  of  the  same  juice  a  few  drops  of  intestinal 
fluid,  or  of  the  extract  prepared  from  the  intestinal  walls,  it  will  be  seen 
that  a  piece  of  fibrin  in  it  dissolves  at  once.  It  is  not  yet  perfectly  clear  how 
this  enterokinase  acts.  It  might  be  even  assumed  that  there  is  not  a  true 
activating  in  this  case,  but  that  the  enterokinase  is  itself  a  proteolytic 
ferment  and  begins  the  cleavage  of  albumin.  We  have  already  seen  that 
pepsin  attacks  the  albumin  molecule  in  an  entirely  different  place  than 
does  trypsin.  It  is  possible  that  the  enterokinase  continues  the  work 
of  the  pepsin  and  gives  up  cleavage-products  to  trypsin  which  the  latter 
is  capable  of  acting  upon.  We  might  also  assume  that  enterokinase 
attacks  trypsinogen  itself,  modifying  it  in  some  way  so  that  trypsin  now 
has  certain  groups  free  whereby  it  can  react  with  albumin,  or  its  cleavage- 
products.  One  might  be  tempted  even  to  assume  that  between  trypsino- 
gen and  enterokinase  a  union  takes  place  and  that  active  trypsin  is 
thereby  formed.  If  this  assumption  were  correct,  then  of  course  the  entero- 
kinase and  trypsinogen  must  always  be  active  in  quite  definite  proportions. 
This  does  not  appear  to  be  the  case,  however,  for  it  is  possible  by  means  of 
but  very  little  enterokinase  to  activate  a  great  deal  of  trypsinogen.  We 
have  here  again  a  reciprocal  effect  of  different  organs.  The  pancreas 
sends  out  a  zymogen,  and  the  cells  of  the  intestinal  membrane  form  the 
activator.  Pawlow  and  his  student  Sawitsch  2  have  shown  by  very  pretty 
experiments  that  the  secretion  of  the  intestine  does  not  invariably  contain 
enterokinase,  whether  the  pancreatic  juice  reaches  the  intestine  or  not.  If 
a  canula  be  introduced  in  an  intestinal  fistula,  then  this  mechanical  irrita- 
tion causes  a  secretion  of  intestinal  juice.  Only  a  small  amount  of  entero- 
kinase is  present  in  this  juice,  which  consists  chiefly  of  water.  In  the 
course  of  a  few  hours  the  intestinal  fluid,  which  is  now  scanty  in  amount, 
contains  almost  no  enterokinase.  If  now  a  few  cubic  centimeters  of 
pancreatic  juice  be  introduced  into  the  intestinal  canal,  then  a  juice  flows 

1  It  should  be  mentioned  here  that  apparently  the  ferments  in  the  pancreatic  juice 
always  contain  a  small  amount  of  trypsin  in  the  active  form.     Cf.  B.  P.  Babkin:  Ber. 
kaiserl.  Militararztl.  Akad.  St.  Petersburg  11,  Nos.  2  and  3,  93  (1904). 

2  W.  Sawitsch:  Soc.  me"d.  russes  St.  Petersburg  (1900-01). 


THE    FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.        523 

out  which  is  rich  in  enterokinase.  Boiled  pancreatic  juice,  however,  has 
no  such*effect.  The  secretion  of  the  intestinal  juice  is,  according  to  this, 
by  no  means  such  a  simple  process  as  has  ordinarily  been  assumed.  Its 
composition  is  determined  by  at  least  two  factors  which  are  largely 
independent  of  one  another.  The  production  of  enterokinase,  and  the 
formation  of  the  other  constituents  of  the  secretion  produced  by  the 
intestinal  membrane  and  its  glands,  are  distinct  processes.  The  intestinal 
juices  have  a  favorable  action  upon  the  digestion  of  albumin,  not  only 
by  reason  of  the  enterokinase,  but,  according  to  many  observations,  also 
on  account  of  the  other  ferments  in  the  pancreatic  juice.  These  juices 
have  on  the  whole  a  quite  similar  effect  to  the  bile. 

In  describing  the  secretion  of  the  stomach,  we  saw  that  the  amount  and 
composition  of  the  gastric  juice  are  dependent  upon  various  external 
influences,  and  that  above  all  psychic  influences  play  an  important  part. 
Is  the  secretion  of  the  pancreatic  juice  similarly  affected?  The  following 
observations  give  us  some  light  with  regard,  to  this  important  question. 
In  the  case  of  herbivora  in  which  the  digestion  is,  so  to  speak,  a  continuous 
process,  the  secretion  of  the  pancreatic  juice  takes  place  continually.  In 
carnivora,  it  is  possible  to  trace  at  once  some  connection  between  the 
introduction  of  food  and  the  subsequent  digestion. 

Pawlow  called  attention,  in  the  first  place,  to  the  following  experiment: 
If  a  few  drops  of  0.5  per  cent  hydrochloric  acid  are  introduced  into  the 
stomach  of  a  dog  having  a  pancreatic  fistula  from  which  only  a  few  drops  of 
pancreatic  juice  are  flowing  in  a  minute,  there  is  then  an  increase  in  the 
secretion  after  a  short  time.  If  instead  of  acid  a  little  lime-water  is  intro- 
duced into  the  dog's  stomach,  the  contrary  effect  is  obtained.  Phosphoric, 
lactic,  citric,  and  acetic  acids  each  have  the  same  effect  as  hydrochloric 
acid.  The  concentration  of  the  acid,  moreover,  greatly  influences  the 
secretion,  as  the  following  experiment  shows  i1  250  cubic  centimeters  of  HC1 
of  the  following  concentrations  were  introduced  into  the  stomach  of  a  dog: 


0.5% 

0.1% 

0.05% 

70.8 

Cubic   centimeters   of   pancreatic  juice  se- 
creted in  one  hour 

79.5 
82  5 

25.7 
26  8 

20  5 

89.4 

32.5 

The  pancreatic  gland  reacts  promptly  with  the  acid,  and  even  with 
concentrations  which  barely  have  an  acid  taste.  Other  irritants,  such  as 
pepper  and  mustard,  are  without  influence.  Acid,  therefore,  is  to  be 
regarded  as  exerting  a  specific  effect  upon  the  pancreas.  Naturally  the 


Pawlow:  Vorlesungen  etc.,  op.  cit.  p.  150. 


524  LECTURE   XXII. 

gastric  juice  has  the  same  effect  as  a  pure  acid  solution  of  the  corresponding 
concentrations.  The  following  experiment  is  important:  If  soda  or  lime- 
water  be  introduced  into  the  stomach  of  an  animal  in  the  midst  of  the 
process  of  digestion,  there  is  a  rapid  diminution  in  the  amount  of  secretion 
from  the  pancreas. 

We  have  here  a  new  link  in  the  chain  representing  the  mutual  dependence 
of  one  organ  upon  another.  The  pancreas  regulates  its  activity  according 
to  that  of  the  stomach,  and  is  governed  chiefly  by  the  acid  produced  in  the 
latter.  The  next  question  that  arises  is  how  the  hydrochloric  acid  of  the 
stomach  effects  the  stimulation  of  the  pancreatic  gland.  There  are  two 
possibilities.  It  may  be  that  the  acid  stimulates  the  peripheral  end- 
apparatus  of  the  centripetal  nerves  in  the  mucous  membrane,  or  that  it 
acts  upon  the  nerve  center  of  the  secretory  cells  of  the  pancreas,  or  upon 
the  cells  themselves,  after  it  has  been  taken  up  by  the  blood.  The  latter 
method  of  action  is  improbable  for  a  number  of  reasons.  Pawlow  showed 
that  the  acid  taken  up  by  the  blood  could  only  have  an  indirect  action; 
namely,  by  diminishing  the  alkalinity  of  the  blood.  Now,  normally,  the 
alkalinity  of  the  blood  is  increased  by  the  production  of  hydrochloric 
acid,  and  even  in  case  of  an  absorption  of  hydrochloric  acid,  it  remains 
higher  than  usual  during  the  period  of  digestion.  Direct  experiment  con- 
firms this  view,  for,  on  the  one  hand,  it  is  not  possible  .to  stimulate  the 
secretion  of  the  pancreatic  gland  by  means  of  introducing  hydrochloric  acid 
into  the  rectum,  while,  on  the  other  hand,  the  action  of  the  hydrochloric 
acid  is  still  felt  even  when  its  passage  out  of  the  stomach  is  prevented.1 

Now  how  shall  we  explain  the  action  of  the  hydrochloric  acid?  Pawlow 
brings  out  the  following  points:  —  Trypsin  reacts  best  in  an  alkaline 
solution,  but  is  still  active  in  a  neutral  or  even  barely  acid  solution.  As 
soon  as  the  amount  of  acid  becomes  in  any  way  considerable,  the  action 
of  the  trypsin  is  prevented.  Now  the  pancreatic  juice  always  contains  an 
abundance  of  alkali  by  means  of  which  the  acid  in  the  chyme  is  neutral- 
ized. The  more  acid  the  stomach  produces,  the  more  acid  reaches  the 
intestine  with  the  chyme,  and  the  more  alkali  is  required  to  combat  the 
injurious  effect  of  the  acid.  The  fact  that  the  secretion  of  the  pan- 
creas is  governed  by  that  of  the  stomach  tends  to  equalize  the  conditions. 
If  the  amount  of  pancreatic  juice  secreted  were  independent  of  the  hydro- 
chloric acid  in  the  chyme,  then  it  would  often  happen  that  the  trypsin 
would  be  made  inactive,  and  the  activity  of  the  pepsin,  which  under  normal 
conditions  is  prevented  by  the  neutralization  of  the  acid  it  requires,  would 
continue  in  the  intestine.  The  whole  arrangement  may  be  traced  in  the 
cycle  of  common  salt,  somewhat  as  follows:  —  The  cells  of  the  stomach 
prepare  hydrochloric  acid  from  the  sodium  chloride  in  the  blood.  The 

1  L.  Popielski:  Inaug.  Diss.  St.  Petersburg  (1896);  Zentr.  Physiol.  10,  405  (1896); 
Pfliiger's  Arch.  86,  215  (1901),  and  Zentr.  Physiol.  16,  43  (1903). 


THE   FUNCTIONS   OF   THE   DIGESTIVE   ORGANS.         525 

more  hydrochloric  acid  there  is  produced,  the  greater  becomes  the  alka- 
linity of  the  blood.  This  excess  of  alkalinity  is  given  up  by  the  blood  to 
the  cells  of  the  pancreas  which  employ  it  in  the  production  of  the  pan- 
creatic juice.  With  the  pancreatic  juice,  this  alkali,  chiefly  as  sodium 
carbonate,  flows  into  the  intestines,  and  meets  there  the  hydrochloric  acid 
from  the  stomach.  Here  again  common  salt  is  formed  which  may  enter 
into  the  circulation  anew.  At  the  same  time,  by  means  of  such  a  mech- 
anism the  alkalinity  of  the  blood  varies  only  within  narrow  limits.  We 
should  not,  however,  imagine  that  the  process  takes  place  in  such  a  simple 
form  that  the  cells  of  the  pancreas  are  immediately  brought  into  activity 
by  the  increased  alkalinity  of  the  blood,  which,  in  turn,  is  caused  by  the 
production  of  hydrochloric  acid  in  the  stomach.  Plausible  though  such  an 
assumption  may  be,  it  does  not  correspond  with  the  results  of  experimental 
research.  The  production  of  acid  does  not  have  such  a  direct  influence 
upon  the  activity  of  the  cells  in  the  pancreas.  We  must  remember  that 
hydrochloric  acid  introduced  from  without,  also  effects  the  production 
of  the  pancreatic  juice.  In  the  last  case  the  alkalinity  of  the  blood  is 
diminished  rather  than  increased.  Although  the  above-described  salt- 
cycle  appears  to  be  a  very  suitable  arrangement,  it  does  not,  on  the  other 
hand,  stand  in  direct  connection  with  the  action  of  the  acid  upon  the 
function  of  the  pancreatic  gland.  We  must,  on  the  contrary,  conceive  this 
to  be  due  to  some  phenomenon  brought  about  by  the  action  of  the  acid 
upon  the  membrane. 

We  shall  soon  come  to  a  very  important  observation  of  Bayliss  and  Star- 
ling which  will  shed  considerable  light  upon  the  nature  of  the  action  of 
the  hydrochloric  acid. 

It  is  interesting  to  find  that  even  the  composition  of  the  pancreatic  juice 
is  adjusted  to  that  of  the  acid  in  the  chyme,  for,  as  Walther  1  has  showed, 
the  amount  of  organic  material  in  the  former  is  regulated  by  the  amount  of 
acid  in  the  latter.  The  juice  produced  by  hydrochloric  acid  alone  contains 
less  organic  material  and  more  alkali  than  the  normal.  Here  again  we 
meet  with  the  same  conditions  as  in  the  secretion  of  the  gastric  and  intes- 
tinal juices.  Likewise  the  formation  of  the  pancreatic  juice  is  not  that  of  a 
simple  substance.  It  must  not  be  thought  that  the  cells  of  the  pancreas 
always  yield  one  and  the  same  secretion.  At  one  time  the  juice  is  rich  in 
ferments,  and  at  another  time  alkali  predominates.  For  the  present  we  do 
not  know  whether  this  is  due  to  the  fact  that  cells  are  influenced  differ- 
ently by  various  kinds  of  nervous  stimulation,  or  whether  particular  cells 
are  provided  with  quite  definite  functions.  The  fact  that  even  the  juice 
rich  in  alkali,  which  is  produced  by  the  action  of  acid  alone,  always  con- 
tains ferments,  makes  it  seem  probable  that  the  action  of  the  individual 
cells  is  governed  by  the  nature  of  the  stimulation  it  receives,  and  that  it  is 


Inaug.  Diss.  St.  Petersburg  (1896). 


526  LECTURE  XXII. 

hardly  right  to  believe  that  certain  cells  produce  the  ferments  while  others 
merely  give  up  salts. 

At  all  events,  in  considering  the  work  of  digestion,  we  are  constantly 
meeting  with  an  extremely  sensitive  means  for  regulating  the  work  of  the 
cells.  They  do  not  always  act  in  the  same  way,  but  adjust  their  action 
to  the  prevailing  conditions.  In  considering  the  functions  of  the  gland-cells 
we  gain  considerable  insight  into  the  activity  of  the  cells  of  the  animal 
organism  in  general.  We  are  led  to  infer  that  even  the  individual  cells  of 
the  body  are  to  a  considerable  degree  dependent  upon  one  another.  They 
adjust  their  work  in  the  same  way  as  the  gland-cells,  to  the  given  condi- 
tions. To  be  sure,  it  is  perfectly  possible,  and  in  fact  most  probable,  that 
those  cells  of  the  body  which  are  not  directly  connected  with  the  work  of 
the  intestine,  are  much  more  regular  in  their  activity  than  the  cells  of  the 
intestine  and  the  associated  glands  which  are  constantly  meeting  with  new 
conditions.  The  intestine  forms  a  solid  barrier  between  the  heterogeneous 
compounds  in  the  food  and  the  homogeneous  building-material  for  the 
blood  and  tissues,  the  composition  of  which  has  been  established  by  the 
entire  development  of  the  given  animal  species.  The  destructive  activity 
of  the  digestive  ferments,  together  with  the  syntheses  taking  place  in  the 
intestine,  enables  the  cells  of  the  body  to  work  within  certain  limits  always 
under  the  same  conditions.  At  the  same  time,  the  greater  demands  which 
are  now  and  then  placed  upon  an  organ,  influence  the  cell  work  quite 
specifically. 

The  activity  of  the  pancreas  is  not  dependent  upon  the  acid  content 
alone  of  the  food  as  it  reaches  the  duodenum.  It  has  been  found  that  fats, 
likewise,  have  an  effect.  We  have  already  seen  that  such  food  diminishes 
the  amount  of  gastric  juice  secreted.  The  secretion  of  the  pancreatic 
juice  cannot  then,  as  in  the  case  of  meats,  be  influenced  by  an  increased 
secretion  of  hydrochloric  acid.  Fats,  on  the  contrary,  stimulate  directly 
the  secretion  of  pancreatic  juice.  This  may  be  shown  by  means  of  a  dog 
provided  with  both  gastric  and  intestinal  fistulas.1  If  after  waiting  until 
there  is  practically  no  gastric  secretion,  olive  oil  is  allowed  to  flow  into 
the  stomach,  then  the  slight  amount  of  gastric  juice  secreted  will  have  an 
alkaline  reaction.  At  the  same  time  there  will  be  a  marked  increase  in  the 
amount  of  pancreatic  juice.  It  is  questionable  whether  the  fats,  and  the 
soaps  produced  from  them,  have  the  same  point  of  attack  as  the  hydro- 
chloric acid.2 

It  has  proved  very  difficult  to  ascertain  whether  the  secretion  of  the  pan- 
creas is  influenced  by  the  same  chemical  substances  as  that  of  the  stomach. 
This  could  be  answered  satisfactorily  only  when  there  was  no  opportunity 
given  for  the  hydrochloric  acid  itself  to  exert  a  stimulation.  Under  such 

1  N.  Damaskin:  Verhandl.  Gesellsch.  russ.  Aerzte,  St.  Petersburg  (1896). 
a  B.  P.  Babkine:  Arch,  des  Sciences  biol.  11,  No.  3  (1905). 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.        527 

conditions,  it  was  found  that  even  water  is  to  be  regarded  as  a  direct 
stimulant  of  the  pancreas.  The  extractive  substances  from  beef,  on  the 
other  hand,  did  not  cause  any  stimulation.  Quite  recently  the  influence 
of  alcohol  upon  the  pancreatic  secretion  has  been  studied,1  and  in  this 
case  it  was  found  that,  while  the  amount  of  the  secretion  was  augmented, 
the  juice  then  had  less  digestive  power.  Alcohol  also  appears  to  have  a 
direct  action  upon  the  ferments  or  their  antecedents.  If  alcohol  is  added 
to  pancreatic  juice,  then  the  digestive  action  of  the  latter  upon  starch  and 
albumin  is  much  lessened,  while  on  the  other  hand  the  action  upon  the 
fat-splitting  ferment  is  favorable. 

It  was  highly  important  to  establish  the  fact  that  the  psychic  factor 
also  played  a  considerable  part  in  the  work  of  the  pancreas.  The  vagus 
provides  this  organ  as  well  as  the  stomach  with  secretory  nerves.  Further- 
more, it  is  also  claimed  that  the  splanchnic  sends  fibres  to  the  pancreas. 
It  was  extremely  difficult  to  determine  whether  the  secretion  of  the  pan- 
creatic gland  was  effected  by  a  fictitious  meal,  and  for  the  following 
reasons:  We  have  seen  that  the  secretion  produced  by  the  membrane 
of  the  stomach,  and  its  glands,  is  greatly  dependent  upon  psychic  influ- 
ences. A  subsequent  increase  in  the  amount  of  pancreatic  juice  secreted 
may,  therefore,  take  place  on  account  of  the  increased  acid  production  in 
the  stomach;  i.e.,  in  this  case  the  pancreas  would  be  merely  indirectly 
affected  by  the  fictitious  meal.  Now  we  know  that  the  secretion  of  the 
stomach  does  not  take  place  at  once,  but  only  after  a  latent  period  of  about 
four  and  one-half  minutes.  The  pancreatic  secretion  similarly  begins  two 
or  three  minutes  after  it  has  become  stimulated  by  acid.  It  was  found 
that  the  augmented  pancreatic  secretion  resulted  within  two  or  three 
minutes  after  the  beginning  of  the  fictitious  meal,  so  that  from  this  the 
conclusion  may  be  drawn  that  the  gland  is  directly  influenced  psychically. 
It  is  important  that  the  pancreatic  gland,  in  spite  of  its  dependence  upon 
the  other  organs,  especially  the  stomach,  still  has  a  considerable  amount 
of  independence,  so  that  even  in  the  absence  of  stimulation  from  the 
stomach,  it  can  perform  its  functions.  Experience  gained  from  day  to  day 
teaches  us  that  if,  for  example,  there  is  an  insufficient  amount  of  hydro- 
chloric acid  formed  in  the  stomach,  digestion  is  not  prevented,  but  still 
progresses  to  a  quite  remarkable  extent. 

We  must  in  addition  consider  a  very  important  discovery  for  which  we 
will  have  to  thank  two  Englishmen,  Bayliss  and  Starling.2  They  showed 
that  by  means  of  4  per  cent  hydrochloric  acid  a  substance  could  be  extracted 
from  the  mucous  membrane  of  the  intestine  which,  when  introduced  into 
the  circulation,  increased  the  flow  of  pancreatic  juice.  They  called  this 
substance  secretin.  They  have  assumed  that  this  substance  is  not  present 


>  A.  Gizelt:  Zentr.  Physiol.  19,  769  (1906). 

2  J.  Physiol.  30,  61  (1903);  Proc.  Roy.  Soc.  73,  310  (1904). 


528  LECTURE  XXII. 

as  such  in  the  intestinal  membrane,  but  that  its  antecedent,  prosecretin, 
is  there,  and  becomes  changed  into  secretin  on  being  acted  upon  by  acid; 
i.e.,  it  may  be  set  free  in  this  way  from  some  other  compound.  It  might 
also  be  assumed,  of  course,  that  the  prosecretin  undergoes  an  atomic 
rearrangement  in  the  molecule.  Now  how  shall  we  regard  the  action  of 
the  secretin  under  normal  conditions?  We  must  remember  that  Pawlow 
found  that  the  hydrochloric  acid  from  the  stomach  stimulated  the  secre- 
tion of  pancreatic  juice.  We  have  already  shown  how  hydrochloric  acid, 
directly  or  indirectly,  by  altering  the  alkalinity  of  the  blood,  can  excite 
into  activity  the  pancreas,  and  have  left  it  open  as  to  how  the  acid  acts 
upon  the  intestinal  membrane.  'The  work  of  Bayliss  and  Starling  may 
perhaps  serve  to  explain  how  the  hydrochloric  acid  can  influence  the  pan- 
creatic gland.  Evidently  it  is  constantly  changing  prosecretin  into  secretin. 
As  quickly  as  the  latter  is  formed,  it  is  taken  into  the  circulation,  and 
now  acts  in  some  way  upon  the  gland.  It  seems  most  probable  from  cer- 
tain observations  that  secretin  affects  the  blood-vessels  in  the  pancreas 
and  increases  the  circulation.  This  does  not  necessarily  imply  that  there 
is  not  some  specific  action  as  well.  This  would  seem  quite  likely  from 
the  fact  that  secretin  stimulates  only  the  pancreas  to  any  extent.  Now 
this  fact  gives  to  the  hydrochloric  acid  of  the  stomach  an  entirely  new 
significance.  Not  only  does  this  aid  us  in  our  knowledge  concerning  the 
action  of  acid  upon  the  intestinal  membrane,  but  we  obtain,  at  the  same 
time,  new  prospects  for  further  investigations  concerning  the  cell-work  of 
the  glands  and  tissues.  Even  though  we  may  be  a  long  way  from  being 
able  to  understand  the  entire  chain  of  processes,  from  the  formation  of 
the  hydrochloric  acid  in  the  stomach  to  the  production  of  the  secretion 
on  the  part  of  the  pancreas,  and  understand  the  phenomena  only  approx- 
imately, still  we  are  justified  in  hoping  from  the  work  of  Pawlow  and  of 
Bayliss  and  Starling  that  in  following  the  paths  now  broken  it  will  not 
be  very  long  before  one  link  after  another  will  be  added  until  finally  the 
complete  chain  is  forged.  To  be  sure,  there  remain  countless  problems 
to  be  solved.  We  should  like  to  know  exactly  what  prosecretin  is,  and 
to  what  class  of  chemical  compounds  it  belongs.1  The  fact  that  it  is  not 
a  ferment  is  shown  by  its  being  unchanged  by  moderate  heat.  The  intes- 
tine, therefore,  concerns  itself  not  only  with  the  absorption  and  assimilation 
of  the  food,  but  takes  part  to  a  considerable  extent  in  the  digestion  itself. 
The  anatomical  evolution  of  a  unit  from  the  intestine  and  its  accessory 

1  Popielski,  Zentr.  Physiol.  19,  801  (1906),  has  recently  proved  that  unquestionably 
HC1  also  reflexively  influences  the  secretion  of  the  pancreas  by  its  action  upon  the  intes- 
tinal membrane.  He  believes  that  secretin  belongs  to  the  group  of  peptones.  If  this 
be  true  we  have  here  a  case  of  one  of  the  products  of  digestion  acting  upon  this  pancre- 
atic secretion.  The  discovery  of  Bayliss  and  Starling  will  of  course  only  receive  its  full 
value  when  it  is  possible  to  isolate  the  secretin,  and  study  by  itself  the  action  of  HC1 
upon  it. 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.        529 

glands,  the  liver  and  the  pancreas,  also  to  a  certain  extent  corresponds  to 
the  physiological  significance.  The  work  of  digestion  is  not  entirely  rele- 
gated to  these  glands,  but  the  intestines  help  to  a  considerable  extent. 

From  what  we  know  concerning  the  work  of  the  stomach,  and  the  intestine 
with  its  accessory  glands,  we  <jan  readily  understand  at  how  many  places 
the  total  work  of  these  organs  may  be  disturbed,  and  how  many  disturb- 
ances may  result  from  the  loss  of  a  single  function.  Let  us  imagine,  for 
example,  that  the  stomach  fails  to  secrete  hydrochloric  acid.  First  of  all 
the  food  will  not  be  utilized  in  the  system  to  so  good  an  advantage.  To 
be  sure,  our  knowledge  of  cookery  enables  us  to  overcome  many  such  diffi- 
culties. If  we  were  compelled  to  rely  upon  food  in  its  original  condition, 
then  the  effect  of  the  loss  of  hydrochloric  acid  would  be  far  more  pronounced. 
Thus,  for  example,  connective  tissue  is  scarcely  attacked  at  all  by  trypsin, 
while  it  is  readily  digested  by  means  of  pepsin  in  acid  solutions.  Thus  the 
albumins  present  in  such  tissue  would  reach  the  intestine  in  an  undigested 
condition.  An  increased  secretion  of  trypsin  would  be  required  on  account 
of  the  deficient  preliminary  digestiorr.  The  stimulation  usually  brought 
about  by  means  of  hydrochloric  acid,  however,  would  not  take  place. 
Thus  one  disturbance  follows  another.  It  is  not  safe  to  assume  that  in 
such  cases  the  pancreas  would  entirely  fail  to  undergo  any  stimulation. 
We  have  seen,  on  the  contrary,  that  it  is  a  fairly  independent  organ, 
and  may  be  stimulated  by  fats  and  by  water  as  well  as  by  psychic 
events. 

The  knowledge  of  all  these  mutual  relations  with  regard  to  the  most 
varied  functions  of  different  organs  at  once  explains  the  therapeutic 
measures  that  are  taken  in  case  of  stomach  trouble,  whether  it  be  on 
account  of  nervous  or  organic  disease.  Now  we  understand  how  the 
so-called  stomachics  have  an  effect,  and  why  under  some  conditions  hydro- 
chloric acid  itself  is  introduced  into  the  stomach.  On  the  other  hand,  it 
becomes  clear  to  us  how  cautious  we  should  be  with  the  use  of  alkalies. 
They  serve  not  only  to  neutralize  the  gastric  secretion,  but  they  also  lessen 
the  secretion  of  the  pancreatic  juice.  We  are  now  able  to  view  in  a  clear 
light  the  functions  of  the  intestine  in  the  economy  of  the  animal  organism. 
It  seems  to  us  not  at  all  impossible  that  a  faulty  function  on  the  part 
of  the  intestine  in  any  one  of  its  various  functions  has  an  influence  in 
much  greater  measure  than  is  ordinarily  assumed  upon  numerous  patho- 
logical processes.  Not  the  least  cause  of  diseases  of  metabolism  is  an 
anomally  in  the  complicated  processes  of  the  intestine.  In  the  intestine 
the  cleavage-products  of  proteins,  the  fats,  and  certain  other  compounds, 
are  again  welded  together.  A  faulty  synthesis,  or  a  building-up  in  the 
wrong  direction,  must  immediately  have  its  effect  upon  the  general  meta- 
bolism, for  the  ferments  in  the  cells  are  only  adjusted  to  react  with  quite 
definite  compounds.  We  make  these  suggestions  merely  to  show  what  a 


530  LECTURE  XXII. 

deep  significance  is  to  be  ascribed  to  the  intestine  in  the  general  metabolism 
of  the  organism. 

We  have  up  to  this  point  merely  considered  the  pancreatic  juice  as  such, 
and,  with  the  exception  of  its  alkali  content,  have  paid  little  attention  to 
the  secretion  of  its  individual  ferments.  We  have  seen  that  trypsin  and 
steapsin  are  secreted  as  zymogens,  while  for  the  diastase  arguments  have  also 
been  advanced,  though  probably  wrongly,  in  favor  of  a  zymogen  condition. 
The  knowledge  of  the  fact  that  the  two  first-named  ferments  exist  in  two 
states,  was  of  great  importance  for  subsequent  investigation,  and  above 
all  it  was  very  significant  that  trypsinogen  was  activated  by  a  constituent 
of  the  intestinal  fluid,  namely  enterokinase.  In  introducing  pancreatic 
fistulae,  usually  the  entrance  point  of  the  principal  duct  from  the  pancreas 
into  the  duodenum  is  sought,  and  then  the  papillae,  together  with  the  piece 
of  intestinal  membrane  bearing  it,  is  cut  out  from  the  alimentary  canal  and 
sewed  into  the  wound  in  the  body.  If  the  pancreatic  juice  flowing  through 
such  a  fistula  be  examined,  it  will  be  found  that  it  is  always  active.  This 
is  due  to  the  fact  that  the  pancreatic  juice  thus  obtained  is  always  mixed 
with  some  secretion  from  the  piece  of  intestine.  If  it  be  desired  to  obtain 
the  pancreatic  juice  in  an  inactive  condition,  this  little  piece  of  intestinal 
membrane  must  be  removed  completely.1  It  has  been  found  that  even 
such  juice,  under  certain  conditions,  may  contain,  besides  the  zymogens, 
active  ferments  as  well.  Thus  we  know  that  by  the  introduction  of  acid 
and  of  soaps  into  the  intestine  a  juice  more  or  less  rich  in  active  ferments 
results.  Again,  in  the  case  of  nourishment  with  a  mixed  diet,  there 
is  obtained  a  varying  amount  of  active  ferments,  the  quantity  depending 
upon  the  nature  of  the  food.2  When  meat  is  eaten,  for  example,  the 
largest  amount  of  zymogens  is  obtained,  while  the  least  amount  results 
from  a  milk  diet.  Bread  occupies  an  intermediate  position. 

Before  the  fact  was  known  that  the  pancreatic  ferments  are,  for  the 
most  part,  given  up  in  the  form  of  zymogens,  and  that  these  are  activated 
by  the  intestinal  juices,  it  was  considered  as  proven  that  each  food  caused 
the  production  of  all  three  ferments,  but  that  the  fat-splitting  ferment 
was  present  in  largest  amount.  As  Babkin  has  shown,  this  specialization 
does  not  take  place.  The  three  principal  ferments  of  the  pancreatic  juice 
are,  under  physiological  conditions,  secreted  practically  evenly.  If  the 
value  of  the  pancreatic  juice  obtained  after  eating  a  certain  kind  of  food 
is  based  upon  the  amount  of  proteolytic  ferment  the  juice  contains,  it  is 
found  that  milk  produces  a  secretion  of  greatest  digestive  power.  The 
two  other  ferments,  diastase  and  steapsin,  are  likewise  present  in  consid- 
erable amount.  The  activity  of  these  two  ferments  remains  in  this  case 


1  B.  P.  Babkin:  Ber.  kaiserl.  militararztl.  Akad.  zu  St.  Petersburg  9,  Nos.  2  and  3, 
93  (1904). 

2  Babkin:  ibid.  11,  Nos.  2  and  3,  p.  93  (1904). 


THE   FUNCTIONS   OF  THE   DIGESTIVE   ORGANS.         531 

about  the  same  for  several  hours.  After  eating  meat,  the  digestive  power 
for  albumin  sinks  very  rapidly  during  the  second  hour,  only  to  rise  again 
considerably  above  its  original  value  in  the  following  hours.  Diastase 
and  steapsin  behave  similarly. 

A.gain,  the  amount  of  juice  depends  upon  the  nature  of  the  food.  Bread 
produces  the  most  secretion,  then  follows  meat,  while  milk  occupies  the  last 
place. 

We  must  mention,  in  passing,  the  fact  that  it  has  been  suggested  that 
the  spleen  also  is  related  to  the  secretion  of  the  pancreas,  and  takes 
part  in  activating  the  trypsinogen.  It  has  been  observed  that  an  extract 
made  from  the  spleen,  which  has  been  removed  during  digestion,  strength- 
ens the  action  of  the  pancreatic  juice.  Pawlow,  however,  states  that  he 
could  not  find  that  the  secretion  produced  from  animals  with  the  spleen 
missing  had  less  digestive  power  than  from  those  with  the  organ  intact.1 

Under  normal  conditions,  a  single  foodstuff  does  not  usually  come  by 
itself  under  the  influence  of  the  secretion  of  the  pancreas,  and  of  the  walls 
of  the  intestine,  but  rather  a  mixture  of  foods.  The  relations  are  further 
complicated  by  reason  of  the  fact  that  it  is  not  these  foods  themselves, 
but  rather  their  cleavage-products,  which  are  acted  upon.  For  the  present, 
the  effect  of  this  heterogeneous  mixture  of  products  cannot  be  stated.  We 
can  merely  assume  from  the  work  of  Pawlow  and  his  school,  performed 
under  uniform  conditions,  that  there  are  a  great  many  ways  here  in  which 
the  system  adapts  itself  to  the  prevailing  conditions.  We  have  already 
mentioned  the  fact  that  the  acid  chyme  from  the  stomach  does  not  enter 
the  duodenum  in  a  continuous  stream,  but  that  the  contents  of  the  stomach 
leaves  it  intermittently  in  relatively  small  amounts.  These  portions  are 
at  once  energetically  digested.  The  products  formed  by  digestion  are 
constantly  being  absorbed.  Even  when  a  very  large  quantity  of  food  is 
eaten,  there  is  never  a  large  amount  of  chyme  in  the  intestine.  The  extent 
to  which  the  food  is  utilized  depends,  as  we  shall  see  later  on,  largely 
upon  its  nature.  Naturally  the  condition  of  the  intestine  also  comes  into 
consideration.  In  case  -of  increased  peristalsis,  the  absorption  may  be 
lessened.  The  unabsorbed  residue,  together  with  the  secretions  of  bile, 
pancreas,  intestinal  membrane  and  its  glands,  compose  the  faeces,  or  stools. 
The  absorption  takes  place  throughout  the  entire  small  intestine,  but  is 
undoubtedly  most  energetic  in  the  jejunum.  We  must  mention  in  this 
connection  erepsin,  which,  according  to  Cohnheim,  acts  like  trypsin  upon 
peptones,  and  assists  in  their  absorption. 

The  chyme  is  carried  on  its  way  by  peristalsis.  The  movements  of  the 
intestines  'are  regulated  by  the  central  nervous  system.  Innervation 
is  provided  in  part  by  the  vagus  and  partly  by  the  splanchnic  nerves. 

1  Cf.  Oskar  Prym:  Pfliiger's  Arch.  104,  433  (1904). 


532  LECTURE  XXII. 

The  latter  are  said  to  contain  inhibitory  fibers.  The  innervation  relations 
are,  however,  not  perfectly  understood. 

We  must  now  turn  our  attention  to  the  absorption  of  the  digested  pro- 
ducts. We  approach  this  part  of  the  subject  with  considerable  hesitancy, 
for  we  must  admit  at  the  start  that  we  are  not  yet  able  to  give  a  full  account 
of  the  nature  of  the  absorption  process.  We  can  indeed  affirm  that 
undoubtedly  physical  forces  come  into  play  here,  and  that,  for  example, 
osmosis  plays  a  part,  as  is  obvious  from  the  already-mentioned  observations 
of  Overton  on  the  solubility  of  lipoids;  and  similarly  we  cannot  doubt  that 
the  surface-tension  is  to  be  regarded  as  important  here,  in  the  sense  sug- 
gested by  Traube.1  On  the  other  hand,  we  are  very  well  aware  that  none 
of  the  attempted  explanations  of  absorption  have  of  themselves  brought 
the  entire  complicated  process  nearer  to  our  comprehension.  As  soon  as 
a  single  phenomenon  in  a  single  process  is  applied  to  the  entire  absorption, 
the  explanation  in  all  cases  appears  arbitrary. 

We  are  not  able  in  explaining  absorption,  to  circumvent  the  conception 
of  a  specific  action  on  the  part  of  the  cells.  We  can  indeed  believe  that 
probably  a  purely  physical  explanation  will  account  for  an  inter-epithelial 
absorption.  The  greater  part  of  the  products  of  digestion  will,  however, 
be  taken  up  by  the  cells  themselves,  and  these  are  undoubtedly  very  active 
in  their  work.  We  cannot  imagine,  for  example,  that  the  amino  acids 
and  polypeptides,  which  represent  decomposition  products  of  the  proteins, 
penetrate  into  the  cells  purely  on  account  of  physical  reasons  without 
active  cooperation  on  the  part  of  the  cells  themselves.  We  must  not 
forget  that  syntheses  immediately  follows  the  absorption;  i.e.,  in  other 
words,  the  activity  of  the  cells  then  begins,  and,  indeed,  as  the  relatively 
constant  composition  of  the  serum  shows,  in  a  quite  definite  direction. 
We  have  no  reason  for  assuming  that  in  the  epithelium  of  the  intestine  and 
the  cells  of  this  organ,  certain  forces  unknown  to  us  are  at  work.  If  we 
were  to  make  any  such  assumption,  it  would  be  entirely  without  empirical 
justification.  Although,  at  present,  we  are  denied  an  accurate  insight 
into  the  nature  of  absorption,  still  on  the  other  hand  our  knowledge  of 
the  work  performed  by  the  cells  is  constantly  increasing.  The  intestinal 

1  It  would  not  be  difficult  with  the  aid  of  the  H.  J.  Hamburger's  "  Osmotischer  Druck 
und  lonenlehre  in  den  medizinischen  Wissenschaften "  (1902)  to  cite  the  different 
views  held  regarding  intestinal  absorption.  On  the  other  hand,  it  would  be  hard, 
without  going  into  a  detailed  explanation  of  the  laws  and  investigations  of  physical 
chemistry,  to  give  a  clear  picture  of  the  different  hypotheses  in  this  narrow  field.  We 
would  refer  the  reader,  therefore,  to  the  above  book  and  to  the  following  literature: 
Rudolph  Hoeber:  Pfliiger's  Arch.  70,  624  (1898);  74,  246  (1899);  86,  199  (1901);  94,  337 
(1903);  O.  Cohnheim:  Z.  Biol.  36,  129  (1897);  38,443  (1899),  and  39,167  (1900);  also 
Z.  physiol.  Chem.  33,  9  (1901);  35,  396  and  416  (1902).  J.  Traube:  Pfluger's  Arch. 
105,  541  and  559  (1904).  Cf.  also  Martin  Heidenhain:  Anatomische  Hefte,  79-80, 
26,  2-3  (1904).  Published  by  Merkel  and  Bonnet. 


THE   FUNCTIONS   OF  THE   DIGESTIVE  ORGANS.         533 

absorption  is  to  be  regarded  as  a  process  which  is  no  more  complicated 
than  the  formation  of  a  secretion.  In  the  latter  case  cells  take  away 
certain  substances  from  the  blood,  while  in  the  former  case  other  substances 
are  taken  from  the  digesting  mixture.  Just  as  the  cells  of  the  gland  show 
a  selective  power,  so  also  those  of  the  intestine  have  the  power  of  choosing 
their  material.  In  considering  the  action  of  ferments  we  emphasized  their 
specific  action  and  suggested  that  this  is  due  to  the  peculiar  structure  of 
the  ferment  molecule.  We  can  apply  the  same  reasoning  to  the  cells 
themselves,  and  believe  that  they  are  specific  in  their  entire  construc- 
tion, and  similarly  are  merely  able  to  take  up  substances  having 
particular  atomic  groupings  in  the  molecule.  Indeed,  we  cannot 
abandon  the  thought  that  the  cells  of  the  intestine  in  a  certain  sense  form 
a  secretion  from  the  substances  obtained  from  the  food  which  they  give 
up  on  the  other  side  of  the  intestinal  wall.  As  the  gland-cells  take  the  raw 
material  from  the  blood  for  the  formation  of  their  specific  secretion,  and 
then  in  a  short  time  throw  it  off  only  to  build  up  more  of  it,  so  here  we 
can  imagine  that  the  cells  in  the  intestine  carry  on  their  work  in  a  similar 
manner,  and  acting  together  eventually  give  to  the  blood  a  homogeneous 
material.  Certain  residues  are  taken  up  by  the  lymph  where  they  are 
carried  first  to  the  mesenteric  glands,  from  thence  to  be  gradually  given 
up  for  further  metabolism. 

It  would  be  absurd  to  consider  absorption  to  be  a  result  of  an  unknown 
force,  merely  because  we  are  at  present  without  insight  into  the  process. 
It  is  not  without  interest  in  this  connection  to  recall  an  example  which 
at  first  glance  appeared  to  show  strikingly  an  actual  intelligence  on 
the  part  of  unicellular  organism,  but  which  can  be  explained  more 
simply.  We  refer  to  the  observation  of  Cienkowski.1  He  studied  the 
absorption  of  nourishment  by  the  Vampyrella  Spirogyrce.  It  is  a  micro- 
scopically-small, naked,  reddish-colored  cell.  This  simple  being,  iri 
which  not  even  a  nucleus  is  discernible,  seeks  out,  among  all  the  various 
algse  that  are  at  hand,  always  a  certain  especial  kind,  and  leaves  untouched 
all  other  varieties.  When  it  has  come  in  contact  with  the  suitable  kind  of 
Spirogyra,  it  places  itself  firmly  next  to  the  cell-wall,  dissolves  it  and 
sucks  in  the  contents.  We  now  know  enough  concerning  the  action  of 
ferments,  however,  to  show  that  the  fact  that  this  kind  of  Vampyrella 
feeds  only  upon'  special  algse  is  not  so  remarkable.  It  is  quite  certain 
that  the  cell-wall  is  dissolved  by  means  of  a  ferment.  The  ferments  are 
evidently  capable  of  acting  only  upon  a  certain  kind  of  alga.  We  mention 
this  example  at  this  place  especially  to  show  how  we  should  look  upon  the 
active  absorption  of  substances  on  the  part  of  the  cells.  It  may  be  merely 

1  Arch,  mikroskop.  Anat.  1,  203  (1865).  Cited  by  Bunge  in  his  Lehrbuch  der  Physi- 
ologie  des  Menschen,  Vol.  II,  p.  4  (1901). 


534  LECTURE  XXII. 

pointed  out,  that  the  cells  come  into  consideration  according  to  the  way 
that  they  are  constructed,  and  that  evidently  chemical  processes  play  an 
important  part  in  the  phenomena.  In  no  case  should  it  be  implied  that 
forces  unknown  to  us  come  into  play.  It  is  self-evident  that  we  should 
recognize  clearly  just  how  far  we  can  go  in  accordance  with  observed  facts 
and  as  to  where  the  realms  of  pure  speculation  begin.  Unquestionably 
we  are  at  present  far  from  understanding  the  action  of  the  cells.  As  long 
as  we  do  not  understand  the  composition  of  albumin  and  especially  that 
of  the  ferments,  we  cannot  expect  to  receive  much  light  upon  the  numerous 
problems  which  we  meet  with  in  studying  the  work  of  the  cells. 

The  absorption  of  the  individual  foodstuffs,  their  further  destiny  in 
the  tissues  and  eventual  combustion,  we  have  already  considered  in  detail, 
so  that  we  will  now  merely  consider  one  other  function  of  the  intestine, 
namely,  the  formation  of  the  faeces  and  their  removal  from  the  system. 
We  have  already  found  that  the  amount  of  excreta  varies  with  the  nour- 
ishment. The  color  of  the  faces  changes  similarly.  Where  an  abundance 
of  meat  is  eaten  the  scybala  are  dark  or  grayish  colored,  while  a  diet 
largely  of  bread  makes  the  color  lighter.  The  bile-pigments  have  a  good 
deal  to  do  with  the  color  of  the  faeces,  although  it  is  usually  their  trans- 
formation product,  stercobilin,  which  is  present.  The  faeces  contain  besides 
indigestible  substances,  the  secretion  of  the  intestines  and  of  the  accessory 
glands,  and  a  certain  amount  of  digestible  matter  which  was  not  absorbed 
for  some  reason  or  other.  We  also  meet  with  products  of  putrefaction 
such  as  skatole,  indole,  purine  bases,  lime  and  magnesia  soaps  and  other 
substances.  The  faeces  furthermore  always  contain  inorganic  salts,  whether 
it  be  due  to  the  fact  that  they  were  not  absorbed  from  the  food,  or  whether 
they  were  eliminated  in  the  intestines. 

The  formation  of  the  faeces  takes  place  in  the  large  intestine.  Here  the 
unabsorbed  material  passes,  and  becomes  thickened  by  loss  of  water. 
Without  doubt,  in  the  case  of  the  herbivora,  the  ferments  continue  their 
action  in  the  large  intestine,  and  utilize  for  the  organism  certain  amounts 
of  otherwise  undigested  material.  In  the  carnivora,  however,  there  is 
no  digestion  worth  considering  in  the  large  intestine. 

We  have  now  mentioned  all  the  functions  of  the  digestive  organs.  We  are 
well  aware  that  we  have  failed  to  give  a  clear  picture  of  the  total  work  of 
digestion.  Still,  we  are  able  to  take  up  certain  phases  sorhewhat  in  detail. 
On  the  other  hand,  so  many  new  vistas  in  this  field  have  been  opened 
up  by  the  investigations  of  Pawlow  and  his  school  and  of  Bayliss  and 
Starling,  and  so  many  new  questions  remain  to  be  answered,  that  we  no 
longer  can  have  any  doubt  that  the  isolated  discoveries  obtained  here 
and  there  will  before  long  be  welded  together  into  an  organic  whole,  so 
that  little  by  little  we  shall  win  more  and  more  from  the  vast  field  of 
the  unknown. 


LECTURE   XXIII. 

THE   BLOOD. 
COAGULATION.     COMPOSITION. 

BLOOD  is  the  intermediary  in  the  general  metabolism.  It  carries  in  part 
directly  from  the  intestine,  and  in  part  indirectly  by  the  aid  of  the  lymphatics, 
the  proper  nourishment  for  each  individual  cell  of  the  body.  The  oxygen, 
which  is  so  indispensable  for  the  work  of  the  cell,  is  also  carried  to  it  by 
the  blood.  On  the  other  hand,  the  cells  give  up  the  products  of  their 
activity,  whether  as  residues  from  the  various  combustion  processes,  or 
whether  as  secretion  products  which  are  yet  to  play  an  important  part 
in  the  total  metabolism,  to  the  blood.  From  all  this  it  is  obvious  what 
a  dominating  position  the  blood  holds  in  the  animal  organism.  In  contrast 
to  the  other  tissues,  it  is  a  liquid  which  is  kept  in  constant  circulation  by 
the  action  of  the  heart.  The  blood  always  contains  numerous  cells, 
especially  the  red  and  the  white  blood-corpuscles.  We  have  already  dis- 
cussed the  important  part  that  the  former  play  in  external  and  internal 
respiration.  Besides  these  form-elements  there  are  blood-plates,  the  sig- 
nificance of  which  has  never  been  explained  satisfactorily.  The  cell 
elements  of  the  blood  lie  suspended  in  a  liquid  rich  in  albumin,  the  plasma. 
They  may  be  removed  from  the  latter  by  a  centrifugal  machine.  The 
clear  yellowish  plasma  is  then  obtained  above  the  deposited  blood-cor- 
puscles. This  separation  into  these  form-elements  and  the  plasma  can  be 
effected,  however,  only  under  quite  definite  conditions.  If  we  take  blood 
from  any  blood-vessel  (usually  the  carotid  is  chosen),  and  simply  allow  it 
to  stand,  it  soon  undergoes  a  peculiar  transformation.  There  settles  over 
the  bottom  of  the  dish  containing  it  a  firm  coagulum  which  incloses  the 
corpuscles.  Above  this  so-called  blood-clot  there  is  a  clear  liquid  which  is 
very  similar  to  the  plasma,  but  is,  notwithstanding,  an  entirely  distinct 
substance,  as  we  shall  soon  see.  This  liquid  produced  by  the  contraction 
of  the  blood-corpuscles,  and  whose  volume  subsequently  increases  con- 
siderably, is  called  the  serum.  If,  instead  of  merely  allowing  the  blood  to 
stand,  it  is  stirred  vigorously  with  a  wooden,  or  glass,  stirring  rod,  imme- 
diately after  taking  it  from  the  animal,  a  different  coagulum  is  soon  formed 
which  is  known  as  fibrin.  In  this  case  the  blood-corpuscles  remain  for 
the  most  part  suspended  in  the  serum.  This  mixture  of  serum  and  blood- 
corpuscles  is  spoken  of  as  defibrinated  blood.  The  difference  between  the 

535 


536  LECTURE  XXIII. 

two  experiments  lies  merely  in  the  fact  that  when  there  is  a  spontaneous 
coagulation  of  the  blood,  the  fibrin  holds  the  blood-corpuscles  within  its 
meshes  and  only  squeezes  out  the  serum,  while  by  beating  the  blood  the 
fibrin  is  separated  from  the  blood-corpuscles. 

The  question  that  interests  us  first  of  all  is  as  to  the  difference  between 
the  plasma  and  the  serum.  Whereas  the  normal  blood,  as  it  circulates 
through  the  blood-vessels,  consists  essentially  of  only  two  constituents, 
plasma  and  blood-corpuscles,  clotted  blood  contains  three,  —  namely,  the 
blood-corpuscles,  serum,  and  fibrin.  In  both  conditions  of  the  blood  we 
find  the  corpuscles.  They  remain  unchanged,  or  at  least  the  red  corpuscles 
do,  as  far  as  we  know.  The  plasma,  on  the  other  hand,  separates  into  two 
parts,  serum  and  fibrin.  The  following  scheme  represents  these  relations: 


Blood 


Blood-corpuscles       Plasma 

Fibrin        Serum 


Blood-clot  (when  formed 
spontaneously) 


Blood 


Blood-corpuscles         Plasma 
Serum          Fibrin 


Defibrinated  blood 


Fibrin  is  unquestionably  formed  from  the  plasma.  It  was  conceivable 
that  it  is  present  as  such  in  the  blood  under  normal  conditions,  being 
held  in  solution  while  the  blood  is  circulating  in  the  body  and  only 
caused  to  precipitate  under  definite  conditions.  On  the  other  hand,  it 
was  also  believed  possible  that  fibrin  is  not  present  as  such  in  the  blood, 
i.e.,  the  plasma,  except  in  the  form  of  a  preliminary  stage  of  its  development. 
Careful  investigation  soon  showed  the  latter  view  to  be  the  correct  one.  It 
is  perfectly  plain  that  this  peculiar  and  remarkable  phenomenon  of  the  clot- 
ting of  blood  which  has  attracted  the  attention  of  many  investigators  even 
in  remote  ages,  affords  to  the  animal  an  important  means  of  protection 
against  undue  loss  of  blood,  sufficient  in  most  cases  to  cause  the  bleeding 
to  cease. 

The  first  thorough  and  systematic  investigations,  upon  which  our  whole 
theory  of  blood  coagulation  is  based,  were  made  by  the  two  scientists 
Buchanan  l  and  Alexander  Schmidt.2  Each  of  these  men,  working  inde- 
pendently, has  explained  the  essential  points  concerning  the  clotting  of 
blood.  Buchanan  made  the  important  observation  that  hydrocele  fluids 


1  Proc.  Philosoph.  Soc.  Glasgow,  2,  1844  (1845). 

3  Arch.  Anat.  Physiol.  1861,  1862;  Pfliiger's  Arch.  6,  445  (1872);  9,  354  (1874);  11, 
291  and  515  (1875);  13,  103  (1876).  For  the  literature  on  the  subject,  see  P.  Morawitz: 
Ergeb.  Physiol.  4,  307  (1905).  Other  comprehensive  works  on  the  clotting  of  blood  to 
which  we  would  call  attention  are,  Alexander  Schmidt:  Die  Lehre  von  den  fermenta- 
tiven  Gerinnungserscheinungen  (1876);  Zur  Blutlehre  (1892)  and  Weitere  Beitrage 
zur  Blutlehre  (1895);  Arthus:  Neuere  Arbeiten  zur  Blutgerinnung  (1899);  E.  Schwalbe: 
Beitrage  zur  Chemie  und  Morphologic  der  Koagulation  des  Blutes  (1900);  A.  Schitten- 
helm:  Zentr.  Stoffwechs.  u.  Verdauungs  Krankheiten,  6,  143  (1905). 


THE   BLOOD.  537 

which  of  themselves  do  not  clot,  immediately  coagulate  if  a  little  blood- 
serum,  or  a  clot  of  blood,  be  added  to  them.  Now  blood-serum  by  itself 
does  not  clot;  it  is,  in  fact,  formed  by  the  clotting  of  blood.  Thus  the 
union  of  two  liquids,  either  of  which  alone  is  not  capable  of  forming  a  clot, 
produces  coagulation.  Buchanan  concluded  from  this,  and  correctly, 
that  two  substances  are  necessary  for  the  formation  of  blood-clot.  He 
assumed  one  of  these  to  be  fibrin,  while  the  other,  probably  originating 
from  the  white  corpuscles,  acted  upon  the  fibrin  and  converted  it  into  an 
insoluble  form.  Denis1  attempted  to  isolate  this  "soluble  fibrin."  He 
first  prevented  coagulation  by  collecting  the  blood  in  one-sixth  its  volume 
of  a  saturated  sodium  sulphate  solution.  He  then  allowed  the  heavier 
blood-corpuscles  to  settle  out,  and  precipitated,  by  the  addition  of  common 
salt,  an  albuminous  substance  from  the  plasma  which  he  had  siphoned  off. 
This  substance  dissolved  in  water,  but  coagulated  after  a  short  time;  we 
will  give  to  it  the  name  of  fibrinogen.  It  may  be  considered  as  the  ante- 
cedent of  fibrin.  Buchanan  recognized  the  fact  that  a  second  substance 
was  probably  necessary  to  change  fibrinogen  into  fibrin.  Our  thanks  are 
due  to  Alexander  Schmidt,  however,  for  showing  that  the  coagulation 
process  is  due  to  a  fermentation.  He  succeeded  in  isolating  a  substance 
from  the  blood-serum  which  was  capable  of  causing  the  separation  of  a 
large  quantity  of  fibrin.  The  substance  becomes  inactive  after  it  has  been 
heated  to  100°  C.  Its  optimum  of  activity  lies  at  37°  C.  This  substance 
Schmidt  designated  as  fibrin  ferment.  By  its  action  upon  fibrinogen, 
fibrin  is  formed.  The  circulating  blood  does  not  contain  the  fibrin  fer- 
ment. It  is  formed,  according  to  the  experiments  of  Schmidt,  by  the 
disintegration  of  the  white  corpuscles.  We  must  mention  here  that  he 
himself  did  not  regard  the  formation  of  the  fibrin  ferment  as  such  a  simple 
process.  He  did  not  assume  the  presence  of  an  antecedent,  but  believed 
that  fibrin  was  formed  from  two  entirely  distinct  substances,  a  fibrino- 
genous  substance  and  a  fibrinoplastic  one.  Olof  Hammarsten 2  dis- 
puted this  view,  and  attributed  the  fermentative  action  to  a  conversion  of 
fibrinogen  into  fibrin.  Other  investigation  has  shown  that  Hammarsten's 
theory  is  correct. 

There  is  still  another  important  point  to  mention.  Alexander  Schmidt 
pointed  out  that  the  formation  of  blood-clot  also  required  the  presence  of 
neutral  salts.  According  to  his  views,  all  soluble  salts  of  the  alkalies  and 
alkaline  earths  reacted  similarly.  Hammarsten  noticed,  on  the  other 


1  Nouvelles  Etudes  chimiques,  physiologiques  et  me'decines  sur  les  substances  albu- 
minoids (1856),  and  M^moire  sur  le  sang  (1859). 

2  Nova  acta  Reg.  Soc.  Sclent.  Upsala,  Ser.  3,  10,  1  (1875) ;  Upsala  lakareforenings 
forhandlingar,  11,  1876;  Pfliiger's  Arch.  17,  413  (1878);  18,  38  (1878);  19,  563  (1879); 
22,  443  (1880);  30,  437  (1883).     See  also  Fre"dericq:  Bull,  de  1'acad.  roy.  Belgique,  2 
s&ie,  44,  7  (1877). 


538  LECTURE  XXIII. 

hand,  that  calcium  chloride  exerts  a  particularly  favorable  action  upon 
the  rapidity  of  the  coagulation.  The  necessity  for  the  presence  of  lime- 
salts  was  proved  clearly  by  Arthus,  and  Arthus  and  Pages.1  They  showed 
that  blood  collected,  as  it  flows  from  the  animal's  body,  in  a  solution 
of  alkali  oxalate  does  not  clot.  If,  however,  a  slight  excess  of  lime- 
salts  is  added  to  this  oxalate  plasma,  a  clotting  at  once  takes  place. 
It  is  tempting  to  compare  the  clotting  of  blood  with  the  coagulation  of 
casein  by  rennin.  The  latter  would  correspond  to  the  fibrin  ferment. 
This  ferment  changes  fibrinogen  into  fibrin,  which  may  form  an  insoluble 
calcium  salt,  and  is  precipitated.  This  simple  explanation  of  the  clotting 
of  blood  has,  however,  been  shown,  to  be  incorrect.  The  lime-salts  must 
act  in  some  other  way. 

In  order  to  understand  the  clotting  of  blood,  and  the  processes  which 
take  place  in  this  connection,  it  is  necessary  to  bear  in  mind  the  following 
points.  In  discussing  the  digestive  ferments  we  were  constantly  confronted 
by  the  fact  that  the  ferments  as  such  are  not  given  up  by  the  cells,  but  in 
the  form  of  their  antecedents,  to  which  in  general  we  gave  the  name  of 
zymogens.  The  transformation  of  these  inactive  substances  into  active 
ferments  is  brought  about  by  various  agents.  How  was  it  with  trypsino- 
gen?  We  remember  that  this  was  changed  into  trypsin  by  the  so-called 
enterokinase  which  is  given  up  by  the  epithelial  cells  of  the  intestinal 
membrane,  and  is  contained  in  the  intestinal  juices.  Again  we  remember 
that  a  substance  called  secretin  has  been  obtained  from  the  blood,  which 
incites  the  gland-cells  of  the  pancreas  into  greater  activity.  The  secretin 
is  likewise  found  in  the  intestinal  -membrane  in  a  preliminary  stage,  which 
is  activated  by  acid.  We  do  not  know  how  secretin  influences  the  action 
of  the  pancreas,  whether  it  acts  directly  upon  the  gland-cells  or  indirectly 
by  increasing  the  blood-supply.  At  all  events  it  is  evident  that  the  forma- 
tion of  ferments  is  a  very  complicated  process,  and  even  when  the  zymogen 
has  been  formed  it  does  not  at  all  signify  that  the  fermentation  will  take 
place. 

In  accordance  with  this  aspect,  we  must  next  find  out  whether  the  fibrin- 
ferment,  sometimes  called  thrombin,  possesses  a  zymogen  stage  in  its 
development,  and  if  so,  how  it  is  brought  into  activity.  Further  investi- 
gation has  in  fact  shown  that  the  fibrin-ferment  does  exist  originally  in  an 
inactive  form.  We  will  call  this  simply  the  zymogen  of  the  fibrin-ferment. 
This  zymogen  may  be  obtained  in  large  amounts  from  the  oxalate  plasma 
and  becomes  active  only  after  being  treated  with  calcium  chloride  solution. 
In  this  way  the  fibrin-ferment  is  obtained.  This  ferment  is  capable  of 
causing  coagulation  in  the  oxalate  plasma,  from  which  the  calcium  salts 

1  Arthus:  Doctor's  Thesis,  Paris,  1890.  Arthus  and  Pages:  Arch.  Physiol.  22,  739 
(1890);  Arthus:  Compt.  rend.  soc.  biol.  46,  435  (1893);  Arch.  Physiol.  1896,  47,  and 
Compt.  rend.  soc.  biol.  64,  526  (1902). 


THE   BLOOD.  539 

have  been  precipitated.  According  to  this,  it  is  easy  to  assume  that  the 
calcium  salts  effect  the  activating  of  the  zymogen.  The  plasma  normally 
contains  only  the  zymogen  of  the  fibrin-ferment  and  not  the  ferment  itself. 
In  clotting  blood,  the  ferment  is  made  active  under  the  influence  of  calcium 
salts,  and  is  now  exerting  its  action  upon  the  fibrinogen.  If,  on  the  other 
hand,  the  calcium  salts  are  removed  by  precipitation  with  oxalic  acid 
before  the  coagulation  has  taken  place,  then  the  blood  does  not  show  the 
same  tendency  to  form  a  clot,  because  the  zymogen  remains  unchanged, 
and  in  this  condition  it  is  perfectly  inactive.  Further  support  for  the  view 
that  the  calcium  salts  are  only  active  in  this  phase  of  the  coagulation,  and 
that  they  do  not  take  part  directly  in  the  conversion  of  fibrinogen  into 
fibrin,  is  shown  by  the  work  of  Hammarsten.  He  pointed  out  that  only 
those  calcium  compounds  need  be  considered  which  are  present  in  such  a 
state  that  the  calcium  is  precipitable  by  oxalic  acid.  The  oxalate  plasma 
contains  calcium,  in  addition,  which  is  evidently  present  in  the  form  of 
complex  organic  compounds.  It  is  possible  now  to  convert  fibrinogen 
into  fibrin  by  the  action  of  the  fibrin-ferment  in  the  absence,  of  lime  salts 
that  can  be  thrown  down  by  oxalate.  This  experiment  is  perfectly  analo- 
gous to  that  with  the  oxalate  plasma.  Hammarsten  was  able  also  to  show 
that  the  fibrin  could  not  be  regarded  as  a  calcium  compound.  We  do  not 
know  exactly  how  the  calcium  salts  cause  this  conversion  of  zymogen 
into  ferment.  It  is  possible  that  it  acts  directly  upon  the  zymogen,  but 
it  is  likewise  conceivable  that  the  calcium  salts  have  an  indirect  action  in 
regulating  the  conditions.  For  the  present,  however,  we  shall  consider  that 
they  themselves  take  part  directly  in  the  conversion  of  the  zymogen  into 
ferment,  and  that  otherwise  they  have  nothing  whatever  to  do  with  the 
formation  of  the  fibrin. 

We  shall  at  this  place  mention  that  quite  recently  it  has  been  noticed 
that  calcium  salts  exert  an  activating  effect  upon  trypsinogen.  If  inactive 
pancreatic  juice  be  treated  with  sodium  fluoride  it  will  remain  in  this  con- 
dition, and  is  only  activated  by  the  addition  of  calcium  salts.  In  such  a 
case  as  this  the  calcium  salt  evidently  does  not  act  directly  upon  the  zymo- 
gen. If  the  pancreatic  juice  be  filtered  through  collodion,  then  it  will  no 
longer  be  activated  by  the  addition  of  the  calcium  salt.  Delezenne,1  who 
performed  this  last  experiment,  believes  that  some  substance  is  held  back 
on  filtering  the  pancreatic  juice  through  collodion,  which  is  capable  of 
activating  the  trypsinogen.  The  calcium  salts  serve  in  some  way  to 
activate  the  unknown  substance  just  as  it  is  possible  that  enterokinase 
may  have  an  antecedent.  If  we  apply  this  observation,  which  to  be  sure 
has  never  been  explained  entirely  satisfactorily,  to  the  coagulation  of  the 
blood,  then  we  should  have  to  assume  that  the  zymogen  of  the  fibrin-fer- 
ment is  activated  by  a  substance  which  corresponds  to  enterokinase,  and 

1  Compt.  rend.  soc.  biol.  No.  33  (1905). 


540  LECTURE  XXIII. 

that  this  activator  is  likewise  present  in  the  blood  in  an  inactive  condition, 
and  is  only  changed  into  the  active  condition  by  the  presence  of  calcium 
salts.1 

We  must  recall  one  other  fact  that  we  met  with  in  discussing  the  diges- 
tive ferments.  We  mentioned  that  the  bile,  and  the  intestinal  juices  in 
general,  had  the  property  of  augmenting  the  action  of  the  pancreatic  juice. 
According  to  our  present  knowledge,  this  does  not  consist  merely  in  chang- 
ing zymogen  into  ferment.  The  above-mentioned  secretions  accelerate 
directly  the  fermentation  process.  Until  we  understand  the  nature  of 
ferments  better,  there  is  naturally  but  little  prospect  of  our  being  able 
to  comprehend  the  accelerating  effect.  We  can  only  mention  the  fact, 
and  state  in  addition  that  there  are  other  substances  known  which 
tend  to  retard  the  action  of  ferments  without  in  any  way  injuring  them 
directly. 

We  must  also  ascertain  whether  there  are  substances  which  tend  to 
accelerate  the  action  of  the  fibrin-ferment.  It  has  indeed  been  long  recog- 
nized that  there  are  substances  which  accelerate  the  clotting  of  the  blood. 
Even  Buchanan  noticed  an  acceleration  produced  by  certain  tissues. 
Rauschenbach 2  has  proved  beyond  question  that  there  are  substances 
present  in  the  cells  of  the  tissues  which  aid  in  the  formation  of  the  clot.  He 
found  a  particularly  favorable  action  on  the  part  of  those  tissues  which 
were  rich  in  nuclein  substances.  Foa  and  Pellacani 3  showed  further  that 
the  injection  of  the  juices  from  various  tissues  caused  intravascular  coagu- 
lation. This  caused  a  tedious,  unfruitful  discussion  as  to  whether  the 
substances  present  in  the  cells  of  the  tissues  were  to  be  considered  as 
corresponding  to  the  fibrin-ferment,  or  whether  they  merely  augmented 
its  action  upon  the  plasma.  The  first  assumption  is  a  tempting  one.  In 
the  first  place,  according  to  many  observations  the  leucocytes  are  the  ante- 
cedents of  the  fibrin-ferment.  It  would  be  of  itself  not  inconceivable  that 
other  cells  in  the  body  should  produce  similar,  or  the  same,  products, 
especially  as  it  is  well  known  that  after  death  a  coagulation  takes  place  in 
the  cells  which  may  be  considered  as  perfectly  analogous  to  the  clotting  of 
blood. 

Certain  observations,  however,  make  it  seem  more  probable  that  the 
coagulation  action  of  the  tissue  extracts  depends  upon  a  quite  different 
process  than  the  direct  introduction  of  fibrin-ferment.  Above  all,  the  work 


1  It  is  probably  true  that  the  lime  salts  do  not  directly  cause  the  activation  of  the 
fibrin-ferment  zymogen,  for  it  is  not  easy  to  see  otherwise  how  the  blood  can  contain 
the  two  substances  side  by  side  without  their  reacting  together.     The  calcium  salts  are 
only  brought  into  activity  when  the  fibrin-ferment  zymogen  has  been  changed  in  some 
way. 

2  Ueber   die  Wechselwirkungen  zwischen  Protoplasma  und   Biutplasma.   Dorpat, 
1883. 

8  Arch.  Science  med.  7,  113  (1883). 


THE   BLOOD.  541 

of  Delezenne  1  should  be  mentioned  in  this  connection.  He  showed  that 
the  blood  of  birds,  reptiles,  Batrachia,  and  fish  coagulated  but  very  slowly 
of  itself.  If  for  example  the  blood  of  a  bird  be  carefully  removed  so  that 
it  does  not  come  in  contact  at  all  with  the  tissues,  it  can  be  kept  in  vessels, 
out  of  contact  with  dust,  for  a  long  time,  without  forming  a  clot.  By 
centrifugalizing  such  blood,  plasma  can  be  obtained  which  keeps  until  it 
putrefies  without  the  formation  of  any  clot.  If,  however,  a  little  blood,  or 
a  little  juice  from  the  tissues,  be  added  to  such  cell-free  plasma,  there  is  at 
once  a  formation  of  fibrin.  If  the  blood  clots  of  itself,  then  we  notice  that 
the  clot  is  formed  first  at  a  place  where  there  is  present  a  considerable 
amount  of  leucocytes.  This  experiment  cannot  be  carried  out  with 
the  blood  of  mammals,  for  it  coagulates  too  quickly.  Evidently  their 
leucocytes  are  less  resistant  than  those  of  the  above-mentioned  classes 
of  animals.  The  objection  may  be  raised  that  in  every  case  there  is 
the  possibility  that  active  fibrin-ferment  may  be  carried  to  the  blood  of 
plasma  by  the  juices  from  the  tissues,  while  the  zymogen  of  this  fibrin- 
ferment  which  is  contained  in  the  blood  itself,  for  some  reason  is  not 
changed  into  the  active  form.  Morawitz  2  has  proved,  however,  that  this 
objection  is  not  well  founded.  He  showed  that  the  juice  from  the  tissues, 
even  in  the  presence  of  calcium  salts,  was  incapable  of  causing  a  fibrinogen 
solution  to  coagulate.  If,  however,  the  extract  from  the  tissues  be 
added  to  the  blood  itself,  there  is  a  marked  acceleration  of  the  coagulation 
provided  that  the  lime-salts  are  present.  In  the  absence  of  lime-salts,  the 
extracts  from  the  tissues  are  without  action. 

Alexander  Schmidt  distinguished  between  accelerating  and  retarding 
substances  for  the  coagulating  of  the  blood.  He  believed  that  these  are 
present  in  the  leucocytes,  and  in  all  other  cells  of  the  bodies.  The  former 
class  of  substances  may  be  extracted  with  alcohol,  while  the  latter  cannot. 
We  can  imagine  that  the  substances  which  accelerate  the  clotting  of  blood 
serve  to  activate  the  zymogen  of  the  fibrin-ferment.  Under  normal  condi- 
tions, i.e.,  while  the  blood  is  circulating  through  the  blood-vessels,  there  is 
an  equilibrium  between  these  substances  that  accelerate  and  those  that 
retard  its  coagulation,  whereas  when  clotting  takes  place,  this  equilibrium 
is  disturbed  in  favor  of  the  former.  Plausible  though  this  hypothesis 
may  be,  it  must  be  emphasized  that  it  is  not  based  upon  a  careful  analysis 
of  the  separate  processes. 

If  we  draw  a  picture  of  blood-coagulation  in  accordance  with  what  has 
been  stated  above,  we  may  assume  it  to  be  well  established  that  the  blood, 
or,  better,  the  plasma,  contains  a  substance,  fibrinogen,  which  is  an  ante- 
cedent of  fibrin.  This  transformation  of  fibrinogen  into  fibrin  is  to  be 


1  Compt.  rend.  soc.  biol.  48,  782;  Compt.  rend.  122,  1281  (1896);  Arch.  Physiol.  1897, 
333;  Compt.  rend.  soc.  biol.  49,  462,  489,  and  507  (1897). 

58  Arch.  klin.  Med.  79,  1  (1904);  Hofmeister's  Beitr.  4,  381  (1903);  5,  133  (1904). 


542  LECTURE  XXIII. 

regarded  as  the  result  of  fermentation.  The  fermentation  is  brought 
about  by  the  fibrin-ferment  which  does  not  occur  as  such  in  the  blood  but 
is  probably  present  in  the  plasma  in  an  inactive  condition,  the  zymogen  of 
the  fibrin-ferment.  In  order  for  the  zymogen  to  become  active,  a  second 
substance  must  act  upon  it.  A  true  activation  must  take  place.  The 
exact  nature  of  the  activator  of  the  zymogen  is  at  present  unknown.  It 
is  not  impossible  that  calcium  salts  bring  about  this  effect.  Certain 
observations,  however,  make  it  appear  improbable  that  the  calcium  salts 
take  part  directly  in  the  formation  of  the  ferment  from  its  zymogen  con- 
dition. Some  facts  indicate  that  a  peculiar  kinase  is  active,  which  is 
itself  set  free  in  some  way  so  that  it  can  act  upon  the  zymogen.  Appar- 
ently it  is  here  that  the  calcium  salts  come  into  play.  It  may  be  mentioned, 
in  addition,  that  two  antecedents  of  the  zymogen  have  been  described  in 
the  literature.  One  of  these,  which  has  not  been  mentioned,  is  said  to 
be  activated  by  acids  or  alkalies.  It  has  been  found,  namely,  that  the 
serum  from  clotted  blood,  which  of  itself  contains  but  little  active  ferment, 
will  become  very  active  upon  the  addition  of  acid  or  alkali.  There  is, 
nevertheless,  no  ground  for  assuming  that  there  are  two  kinds  of  zymogen 
present.  We  agree  with  Morawitz  that  the  fibrin-ferment,  for  some  reason 
or  other,  becomes  inactive  after  the  blood-clot  has  formed.  It  is  simplest 
to  assume  that  the  fibrin-ferment  unites  with  some  other  compound, 
whereby  its  active  group  is  rendered  inactive.  It  is  equally  plausible  that 
by  means  of  some  intramolecular  transformation,  perhaps  the  formation 
of  an  anhydride,  the  inactive  condition  of  the  ferment  is  again  obtained. 
The  alkali  or  acid  which  is  added  to  the  serum  would  in  the  first  instance 
set  the  ferment  free,  whereas,  according  to  the  latter  view,  the  anhydride 
form  would  be  lost.  At  all  events,  it  is  unnecessary  to  assume  that  the 
fibrin-ferment  has  two  antecedents.  It  is  evident  from  this  attempted 
explanation,  what  a  complicated  process  the  clotting  of  blood  really  is, 
and  how  many  different  minor  processes  must  be  cleared  up  before  we  shall 
be  able  to  understand  the  whole  phenomenon  of  blood-coagulation. 

The  point  that  is  of  chief  interest  to  us  here,  is  as  regards  the  nature  of 
the  fermentation.  Does  a  hydrolysis  take  place,  an  oxidation,  a  reduction, 
or  what?  The  first  assumption  only  need  be  discussed.  Formerly,  it  was 
believed  that  the  fibrinogen  took  on  water  and  formed  fibrin  together  with 
a  substance  soluble  in  water,  which  was  called  fibrin-globulin.  Recently 
every  justification  for  such  an  assumption  has  been  denied,  and  mainly 
because  it  is  possible  to  prepare  solutions  of  fibrinogen  which  will  not  split 
off  fibrin-globulin  either  by  clotting  or  coagulating  by  heat.1  According 
to  the  more  recent  view,  the  formation  of  fibrin  results  from  an  intra- 
molecular rearrangement  of  the  atoms.  There  is  at  present  no  prospect  of 
deciding  this  question  definitely.  Fibrinogen  is  an  albuminous  substance, 


Huiskamp:  Z.  physiol.  Chem.  44,  182  (1905). 


THE   BLOOD.  543 

of  which  we  merely  know  that  it  is  closely  related  to  the  globulins,  and 
fibrin  also  belongs  to  the  proteins.  It  is  perfectly  possible  that  fibrinogen 
consists  of  several  molecules  of  fibrin  which  take  up  water  and  disintegrate, 
whereby  eventually  fibrin  is  formed,  so  that  although  fibrin  is  formed  from 
fibrinogen,  the  coagulation  is  essentially  a  hydrolytic  decomposition. 
There  are  no  facts  known  at  present  which  contradict  such  an  assumption. 
Under  ordinary  conditions  when  the  body  is  wounded,  the  blood  flows 
out  from  the  blood-vessels  past  the  tissues.  Its  clotting  is  thereby  accel- 
erated. We  must  here  consider  the  anomalous  behavior  of  the  blood  in 
hemophilia.  This  condition  is  especially  characterized  by  the  fact  that  the 
blood  does  not  clot  readily.  Even  from  the  slightest  wounds  there  is  a 
tendency  to  bleed  freely.  There  may  be  even  such  a  slight  tendency 
for  the  blood  to  clot,  that  a  wound  resulting,  for  example,  from  the 
extraction  of  a  tooth  may  cause  the  patient  to  bleed  to  death.  Hemo- 
philia has  been  of  interest  to  biologists  not  only  on  account  of  this  peculiar 
condition  but  also  by  a  further  peculiarity  which  holds  almost  invariably. 
This  is  the  fact  that  it  is  hereditary,  and,  moreover,  it  is  almost  always 
the  male  members  of  the  so-called  families  vrith  hemophilic  blood,  who 
inherit  this  tendency.  On  the  other  hand,  the  female  members  of  the 
families  alone  transmit  the  anomaly.  The  following  tree  shows  how  this 
tendency  runs:  — 

Family  P 


t 

Family  II 


FT  i  I,  I/ 

•  9  9  9     •  .9  • 

(47yrs.old)    |  |~~          """]/         |    26  yrs.  old      |  13  yrs.  old 

$         $  •         9  <? 

9           (19  yrs.  (15  yrs.  (12  yrs.  (4  yrs.  (1  yr. 

15  yrs.      old)        old)  old)       old)  old) 
old 

The  symbol  $  indicates  those  male  descendants  which  were  normal, 
9  indicates  those  males  having  the  tendency  to  bleed  freely,  and  9  rep- 
resents the  female  members  of  the  family.  We  mention  hemophilia  at 
this  place  because  this  anomalous  behavior,  which  is  hardly  to  be  regarded 
as  a  disease,  inasmuch  as  the  individuals  are  normal  in  every  other  respect, 
ought  to  be  of  assistance  to  us  in  the  study  of  the  coagulation  of  blood. 

1  Abderhalden:  Beitrage  pathol.  Anat.  und  allgem.  Path.  35,  213  (1903).  See 
Stahel:  Inaug.  Dissert.  1903,  Zurich,  1880.  Hoessli:  Inaug.  Dissert.  Basel,  1885.  Sahli: 
Z.  klin.  Med.  56  (1905). 


544  LECTURE  XXIII. 

Here  nature  has  performed  for  us  a  physiological  experiment.  Evidently 
some  link  in  the  chain  of  processes  from  those  which  start  the  coagulation, 
to  those  that  complete  it,  is  missing.  First  it  was  suggested  that  perhaps 
the  calcium  salts  were  not  present.  Direct  experiment  failed  to  confirm 
this.  The  behavior  cannot  result  from  a  deficiency  in  fibrinogen,  for  the 
blood  is  found  to  yield  just  as  much  fibrin  as  normally.  The  remarkable 
thing  is  the  time  that  it  takes  for  the  blood  to  clot.  If  a  trace  of  defibrin- 
ated  normal  blood  is  added  to  the  hemophilic  blood,  the  coagulating  is 
thereby  accelerated. 

It  is  evident  that  this  abnormal  blood  contains  all  of  the  constituents 
that  are  required  for  forming  the  clot.  It  contains  sufficient  fibrinogen, 
sufficient  calcium  salts,  and,  as  far  as  we  are  able  to  find  out,  enough  of  the 
zymogen  which  antecedes  the  fibrin-ferment;  but,  on  the  other  hand,  one 
obtains  the  impression  that  an  insufficient  amount  of  the  agent  is  present, 
which  changes  the  zymogen  of  the  fibrin-ferment  into  the  active  state.  We 
have  designated  this  substance  as  a  kinase,  and  suggested  that  it  occupies 
a  similar  position  to  that  of  enterokinase.  Now  cases  of  hemophilia  have 
been  known  in  which  all  of  the  blood  did  not  show  this  abnormal  behavior, 
but  in  which  it  was  restricted  to  the  blood  from  certain  parts  of  the  body, 
especially  from  the  blood-vessels  in  the  mucous  membrane.  While  injuries 
to  the  skin,  for  example,  caused  a  normal  bleeding,  a  very  slight  injury 
to  the  mucous  membrane  might  cause  enormous  hemorrhages  which  could 
hardly  be  checked  at  all.  Now  there  is  no  doubt  that  there  is  some  ana- 
tomical anomaly  in  the  walls  of  the  blood-vessels  concerned,  for  mere 
scratches  which  would  not  ordinarily  cause  any  bleeding  at  all,  now  cause 
it  to  take  place  profusely.  But  while  it  is  easy  to  understand  that  abnor- 
mally constructed  blood-vessels  may  be  injured  more  readily,  this  does  not 
explain  at  all  why  it  is  that  the  blood  from  them  does  not  coagulate. 

The  characteristic  phenomenon  with  such  bleeding  is  that  the  blood 
constantly  oozes  through  a  loose  clot  exactly  as  through  a  sponge.  The 
coagulum  formed  is  not  connected  properly  with  walls  of  the  injured 
blood-vessels.  At  the  best,  it  is  merely  suspended  from  walls  without 
being  closely  bound  to  them.  It  does  not  fulfill  its  normal  function  of 
checking  the  flow  of  blood.  This  tends  to  lead  one  to  suspect  that  the  walls 
of  the  blood-vessels  themselves  have  something  to  do  with  the  clotting  of 
the  blood,  and  most  probably  in  the  sense  that  the  injured  cells  give  up 
something  which  accelerates  the  coagulation  process.  We  must  designate 
this  substance  as  a  kinase,  and  localize  its  function  in  the  entire  process  to 
that  of  the  preliminary  stage;  i.e.,  we  must  ascribe  to  it  the  property  of 
activating  the  zymogen  of  the  fibrin-ferment.  Consequently  a  chemical 
anomaly  is  closely  connected  with  this  anatomical  one.  It  is  not  impossible 
that  further  studies  based  upon  these  observations  will  eventually  show 
what  parts  of  the  walls  of  the  vessels  take  part  in  the  secretion  of  the  kinase. 


THE   BLOOD.  545 

Naturally  it  does  not  necessarily  follow  that  all  cases  of  hemophilia  result 
from  the  same  cause.  Perhaps  in  different  cases,  different  links  in  the 
whole  chain  of  processes  may  be  missing.  We  have  introduced  this  dis- 
cussion here  not  alone  because  it  apparently  sheds  light  upon  the  process 
of  coagulation,  a  fact  to  which  H.  Sahli  first  called  our  attention,  but 
because  it  seems  to  us  as  highly  significant  that  such  an  extremely  localized 
anomaly  in  the  whole  course  of  a  fermentative  action  should  prove  to  be 
hereditary. 

We  have  up  to  this  point  failed  to  answer  the  question  why  the  blood 
does  not  coagulate  in  the  blood-vessels  of  the  body  under  normal  con- 
ditions. It  is  a  priori  not  so  easy  to  see  why  conditions  could  not  pre- 
vail within  the  blood-vessels  which  would  bring  the  fibrin-ferment  into 
activity.  On  the  other  hand,  the  fact  that  the  coagulation  process  depends 
upon  the  harmonious  action  of  several  distinct  factors,  presents  several 
possibilities  whereby  the  coagulation  in  the  blood-vessels  themselves 
may  be  prevented.  It  is  merely  necessary  to  prevent  the  bringing  into 
activity  of  the  fibrin-ferment.  The  following  experiment1  brings  to  our 
attention  still  another  factor  which  we  have  not  considered  in  the  coagu- 
lation of  blood.  If  blood  is  collected  under  vaseline  or  oil,  it  remains 
perfectly  fluid  for  hours.  It  can  be  stirred  with  a  greased  rod  without  its 
coagulating.  If,  on  the  other  hand,  the  precaution  is  not  taken  to  grease 
the  rod,  coagulation  at  once  takes  place  upon  stirring.  It  is  even  possible 
to  centrifugalize  blood  that  has  been  collected  in  paraffined  vessels,  and 
thus  obtain  plasma,  which  similarly  will  not  clot  for  a  considerable  length 
of  time  if  it  is  kept  in  greased  or  paraffined  vessels.  On  the  other  hand, 
if  such  blood  is  poured  into  an  ordinary  glass  vessel,  it  will  clot  immediately. 
The  contact  of  the  blood  with  something  that  it  can  wet,  seems  to  start  the 
coagulation.  As  this  paraffined  plasma,  after  the  calcium  salts  have  been 
removed  from  it,  does  not  coagulate  when  brought  into  contact  with 
foreign  bodies,  it  is  out  of  the  question  to  believe  that  it  contains  an  active 
ferment.  By  the  process  of  exclusion,  we  may  conclude  that  the  contact 
with  a  foreign  body  in  some  way  accelerates  the  transformation  of  the 
zymogen  into  active  ferment.  One  might  assume  from  this  that  the  reason 
the  blood  does  not  coagulate  in  the  blood-vessels,  with  intact  intima,  is 
that  the  conditions  are  similar  to  that  of  the  greased  vessels  outside  of  the 
body.  In  fact,  we  know  that  if  the  intima  is  in  any  way  injured,  intra- 
vascular  coagulation  readily  sets  in,  which  is  called  a  thrombus  when  it 
merely  stops  up  the  blood-vessel  which  is  injured,  but  is  known  as  embo- 
lism when  the  coagulation  influences  other  blood-vessels  as  well.  The 
blood  is  continually  wetting  the  intima  of  the  blood-vessel  walls.  The 

1  Briicke:  Virchow's  Arch.  12,  100  (1857).  Freund:  Wiener  Med.  Jahrbiicher,  1888, 
259,  and  1889,  554.  Bordet  and  Gengou:  Ann.  Institute  Pasteur,  17,  822  (1903);  18, 
1  (1904). 


546  LECTURE  XXIII. 

fact  that  coagulation  does  not  take  place  cannot  be  due  to  an  insufficient 
adhesion.  The  uninjured  walls  of  the  blood-vessels  appear  to  exert  a 
restraining  influence  upon  the  coagulation.  It  is  indeed  possible  that 
they  also  produce  a  secretion  of  a  negative  catalytic  nature. 

We  have  mentioned  that  it  is  possible  to  prevent  the  clotting  of  blood 
outside  of  the  body  by  collecting  it  in  a  solution  of  ammonium  oxalate. 
Sodium  fluoride  acts  similarly.  The  cause  of  the  failure  of  coagulation  to 
begin  is  to  be  considered  as  due  to  the  precipitation  of  the  lime-salts 
as  oxalate  or  fluoride.  The  addition  of  neutral  salts  in  sufficient  concen- 
tration, or  cooling  the  blood,  also  tends  to  prevent  the  formation  of  a  clot. 
The  influence  of  both  measures  is  due  to  a  restraining  of  the  action  of  the 
ferment.  Now  we  know  of  a  number  of  substances  which  may  be  intro- 
duced into  the  circulation  so  that  the  blood  which  is  subsequently  removed 
will  not  coagulate.  Commercial  peptone  is  such  a  substance.1  We  may  state 
in  this  connection  that  peptone  acts  differently  in  the  case  of  different 
animal  species,  and  in  fact  with  one  individual  of  a  species  it  may  prevent 
coagulation,  in  another  merely  retard  the  formation  of  coagulum,  while 
in  a  third  member  of  the  same  species  it  will  be  apparently  without  effect. 
This  indicates  that  the  influence  of  peptone  upon  the  process  of  blood-coagu- 
lation is  not  so  simple  as  is  the  case  with  oxalic  acid  for  example.  It  is 
important  also  to  find  that  it  takes  from  ten  to  fifteen  times  as  large  a  dose 
of  peptone  to  prevent  the  coagulation  in  a  test-tube  as  is  required  in  the  case 
of  injection  into  the  organism.  It  has  never  been  found  possible  to  localize 
in  any  way  this  action  of  the  peptone,  although  apparently,  in  the  light  of 
recent  investigations,  the  action  is  not  due  to  the  peptone  itself,  but  to 
impurities  present  in  commercial  peptone.  How  this  effect  is  produced 
is  entirely  unknown  to  us.  It  has  been  suggested  that  it  causes  the  for- 
mation in  the  body  of  substances  which  tend  to  prevent  the  coagulation. 
It  has  been  established  that  peptonized  blood  contains  all  the  elements 
which  are  considered  as  necessary  for  the  clotting.  In  spite  of  this  fact 
the  harmonious  course  of  the  entire  chain  of  processes  is  in  some  way 
disturbed.  We  can  indeed  imagine  that  by  the  failure  of  some  one 
of  the  substances  which  aid  in  the  coagulating  process,  the  clotting  is 
prevented.  The  disturbance  is  at  all  events  to  be  sought  in  the  group  of 
processes  by  which  the  activating  of  the  zymogen  of  the  fibrin-ferment  is 
effected. 

Other  substances  are  known  which  act  similarly  to  peptone.  We  will 
mention  the  serum  of  Murcena  2  and  the  extract  of  crabs'  muscles  and  of 


1  Schmidt-Miilheim:    Arch.     Anat.     Physiol.     180,    33.      Albertoni:    Zentr.    mecL 
Wissensch.  1880,  No.  32.     Fano:  Arch.  Anat.  Physiol.  1881,  277. 

2  Mosso:  Ann.  chim.  farm.  8,   198  (1888),  and  Arch,  exper.  Path.  Pharm.  25,  111 
(1891).     Delezenne:  Arch,  physiol.  646  (1897),  and  Compt.  rend.  soc.  biol.  49,  42  and 
228  (1897).     Heidenhain:  Pfliiger's  Arch.  49,  209. 


THE   BLOOD.  547 

snails.  The  characteristic  of  these  substances  which  prevent  clotting  is, 
to  repeat,  that  they  evidently  do  not  themselves  directly  affect  the  coagu- 
lation process,  but  excite  the  organism  to  the  formation  of  products  which 
tend  to  prevent  the  blood  from  forming  a  clot. 

Besides  these  substances  which  exert  a  secondary  effect  upon  the 
coagulation,  we  know  of  substances  which  directly  prevent  it.  To  these 
substances  belongs  hirudin,  which,  by  reason  of  the  extensive  studies  of 
Jakobj,  has  recently  excited  much  interest.  Hirudin  is  formed  in  the  oral 
glands  of  leeches.1  It  is  quite  stable  towards  heat  and  is  soluble  in  water. 
After  injection  into  the  organism  it  appears  unchanged  in  the  urine.  It 
is  not  yet  perfectly  clear  how  hirudin  acts.  It  is  apparently  able  to  neu- 
tralize a  part  of  the  fibrin  ferment.2  It  is  still  an  open  question  how  we 
can  best  picture  this  process.  It  is  usually  assumed  that  the  active  ferment 
possesses  groups  which  enable  it  to  react  with  definite  groups  of  other 
compounds.  These  groups  impart  to  the  ferment  its  specific  nature.  If 
now  the  ferment  comes  in  contact  with  a  substance  which  is  capable  of 
engaging  these  groups,  i.e.,  combining  with  them  for  example,  the  ferment 
then  becomes  inactive.  Substances  like  hirudin  have  been  obtained  from 
other  blood-sucking  animals,  e.g.,  from  the  wood-tick  (Ixodes  ricinus)  and 
from  Anchylostomum  caninum. 

It  is  an  old  observation  that  the  blood  of  animals  which  have  died  from 
snake-bite,  often  does  not  coagulate.3  The  poison  from  the  cobra  especially 
has  been  carefully  studied.  It  is  supposed  to  contain  a  substance  which 
acts  upon  the  kinase,  i.e.,  the  activator  of  the  zymogen  of  the  fibrin-ferment. 
It  is  clear  that  if  the  function  of  this  activator  is  disturbed,  a  coagulation 
cannot  take  place. 

Besides  the  substances  which  prevent  the  coagulation  of  blood,  we  know 
of  others  which  accelerate  it.  In  this  respect  we  will  recall  the  effect  of 
calcium  salts.  Their  internal  application  is  said  to  favor  the  formation  of 
blood-clot.  Another  substance  which  is  used  much  more  extensively 
for  this  purpose  is  gelatin.4  It  is  altogether  impossible  to  state  why  this 
property  should  be  ascribed  to  gelatin,  and  if  it  really  does  exert  the 
desired  effect  it  is  still  more  difficult  to  explain  it.  At  all  events,  the  state- 
ments concerning  it  that  are  to  be  found  in  the  literature  are  very  con- 
tradictory. 

We  have  up  to  the  present  time  intentionally  disregarded  a  question  of 


1  Haycraft:  Arch,  exper.  Path.  Pharm.  18,  209  (1884).     Franz:  ibid.  49,  342  (1901). 
Andreas  Bodong:  ibid.  52,  242  (1904). 

2  Fuld  and  Spiro:  Hofmeister's  Beitr.  5,  171  (1904).     P.  Morawitz:  Arch.  klin.  Med. 
79,  432  (1904). 

3  Fontana  :    On    Poisons.   London,   1787.      Morawitz:    Arch.    klin.    med.   80,   340 
(1905). 

4  Dastre  and  Floresco:  Compt.  rend.  soc.  biol.  48,  243  and  358;  Arch,  physiol.  28, 
302. 


548  LECTURE  XXIII. 

deep  significance,  namely,  that  of  the  origin  of  fibrindgen.  This  is  something 
of  which  we  have  no  positive  information.  Apparently  the  liver  plays  an 
important  part  in  its  production.  P.  Nolf  l  found  that  after  extirpation 
of  the  liver  the  fibrinogen  content  of  the  blood  decreased  rapidly.  Experi- 
ments performed  by  M.  Doyon,  A.  Morel,  and  N.  Kareff  2  point  in  the  same 
direction.  They  showed  that  after  sub-acute  poisoning  of  dogs  with  phos- 
phorus oil,  which  causes  a  fatty  degeneration  of  the  liver,  there  is  a  decrease 
in  the  fibrinogen  content  of  the  blood  plasma,  which  lessens  the  coagula- 
tion power  of  the  blood.  With  a  cock  it  was  not  found  possible  to  cause 
a  fatty  degeneration  of  the  liver  by  phosphorus  poisoning,  and  it  was 
likewise  impossible  in  this  case  to  cause  fibrinogen  to  disappear  from  the 
plasma.  It  is  entirely  impossible  to  draw  binding  conclusions  from  these 
experiments,  for  both  the  extirpation  of  the  liver  and  poisoning  by 
phosphorus  are  attacks  whose  effect  upon  the  action  of  the  whole 
organism  cannot  be  disregarded.  It  is  possible  that  the  liver  not  only 
influences  the  production  of  fibrinogen,  but  other  phases  of  the  coagulation 
process  as  well.  We  shall  expect  further  experiments  in  this  direction. 

In  the  coagulation  process  we  have  become  acquainted  with  a  very 
essential  property  of  the  blood.  We  shall  now  turn  to  the  individual  con- 
stituents of  defibrinated  blood,  the  serum  and  blood-corpuscles.  The 
former  consists  chiefly  of  two  different  albuminous  substances,  a  globulin 
and  an  albumin.  We  shall  not  stop  here  to  discuss  the  unedifying  question 
as  to  whether  these  proteins  are  simple  substances  or  not.  This  cannot  be 
decided  in  the  light  of  our  present  knowledge,  and  even  if  it  is  possible  by 
fractional  precipitation,  or  by  "salting  out,"  to  effect  a  separation  into 
simpler  constituents,  but  little  gain  is  made  in  our  knowledge  of  these  two 
proteins,  for  even  these  fractions  cannot  be  characterized,  by  the  means 
now  at  hand,  nor  upon  the  present  basis  of  protein  chemistry,  as  simple 
substances.  Besides  these  proteins,  we  find  varying  amounts  of  fat  in 
blood-serum.  After  a  meal  rich  in  fat,  the  amount  present  in  the  serum 
may  become  so  large  as  to  give  it  a  milky  appearance.  Serum  invariably 
contains  cholesterol  and  lecithin,  and  in  fact  the  former  is,  as  we  have 
already  stated,  largely  present  in  the  form  of  fatty-acid  esters.  A  sugar, 
d-glucose,  is  also  present  in  serum.  The  amount  of  the  latter  varies,  but 
only  within  narrow  limits. 

We  have  already  seen  that  the  blood,  besides  providing  nourishment, 
also  serves  to  carry  the  end-products  of  metabolism  away  from  the  cells. 
For  this  reason  we  constantly  meet  with  such  products  in  the  blood.  It 
is  certain  that  they  belong  for  the  most  part  to  the  plasma,  or  its  serum. 
Their  presence  remained  for  a  long  time  undiscovered,  because  from 
moment  to  moment  but  small  amounts  of  such  substances  are  present. 


1  Bull.  Acad.  roy.  Belgique,  1905,  81. 

2  Compt.  rend.  140,  800  (1905). 


THE   BLOOD.  549 

As  soon  as  they  are  formed,  they  are  given  up  by  the  cells  to  the  blood 
and  immediately  leave  the  body.  Such  substances  are  urea,  uric  acid, 
creatine,  hippuric  acid,  and  conjugated  glucuronic  acids,  all  of  which  we 
may  in  a  sense  regard  as  end-products  of  metabolism.  Blood-serum  is 
never  perfectly  colorless.  It  always  has  a  yellow  tint,  the  color  being 
ascribed  to  a  certain  dyestuff,  called  lutein.  Its  chemical  nature  is 
wholly  unexplained.  Serum  always  contains  inorganic  constituents,  and 
the  amount  appears  to  be  very  constant.  It  would  be  highly  interesting 
to  have  definite  knowledge  concerning  the  distribution  of  the  inorganic 
substances,  and  above  all  concerning  the  way  they  are  combined  in  the 
blood,  plasma,  and  serum.  Unfortunately,  there  are  no  known  methods 
for  giving  us  such  information.  At  present  we  are  forced  to  rely  upon  the 
chemical  examination  of  the  ash,  the  results  of  which  naturally  have  but 
a  relative  value.  In  this  way  we  are  able  to  ascertain  what  constituents 
are  present  in  the  ash,  but  we  obtain  absolutely  no  information  as  to  how 
the  phosphoric  acid,  for  example,  is  combined  in  the  blood  or  plasma. 
This  phosphoric  acid  may  arise  from  inorganic  phosphates,  or  from  organic 
phosphorus  compounds,  such  as  lecithin,  nucleic  acid,  etc.  The  value  of 
an  ash  analysis  can  be  increased  by  attempting  to  determine  in  what  dif- 
ferent way  the  respective  amounts  of  the  constituents  may  have  been 
combined.  It  would  be,  of  course,  likewise  desirable  to  obtain  by  physico- 
chemical  methods  some  idea  as  to  the  content  of  the  blood  and  of  the 
plasma  in  electrolytes  and  non-electrolytes.  As  the  most  important 
result  of  physico-chemical  investigation  of  the  blood,  we  will  mention  the 
highly  interesting  observations  of  Hoeber  l  that  the  concentration  of  the 
hydroxyl  ions  in  blood-serum  and  in  the  blood  is  almost  exactly  the  same 
as  that  of  distilled  water.  Both  liquids  are  from  this  point  of  view  to  be 
considered  as  neutral. 

Blood  always  contains  cells,  namely,  the  red  and  white  corpuscles. 
Whereas  the  latter  are  to  be  regarded  as  true  cells,  the  former  are,  in  man 
and  mammals,  not  to  be  considered  as  perfect  cell-structures.  Only  in 
the  beginning  of  their  development  do  they  possess  a  nucleus,  which  they 
lose  as  soon  as  they  become  active  in  the  blood.  The  red  corpuscles  of 
birds,  reptiles,  amphibia,  and  fishes  do,  however,  contain  nuclei.  In  spite 
of  extensive  investigations  but  little  is  known  concerning  the  chemical 
construction  of  the  red  corpuscles.  It  is  true  that  we  know  fairly  well 
what  components  are  present,  but  we  do  not  understand  how  they  are 
combined.  The  red  corpuscles  do  not  possess  any  true  membrane.  It 
has  been  assumed  that  they  consist  of  stroma  filled  with  liquid.2  They  are 


1  Pfliiger's  Arch.  81,  522  (1900).     Geza  Farkas:  Mathematikai  6s  termeszettudo- 
manyi  £rtesito,  21,  Vol.  1  (1902).     P.  Fraenkel:  Pfliiger's  Arch.  96,  601  (1903). 

2  H.  J.  Hamburger:  Osmotischer  Druck  und  lonenlehre  in  den  medizinischen  Wis- 
senschaften,  Wiesbaden,  1902.     Cf.  Rollett:  Pfluger's  Arch.  82,  199  (1900). 


550  LECTURE  XXIII. 

enveloped  with  a  substance  similar  to  fat  which  forms  a  semi-permeable 
wall.  It  is  certain  that  the  red  blood-corpuscles,  also  called  erythrocytes, 
do  not  take  up  all  substances.  The  wall  will  not  allow  many  salts  to  pass 
through,  though  it  is  easily  penetrated  by  water.  If  the  erythrocytes  are 
placed  in  a  solution  of  common  salt,  whose  osmotic  pressure  corresponds 
exactly  to  that  of  blood-plasma,  the  blood-corpuscles  will  remain  unchanged. 
Such  a  salt  solution  is  said  to  be  isotonic.  Its  concentration  is  different 
for  different  species  of  animals,  and  is  called  a  "  physiological  salt  solution. " 
In  the  case  of  mammals  such  a  solution  contains  0.9  per  cent  of  sodium 
chloride.  If  there  is  more  salt  present  in  the  solution,  it  is  said  to  be 
hyperisotonic,  in  which  case  the  red  corpuscles  will  give  up  water  to 
the  solution  and  shrink  in  size.  Conversely  in  a  hypisotonic  salt  solution 
(one  containing  less  salt  than  an  isotonic  solution)  the  corpuscles  take 
up  water  and  swell.  This  swelling  may  take  place  to  such  an  extent 
that  the  red  corpuscles  lose  the  characteristic  pigment  which  passes 
into  solution.  In  this  case  the  blood  undergoes  a  peculiar  transfor- 
mation. Whereas  it  was  opaque  before,  it  now  becomes  a  clear,  trans- 
parent, red-colored  liquid.  The  blood  is  said  to  be  "laked."  *  In  the 
laked  blood,  the  blood-corpuscles  robbed  of  their  hemoglobin,  the  so-called 
"shades,"  are  found  in  which  only  stroma  is  present.  The  "shades" 
appear  under  the  microscope  as  colorless  structures,  often  retaining  the 
form  of  the  erythrocytes.  The  red  corpuscles  are  not  impenetrable  to  all 
substances.  Urea,  for  example,  is  taken  up  by  the  blood-disks.  If  urea 
is  added  to  blood  it  distributes  itself  equally  between  the  blood-corpuscles 
and  the  plasma.  Its  solutions,  therefore,  exert  no  osmotic  pressure  upon 
the  red  corpuscles.  The  latter  behave  in  urea  solutions  of  all  concentra- 
tions exactly  as  in  distilled  water.  They  give  up  their  hemoglobin  to  the 
urea  solution;  this  is  not  the  case  if  the  urea  is  added  to  an  isotonic  solution 
of  common  salt.  We  know  of  certain  substances,  such  as  ammonium 
chloride,  for  example,  which  behave  differently  from  urea  in  the  last  case. 
The  wall  surrounding  the  red  corpuscles  is  readily  penetrated  by  this  salt, 
and  the  hemoglobin  goes  into  solution  even  if  the  ammonium  chloride  is 
added  to  an  isotonic  common  salt  solution.  Ammonium  chloride,  there- 
fore, has  a  poisonous  action  upon  the  blood-corpuscles.  A  great  many 
experiments  have  been  carried  out  with  regard  to  the  permeability  of  the 
red  corpuscles.  At  present  they  do  not  give  us  much  information  con- 
cerning the  behavior  of  the  blood-corpuscles  in  the  blood  itself,  and  con- 
cerning the  substances  dissolved  in  the  plasma.  We  are  not  justified  in 
applying  experiments  performed  under  peculiar  conditions  to  the  blood 
itself  as  it  exists  in  the  living  organism. 

The  exit  of   the  pigment  from  the  red  corpuscles,  a  process  which  is 

1  Hans  Koeppe:  Pfliiger's  Arch.  103,  140  (1904);  ibid.  107,  86,  183  (1905). 


THE   BLOOD.  551 

designated  as  hemolysis,  can  be  brought  about  in  quite  a  number  of  different 
ways,  as,  for  example,  by  freezing  the  blood  and  then  thawing  it.  Hemo- 
lysis is  also  effected  by  certain  bacterial  metabolic  products,  by  those  of  the 
higher  plants,  and  also  those  of  animals.  We  shall  subsequently  take  up 
this  process  more  in  detail. 

The  constituent  of  the  red  corpuscle  which  has  been  best  studied 
as  regards  its  functions,  is  the  pigment  of  blood,  hemoglobin,  which  we 
have  already  met  with  in  the  discussion  of  the  respiratory  exchange. 
Before  discussing  its  chemical  construction,  we  will  consider  the  above- 
mentioned,  cellular  constituent  of  the  blood,  the  white  corpuscles,  and 
briefly  take  up  the  composition  of  the  blood  as  a  whole,  and  its  content  of 
individual  substances.  The  white  corpuscles  are  fully  endowed  cells. 
They  are  not  uniform,  but  occur  in  various  shapes  and  sizes.  It  is  extremely 
difficult  to  say  much  about  the  sphere  of  activity  of  these  bodies,  also 
called  leucocytes.  Their  function  has  never  been  satisfactorily  explained. 
They  have  frequently  been  designated  as  agents  of  transportation.  It  is 
very  probable  that  they  play  an  important  part  in  this  function  of  metabo- 
lism, and  accomplish  the  exchange  of  substance  between  the  cells  of 
different  organs.  The  number  of  leucocytes  can  increase  extraordinarily 
under  certain  conditions.  This  phenomenon  is  most  strikingly  illustrated 
in  cases  of  infection,  in  which  case  the  seat  of  infection  is,  under  normal 
conditions,  surrounded  very  quickly  by  a  cordon  of  leucocytes.  They 
are  by  no  means  limited  to  the  blood  circulation.  They  can  leave  this 
and  penetrate  into  the  tissues.  The  white  corpuscles  play  a  quite  different 
part  in  the  blood  from  that  of  the  red  ones.  They  are  not  peculiar  to  the 
blood,  but  merely  make  use  of  it  as  a  vehicle.  They  enter  and  leave  it 
quite  at  will.  They  are  to  be  considered  as  independent  entities.  This 
is  evident  from  the  fact  that  they  are  independent  of  the  nervous  sys- 
tem and  can  move  themselves  forward,  autonomously  like  the  amoeba3, 
by  sending  out  pseudopodia.  It  is  possible  that  the  blood  contains, 
besides  leucocytes,  which  are  only  temporarily  present,  others  which 
stand  in  more  intimate  relations  to  the  blood.  We  are  not  at  all  sure 
whether  we  are  to  regard  the  white  corpuscles  as  forming  a  physiological 
unit,  or  whether  certain  of  them  have  special  tasks  to  fulfill.  Our  experi- 
ence with  pathological  processes  makes  it  seem  more  probable  that  differ- 
ent tasks  fall  to  leucocytes  of  different  forms.  The  large  accumulation 
of  leucocytes  during  intestinal  digestion  remains  absolutely  unexplained. 
It  is  extremely  probable  that  they  in  some  way  take  part  in  the  digestive 
process,  being  perhaps  active  in  the  assimilation  of  the  food.  The  fact 
that  they  are  able  to  take  up  substances  directly,  and  transport  them  away, 
is  shown,  for  example,  by  observations  concerning  the  absorption  of  iron. 
It  is  not  at  all  difficult,  particularly  after  administration  of  inorganic 
iron  salts,  to  find,  by  testing  with  ammonium  sulphide,  many  white 


552  LECTURE  XXIII. 

corpuscles  heavily  laden  with  particles  of  iron,  which  they  carry  to  the 
nearest  lymphatic.  Many  discoveries  show  distinctly  that  the  leucocytes 
endeavor  to  carry  away  foreign  substances  from  the  body.  It  may  be 
regarded  as  positively  established  that  they  play  an  active  part  during 
infectious  diseases  in  striving  to  make  the  injurious  products  of  the  metabo- 
lism of  micro-organisms  harmless,  although  it  is  going  a  little  too  far  to 
assume  that  the  leucocytes  alone  have  this  tendency.  The  leucocytes 
also  serve  to  disintegrate  dead  tissue.  In  this  direction,  the  solution  of 
the  masses  of  fibrin,  which  fill  the  bronchi  and  the  finest  bronchioles  during 
pneumonia,  is  very  interesting.  There  is  in  this  case,  as  we  have  already 
indicated  at  another  place,  a  regular  digestive  process  that  comes  into 
play.  The  fibrin  is  decomposed  into  its  constituents  and  these  are 
resorbed. 

We  cannot  say  much  concerning  the  structure  of  the  white  blood- 
corpuscles.  They  contain,  as  cells,  all  those  constituents  which  we  usually 
meet  with  in  cells.  There  is  not  much  use  in  mentioning  these  constituents, 
for  we  are  not  able  at  present  to  draw  any  conclusions  from  them,  or  from 
their  union  with  the  other  building  stones  of  the  protoplasm  and  nucleus, 
concerning  the  participation  of  this  or  that  substance  in  the  exercise  of 
definite  functions.  As  soon  as  our  investigations  reach  the  cell,  the 
enigma  is  too  great. 

In  addition  to  the  leucocytes  we  find  the  blood-plates,  which  we  have 
already  mentioned.  These  are  colorless,  gummy  disks  of  a  round  form. 
They  are  said  to  possess  all  the  characteristics  of  true  cells,  and  to  be 
also  capable  of  active,  amoeboid  movement.  They  undoubtedly  partici- 
pate in  the  clotting  of  blood.  It  is,  however,  still  a  disputed  question  as 
to  the  point  in  the  entire  coagulation  process  at  which  their  activity 
begins. 

Let  us  now  return  to  the  composition  of  the  blood  itself.  We  must  at 
once  state  that  the  blood,  in  its  natural  state,  is  almost  never  utilized  for 
quantitative  analytical  determinations.  Almost  all  of  the  investigations  in 
this  direction  have  been  made  with  defibrinated  blood.  In  the  first  place,  we 
are  interested  to  know  the  relative  amounts  of  blood-corpuscles  and  serum. 
This  varies  with  different  kinds  of  animals,  and  even  in  different  animals 
of  one  and  the  same  species.  Moreover,  the  estimation  of  the  number  of 
blood-corpuscles,  and  the  amount  of  the  serum,  cannot  be  made  very 
exactly.  It  is  an  indirect  determination.  We  will  briefly  mention  here 
that  method  upon  which  the  figures  that  we  shall  give  below  have  been 
based.  It  is  that  of  Hoppe-Seyler.1  The  blood-corpuscles  may  be 
separated  from  the  serum  by  means  of  the  centrifuge.  By  repeatedly 
stirring  the  blood  with  an  isotonic  salt  solution,  and  renewed  centri- 

1  Handbuch  der  physiol.  und  pathol.  chem.  Analyse,  p.  272  (1883). 


THE   BLOOD.  553 

fugalizing,  the  serum  lying  between  the  separate  blood-corpuscles  is 
eventually  removed.  In  these  blood-corpuscles  we  can  determine  the 
sum  of  the  hemoglobin  and  protein.  If  in  addition  the  hemoglobin  and 
albumin  content  of  the  total  blood  and  the  albumin  content  of  the  serum 
are  determined,  then  from  these  values  the  relative  amounts  of  serum  and 
blood-corpuscles  in  the  blood  as  a  whole  can  be  estimated.  We  may  cite 
an  example: l 

One  thousand  grams  of  defibrinated  beef-blood  contain  on  an  average 
172.9  grams  of  hemoglobin  plus  albumin. 

In  the  blood-corpuscles  from  1000  grams  of  the  same  blood  there  were 
found  124.0  grams  of  hemoglobin  plus  albumin.  1000  grams  serum  con- 
tained 72.5  grams  of  albumin. 

In  the  serum  from  1000  grams  of  blood  there  was  present,  therefore, 
172.9  -  124.0  =  48.9  grams  of  albumin. 

Accordingly,  we  may  compute  the  amount  of  serum  in  1000  grams  of 
defibrinated  blood  as  follows: 

48  9 

=^-=     .100  =  67.45  per  cent  serum. 

72.  o 


100 


i 
-  67.45  =  32.55  per  cent  blood-corpuscles. 


After  having  established  the  relative  amounts  of  serum  and  blood- 
corpuscles,  then  from  an  analysis  of  the  blood  as  a  whole,  and  of  the  serum 
alone,  we  can  estimate  how  much  of  each  substance  is  present  in  the  blood- 
corpuscles. 

G.  von  Bunge  2  has  shown,  by  means  of  the  following  observation,  that 
this  method  gives  us,  within  certain  limits,  quite  reliable  results.  The 
blood-corpuscles  of  pig's  blood  contain  no  soda.  This  enables  us  to  com- 
pute the  relative  amounts  of  serum  and  blood  corpuscles  by  merely  deter- 
mining the  amount  of  soda  in  the  blood,  as  a  whole,  and  in  the  serum  by 
itself. 

Bunge  found  in  1000  grams  of  defibrinated  pig's  blood,  2.406  grams  Na2O 
in     "         "       "  the  serum      .....    4.272  grams  Na2O 
Pig's  blood  therefore  contains 

100  =  56.3  per  cent  serum. 


100-56.3  =  43.7  per  cent  blood-corpuscles. 

Now  if  the  calculation  was  made  with  reference  to  the  albumin  content, 
as  in  the  first  case  cited,  he  obtained  the  values:  56.6  per  cent  serum  and 
43.4  per  cent  blood-corpuscles. 


1  Cf.  Abderhalden:  Z.  physiol.  Chem.  23,  521  (1897);  25,  67  (1898). 
a  Z.  Biol.  12,  191  (1876). 


554 


LECTURE  XXIII. 


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556  LECTURE  XXIII. 

The  results  obtained  in  the  analysis  of  the  blood  of  different  species  of 
animals  are  given  on  pages  554  and  555, *  now  emphazing,  however,  that 
the  analyses  of  the  ash  have  only  a  relative  value,  but  on  the  other  hand 
such  values  may  well  serve,  and  in  fact  have  served,  as  a  foundation  for 
further  inquiry,  although  the  methods  employed  are  not  yet  such  that  the 
analytical  results  will  prove  fruitful  in  all  directions. 

From  the  table  it  is  evident  that  the  serum  from  various  animal  species 
is  of  much  the  same  composition.  There  are,  however,  marked  differences 
in  the  composition  of  the  blood  as  a  whole,  and  of  the  blood-corpuscles. 
It  is  interesting  that  the  blood  of  related  animals  is  very  similar.  This 
is  apparent  when  we  compare,  for  example,  the  relative  amounts  of  the 
separate  constituents  of  the  blood-corpuscles  of  the  carnivora  with  those 
of  the  ruminants.  It  is  certainly  not  without  significance  that  the  blood 
of  both  these  families  contains  considerable  soda,  while  that  of  the  horse, 
pig,  and  rabbit  contains  none  at  all.  Certain  constituents,  as,  for  example, 
sugar,  fat,  and  lime,  are  apparently  wanting  in  the  blood-corpuscles.  It 
is  rather  questionable  whether  we  can  assume  that  the  substances  are 
entirely  absent.  The  methods  employed  are  not  sensitive  enough  to  make 
such  a  decision  possible.  To  be  sure,  the  fact  that  this  result  has  been 
repeatedly  obtained  speaks  in  favor  of  its  correctness.  We  may  call 
attention  to  the  fact  that  quite  recently  glucuronic  acid  has  also  been 
found  in  the  blood-corpuscles. 

We  should  mention  the  fact  that  the  amount  of  blood  contained  in  dif- 
ferent animals  has  been  estimated.  A  sample  of  blood  was  taken  from  the 
animal  in  question,  after  which  it  was  bled  to  death,  and  the  blood-vessels 
washed  out  with  water,  until  the  latter  came  out  perfectly  clear  and  color- 
less. The  wash-water  was  mixed  with  the  blood,  collected,  leaving  out 
the  first  sample,  and  the  total  volume  estimated.  Then  the  first  sample 
was  diluted  with  water  until  it  corresponded  in  shade  with  the  other 
mixture.  In  this  way  it  was  easy  to  compute  the  amount  of  blood  con- 
tained in  the  animal. 

This  method  is  not  very  accurate,  and  there  are  several  sources  of  error. 
It  is,  in  fact,  impossible  to  remove  all  the  blood  from  the  body  in  such  a 
way.  In  the  case  of  dogs  the  weight  of  the  blood  amounts  to  from  seven 
to  nine  per  cent  of  the  dog's  weight,  in  rabbits  the  blood  corresponds  to 
from  five  to  nine  per  cent,  while  in  man  it  is  only  from  one-sixteenth  to 
one-thirtieth  of  the  body- weight. 

In  human  beings,  a  cubic  millimeter  of  blood  contains  on  an  average 
5,000,000  red  corpuscles  in  the  case  of  males,  and  4,500,000  in  females. 
There  is  usually  one  white  corpuscle  for  every  350  to  500  red  ones.  Nat- 
urally these  values  vary  according  to  the  blood-vessel  from  which  the 

1  E.  Abderhalden:  Z.  physiol.  Chem.  25,  67  (1898). 


THE  BLOOD.  557 

sample  is  taken.  We  know;  furthermore,  that  certain  conditions  greatly 
affect  these  values.  Thus  it  is  well  known  that  when  a  large  amount 
of  water  is  passed,  the  blood  may  become  thickened,  while  inanition  has 
the  same  effect.  Vasomotor  influences  also  can  cause  changes  in  the 
composition  of  the  blood  throughout  the  entire  'organism.  More  and  more 
it  has  become  recognized  that  it  is  not  always  possible  to  draw  conclusions 
concerning  the  behavior  of  the  blood  as  a  whole  from  the  examination  of 
a  single  sample.  For  experimental  work  it  is  naturally  most  satisfactory 
to  withdraw  all  of  the  blood,  but  when  this  is  not  possible,  it  is  always 
advisable  to  make  several  examinations  of  different  samples,  remembering 
at  the  same  time  that  we  are  dealing  with  only  relative  values. 


LECTURE   XXIV. 
BLOOD   AND   LYMPH. 

IN  discussing  the  respiratory  exchange,  we  called  attention  to  the 
important  part  played  by  the  red  blood-corpuscles  in  this  process;  namely, 
their  significance  in  the  transportation  of  oxygen.  We  mentioned  the 
important  fact  that  it  is  not  the  entire  red  corpuscle  which  combines  with 
the  oxygen,  but  that  this  power  is  limited  to  the  pigment  contained  in  it, 
which  is  known  as  hemoglobin.  This  substance  is  not  a  simple  compound. 
It  consists  of  two  components,  which,  according  to  their  chemical  nature, 
belong  to  two  entirely  distinct  classes.  One  of  these  components,  globin, 
is  a  protein.  On  account  of  the  relatively  large  proportion  of  bases  which 
it  contains,  and  especially  of  histidine,  it  is  classed  with  the  histones.  We 
have  already  mentioned  that  this  classification  is  to  be  regarded  as  a 
temporary  one.  Globin  contains  the  same  constituents  as  are  usually 
present  in  proteins.1  The  other  component,  which  may  be  separated 
fairly  easily  from  the  globin,  contains  iron  and  is  designated  as  hemochro- 
mogen. In  the  presence  of  oxygen  the  latter  is  readily  oxidized  to  hematin. 
In  spite  of  a  great  deal  of  careful  investigation,  our  knowledge  concerning 
the  nature  of  the  combination  between  globin  and  hemochromogen  is  still 
very  incomplete.  We  merely  know  that  about  4  per  cent  of  hemochromogen 
can  be  obtained  from  hemoglobin.2  It  is  still  unsettled  whether  we  are 
justified  in  assuming  that  one  molecule  of  globin  unites  with  one  molecule 
of  the  iron-containing  constituent,  or  whether  several  molecules  of  globin 
are  in  combination  with  a  single  molecule  of  hemochromogen.  There  is 
in  fact  no  absolute  proof  at  hand  that  even  globin  itself  is  a  simple 
substance.  We  are  emphasizing  these  uncertainties,  which  in  part 
have  been  mentioned  elsewhere,  because  hemoglobin  has  been  usually 
chosen  as  a  foundation  for  the  calculation  of  the  molecular  weights  of 
proteins. 

When  oxygen  combines  with  hemoglobin,  oxyhemoglobin  is  formed,  and 
this  compound  crystallizes  readily.  From  squirrels  it  crystallizes  in  six- 
sided  plates  of  the  hexagonal  system,  while  that  from  other  animal  species 
crystallizes  in  needles,  prisms,  tetrahedrons  or  plates  of  the  orthorhombic 
system.  The  solubility  of  the  oxyhemoglobins  from  different  species  of 
animals  is  widely  different.  That  from  dogs,  for  example,  is  less  soluble 

1  Abderhalden:  Z.  physiol.  Chem.  37,  484  (1903). 
3  F.  N.  Schulz:  ibid.  24,  449  (1898). 

558 


BLOOD  AND  LYMPH. 


559 


than  that  from  cats.1  More  soluble,  and  for  that  reason  more  difficult  to 
prepare,  are  the  oxyhemoglobins  from  the  blood  of  men,  cattle,  and  pigs.2 
It  has  been  attempted  to  draw  conclusions  concerning  the  uniformity  or 
differences  in  the  different  kinds  of  oxyhemoglobin  by  studying  their  ele- 
mentary compositions.  We  shall  cite  a  few  of  such  analyses  in  the  table 
below,  but  will  state  again,  that  the  elementary  composition  of  such  com- 
plicated compounds  signifies  scarcely  anything  at  all.  Even  if  it  were 
possible  to  decompose  hemoglobin  quantitatively  into  simpler  components, 
we  would  not  be  justified  in  assuming,  if  we  obtained  the  same  relative 
amounts  of  the  various  constituents,  that  the  different  kinds  of  hemoglobin 
were  uniform.  It  may  be  that  the  various  amino  acids  are  arranged  in 
a  different  order  in  the  globin  molecule,  to  say  northing  of  the  various  possi- 
bilities for  the  formation  of  isomers.  We  hold  that  it  is  extremely  essential 
to  emphasize  the  fact  that  the  elementary  analyses  of  proteins  and  their 
complicated  cleavage-products  should  only  be  used  with  great  caution  as 
a  basis  for  drawing  conclusions,  or  for  further  investigations,  and  that  the 
real  value  of  each  ultimate  analysis  is  but  very  slight. 

ELEMENTARY  ANALYSIS  OF  OXYHEMOGLOBIN. 

In  per  cents. 


C 

H 

N 

S 

0 

Fe 

P 

Horse's  blood                

54.75 

6  98 

17.35 

0  42 

20  12 

0  38 

0  3 

Dog's  blood     

54.57 

7.22 

16.38 

0.57 

20  43 

0.34 

0  4 

Cat's  blood 

54  60 

7  25 

16  52 

0  62 

20  66 

0  35 

0  • 

Pig's  blood 

54  17 

7  38 

16  23 

0  66 

21  37 

0  43 

0  5 

Beef  blood                  

54.42 

7.18 

17.45 

0  48 

20  07 

0  40 

0  5 

Guinea  pig's  blood   
Squirrel's  blood 

54.12 
54  09 

7.36 
7  39 

16.78 
16  09 

0.58 
0  59 

20.68 
21  44 

0.487 
0  47 

7 

Goose's  blood     .    .               .        ... 

54.26 

7  10 

16  21 

0  54 

20  69 

0  43 

0  347 

Hen's  blood    

52.47 

7.19 

16.45 

0.86 

22.5 

0  34 

0  20* 

We  find  from  these  analyses  that  the  hemoglobin  of  mammals  contains 
the  elements  carbon,  hydrogen,  nitrogen,  sulphur,  oxygen,  and  iron,  while 
that  of  birds  contains  phosphorus  in  addition.  It  is  very  questionable 
whether  the  phosphorus  content  is  due  to  a  peculiarity  of  the  oxyhemo- 
globin in  birds  or  whether  it  is  not  rather  due  to  an  impurity.  We  remem- 

1  Abderhalden:  Z.  physiol.  Chem.  24,  545  (1898),  and  F.  Kriiger:  Z.  Biol.  26,  469 
(1890),  and  Z.  physiol.  Chem.  25,  256  (1898). 

G.  Hufner:  Beitrage  zur  Lehre  vom  Blutfarbstoff  (1887). 

Abderhalden:  Z.  physiol.  Chem.  37,  484  (1903). 

A.  Jaquet:  Dissert.  Basel,  1899,  and  Z.  physiol.  Chem.  12,  285  (1888). 

J.  C.  Otto:  ibid.  7,  57  (1882). 

According  to  the  author's  analyses. 

Hoppe-Seyler:  Med.-Chem.  Untersuchungen,  p.  366  (1868). 


560  LECTURE  XXIV. 

ber  that  the  red  blood-corpuscles  of  birds  contain  nuclei  and  considerable 
amounts  of  nuclein  substances.  It  is  perfectly  possible  that  the  presence  of 
such  an  impurity  accounts  for  the  apparent  phosphorus  content  in  the  hemo- 
globin of  different  species  of  birds,  whose  blood  has  been  studied.  This 
assumption  appears  more  probable  when  we  state  that  the  oxyhemoglobin 
from  birds  has  never  been  prepared  in  a  satisfactory  manner,  nor  purified 
to  the  extent  accomplished  with  that  from  animals,  and,  moreover,  if  we 
examine  the  beautifully  formed  crystals  under  the  microscope,  we  shall 
find  that  they  may  include  within  themselves  considerable  amounts  of 
impurity.  In  the  hemoglobin  from  horses,  pigs,  and  cattle,  two  atoms  of 
sulphur  are  present  for  each  atom  of  iron,  while  in  the  blood  of  dogs,  the 
iron  is  to  the  sulphur  as  1:3.  We  may  also  mention  the  fact  that  the 
various  oxyhemoglobins  contain  different  amounts  of  water  of  crystalliza- 
tion. It  is  still  an  open  question  whether  the  oxyhemoglobin  from  one  and 
the  same  species  of  animals  is  always  identical.  C.  Bohr  1  holds  that  this 
is  not  the  case.  He  believes  he  has  proved  that  differences  exist  by  deter- 
mining the  power  of  combining  with  oxygen  in  different  fractions  of  crystals 
from  a  single  kind  of  blood.  Hlifner,2  whose  investigations  in  this  field 
have  been  thorough  and  most  carefully  made,  holds  that  such  an  assumption 
is  not  justifiable.  It  must  be  admitted  that  it  is  not  easy  to  prove  beyond 
all  doubt  that  there  is  an  actual  difference  in  different  oxyhemoglobins. 
There  is  always  the  possibility  that  the  observed  differences  may  arise  from 
secondary  changes  which  have  taken  place  in  the  oxyhemoglobin  that  is 
under  examination. 

As  regards  the  combination  of  the  oxygen  in  hemoglobin,  we  have 
already  seen  that  only  the  hemochromogen  takes  part  in  this,  and  that  the 
iron  is  of  much  significance  here. 

The  spectroscopic  behavior  of  oxyhemoglobin  is  very  characteristic.  A 
dilute  solution  shows  in  the  spectroscope  two  absorption  bands  in  the  yellow 
and  green,  between  the  Fraunhofer  lines  D  and  E.  The  band  near  the  D 
line  is  narrower  than  that  near  the  E  line.  Arterial  blood  gives  the  same 
absorption  spectrum  on  account  of  the  presence  of  oxyhemoglobin  in  it. 
We  must  also  add  that  reduced  oxyhemoglobin,  the  true  hemoglobin,  like- 
wise shows  characteristic  absorption  bands.  A  solution  of  hemoglobin, 
of  not  too  great  a  concentration,  shows  a  single  broad  band,  not  very 
sharply  defined,  lying  between  the  D  and  E  lines;  in  fact,  this  band  extends 
a  little  beyond  the  D  line  into  the  red  end  of  the  spectrum.  Venous  blood 
shows  such  a  spectrum,  although,  except  in  cases  of  suffocation,  there  is 
always  some  oxyhemoglobin  present.  The  greater  part  of  the  oxyhemo- 
globin in  such  blood  has,  however,  been  reduced.  Consequently  venous 
blood  does  not  have  the  bright  red  color  of  arterial  blood.  It  is  darker 

1  Zentr.  Physiol.  4,  249  (1890). 
3  Arch.  Anat.  Physiol.  1894,  130. 


BLOOD  AND  LYMPH.  561 

and  has  a  more  violet  color.  The  shade  of  color  naturally  varies  accord- 
ing to  the  ratio  of  the  oxyhemoglobin  to  the  hemoglobin.  Hemoglobin 
is  more  readily  soluble  in  water,  and  for  this  reason  more  difficult  to  prepare 
and  maintain  in  a  crystalline  form.  It  may  be  obtained  easily  from  oxy- 
hemoglobin by  the  withdrawal  of  oxygen,  and  this  may  be  accomplished 
by  placing  the  oxyhemoglobin  in  vacuum,  conducting  an  indifferent  gas 
through  its  solution,  or  by  the  use  of  a  reducing  agent.  Beautiful  crystals 
of  hemoglobin  are  also  obtained  by  allowing  a  solution  of  oxyhemoglobin 
to  stand  for  some  time  in  a  sealed  glass  tube.1  The  oxygen  of  the  oxy- 
hemoglobin is  gradually  consumed,  and  hemoglobin  is  formed  by  the 
reduction. 

Carbon  monoxide  2  may  take  the  place  of  oxygen  in  the  oxyhemoglobin 
molecule.  It  evidently  is  fastened  at  the  same  part  of  the  molecule  as  the 
oxygen,  for  it  replaces  the  latter  by  its  action  upon  oxyhemoglobin,  and 
makes  it  incapable  of  combining  with  oxygen  except  in  the  presence  of  a 
large  excess  of  the  latter  gas.  It  is  herein  that  the  poisonous  action  of 
carbon  monoxide  lies.  Carbon-monoxide-hemoglobin  can  be  obtained  in  a 
crystalline  form,  its  crystals  being  isomorphous  with  those  of  oxyhemo- 
globin.  Its  absorption  spectrum  is  very  similar.  It  also  shows  two  absorp- 
tion bands,  which  are,  however,  nearer  the  violet  end  of  the  spectrum.  The. 
action  of  reducing  agents  does  not  have  the  effect  upon  its  spectrum  that 
is  obtained  with  oxyhemoglobin.  The  two  absorption  bands  do  not  dis- 
solve into  one  band,  or  at  least  not  within  a  short  time. 

Hemoglobin  is  also  capable  of  combining  with  nitric  oxide,3  NO,  and 
this  last  gas  is  even  capable  of  driving  carbon  monoxide  out  of  its  combina- 
tion in  the  blood.  Nitric-oxide-hemoglobin  is  also  crystalline  and  very 
stable.  It  shows  an  absorption  spectrum  very  similar  to  that  of  oxy- 
hemoglobin except  that  the  bands  are  paler.  It  is  even  less  affected  by 
reducing  agents  than  is  the  carbon-monoxide  compound. 

The  action  of  hydrogen  sulphide  4  upon  oxyhemoglobin  gives  rise  first 
of  all  to  the  formation  of  hemoglobin.  Then,  little  by  little,  a  greenish- 
black  coloration  is  formed,  which  reminds  one  of  the  appearance  of  a  trace 
of  ferrous  sulphide.  This  green  shade  is  due  to  the  formation  of  sulph- 
hemoglobin,  which,  however,  has  never  been  prepared  in  a  pure  state.  It 
may  be  distinguished  from  hemoglobin  by  means  of  its  spectral  behavior. 


1  G.  Hiifner:   Z.  physiol.  4,  382  (1880).     If  oxyhemoglobin  is  allowed  to  stand  for 
two  weeks  in  a  quiet  place  at  40°  C.,  crystals  from  1  to  2  centimeters  long  can  be 
obtained. 

2  G.  Hiifner:  Arch.  Anat.  Physiol.  1895,  209,  213.    Hiifner  and  Kiister:  ibid.  1904, 
387. 

3  L.   Hermann:   Arch.  Anat.    Physiol.   1865,  469.     Hufner  and   Reinbold:    1904, 
Suppl.  II,  391. 

4  Hoppe-Seyler:    Zentr.    Med.    Wissensch.    1863,    No.   28,   p.  433.     T.   Araki:  Z. 
physiol.  chem.  14,  405  (1890).     E.  Harnack:  Ibid.  26,  558,  (1898-99). 


562  LECTURE  XXIV. 

It  shows  one  absorption  band  in  the  green,  and  another  in  the  orange-red, 
between  the  C  and  D  lines.  If  hydrogen  sulphide  acts  upon  hemoglobin 
in  the  presence  of  oxygen,  the  hemoglobin  is  completely  decomposed,  so 
that  the  product  formed,  as  well  as  its  derivatives,  no  longer  shows  a  char- 
acteristic absorption  spectrum. 

Quite  different  from  the  above  compounds  is  carbohemoglobin,  in  which 
carbon  dioxide  is  present,  but  combined  at  a  different  place  in  the  molecule 
from  that  occupied  by  the  oxygen  in  oxyhemoglobin.  In  fact,  carbon 
dioxide  and  oxygen  are  taken  up  by  hemoglobin  quite  independently  of 
one  another.  The  carbonic  acid  is  evidently  combined  with  globin,  while 
oxygen  combines  with  'hemochromogen. 

Methemoglobin 1  also  occupies  a  unique  position.  It  corresponds  to 
oxyhemoglobin  in  its  composition,  and  differs  from  it  merely  in  holding 
the  oxygen  in  a  firmer  state  of  combination.  It  may  be  formed  from  the 
latter  on  standing,  or  be  prepared  by  the  action  of  various  agents,  such 
as  iodine,  chlorates,  permanganates,  nitrites,  nitrates,  palladium  hydride, 
pyrogallol,  quinol,  or  ozone.  The  formation  of  methemoglobin  has  also 
been  observed  by  the  action  of  aniline,  toluidine,  acetanilide,  acetopheneti- 
dine,  and  glycerol  upon  oxyhemoglobin.  Methemoglobin  may  be  formed 
even  in  the  circulating  blood,  when  it  comes  in  contact  with  substances 
such  as  amyl  nitrite,  nitrobenzene  and  antifebrin. 

The  oxygen  cannot  be  removed  from  methemoglobin  by  reducing  the 
partial  pressure  of  this  gas.  At  present  it  is  not  known  just  how  this 
transformation  of  oxyhemoglobin  into  methemoglobin  is  effected.  It 
has  been  established  positively  that  both  compounds  contain  the  same 
amounts  of  oxygen.  Reducing  agents  tend  to  convert  methemoglobin 
back  into  oxyhemoglobin.  Methemoglobin  crystallizes  in  brownish-red 
needles,  prisms,  and  also  in  six-sided  plates.  It  is  most  readily  prepared 
by  adding  potassium  ferricyanide  solution  to  a  solution  of  oxyhemoglobin 
and  then,  after  cooling  to  0°  C.,  adding  one-fourth  its  volume  of  alcohol. 
In  acid  solutions  methemoglobin  shows  an  absorption  spectrum  of  a  band 
in  the  orange-red  between  the  C  and  D  lines,  and  a  second  paler  band  in 
the  blue  between  the  G  and  F  lines.  Besides  these  absorption  bands, 
the  acid  solutions  show  two  other  bands  in  the  same  place  as  the  bands 
which  characterize  the  spectrum  of  oxyhemoglobin.  It  seems  probable 
that  these  last  two  bands  are  not  characteristic  of  methemoglobin,  but 
are  due  to  the  presence  of  some  oxyhemoglobin  as  impurity.  In  alkaline 
solutions  methemoglobin  shows  three  lines,  one  on  either  side  of  the  D  line, 
and  one  near  the  E  line.  The  spectrum  of  methemoglobins  is,  in  fact, 
very  similar  to  that  of  hematin. 

1  Hoppe-Seyler:  Zentr.  med.  Wissensch.  1863,  No.  28.  G.  Hiifner:  Z.  physiol. 
Chem.  8,  366  (1884).  Hiifner  and  Otto:  ibid.  7,  65  (1882-83).  A.  Jaderholm:  Z. 
Biol.  16,  1  (1880);  20,  419  (1884).  R.  von  Zeyneck:  Arch.  Anat.  Physiol.  1899,  460. 


BLOOD  AND  LYMPH.  563 

It  is  highly  probable  that  hemoglobin  not  only  occurs  in  the  red  blood- 
corpuscles,  but  in  the  muscles  as  well.  The  latter  likewise  contain  a  red 
pigment  which  cannot  be  washed  out  by  way  of  the  vascular  system,  and 
which,  according  to  its  entire  behavior,  is  certainly  closely  related  to 
hemoglobin.  The  relation  of  this  pigment  to  hemoglobin  has  never  been 
satisfactorily  explained. 

Hemoglobin  is  decomposed  by  gentle  attack  into  its  two  components, 
globin  and  hemochromogen.  The  separation  can  be  effected,  for  ex- 
ample, by  adding  a  few  drops  of  dilute  acid  to  a  hemoglobin  solution  which 
is  free  from  salts.  Acid  hemoglobin  is  formed  as  an  intermediate  product. 
It  shows  an  absorption  spectrum  similar  to  that  of  methemoglobin.  By 
more  energetic  action  of  the  acid,  hemochromogen  is  split  off,  but  only 
when  the  solution  is  kept  out  of  contact  with  the  air.  In  the  presence 
of  air,  hematin  is  always  formed;  from  the  latter,  by  reduction,  hemo- 
chromogen may  be  obtained.  The  digestive  juices  of  the  stomach  and 
pancreas  are  also  capable  of  effecting  this  separation  of  hemoglobin  into 
its  two  constituents. 

Hematin,  whose  reduction  product,  hemochromogen,  plays  such  an 
important  part  in  allowing  the  blood  to  combine  with  oxygen,  has  been 
carefully  studied  in  recent  years.  Although  its  constitution  has  not  been 
established  positively,  still  we  are  now  able  to  explain  certain  relations 
existing  between  it  and  other  compounds  of  similar  construction.  The 
most  important  work  in  this  field  has  been  that  of  Nencki  *  and  that  of 
William  Kiister.2  According  to  Kiister,  the  empirical  formula  of  hema- 
tin is  C34H34N4FeO5.  Nencki  and  Sieber  assume  its  formula  to  be 
Cs2H32N4FeO4.  The  starting-point  of  these  investigations  was  not 
usually  hematin  itself,  but  its  hydrochloric  acid  ester,  hemin,  or  Teich- 
mann's  crystals  as  it  is  sometimes  called.  Several  different  formula 
have  been  proposed  for  this  ester. 

It  is  questionable  whether  hemin  is  actually  to  be  regarded  as  the 
hydrochloric  acid  ester  of  hematin.  Nencki  in  his  work  stated  that 
it  was  not  formed  by  merely  annexing  the  hydrochloric  acid  to  the 
hematin  molecule,  but  that  there  was  a  replacement  of  an  OH  group  by 
chlorine  : 


4  +  HC1  = 
Hematin  Hemin 


1  Nencki  and  Sieber:    Arch,  exper.  Path.  Pharm.  24,  430  (1888),  and  Monatsh.  9, 
115   (1888).     Nencki  and  Rotschy:    ibid.   10,  568   (1889).     Nencki  and  Zaleski:    Z. 
physiol.  Chem.  30,  384  (1900);  Ber.  34,  997  (1901). 

2  Ber.  27,  572  (1894);    29,  821   (1896);    30,  105  (1897);    Z.  physiol.  Chem.  28,  1 
(1899);    29,    185    (1900);    Ber.    32,    678  (1899);  33,  3021   (1900);    35,   1268,  2948 
(1902)  ;    Ann.  315,   174  (1900).      Z.  physiol.  Chem.   44,  391   (1905)  ;    Ann.  345,   1 
(1906). 


564  LECTURE  XXIV. 

The  iron  in  hematin  may  be  removed  easily  by  the  action  of  acid.  A 
product  free  from  iron  is  thus  obtained  which  is  known  as  hematopor- 
phyrin and  is  given  the  formula  Ci6Hi8N2O3.  Thus,  for  example,  we 
may  allow  hydrobromic  acid  to  act  upon  hematin: 


H2O  +  2  HBr  =  2  C16H18N2 
Hematin  Hematoporphyrin 

By  reduction  of  hematoporphyrin,  mesoporphyrin  Ci6Hi8N202  is  ob- 
tained, or  if  the  reducing  agent  is  more  energetic,  hemopyrrole,  C8Hi3N,  is 
formed.  This  last  substance  is  methyl-propyl-pyrrole  : 

HC  -  C  —  CH2  .  C2H5 

II         II 
HCX/C-CH3 

N 
H 

By  oxidizing  hematin,  Kiister  obtained  two  crystalline  acids,  which  he 
designated  as  hematinic  acids.  One  of  these  is  a  dibasic  acid  with  the 
empirical  formula  C8H9NO4,  while  the  other  is  to  be  regarded  as  the 
anhydride  of  a  tribasic  acid.  C8H8O5.  The  formation  of  these  two  hema- 
tinic acids  is  illustrated  by  the  following  schema: 


.  C.CH3  CO—  C.CH3 

HN(        |  ->   HN(        n 

N  CH  =  C  .  CH2  .  CH2  .  CH3  N  CO—  C  .  CH2  .  COOH 

Hemopyrrole  or  Methylpropylpyrrole  Dibasic  hematinic  acid 

00—  C.CH3 

o(        n 

XCO—  C  .  CH2  .  CH2  .  COOH 
Partial  anhydride  of  tribasic  hematinic  acid. 

The  last  compound,  by  losing  carbon  dioxide,  goes  over  into  the  anhy- 
dride of  methyl-ethyl-maleic  acid,  C7H8O3. 

If  we  assume  that  hematin  is  a  simple  substance  and  not  a  mixture, 
and  that  its  transformation  into  hematoporphyrin  takes  place  quanti- 
tatively according  to  the  equation, 

C32H32N4Fe04  +  2  H2O  -  Fe  =  2  Ci6Hi8N203, 

then  it  is  very  easy  to  go  a  step  farther  and  assume  that  hematin  is  con- 
structed of  two  symmetrical  halves  connected  together  by  means  of  an 
atom  of  iron.  Now,  as  we  have  seen  above,  hematin  and  hematopor- 
phyrin, by  undergoing  an  oxidation  and  hydrolysis,  both  give  rise  to  the 
same  acids  and  to  the  same  extent.  As  these  cleavage-products  each 
contain  eight  atoms  of  carbon,  it  may  be  safely  assumed  that  hemato- 
porphyrin likewise  is  composed  of  two  equal  parts.  As  was  mentioned, 


BLOOD  AND  LYMPH.  565 

the  hematinic  acids  are  to  be  regarded  as  the  oxidation  products  of 
hemopyrrole.  On  this  basis  we  can  assign  to  hemin,  the  hydrochloric 
ester  of  hematin,  the  following  structural  formula: 

CH3  .  C— C— CH  =  C(OH)— C  =  C— CH  =  CH— C— C— CH3 

II     II  II  II     II 

HC    CH  O     FeCl  HC    CH 


\  / 

NH 


\  / 
NH 


CH3  .  C— C— CH=C(OH)— C=C— CH=CH— C— C— CH3 

II     II  II      II 

HC    CH  HC    CH 

\  /  \  / 

NH  NH 

The  correctness  of  the  above  formula  has  not  been  established  in  all  its 
details.1  It  should  serve  merely  to  give  us  an  approximate  picture  of  the 
structure  of  hematin.  We  will  state  in  this  connection  that  the  question 
has  been  discussed  often,  whether  the  hematin  of  different  species  of  ani- 
mals, or  even  of  animals  in  the  same  species,  has  a  uniform  composition, 
or  whether  we  shall  have  to  assume  the  existence  of  different  hematins. 
This  question  arose  from  the  fact  that  different  observers  claimed  to  isolate 
hemins  of  different  compositions  so  that  the  hematins  from  which  they 
were  made  must  have  been  different.  The  most  recent  investigations, 
however,  make  it  seem  more  probable  that  there  is  but  one  hematin.2 
The  observed  differences  in  the  composition  of  hemin  may  be  explained 
partly  by  the  different  ways  in  which  the  substance  was  prepared,  and 
partly  by  the  tendency  that  hemin  has  of  crystallizing  out  together  with 
a  portion  of  the  solvent. 

From  the  experiments  performed  in  the  attempt  to  explain  the  consti- 
tution of  hematin,  interesting  relations  have  been  discovered  between  it 
and  a  color-principle,  which  for  a  long  time  has  been  assumed  to  exert 
quite  similar  biological  functions.  We  refer  to  chlorophyll,  the  pigment 
of  green  plants;  although  it  would  be  perhaps  better  to  include  under  the 
name  chromophyll  all  the  different  pigments  of  the  vegetable  kingdom 
which  exert  parallel  functions.  At  present,  however,  chlorophyll,  the 
green  pigment,  is  the  only  one  of  such  substances  which  has  been  studied 
exhaustively.  It  is  hardly  to  be  doubted  that  the  other  pigments  in  the 
vegetable  kingdom  which  play  the  same  part  in  plant  economy  as  that 
of  chlorophyll  have  quite  similar  compositions.  We  have  already 
stated  that  we  are  not  justified  in  regarding  the  function  of  chlorophyll 
as  parallel  to  that  of  hemoglobin,  or  to  hemochromogen.  It  appears, 


1  Cf  Lecture  XVII,  p.  396. 

2  William  Kiister:    Z.  physiol.    Chem.  29,  185  (1900);    40,  391  (1904).     K.  A.  H. 
Morner:  ibid.  41,  542  (1904). 


566  LECTURE  XXIV. 

on  the  contrary,  that  chlorophyll  participates  in  the  metabolism  of 
plants,  and  especially  in  the  assimilation  processes,  in  a  way  that  finds 
no  analogy  in  the  case  of  the  pigment  of  the  blood.  We  may  say, 
however,  that  a  comparison  of  the  disintegration  products  of  chloro- 
phyll with  those  of  hematin,  or,  better,  with  those  of  hematoporphyrin, 
shows  considerable  similarity  between  these  apparently  unlike  substances. 
And  yet  we  cannot  rightly  draw  any  conclusions  from  this  agreement  as 
to  the  biological  uniformity  of  the  pigment  of  the  blood  and  that  of  green 
leaves.  Chlorophyll  contains  no  iron,  while  in  the  case  of  hematin  its 
functional  individuality  apparently  depends  upon  the  presence  of  this 
element.  It  is  far  more  fitting  to  conclude  that  the  close  relationship 
between  chlorophyll  and  hematin,  or  its  iron-free  decomposition  product 
hematoporphyrin,  is  explained  by  the  fact  that  hematin  is  formed  from 
chlorophyll.  Unfortunately,  no  one  has  been  able  to  prove  positively 
that  chlorophyll  is  actually  the  mother-substance  of  hematin.  Chlorophyll 
is  unquestionably  transformed  to  a  considerable  extent  while  in  the  ali- 
mentary canal;1  apparently  various  decomposition  products  are  formed. 
It  is  not  impossible  that  the  animal  organism  may  make  use  of  these 
products  for  the  synthesis  of  hematin.  We  make  this  suggestion  because 
again  and  again  we  are  forced  to  admit  that  the  animal  organism  is  greatly 
dependent  upon  the  synthetical  work  of  the  vegetable  kingdom.  To  be 
sure,  the  animal  cells  are  capable  of  effecting  complicated  synthesis,  but 
they  require  for  this  purpose  building  material  which  has  already  been 
well  worked  over.  The  plant  cells  are  capable  of  producing  such  material 
from  the  elements.  Now  hematin  is  a  compound  of  highly  complicated 
structure.  It  is  then  hardly  probable  that  the  animal  organism,  which 
in  every  other  case  makes  use  when  possible  of  the  building  stones  fur- 
nished by  the  vegetable  kingdom  for  accomplishing  its  synthesis,  leaves 
this  material  available  for  the  construction  of  hemochromogen  actually 
untouched,  and  instead  effects  the  complicated  synthesis  of  hematin  from 
the  very  simplest  material.  Here  unquestionably  is  a  great  gap  in  our 
present  knowledge,  —  a  gap  which  has  resulted  from  the  attempt  to  decide 
the  question  whether  inorganic  iron  compounds  or  only  organic  ones  can 
be  utilized  by  the  animal  cells  for  the  synthesis  of  hematin.  We  have 
already  shown  what  a  subordinate  position  is  taken  by  the  iron  assimila- 
tion compared  to  the  formation  of  the  complicated  hematin  molecule. 
We  cannot  yet  decide  this  question,  but  desire  to  leave  the  impression 
that  it  is  by  no  means  improbable  that  the  herbivora  obtain  in  the  chlo- 
rophyll of  their  fodder  the  building  material  for  that  component  of  hematin 
which  contains  the  iron;  and  that  the  carnivora  also  utilize  the  color- 
principle  of  the  blood  which  is  contained  in  their  food  for  the  formation  of 
their  own  hemochromogen,  perhaps,  to  be  sure,  only  after  the  hematin  in 


1  Cf.  L.  Marchlewski:  Z.  physiol.  Chem.  41,  33  (1904). 


BLOOD  AND  LYMPH.  567 

the  food  has  undergone  a  more  or  less  complete  preliminary  disintegration. 
The  fact  that  large  amounts  of  decomposition  products  of  chlorophyll  are 
found  in  the  faeces  of  herbivora,  does  not  in  any  way  speak  against  the 
above  assumption.  We  unfortunately  know  nothing  regarding  the  extent  to 
which  hematin  is  destroyed  and  newly  formed  in  the  animal  organism.  In 
the  yolk  of  eggs,  and  also  in  the  vegetable  kingdom,  we  meet  with  nuclein- 
like  substances  which,  as  we  have  said,  are  very  similar  in  their  elementary 
composition  to  hemoglobin.  It  is  indeed  possible  that  these  substances 
are  used  as  the  raw  materials  for  the  hematin  synthesis.  We  do  not  in 
any  case  need  to  assume  that  the  animal  cell  accomplishes  the  complicated 
construction  of  hemochromogen  from  simple  building  material.  We  only 
wish  to  sound  another  warning  against  drawing  any  conclusions  from  the 
elementary  composition  of  such  complicated  products.  The  formation  of 
hemoglobin,  and  especially  of  hematin,  in  the  animal  organism  is  a  process 
which  remains  absolutely  unexplained.  The  question  whether  iron  in  an 
inorganic  or  organic  condition  is  assimilated  in  order  to  take  part  in  the 
synthesis,  is  far  less  interesting  than  that  concerning  the  building  material 
of  the  hematoporphyrin.  In  order  to  make  our  position  perfectly  clear, 
we  will  repeat  again  that  we  hold  it  to  be  perfectly  possible  that  iron  itself, 
or  in  the  form  of  salts,  may  be  utilized  as  such  for  combining  the  two 
hematoporphyrin  molecules,  i.e.,  in  other  words  the  iron  is  not  necessarily 
an  organic  constituent  of  hematin  or  of  hematoporphyrin,  and  perhaps 
it  can  take  part  in  the  synthesis  only  after  it  has  been  set  free  from  any 
organic  compounds  which  may  contain  it.  A  glance  at  the  above  tentative 
formula  of  hematin  gives  us  some  idea  of  the  separate  phases  in  its 
construction. 

In  the  breaking  down  of  chlorophyll,  Schunck  and  Marchlewski 1  ran 
across  a  derivative  which  they  called  phylloporphyrin.  It  has  the  fol- 
lowing empirical  formula,  CiaHig^O.  Hematoporphyrin  corresponds  to 
the  formula,  Ci6Hi8N2O3.  According  to  this  the  two  compounds  differ 
from  one  another  in  the  amount  of  oxygen  which  they  contain.  March- 
lewski 2  showed  that  both  of  these  substances  are  to  be  regarded  as  dif- 
ferent oxidation  products  of  one .  and  the  same  mother-substance,  by 
obtaining  hemopyrrole,  as  well  as  the  hematinic  acids,  from  phyllopor- 
phyrin. Thereby  the  close  relationship  between  phylloporphyrin  and 
hematoporphyrin  was  established. 

Nencki  and  Zaleski 3  attempted  to  transform  hematoporphyrin  directly 
into  phylloporphyrin.  They  were  able,  however,  to  remove  but  one  of 
the  hydroxyl  groups  from  the  hematoporphyrin.  They  obtained  the 
so-called  mesoporphyrin  which  occupies  an  intermediate  position  between 

.»  Ann.  278,  329  (1894);   284,  81  (1895);   288,  209  (1895);  290,  306  (1896). 
2  J.  pr.  Chem.  65,  161  (1902). 
8  Ber.  34,  997  (1901). 


568  LECTURE  XXIV. 

hemato-  and  phyllo-porphyrin.     The  following  formulae  show  the    close 
relationship  between  these  last  two  compounds: 


CH2  CH2 

/  \  /  \ 

HC—  C        C(OH)—  (OH)C        C—  CH 

II      II          I  I         II      II 

HC    C        CH  HC        C     CH 

\  /    \  /  X.  .s'  \  /   \  / 

NH   CH2     \/          CH2    NH 

O 
Hematoporphyrin  :  Ci6Hi8N2O3. 

CH2  CH2 

/  \  /  \ 

HC—  C        CH  -  HC        C  --  CH 

II     II        I  I        I!        II 

HC—  C        CH        HC        C        CH 
\/\/\          /"  \  /  \  / 
NH    CH2  \/        CH2  NH 

O 
Phylloporphyrin  :  Ci6Hi8N2O. 

Now  that  we  have  shown  the  relations  of  hematin  to  chlorophyll,  we 
shall  return  to  the  pigment  of  the  blood  and  describe  the  products  formed 
from  its  disintegration.  While  we  are  not  yet  in  a  position  to  give  a 
very  satisfactory  picture  of  the  formation  of  hemoglobin,  or  hematin, 
we  are  better  informed  concerning  its  decomposition  products.  The  red 
corpuscles  are  without  doubt  being  constantly  destroyed,  and  thereby 
hemoglobin  is  set  free.  This  breaks  down,  according  to  our  present 
knowledge,  first  into  hematin  and  globin.  The  latter  is  probably  further 
decomposed  exactly  as  is  usually  the  case  with  proteins.  A  substance 
which  for  a  long  time  has  been  recognized  as  one  of  the  decomposition 
products  of  hematin,  is  a  pigment  occurring  in  the  bile  which  is  known 
as  bilirubin,  and  has  the  empirical  formula  Ci6Hi8N2O3  which  corresponds 
to  that  of  hematoporphyrin.  That,  as  a  matter  of  fact,  these  two  com- 
pounds are  very  closely  related  to  one  another  has  been  shown  by 
Klister,1  who  obtained  from  bilirubin,  by  the  same  methods  that  were 
used  with  hematin,  two  hematinic  acids  which  correspond  to  those 
obtained  from  hematin.  Bilirubin  and  hematoporphyrin  appear  to  be 
isomers.  The  transformation  of  hematin  into  the  biliary  pigment  takes 
place  in  the  cells  of  the  liver.  If  the  blood  is  injected  under  the  skin  of 
an  animal,  there  will  be  noticed  an  elimination  of  iron  at  that  very  spot. 
The  greater  part  of  the  blood's  pigment,  however,  will  reach  the  circula- 
tion and  be  carried  to  the  liver.  Here  again  the  iron  is  first  of  all 


1  Z.  physiol.  Chem.  26,  314  (1898);    Ber.  32,  677  (1899);    ibid.  35,  1268  (1902); 
Z.  physiol.  Chem.  47,  294  (1906). 


BLOOD  AND  LYMPH.  569 

removed.  The  large  deposits  of  iron  in  the  liver  indicate  the  extent  to 
which  this  process  has  taken  place.  Bilirubin  is  not  the  only  pigment 
present  in  the  bile.  Oxidation  products  are  likewise  present  which 
represent  different  stages  to  which  bilirubin  has  been  oxidized.  We  need 
not  mention  their  names  here,  partly  because  their  relations  to  bilirubin 
are  not  very  well  known,  and  partly  because  it  is  hard  to  decide  which  of 
these  colored  substances  are  previously  formed  in  the  cell  and  which 
result  from  secondary  processes.  The  best  known  of  these  substances  is 
biliverdin,  which  may  be  readily  prepared  from  bilirubin  by  allowing  an 
alkaline  solution  of  it  to  stand  in  contact  with  the  air.  Oxygen  is 
absorbed,  and  the  solution  turns  green.  One  of  the  tests  for  the  biliary 
pigments,  the  so-called  Gmelin's  test  for  bile-pigments,  is  based  upon  the 
readiness  with  which  bilirubin  is  oxidized.  If  a  solution  of  bilirubin- 
alkali  is  cautiously  covered  in  a  test  tube  with  a  little  nitric  acid  con- 
taining some  nitrous  acid,  color  rings  appear  at  the  contact  surface  of  the 
two  liquids  and  in  the  following  order  from  top  to  bottom:  —  green, 
blue,  violet,  red,  and  reddish-yellow.  These  different  colors  are  due  to 
different  stages  resulting  from  the  oxidation  of  bilirubin.  Before  con- 
sidering the  subsequent  destiny  of  the  bile-pigments,  we  must  answer  the 
question  whether  the  liver  is,  under  normal  conditions,  the  only  organ  in 
which  the  bile-pigments  are  formed,  or  whether  it  is  not  perhaps  merely 
the  place  where  these  pigments  are  eliminated. 

Even  Virchow  1  recognized  the  fact  that  peculiar  transformations  take 
place  in  blood  extravasations.  The  protein  component  of  the  hemo- 
globin and  the  remaining  constituents  of  the  blood  disappear  as  such, 
and  there  remain  beautifully  formed  crystals  of  brick-red  to  ruby-red 
color.  They  are  known  as  hematoidin.  This  substance  contains  no 
iron,  and  is  considered  by  many  to  be  identical  with  bilirubin.  According 
to  our  present  knowledge,  nothing  further  can  be  said  concerning  this 
pigment  than  that  it  is  closely  related  to  hematin  and  to  hematopor- 
phyrin.  Besides  this  pigment  we  will  state  that  pigments  containing 
iron  have  also  been  observed  as  being  formed  in  the  tissues,  and  that 
there  has  been  a  constant  endeavor  to  trace  a  relationship  between  all 
the  animal  pigments,  whether  resulting  from  normal  or  from  pathological 
processes,  to  the  blood-pigment.  The  most  pronounced  characteristic 
that  has  been  noted,  however,  in  every  case  is  as  regards  the  presence  or 
absence  of  iron.  We  would  refer  merely  to  what  was  said  in  considering 
the  formation  of  hematoidin  to  show  that  the  iron  content  in  no  way 
indicates  the  origin  of  the  pigment.  Our  knowledge  in  this  direction  is 
still  far  too  limited  for  us  to  predict  much  concerning  the  relations  of  the 
animal  pigments  to  the  other  compounds  found  in  the  tissues. 

1  Virchow's  Arch.  1,  379  and  407  (1847). 


570  LECTURE  XXIV. 

The  fact  that  under  certain  conditions  a  compound  may  be  formed  from 
the  blood-pigment  in  the  tissues  which  is  very  similar  to  the  bile-pigment 
is  proved  by  the  discovery  of  hematoidin.  Whether  under  normal  con- 
ditions such  products  are  formed  in  organs  other  than  the  liver  remains 
undecided.  In  pigeons  it  has  been  found  that  after  ligating  the  bile-duct, 
the  bile-pigments  are  found  at  the  end  of  five  hours  in  the  blood-serum. 
If  at  the  same  time  the  blood-vessels  of  the  liver  are  also  bound,  the  bile- 
pigments  cannot  be  detected  in  the  blood  nor  in  the  tissues  after  several 
hours.1  Minkowski  and  Naunyn 2  arrived  at  the  same  result.  They 
extirpated  the  liver  from  a  goose,  and  exposed  this  goose  together  with  a 
normal  one  to  the  action  of  arseniureted  hydrogen.  Whereas  the  latter 
showed  within  a  short  time  a  copious  elimination  of  urine  containing 
biliverdin,  with  the  former  only  hemoglobin  was  found  in  the  urine. 
Such  experiments  have  not  yet  been  carried  out  with  mammals  on  account 
of  the  great  difficulty  in  completely  extirpating  the  liver  from  them.  We 
may  safely  assume,  that  with  them  also  the  liver  is  the  sole  place  where 
the  bile-pigment  is  formed. 

For  quite  a  time  this  assumption  was  doubted.  It  had  been  observed 
that  if  for  any  reason  the  flow  of  bile  to  the  intestines  was  prevented, 
bile-pigments  would  appear  in  the  tissues.  There  is  a  yellowish  coloration 
of  the  skin  and  of  the  mucous  membrane.  The  complex  of  symptoms 
which  are  produced  when  there  is  such  a  stoppage  in  the  flow  of  the  bile, 
is  known  as  icterus,  or  jaundice.  Formerly  there  was  a  distinction  made 
between  icterus  of  the  above-mentioned  etiology,  also  designated  as 
hepatogenic  icterus,  and  hematogenic  icterus.  The  reason  for  this  was 
because  it  had  been  observed  that  when  for  any  reason  there  was  an 
increased  destruction  of  blood-pigment,  whether  due  to  the  action  of 
poisons  (arseniureted  hydrogen,  ether,  chloroform,  toluylene-diamine)  or 
by  infectious  diseases,  then  bile-pigment  passed  into  the  urine  even 
when  the  flow  of  bile  into  the  intestines  was  unrestricted.  It  was  easy  to 
imagine  from  this  that  in  such  cases  the  blood-pigment  was  directly 
transformed  while  in  the  blood-vessels  into  bile-pigment.  It  is  not 
necessary,  however,  to  make  any  such  assumption.  The  fact  has  been 
established  that  intravenous  injection  of  bilirubin  causes  a  considerable 
increase  in  the  elimination  of  bile-pigment  in  the  bile.3  This  observation 
indicates  that  the  liver  also  can  cause  the  elimination  of  bile-pigment, 
even  when  it  is  circulating  in  the  blood-vessels.  Now  it  is  possible 
that  when  there  is  a  greatly  increased  disintegration  of  the  blood 
it  may  eventually  contain  so  much  hemoglobin,  and  finally  so  much 

1  Hans  Stern:   Arch,  exper.  Path.  Pharm.  19,  39  and  42  (1885). 

2  Ibid.  21,  1  (7)  (1886). 

3  J.  F.  Tarchanoff:    Pfliiger's  Arch.  9,  53  (1874).     A.  Vossius:  Arch,  exper.  Path. 
Pharm.  11,  427  (1879). 


BLOOD  AND  LYMPH.  571 

bile-pigment,  that  it  becomes  impossible  for  the  liver  to  take  away 
all  of  it. 

Stadelmann l  has  shown  it  to  be  very  probable  that  in  spite  of  the  appar- 
ent unhindered  passage  of  bile  into  the  intestine,  nevertheless  there  may 
be  a  stoppage  in  the  flow  of  the  bile.  The  bile  flows  under  a  very  slight 
pressure,  so  that  the  slightest  obstruction  will  stop  it,  and  thereby  cause 
an  absorption  of  bile  by  the  lymphatics.  This  may  result  from  a  greatly 
increased  secretion,  or  from  the  greater  viscosity  of  the  concentrated  bile. 
At  all  events,  according  to  these  observations  we  are  not  justified  in 
assuming  that  the  transformation  of  hematin  into  bile-pigment  takes 
place  in  any  other  organ  than  the  liver. 

We  shall  mention  in  addition  that  the  restricted  flow  of  the  bile 
towards  the  intestines  may  lead  to  severe  nervous  disturbances.  Cerebral 
effects  result,  causing  delirium,  convulsions,  coma,  and  finally  death.  It 
has  never  been  found  possible  to  establish  satisfactorily  the  cause  of  these 
phenomena.  It  is  important  to  know  that  they  almost  invariably  result 
from  chronic  obstructions  to  the  flow  of  the  bile.  It  has  been  assumed 
that  the  absorbed  constituents,  and  their  segregation  in  the  tissues  and 
blood,  were  the  cause  of  these  severe  disturbances.  There  is  no  proof  of 
this,  however.  We  must  not  forget  that  where  there  is  a  chronic  obstruc- 
tion to  the  flow  of  the  bile,  it  is  certain  that  the  metabolism  of  the  whole 
liver  must  suffer  as  a  result.  The  central  position  of  the  liver  in  the 
general  metabolism  has  already  been  indicated.  It  is  clear  that  if  any  one 
of  its  important  functions  is  entirely  abolished,  this  is  likely  to  affect 
the  entire  organism.  On  the  other  hand,  the  objection  may  be  raised 
that  the  liver  can  undergo  all  sorts  of  severe  treatment  without  necessarily 
causing  any  disturbance  in  this  direction.  It  may  be  said,  however,  that 
we  are  not  able  to  draw  conclusions  solely  on  the  basis  of  anatomical 
changes  concerning  the  functional  condition  of  a  tissue.  It  is  an  open 
question  as  to  which  part  is  first  and  most  seriously  affected.  A  serious 
suppression  of  metabolism  in  the  cells  may  take  place  without  there  being 
any  indication  of  it  in  the  external  appearance  of  the  cells  or  of  the  con- 
tents, and,  on  the  other  hand,  there  may  be  very  great  anatomical  changes 
in  a  tissue  without  the  functions  being  other  than  normal,  as  long  as 
the  cell  complex  or  the  constituents  of  the  cells  do  not  take  part  in  a 
pathological  process. 

In  the  transformation  of  hematin  into  bilirubin,  iron  is  split  off.  What 
becomes  of  it  we  do  not  know.  Only  a  part  is  eliminated  with  the  bile 
itself.  It  is  possible  that  it  is  immediately  utilized  again,  or  that  it 
chooses  to  be  eliminated  through  the  intestines. 

The    constituents    of    the    bile,    especially    cholesterol    and    the    bile- 


1  Arch,  exper.  Path.  Pharm.  14,  231  and  422  (1881);   15,  337  (1882);   16,  118  and 
221  (1883). 


572  LECTURE  XXIV. 

pigments,  often  serve  for  the  formation  of  concretions  and  calculi  in 
human  beings.  It  is  not  easy  to  say  what  causes  the  formation  of 
these  concretions,  which  often  lead  to  such  severe  symptoms.  Appar- 
ently the  primary  cause  is  usually  a  catarrh  of  the  bile-ducts.  Crys- 
tals of  the  above-mentioned  substances  are  then,  as  a  secondary  effect, 
deposited  upon  the  diseased  mucous  membrane.  Naturally  changes  in 
the  conditions  of  solubility  and  in  the  relations  of  concentration  also 
play  a  part  in  their  formation.  The  pigment-stones  usually  contain  the 
calcium  compound  of  bilirubin.  Often  mixed  stones  are  found,  although 
quite  frequently  we  meet  with  stones  of  pure  cholesterol  which  show,  in  a 
fractured  surface,  beautiful  clusters  of  crystals. 

The  bile-pigments  appear  in  the  faeces  to  some  extent  as  such.  For 
the  most  part,  they  succumb  to  the  putrefactive  processes  in  the  ali- 
mentary canal,  especially  those  of  the  large  intestine.  There  is  a  reduc- 
tion of  the  bilirubin,  and  urobilin  is  formed.  This  last  substance  may  be 
obtained  directly  by  the  reduction  of  hematin,  or  of  hematoporphyrin.1 
It  is  also  formed  by  oxidation,  when  hemopyrrole  is  allowed  to  stand  in 
contact  with  the  air.2  Finally,  it  has  been  established  that  by  feeding 
hemopyrrole  to  rabbits  an  elimination  of  urobilin  results.  Urobilin, 
like  hematin,  is  supposed  to  contain  four  molecules  of  hemopyrrole  and 
to  have  the  following  empirical  formula:  C32H40O7N4.  It  is  not  abso- 
lutely known  whether  urobilin  is  identical  with  the  so-called  hydrobili- 
rubin  which  is  obtained  by  the  reduction  of  bilirubin.  Urobilin  is 
absorbed  in  the  intestine  and  passes  into  the  urine.  It  helps  to  give 
to  urine  its  yellow  color.  Different  urobilins  have  been  described  as 
present  in  urine,  and  on  the  other  hand  it  has  even  been  asserted  that 
urobilin  is  not  originally  present  as  such  in  the  urine,  but  is  formed  by 
the  action  of  light.  We  need  not  stop  to  discuss  this  question,  because 
at  present  it  is  all  a  matter  of  conjecture,  and  we  are  forced  to  base  our 
assumptions  in  part  upon  some  very  doubtful  observations.  It  is  ex- 
actly the  same  with  the  question  as  to  the  origin  of  urobilin.  No  one 
doubts  that  it  is  formed  in  the  intestines  as  a  result  of  putrefaction,  but 
it  is  questioned  by  many  that  all  the  urobilin  in  the  urine  arises  from  this 
source.  Many  assume  that  urobilin  is  formed  outside  of  the  intestines 
and  in  the  tissues  from  bilirubin. 

Closely  related  to  urobilin  is  urochrome,  the  principal  yellow  pig- 
ment contained  in  urine.  Its  chemical  nature  is  but  little  known. 
Uroerythrin  also  frequently  occurs  in  urine,  and  is  likewise  of  un- 
known composition.  It  is  the  red  pigment  which  causes  the  color 
of  the  sediment  in  urine,  and  is  also  known  as  Sedimentum  later- 
itium. 


1  Nencki  and  Sieber:   Arch,  exper.  Path.  Pharm.  18,  401  (1884). 

2  Nencki  and  Zaleski:  Ber.  34,  997  (1901). 


BLOOD  AND  LYMPH.  573 

Small  amounts  of  hematoporphyrin  are  also  present  in  urine.  It  is  not 
without  interest  that  the  amount  of  this  substance  increases  after  certain 
kinds  of  poisoning,  e.g.  lead,  trional,  sulfonal,  and  in  certain  diseases  of 
the  liver.  The  urine  then  has  the  red  color  of  Burgundy. 

We  have  now  mentioned  what  is  known  of  the  destiny  of  the 
blood-pigment  in  the  animal  organism,  and  have  become  acquainted 
at  the  same  time  with  a  new,  important  function  of  the  liver- 
cells.  We  must  admit  that  there  are  still  many  gaps  which  must  be 
bridged  over  with  regard  to  our  knowledge  of  the  disintegration  of 
hematin,  and  there  are  a  great  many  contradictory  results  obtained  in 
the  study  of  the  final  end-product,  urobilin,  which  remain  to  be 
explained. 

It  might  be  expected  that  some  insight  into  the  construction  of  hemo- 
globin would  be  obtained  if  we  were  able  to  find  out  where  it  is  formed. 
Up  to  the  present  time  this  has  not  been  definitely  settled.  We  are 
inclined  to  believe  that  hemoglobin  is  formed  at  the  place  where  the  red 
blood-corpuscles  come  into  existence,  but  even  the  origin  of  these  cor- 
puscles is  in  doubt.  Bone-marrow  is  chiefly  considered  in  this  connection; 
and  in  cases  of  an  unusual  new  formation  of  the  blood-corpuscles,  the  ex- 
traordinary activity  of  the  cancellous  tissue  is  apparent,  even  to  the  naked 
eye,  by  the  marked  red  coloration.  It  has  been  asserted  frequently  that 
the  spleen  is  also  able  to  produce  red  blood-corpuscles,  but  this  asser- 
tion has  been  contradicted.  It  has  been  attempted  to  decide  this 
question  by  extirpating  the  spleen.  The  operation  is  withstood  quite 
well  by  the  organism.  While  some  authors  have  claimed  that  there 
resulted  a  marked  diminution  in  the  number  of  red  corpuscles,  others 
were  not  able  to  find  this  the  case.  Finally,  the  spleen  has  been  assigned 
a  part  in  the  destruction  of  the  red  corpuscles.  Unquestionably  this 
last  assumption  is  not  well  founded.  To  be  sure,  the  spleen  usually 
contains  iron.  Experience  also  teaches  us  that  the  spleen  is  able  to 
capture  foreign  substances  from  metabolism  and  to  retain  them,  and  on 
the  other  hand,  by  administering  iron  salts  the  iron  content  of  the  spleen 
is  considerably  increased  within  a  short  time,  without  there  being  any 
evidence  of  a  destruction  of  red  blood-corpuscles.  At  all  events,  the  part 
played  by  the  spleen,  either  in  the  formation  or  the  destruction  of  red 
blood-corpuscles,  is  absolutely  unexplained.  The  same  is  true  regarding 
the  function  of  the  so-called  hemal-lymph  glands  which  are  joined  to  the 
aorta  and  differ  from  the  ordinary  lymph-glands  by  the  fact  that  the 
lymph-passages  are  either  missing  or  incompletely  developed.  The 
capillaries  from  the  arteries  pass  directly  into  the  lymph  sinus  and 
into  the  blood-spaces  representing  the  interfollicular  lymphatics,  and 
from  thence  the  veins  lead  out  directly.  The  hemal-lymph  glands  occupy 
anatomically  an  intermediate  position  between  the  ordinary  lymph- 


574  LECTURE  XXIV. 

glands  and  the  spleen.  Their  function  has  never  been  satisfactorily 
explained.1 

We  must  now  mention  an  important  kind  of  cells  which  are  interme- 
diate between  those  of  the  blood  and  of  the  tissues.  The  blood  does  not 
•communicate  directly  with  the  tissue-cells.  It  neither  imparts  nutritive 
material  directly  to  them  nor  receives  the  products  of  metabolism 
directly  from  them.  In  this  connection  the  kidneys  occupy  an  excep- 
tional position,  for  in  them  the  blood-vessels  of  the  Glomeruli  Malpighi 
lie  directly  at  the  end  of  a  uriniferous  tube.  The  reason  for  this  is  clear: 
in  this  way  the  waste-products  contained  in  the  blood  are  given  up  to 
the  urine  as  quickly  as  possible. 

In  the  other  tissues  of  the  body,  the  exchange  of  material  between  the 
blood  and  tissue  takes  place  through  the  lymph.  First  of  all  we  must 
consider  the  formation  of  lymph.  We  may  say  at  once  that  it  has  two 
sources  of  material,  —  the  blood  on  the  one  hand,  and  the  tissues  on  the 
other.  Qualitatively  it  contains  the  same  substances  as  the  blood-plasma. 
Quantitatively,  however,  there  is  a  difference  between  the  two  liquids. 
The  formation  of  the  lymph,  which  penetrates  into  all  of  the  tissues, 
has  been  repeatedly  referred  to  a  purely  physical  process,  as,  for  example, 
that  of  a  filtration.  We  must  admit  that  unquestionably,  purely  physical 
processes  do  come  into  play  in  the  giving  up  of  material  by  the  blood 
and  by  the  tissues  to  the  lymph,  and,  on  the  other  hand,  in  the  passage 
of  material  from  the  lymph  either  into  the  blood  or  tissues.2  We  have  a 
great  many  reasons,  however,  for  not  being  willing  to  admit  that  our 
present  knowledge  concerning  the  formation  of  lymph  and  all  its  func- 
tions is  in  accordance  with  the  assumption  that  only  physical  forces  are 
concerned  here. 

In  considering  processes  which  are  much  easier  to  understand  than 
the  formation  of  lymph,  we  have  constantly  encountered  phenomena 
which  indicate  the  existence  of  a  specific  activity  for  every  individual 
cell,  whether  it  be  that  of  secretion  or  of  absorption.  We  must  admit 
that  it  is  far  more  difficult  to  study  accurately  each  individual  process 
when  the  relations  are  so  complicated  as  they  are  in  the  animal  organ- 
ism. In  every  case  there  are  a  number  of  different  processes  which  we 
at  present  cannot  examine  very  closely.  One  process  crosses  another, 


1  See  J.  Seemann:  Die  blutbildenden  Organe,  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg. 
3,  p.  1  (1904). 

2  See  Bayliss  and  Starling:    J.  Physiol.  16,  159  (1894).     W.  Connstein:    Virchow's 
Arch.  135,  514  (1894);  Pfliiger's  Arch.  59,  350  (1899);  59,  508  (1894);  60,  291  (1894); 
62,  58,  (1895);  63,587  (1896);  H.  J.  Hamburger:    Z.  Biol.  30,   143   (1893);    Arch. 
Anat.  Physiol.  1895,  281;  1897,  132.     R.  Heidenhain:  Pfluger's  Arch.  49,  209  (1881); 
56,  632  (1894);  62,  320  (1895).     A.  Ellinger:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg. 
1  Abt.  1,  p.  355  (1902). 


•    BLOOD  AND  LYMPH.  575 

and  thus  creates  new  conditions,  so  that  one  effect  follows  another 
at  the  most  rapid  rate  imaginable.  It  would  not  be  right  for  us  to 
be  satisfied  with  the  bare  explanation  that  the  activity  of  the  cell 
is  of  a  specific  nature.  Of  course  further  investigations  must  have 
free  play  here.  It  would  be  equally  wrong  to  disregard  the  uncer- 
tainty which  systematic  explanatory  experiments  encounter.  Just  as 
it  is  incorrect  to  maintain  that  a  chemical  process  prevails  in  the  organ- 
ism because  it  is  possible  to  carry  out  certain  processes  in  a  test  tube, 
so  also  we  are  not  justified  in  assuming  that  we  have  established  the 
fact  that  a  purely  physical  process  takes  place  because,  under  certain 
definite  conditions,  we  can  in  this  way  find  a  possible  cause  of  a  certain 
phenomenon.  It  must  be  perfectly  clear  with  each  advance  in  the 
knowledge  of  the  processes  taking  place  in  the  animal  organism  just 
where  the  certainty  exists  and  where  it  ceases.  There  is  no  doubt  that 
the  assumption  of  a  specific  secretion  being  produced  by  the  individual 
cells  has  given  rise  to  an  uncomfortable  feeling  of  insecurity  in  our 
entire  representations  of  the  life  processes.  An  advance  in  the  science  is 
only  possible  when  the  gaps  which  still  exist  in  our  present  information 
are  circumscribed  as  sharply  as  possible.  For  this  reason  we  shall  not 
attempt  to  trace  the  formation  of  lymph  and  its  metabolic  exchanges 
between  the  blood  and  the  tissue-cells  in  accordance  to  physico-chemical 
laws. 

We  should  like  first  of  all  to  abolish  any  idea  that  the  lymph-stream  is 
analogous  to  the  blood-stream  and  carries  the  substances  it  contains 
from  cell  to  cell.  The  lymph  circulates  far  too  slowly  for  it  to  be  able 
to  replenish  the  cells  quickly  enough  with  the  material  which  they  need 
in  cases  of  active  metabolism.  We  must  rather  assume  that  the  lymph 
of  a  given  organ  enters  into  more  intimate  relations  between  the  blood- 
vessels and  the  surrounding  tissue.  G.  von  Bunge l  has  called  our  atten- 
tion to  an  observation  which  well  characterizes  these  relations.  The  milk 
of  animals  whose  young  grow  rapidly  is  very  rich  in  lime.  The  milk  of 
dogs  contains  from  four  to  five  grams  of  lime  per  liter.  A  bitch  weighing 
20  to  30  kilograms  will  secrete  half  a  liter  of  milk  in  24  hours  which  will 
contain  from  two  to  two  and  one-half  grams  of  lime.  A  liter  of  plasma 
contains  only  about  0.2  gram  of  lime,  or  only  TV  to  ^  as  much  as  the  same 
volume  of  milk.  If,  however,  the  epithelial  cells  of  the  mammary  glands 
must  obtain  their  material  for  the  milk  requirements  from  the  transu- 
dated  plasma,  then  during  the  24  hours,  at  least  10  liters  of  plasma  must 
flow  through  the  mammary  glands.  This  is  altogether  out  of  the  ques- 
tion, for  only  one  or  two  liters  of  lymph  flows  through  the  entire  body  in 
the  course  of  a  day,  and  far  less  through  the  mammary  glands.  It 

1  Lehrbuch  der  Physiologic  des  Menschen,  Vol.  II,  p.  289  (1901). 


576  LECTURE  XXIV. 

follows  from  this  that  in  the  walls  of  the  blood-capillaries  of  the  mam- 
mary glands,  a  liquid  rich  in  lime  is  secreted,  and  that,  therefore,  the 
endothelial  cells  of  the  capillary  walls  exercise  a  selection,  as  is  also  the 
case  with  every  cell  of  all  living  organisms. 

It  is  also  possible  that  we  are  dealing  here  with  a  purely  physical 
process  in  which  the  gland-cells  of  the  mammary  gland  constantly  uti- 
lize calcium,  i.e.,  combine  with  it,  and  thus  cause  a  continuous  dif- 
fusion of  calcium.  But  here  again  we  shall  have  to  conjecture  how 
this  may  take  place.  Even  the  end-products  of  metabolism  are  not 
carried  away,  at  least  not  wholly,  by  a  stream  of  lymph.  In  this  case, 
likewise,  these  products  can  evidently  leave  the  lymph  and  penetrate 
into  the  neighboring  blood-capillaries  and  thus  be  eliminated  more 
rapidly.  The  fact  that  lymph  from  different  places,  or  even  from  a 
single  lymphatic  fistula  at  different  times,  has  different  compositions 
speaks  in  favor  of  such  an  assumption. 

Lymph,  as  we  have  said,  is  qualitatively  very  similar  to  the  plasma. 
It  contains  the  same  substances.  Of  especial  interest  is  its  content  of 
fibrinogen  and  fibrin-ferment.  The  amount  of  each  of  these  substances  is, 
however,  very  slight.  Lymph  coagulates  slowly,  and  not  all  at  once. 
Serum-albumin  and  serum-globulin  are  the  two  principal  proteins  which 
have  been  found  in  it.  Lymph  also  contains  cellular  elements,  especially 
the  leucocytes,  in  varying  numbers.  Unfortunately,  we  are  not  very  well 
informed  concerning  the  composition  of  the  tissue-lymph  and  that  of 
the  lymphatics.  Most  of  the  analyses  that  have  been  made  are  of  lymph 
obtained  from  the  thoracic  duct,  which  contains  chyle.  For  this  reason, 
we  are  able  to  say  but  little  concerning  the  formation  of  lymph  and  its 
dependence  upon  definite  conditions.  On  the  other  hand,  the  work  of 
Asher  1  and  his  collaborators  has  served  to  explain  the  relations  between 
the  amount  of  lymph  formed  and  the  work  of  certain  organs.  The  influ- 
ence exerted  by  the  work  of  an  organ  is  best  illustrated  in  the  case  of  the 
salivary  glands.  If  a  strip  of  blotting  paper  moistened  with  vinegar  is 
placed  in  the  mouth  of  a  dog,  there  is  a  copious  secretion  of  saliva,  and  at 
the  same  time  there  is  an  increased  flow  of  lymph  from  the  lymphatics 
of  the  neck.  This  increased  flow  of  lymph  does  not  depend  upon  a  corre- 
sponding increase  in  the  rate  of  flow  of  the  blood.  In  muscular  work, 
likewise,  it  may  be  shown  that  there  is  an  increased  formation  of  lymph. 

We  must  consider,  here,  an  important  discovery,  namely,  that  there 
are  certain  substances  which  incite  the  lymph  flow.  These  are  known  as 
lymphagogues,  and  are  of  two  kinds.  The  lymphagogues  of  the  first  group 
are  obtained  from  the  extracts  of  crab-muscles,  blood-leeches,  anodons, 


1  Asher  and  Barbera:  Z.  Biol.  36,  154  (1897);  37,  261  (1898);  Asher  and  Gies: 
ibid.  40,  180  (1900);  Asher  and  Busch:  ibid.  40,  333  (1900);  Asher  and  Barbera: 
Zentr.  Physiol.  11,  403  (1897). 


BLOOD  AND  LYMPH.  577 

from  the  liver  and  intestines  of  dogs,  and  from  strawberry-extracts,  etc. 
In  this  case,  the  increased  flow  of  the  lymph  can  also  be  attributed  to  the 
increased  activity  of  an  organ,  the  liver  especially.  On  the  other  hand,  it 
has  been  assumed  that  these  substances  act  upon  the  endothelium  of  the 
capillaries  in  such  a  way  that  they  are  incited  to  increased  activity.  To 
the  lymphagogues  of  the  second  group  belong  sugar,  urea,  common  salt, 
etc.  These  cause  an  abundant  lymph  formation,  whereby  the  plasma, 
as  well  as  the  lymph,  becomes  more  dilute.  In  this  case  also  a  specific 
activity  of  the  cells  is  presumed;  here,  that  of  the  tissue  cells. 

It  is  not  difficult  to  understand  that  the  work  of  organs  increases  the 
production  of  lymph;  for,  on  the  one  hand,  the  cells  of  the  active  organ 
require  an  increased  supply  of  nutriment,  and,  on  the  other  hand,  they 
yield  an  increased  amount  of  metabolic  end-products. 

One  might  be  tempted  to  ask  why  the  presence  of  the  lymph  and  the 
liquid  in  the  tissues  is  at  all  necessary,  and  why  it  would  not  be  better  to 
have  a  more  direct  interchange  between  the  blood  and  the  cells  of  the 
tissue.  The  utility  of  this  arrangement  is  very  clear;  for,  in  the  first 
place,  it  is  evident  that  by  the  interposition  of  a  liquid  which  penetrates 
into  the  smallest  spaces  between  the  tissues,  it  is  made  possible  to  effect  a 
more  delicate  exchange  of  material;  and,  on  the  other  hand,  it  prevents 
the  cells  from  being  over-supplied  with  nutriment  at  any  one  time;  and, 
furthermore,  by  this  means  it  is  possible  to  keep  the  composition  of  the 
blood  fairly  constant,  which  would  not  be  the  case  if  the  end-products  of 
the  metabolism  in  an  active  organ  were  given  up  to  the  blood  all  at  once. 
The  lymph  also  serves  as  a  diluting  medium.  An  observation  of  Asher 
supports  this  view.  He  showed  that  normal  lymph  contains  products 
which,  if  directly  introduced  into  the  blood  circulation,  would  give  rise 
to  disturbances,  If,  for  example,  some  of  their  own  lymph  from  the  neck 
be  injected  into  the  internal  carotid  artery  of  dogs,  changes  are  at  once 
produced  in  the  blood  pressure. 

The  organism  also  has  a  means  of  protection  in  the  so-called  lymphatic 
glands,  or  lymph-nodes,  which  are  situated  in  the  course  of  a  lymph-vessel. 
They  have  various  functions.  According  to  the  way  they  are  constructed, 
it  is  easy  to  imagine  that  they,  to  a  certain  extent,  act  as  filters  and  keep 
back  certain  substances  which  are  injurious  to  the  body.  It  is  also  con- 
ceivable that  they  are  able  to  combine  with  substances  which  are  given 
up  to  the  lymph  in  large  amounts.  They  are  constantly  giving  up  leuco- 
cytes, so  that  they  in  this  way  take  part  in  the  general  metabolism. 

Closely  related  to  the  lymph  are  certain  liquids  which  are  secreted  by 
the  serous  membranes,  which  are  provided  with  an  endothelium  and  fulfil, 
for  the  most  part,  purely  mechanical  functions.  These  liquids  are  called 
transudates.  Under  normal  conditions  there  is  but  a  small  amount  of 
these.  They  are  deficient  in  formed  elements.  As  regards  the  formation 


578  LECTURE  XXIV. 

of  the  transudates  the  question  has  been  much  discussed  whether  they 
result  from  a  filtration  from  the  blood-vessels  or  whether  they  represent  an 
"  active"  secretion.  Here  the  relations  are  somewhat  similar  to  those  of  the 
lymph.  The  fact  that  transudates  contain  the  same  substances  as  plasma, 
and,  with  the  exception  of  albumin,  in  about  the  same  proportion,  cannot  be 
regarded  as  an  absolute  proof  of  a  filtration  having  taken  place.  Under 
pathological  conditions  the  amount  of  transudate  may  increase  enormously. 
If  this  formation  results  from  an  inflammatory  process,  it  is  called  an 
exudate.  The  exudates  are  richer  in  cellular  elements.  If  the  amount 
of  the  latter  is  greatly  increased,  we  called  the  liquid  pus. 

Transudates  are  found  normally  in  the  sac  of  the  pericardium,  between 
the  layers  of  the  pleurae,  and  in  the  peritoneum.  To  this  class  of  liquid 
belongs  the  cerebro-spinal  fluid  and  perhaps  also  the  aqueous  humor.  A 
very  similar  liquid  is  found  around  the  joints  and  in  the  bursce  mucosce 
which  is  known  as  synovia.  It  contains  a  substance  similar  to  mucin. 
The  true  transudates  are  composed,  as  we  have  said,  of  the  same  con- 
stituents as  plasma,  and  it  is  noteworthy  that  they  contain  fibrinogen, 
but  hardly  to  an  extent  sufficient  to  permit  spontaneous  coagulation. 

If  we  examine  more  closely  the  relation  between  the  lymph  and  the 
blood,  we  shall  arrive  at  the  conclusion  that,  to  a  certain  extent,  all  the 
cell-elements  of  the  animal  tissues  are  either  directly  or  indirectly  mois- 
tened by  these  fluids.  The  tissues  no  longer  appear  to  us  as  rigid  struc- 
tures, as  it  is  customary  to  consider  them  from  an  anatomical  point  of 
view.  There  are  no  sharp  lines  drawn  between  the  blood,  lymph,  and 
the  body-cells.  There  is  never  any  repose.  A  stream  of  blood  continu- 
ally flows  towards  the  cells,  and  conversely,  the  cells  by  the  aid  of  the 
lymph  send  their  products  to  the  blood,  and  thus  all  the  different  ele- 
ments combine  to  form  a  physiological  unit  for  each  individual  organ,  or 
perhaps  only  for  definite  cell-groups.  We  can  now  understand  what 
great  difficulties  are  met  with  in  the  attempt  to  trace  experimentally  the 
course  of  a  reaction  in  the  animal  organism.  The  lymph  forms  on  the 
one  hand  an  intimate  mean's  of  communication  between  the  blood  and 
the  tissue-cells,  and  on  the  other  hand  it  serves  as  a  barrier  between 
them.  Substances  administered,  whose  participation  in  cell-metabolism 
we  should  like  to  be  able  to  trace,  may  reach  only  as  far  as  the  lymph,  and 
may  be  excluded  from  the  metabolic  processes  of  the  cell  itself.  Whether 
transformations  take  place  in  the  lymph,  or  whether  the  lymph  modifies 
the  products  obtained  from  the  blood  and  prepares  them  so  as  to  meet 
the  existing  demands,  is  something  of  which  we  have  no  information. 
Here  a  great  unexplored  field  lies  before  us. 


LECTURE   XXV. 

THE    ELIMINATION    OF    METABOLIC    PRODUCTS    FROM    THE 

BODY. 

WE  have  already  called  attention  to  the  important  fact  that  the  blood, 
and  especially  the  plasma  or  the  serum,  has  a  remarkably  constant 
composition.  This  holds  true  at  least  within  certain  limits,  and  in  as 
far  as  we  can  detect  by  means  of  our  faulty  methods  of  examination. 
This  relative  constancy  holds  not  only,  as  we  have  shown,  with  regard 
to  the  quantitative  relations  in  which  the  substances  are  present,  but 
also,  as  far  as  we  are  able  to  see,  for  the  qualitative  relations.  Thus  we 
feel  justified  in  assuming,  for  example,  that  the  amount  of  protein  in  the 
blood  may  indeed  vary  somewhat,  but  it  does  not  change  its  nature  in 
spite  of  the  most  varied  forms  of  nourishment.1  We  intentionally  speak 
of  a  relative  constancy,  because  there  can  be  no  such  thing  as  an  absolute 
constancy  in  the  composition  of  the  blood,  for  from  moment  to  moment, 
according  as  this  or  that  organ  comes  into  action,  the  blood  is  bound  to 
receive  quite  different  metabolic  products.  Such  products  are,  however, 
present  in  such  a  state  of  dilution  that  we  can  detect  them  only  in  a  large 
quantity  of  blood.  Again,  during  the  digestive  process  and  when  the 
absorption  and  assimilation  is  at  its  height,  sometimes  this  substance  and 
sometimes  that  one  will  circulate  in  the  blood  to  an  increased  extent. 
As  a  rule,  however,  these  differences  are  so  slight  that  they  cannot  be 
detected  by  the  present  methods  of  analysis.  They  are  usually  concealed 
by  experimental  errors.  At  the  same  time  it  is  perfectly  evident  that 
the  composition  of  the  blood  is  regulated  to  a  remarkable  extent  and 
kept  constant  within  narrow  limits.  There  are  many  ways  in  which 
this  regulation  is  effected,  and  they  are  not  all  of  the  same  nature  as  is 
usually  assumed.  First  of  all,  the  blood  is  kept  from  being  flooded  with 
substances  foreign  to  it,  as  they  are  contained  in  the  food,  by  the  activity 
of  the  intestine.  Were  it  not  for  this,  we  could  not  understand,  as  we 
have  repeatedly  stated,  why  the  composition  of  the  serum  should  always 
remain  qualitatively  and  quantitatively  practically  the  same.  By  means 
of  the  activity  of  the  digestive  ferments,  all  of  the  complicated  and 
widely  different  nutrient  substances,  which  vary  from  day  to  day,  are 


1  Abderhalden  and  Samuely:  Z.  physiol.  Chem.  46,  193  (1905).     Emil  Abderhalden: 
Zentr.  Stoffwechsel-  und  Verdauungskrankheiten  5,  647  (1904). 

579 


580  LECTURE  XXV. 

disintegrated;  and  from  the  resulting  products  the  intestines,  and  per- 
haps the  liver  as  well,  forms  substances  suitable  for  the  body.  The 
intestine  assumes  by  this  function  a  characteristic  position.  It  takes 
care  that  the  tissue-cells  always  receive  the  same  nutriment,  and  makes 
them  absolutely  independent  of  the  nature  of  the  fpod  which  is  eaten. 
We  cannot  be  far  wrong  in  ascribing  to  the  intestine  in  this  sense  an 
important  part  in  the  maintenance  of  the  individuality  of  each  species  of 
animals. 

A  second  mechanism  for  regulating  the  composition  of  the  blood  is 
found  in  the  lymph.  The  exchange  of  material  between  the  blood  and 
tissue-cells  takes  place,  as  we  have  seen,  through  the  lymph.  The  lymph 
receives  substances  from  the  blood  which  the  cells  of  the  tissues  require, 
and  on  the  other  hand  it  gives  up  to  the  blood  the  waste-products  which 
it  receives  from  the  tissue-cells.  It  is  able  to  retain  these  last-mentioned 
substances  for  quite  a  time,  only  gradually  giving  them  up  to  the  blood, 
for  further  elimination  from  the  body. 

The  chief  organs  for  the  elimination  of  the  metabolic  end-products, 
and  of  the  substances  which  the  organism  cannot  utilize,  are  the  kidneys. 
They  guarantee  the  maintenance,  as  far  as  possible,  of  the  blood-uni- 
formity. Under  normal  conditions  they  are  perfectly  adequate  for 
this  purpose.  If  it  happens  that  the  kidneys,  for  some  reason  or  other, 
are  not  able  to  remove  all  of  the  foreign  substances  from  the  blood, 
then  other  organs  attempt  to  act  as  their  substitute.  Most  of  all  the 
different  glands  contained  in  the  organism  may  be  active  in  this  sense, 
and  even  under  normal  conditions  there  is  no  doubt  that  small  amounts 
of  the  waste-products  are  eliminated  in  this  way.  This  is  best  shown 
by  introducing  into  the  body  substances  which  are  foreign  to  it.  Thus, 
if  we  introduce  potassium  iodide  into  the  intestines,  some  of  it  will  soon 
appear  in  the  saliva  and  in  the  sweat.  If  morphine  is  injected  subcu- 
taneously,  a  part  of  it  is  eliminated  in  the  stomach.  Urea  is  likewise 
found  in  sweat,  particularly  when  the  kidneys  are  not  adequate  to  the 
demands  placed  upon  them.  The  intestines  also  form  an  important  organ 
for  elimination,  and  normally.  We  have  already  seen  that  the  alkaline 
earths  and  heavy  metals  are  unquestionably  largely  eliminated  directly  in 
the  intestines,  and  in  fact  chiefly  through  the  rectum.  The  animal  organism, 
furthermore,  is  able  to  combine  many  of  these  foreign  substances  together, 
whereby  the  blood  and  the  tissues  are  prevented  from  being  flooded  with 
them.  Such  substances  may  then  be  eliminated  gradually  in  the  course  of 
several  weeks.  We  have  also  repeatedly  called  attention  to  the  ability 
of  the  tissue-cells,  and  especially  of  the  liver,  to  make  many  substances 
harmless  by  oxidizing  or  reducing  them,  and  in  some  cases  conjugating 
them  with  certain  substances,  such  as  glycocoll,  glucuronic  acid,  sulphuric 
acid,  or  urea. 


THE   ELIMINATION   OF   METABOLIC    PRODUCTS.         581 

The  importance  of  the  other  glands,  large  and  small,  as  organs  for  the 
elimination  of  substances  foreign  to  the  organism  and  of  the  end-products  of 
metabolism  is  insignificant  compared  to  that  of  the  kidneys.  Their  anatom- 
ical structure  characterizes  them  for  the  exercise  of  their  most  important 
function.  In  the  first  place  we  notice  the  peculiar  nature  of  the  blood- 
vessels. The  arteries  form  branches  and  side  twigs;  each  of  the  afferent 
vessels  terminates  in  a  globular  bunch  of  capillaries,  the  glomerulus  or  Mai- 
pighian  tuft.  The  blood  leaves  the  glomerulus  through  a  so-called  efferent 
vessel,  or  Vas  efferens,  which  also  breaks  up  into  a  close  capillary  plexus 
which  surrounds  the  secreting  tubes.  From  this  network  come  venous 
radicals,  which  empty  into  the  veins  of  the  kidneys,  and  through  which 
the  blood,  which  has  meanwhile  been  freed  from  the  metabolic  end-products 
and  other  waste-material,  leaves  the  kidneys.  The  termination  of  the 
afferent  vessels  in  the  Malpighian  tuft  has  awakened  the  most  interest. 
It  is  worth  mentioning  that  these  vessels  are  considerably  narrower  than 
the  corresponding  efferents. 

The  Malpighian  tuft  is  within  the  so-called  Bowman-Muller  capsule. 
This  consists  of  a  thin  pouch  consisting  of  epithelial  cells,  into  which,  as  it 
were,  the  tuft  has  been  pushed.  It  represents  the  beginning  of  a  uriniferous 
tube.  The  latter  are  not  simple  drainage  channels,  but  follow,  first  of  all, 
a  tortuous  path,  the  first  convoluted  tube,  or  tubulus  contortus.  Then  the  tube 
narrows  suddenly  and  describes  a  loop,  reaching  into  the  medulla,  known 
as  Henle's  loop.  The  tube  then  turns  back  towards  the  cortex,  forming 
an  irregular  convoluted  tube,  that  of  Schweigger-Seidel,  which  passes 
through  a  narrower  arch  into  the  straight  collecting  tube.  Several  tubes 
which  have  up  to  this  point  been  entirely  independent,  empty  into  this 
collecting  tube.  It  terminates,  together  with  other  similar  tubes,  at  the 
surface  of  a  papilla  in  the  calyx  of  the  kidney.  We  will  state,  moreover, 
that  the  epithelium  of  these  different  parts  of  a  uriniferous  tube  is  not 
uniform.  We  mention  briefly  these  relations,  in  order  to  show  that  the 
process  of  forming  a  secretion  by  the  kidneys  is  by  no  means  a  very  simple 
process.  There  is  some  reason  for  the  complicated  construction  of  the 
kidneys.  In  considering  the  function  of  the  kidneys,  we  must  hold  close 
to  the  anatomical  relations,  and  attempt  to  explain  the  significance  of  the 
differently  organized  parts  of  the  uriniferous  tubes.  Before  taking  up  the 
question  of  the  secretion  of  the  urine,  we  will  briefly  mention,  in  connection 
with  the  above  brief  description  of  the  construction  of  the  uriniferous 
tubes,  those  researches  which  have  been  undertaken  in  the  attempt  to 
decide  what  the  function  of  each  different  part  of  the  tube  is.  Right  at 
the  start  it  may  be  stated,  that,  according  to  all  we  now  know,  the  urine 
is  not  eliminated  from  the  blood  in  the  form  in  which  it  eventually  reaches 
the  calyx  to  be  emptied  into  the  bladder.  There  is  probably  an  absorption 
of  substances,  partly  of  water  and  partly  of  other  substances,  while  it  is  in 


582  LECTURE  XXV. 

the  tubes.1  To  be  sure,  there  are  a  number  of  experiments  which  do  not 
agree  with  such  an  assumption.2  A  reabsorption  has  been  observed 
only  under  conditions  which  cannot  be  regarded  as  normal.  The  frog  is 
a  particularly  suitable  subject  for  such  experiments.  In  this  animal  the 
kidneys  receive  their  blood  from  two  sources,  the  renal  artery,  and  the 
renal  portal  vein.  The  first  provides  the  Malpighian  body  with  ma- 
terial, while  the  latter  leads  directly  to  the  uriniferous  tubule.  If  the 
renal  artery  is  ligated,  the  secretion  of  urine  stops  completely.  On 
the  other  hand,  if  the  flow  of  blood  through  the  renal  portal  vein  is 
stopped,  then  urine  continues  to  be  secreted.  If  the  uriniferous  tubules 
have  the  function  of  taking  up  water  and  solid  constituents  from  the 
products  secreted  by  Bowman's  capsules  to  give  them  up  to  the  blood 
again,  then  it  would  be  expected  that  after  ligating  the  blood-vessels 
supplying  the  uriniferous  tubule,  that  there  would  be  an  increased 
elimination  of  urine.  This  was,  however,  not  the  case.  On  the  con- 
trary, the  amount  of  urine  diminished.  We  must  regard  this  question 
as  unsettled.  It  is  indeed  conceivable  that  an  absorption  takes  place 
only  under  certain  conditions.  We  must  at  this  place  mention  how 
extremely  difficult  it  is  to  obtain  a  clear  judgment  when  there  is  any 
meddling  with  the  normal  functions  of  the  kidneys.  We  never  know 
exactly  what  the  primary  cause  of  a  phenomenon  is,  and  what  takes  place 
only  secondarily.  Above  all,  we  have  to  consider  the  important  influence 
of  the  blood-supply  upon  the  formation  of  the  urine.  It  is,  for  example, 
perfectly  possible  that  in  the  above  case  the  diminished  secretion  of  the 
urine  may  have  been  caused  by  an  obstruction  in  the  flow  of  the  blood  to 
the  glomeruli.  We  shall  come  to  this  question  again  when  we  discuss 
the  question  of  reabsorption. 

In  order  to  investigate  the  functions  of  the  separate  divisions  of  the 
uriniferous  tube,  substances  have  been  introduced  into  the  circulation 
which  can  be  easily  detected  in  microscopical  preparations.  Thus 
Heidenhain 3  found  that  after  the  injection  of  sodium  sulphindigotate 
into  the  blood,  it  reappeared  in  the  epithelial  cells  of  the  uriniferous 
tubules.  He  concluded  from  this  discovery  that  these  cells  have  the 
function  of  adding  certain  specific  constituents  of  the  urine  to  the  secre- 
tion which  it  receives  from  the  capsules  of  Bowman.  This  is  not  neces- 
sarily true,  for  the  microscopical  pictures  might  equally  well  have 
been  caused  by  a  reabsorption  of  the  dye  from  the  uriniferous  tubule. 
Carmine  has  also  been  used  for  such  experiments,4  and  the  results  of 


1  H.  Ribbert:  Virchow's  Arch.  93,  169  (1883).     W.  M.  Sobieranski :  Arch,  exper. 
Path.  Pharm.  35,  144  (1895). 

2  A.  Gurwitsch:    Pfliiger's  Arch.  91,  71  (1902).     A.  P.  Beddard:  J.  Physiol.  28,  20 
(1901). 

3  R.  Heidenhain:   Arch,  mikro.  Anat.  10,  1  (1874).   Cf.  Pfliiger's  Arch.  9,  1  (1874). 

4  Cf.  Adolf  Schmidt:   Pfliiger's  Arch.  48,  34  (1891). 


THE   ELIMINATION   OF   METABOLIC   PRODUCTS.         583 

these  experiments  also  are  capable  of  more  than  one  interpretation. 
Dreser l  attempted  to  find  out  at  which  place  acid-fuchsin  was  elimi- 
nated. He  injected  daily  three  or  four  cubic  centimeters  of  acid-fuchsin 
into  the  dorsal  lymph-sac  of  frogs.  An  hour  or  so  afterwards  there  was 
no  pigment  present  in  the  glomeruli  nor  in  the  convoluted  tube,  but  only 
in  the  lumen  of  the  central  part  of  the  tube.  If  the  injection  were 
repeated,  the  glomeruli  remained  colorless;  but  in  the  convoluted  tubes, 
the  red  coloration  gradually  extended  into  the  end  of  the  epithelium 
which  is  toward  the  lumen.  Experiments  with  alizarin-carmine  showed 
that  the  coloration  did  not  appear  in  the  Tubidi  contorti,  but  only  in  the 
distal  parts  of  the  tubes.  Dresser  concluded  from  these  experiments  and 
those  with  other  dyes,  that  in  the  convoluted  tubes  secretion  alone  takes 
place,  and  no  reabsorption.  We  see,  therefore,  that  the  decision  as  to 
the  absorption  capacity  of  the  epithelium  of  the  convoluted  tubes  is  entirely 
dependent  upon  the  interpretation  of  these  microscopical  pictures.  As 
long  as  this  problem  cannot  be  decided  positively,  it  is  quite  impos- 
sible to  establish  the  function  of  the  different  parts  of  the  uriniferous 
tubes.  The  same  microscopical  appearance  may  be  regarded  as  resulting 
from  an  absorption  or  from  an  elimination.  The  entire  question  as  to 
the  special  functions  of  the  anatomically  different  parts  of  the  uriniferous 
tubes  remains  absolutely  unsettled  by  the  above  experiments. 

Let  us  now  see  whether  our  knowledge  of  the  functions  of  the  kidneys 
is  sufficient  to  give  us  a  clear  idea  of  the  formation  of  urine.  In  the  first 
place  we  must  state  that  it  has  never  been  found  possible  to  detect  posi- 
tively the  presence  of  secretory  nerves  in  the  epithelium  of  the  kidneys. 
All  the  nervous  influences  which  have  shown  an  effect  upon  the  elimina- 
tion of  urine  can  be  either  directly  or  indirectly  attributed  to  a  change 
in  the  innervation  of  the  blood-vessels.  The  amount  of  the  blood  circu- 
lating is  closely  related  to  the  amount  of  urine  secreted.  This  relation  is 
almost  self-evident,  for  the  greater  the  amount  of  blood  passing  through  the 
kidneys,  the  greater  will  be  the  opportunity  for  the  cells  of  the  kidney 
to  form  their  secretion.  The  blood-pressure  also  is  to  be  considered. 
The  whole  arrangement  of  the  glomeruli  is  such  that  the  blood  must  pass 
the  Malpighian  body  with  a  relatively  high  pressure.  In  this  respect  the 
above-mentioned  behavior  of  the  efferent  vessels  is  important,  which  are 
considerably  narrower  than  the  afferents.  Ludwig 2  makes  use  of  this 
fact  for  the  foundation  of  his  much-discussed  theory  of  urine-elimination. 
He  attempted  to  make  his  explanation  as  mechanical  as  possible,  and 
assumed  first  of  all  that  there  was  a  filtration  through  the  glomeruli  at 


1  H.  Dreser:    Z.  Biol.  21,  41   (1885).     Cf.  P.  Griitzner:    Pfliiger's    Arch.  24,  441 
(1881).     M.  Nussbaum:   ibid.  16,  139  (1878);   17,  580  (1879). 

2  Ludwig:    Wagner's    Handworterbuch  der   Physiol.  2,  629  (1844);    Wiener  med. 
Wochenschr.  14,  No.  13,  14  (1864);   Sitzber.  Kais.  Akad.  Wissensch.  48  (1863). 


584  LECTURE  XXV. 

the  beginning  of  the  uriniferous  tubes.  According  to  this,  the  urine 
would  show  a  very  similar  composition  to  that  of  the  plasma  of  the  blood. 
This,  however,  is  not  the  case.  Ludwig  furthermore  assumed  that  there 
was  a  re-absorption  in  the  uriniferous  tubes,  both  of  water  and  of  dis- 
solved substances.  Very  soon,  however,  important  objections  were  raised 
against  this  theory  of  a  filtration  of  all  of  the  constituents  of  urine. 
Above  all,  it  was  pointed  out  that  while  it  was  comprehensible  that  the 
proteins  in  the  blood  could  not  pass  through  the  vascular  endothelium,  on 
the  other  hand  it  would  be  expected  that  certain  other  substances,  for 
example  sugar,  which  is  always  present  in  the  plasma,  would  filter  through 
into  the  urine.  This  is,  however,  not  the  case  under  normal  conditions, 
and  the  same  is  true  of  certain  other  substances.  To  account  for  this  it 
has  been  suggested  that  perhaps  the  sugar  may  not  circulate  as  such  in 
the  blood,  but  that  it  is  combined  with  some  other  compound  which 
will  not  filter  through  the  medium.  There  is  no  support  for  any  such 
assumption.  The  quantitative  composition  of  the  urine  also  speaks 
against  any  such  simple  filtration  process  taking  place  in  the  formation 
of  urine.  The  plasma  contains  about  0.05  per  cent  of  urea.  We  would 
then  expect  the  urine  to  contain  about  the  same  amount  of  this  sub- 
stance, whereas  in  fact  about  2  per  cent  is  usually  present.  If  we  are  to 
retain  the  idea  of  a  pure  filtration,  then  we  must  necessarily  assume 
that  the  urine  is  concentrated  in  the  uriniferous  tubes  to  about  ^  of  its 
original  volume.  It  has,  furthermore,  been  found  that  if  the  supply  of 
blood  to  the  kidneys  is  entirely  stopped,  that  the  secretion  of  urine 
ceases;  but,  on  the  other  hand,  when  the  blood  is  allowed  to  flow  again 
through  the  kidneys,  it  is  about  45  minutes  before  the  secretion  of 
urine  begins.  If  we  believe  that  the  endothelium  of  the  glomerulus 
and  that  of  Bowman's  capsule  is  a  mere  filtering  membrane,  it  is  hard 
to  account  for  the  long  cessation  of  its  function. 

Especially  quite  recently,  more  and  more  facts  have  become  known, 
which  indicate  that  the  kidneys  act  analogously  to  other  glands  during 
the  formation  of  their  secretion.  For  one  thing,  it  has  been  observed 
that  an  increased  secretion  causes  a  rise  of  temperature,  and  that  when 
there  is  more  work  done  by  the  kidneys,  there  is  more  oxygen  consumed 
and  more  carbonic  acid  produced.1  Our  present  knowledge  teaches  us 
that  we  cannot  be  far  wrong  in  assuming  that  practically  the  whole 
function  of  the  kidneys  is  analogous  to  that  of  the  other  glands  and  that 
no  simple  filtration2  can  take  place;  both  the  epithelium  of  the  glome- 
rulus, as  well  as  that  of  the  uriniferous  tube,  probably  produce  an  actual 
secretion.  We  know  of  various  substances  which  increase  the  secretion 


1  J.  Bancroft  and  T.  G.  Brodie:  J.  Physiol.  32,  18  (1904). 

2  Cf.  Torald  Sollmann:    Ann.  J.  Physiol.  13,  241  (1905).     W.  Filehne  and  J.  Biber- 
feld:  Pfluger's  Arch.  Ill,  1  (1906). 


THE   ELIMINATION   OF   METABOLIC   PRODUCTS.        585 

of  urine,  just  as  we  have  met  with  such  substances  in  the  study  of  other 
glands.  To  be  sure,  it  has  been  shown  that  a  great  many  of  these  sub- 
stances are  capable  of  exerting  only  indirectly  an  influence  upon  the 
kidney-cells,  by  affecting  the  flow  of  the  blood  through  the  kidneys  on 
the  way  to  the  vascular  innervation.1  For  other  substances,  the  result 
cannot  be  traced  to  this  cause. 

In  order  to  prevent  misunderstandings,  we  will  at  once  state  that  purely 
physical  processes  undoubtedly  do  play  an  important  part  here  as  in  the 
case  of  all  absorption  and  secretion  processes  in  the  animal  organism. 
It  is  perfectly  possible  that  a  pure  filtration  process  may  act  in  conjunction 
with  other  processes  in  the  formation  of  urine.  At  the  same  time  it  would 
be  wrong  to  assume  that  the  existence  of  a  nitration  process  is  proved. 
We  can  only  infer  that  it  takes  place,  and  are  at  once  compelled  to  make 
the  auxiliary  hypothesis  of  the  reabsorption  by  the  epithelium  of  the 
uriniferous  tubes.  Another  possibility  seems  to  us  as  far  more  probable, 
namely,  that  the  Malpighian  tuft  is  not  the  sole  place  where  the  constituents 
of  the  urine  are  secreted.  We  have  already  seen  that  the  efferent  vessels, 
after  emerging  from  the  tuft,  again  break  up  into  a  capillary  network, 
which  surrounds  the  secreting  tubes  in  the  cortex.  This  behavior  of  the 
blood-vessels  must  surely  be  of  some  significance  in  the  formation  of  the 
urine.  It  is  possible  that  a  back-absorption  takes  place  here,  but  it  is  also 
conceivable  that  the  epithelium  of  the  uriniferous  tube  is  only  able  to 
withdraw  definite  substances  from  the  blood,  concentrates  them,  and 
finally  sends  them  on  at  different  periods  towards  the  lumen  of  the  tubes. 
First  of  all,  we  must  remember  that  the  Bowman's  capsule  possesses  numer- 
ous finely  branching  nerve-fibers,  which  originate  in  the  vasomotor  nerves. 
The  blood-capillaries,  also,  are  abundantly  supplied  with  nervous  plexuses. 
Furthermore,  it  has  been  found  that  nervous  branches  exist  which  supply 
the  uriniferous  tubes;  and  in  fact  we  see  separate  plexuses  of  non- 
medullated  fibres,  arising  especially  from  the  Tubuli  contorti.  Such 
nerve-endings  have  also  been  observed  for  the  epithelium  of  the  Bow- 
man's capsule,  for  the  straight  tube  and  also  for  the  collecting  tubes. 
The  fact  that  the  vessels  of  the  kidneys,  and  especially  those  of  the 
capillaries  of  the  cortex  have  such  an  extensive  innervation,  suffices  to 
account  for  the  sensitiveness  of  the  renal  vessels  to  all  sorts  of  different 
influences.  More  and  more  it  has  become  evident  that  a  great  number 
of  those  substances  to  which  has  been  ascribed  a  specific  action  upon 
the  parenchyma  of  the  kidneys,  only  influence  the  formation  of  urine  by 
accelerating  or  retarding  the  flow  of  the  blood.  The  intimate  dependence 
of  the  secretion  of  the  kidneys  on  the  blood-supply  may  have  been  the 
chief  reason  for  assigning  to  the  kidneys  a  position  different  from  that  of 
the  other  organs  of  the  body. 


1  Cf.  O.  Loewi:   Arch,  exper.  Path.  Pharm.  53,  15,  33,  and  49  (1905). 


586  LECTURE  XXV. 

We  have  repeatedly  learned  that  other  glands  are  to  a  certain  extent 
independent  of  the  blood-supply.  Thus  the  pancreas  is  constantly  forming 
its  secretion,  but  gives  it  up  only  after  certain  kinds  of  stimulation.  It  is 
otherwise  with  the  kidneys.  Their  activity  is  different,  because  their  func- 
tion has  an  entirely  different  significance  from  that  of  all  the  other  glands. 
The  kidneys  must  be  very  delicately  adjusted  to  the  composition  of  the 
blood.  They  are  obliged  to  work  very  rapidly  in  all  cases,  and  are  not 
obliged  in  every  case  to  follow  stimulations  which  are  communicated 
to  them  reflexively  by  the  nervous  system.  The  chemical  nature  of  the 
blood  invariably  has  an  influence.  Now,  is  this  because  the  vasomotor 
nerves  are  directly  influenced  by  the  composition  of  the  blood,  so  that,  for 
example,  an  enlargement  of  the  vessel  or  restriction  of  it  will  be  effected, 
or  because  certain  components  of  the  urine  act  directly  upon  the  epithelium 
of  the  uriniferous  tubes?  We  hold  that  the  last  assumption  is  very  prob- 
able, and  imagine  that  certain  specific  substances  are  captured  by  this 
epithelium,  which  are  concentrated  and  then  given  up  again.  Only  in 
some  such  way  as  this  are  we  able  to  account  for  the  relatively  high  con- 
centration of  the  urea.  There  are  quite  a  number  of  different  observations, 
which  indicate  such  a  specific  function  of  the  kidney  epithelium.  A  few 
examples  will  be  cited.  The  elimination  of  uric  acid  has  been  studied 
most  closely,  and  its  presence  is  easy  to  detect.1  If,  for  example,  a  solu- 
tion of  uric  acid  in  piperazine  is  injected  subcutaneously  into  rabbits, 
there  takes  place  first  of  all  a  considerable  diuresis.  In  from  twenty 
minutes  to  an  hour  uric  acid  may  be  detected  in  the  tubes  of  the  med- 
ulla. The  glomeruli  and  Bowman's  capsules  are  perfectly  free  from 
deposits  of  uric  acid;  but,  on  the  other  hand,  the  epithelium  of  the  con- 
voluted tubes  contains  granules  of  uric  acid,  and  chiefly  in  the  end  of  the 
tubes  facing  the  lumen.  Anten  2  obtained  corresponding  results  in  the 
kidneys  of  dogs.  He  cut  out  the  kidneys  from  the  general  circulation  of 
a  live  dog,  and  then  passed  a  solution  of  freshly-precipitated  silver  chloride 
in  ammonia  through  the  organs,  in  order  to  precipitate  the  uric  acid  present 
as  silver  urate.  The  kernels  of  the  silver  salt  were  found  chiefly  in  the 
cells  of  the  convoluted  tubes,  and  particularly  at  the  basal  part  of  the 
cells.  The  epithelium  of  the  ascending  tube  of  Henle's  loop  also  showed 
isolated  accumulations,  but  this  was  not  the  case  with  the  descending  part 
of  the  loop.  One  might  naturally  be  inclined  to  object  that  the  appear- 
ance noted  might  result  from  a  reabsorption  just  as  well  as  from  a  secre- 
tion of  the  uric  acid.  There  are,  however,  so  many  observations 3  of 


1  Cf.  Sauer:  Arch,  mikros.  Anat.  53,  218  (1899).     W.  Ebstein  and  A.  Nicolaier:  Ex- 
perimentelle  Erzeugung  von  Harnsteinen,  Wiesbaden,  1891,  and  Virchow's  Arch.  143, 
337  (1896).     O.  Minkowski:   Arch,  exper.  Path.  Pharm.  41,  375  and  410  (1898). 

2  Henri  Anten:   Arch,  internat.  de  pharmacodynamie  et  de  therapie,  8,  455  (1901). 

3  Cf.  Courmont  et  Andre":  J.  physiol.  et  pathol.  general,  7,  255  (1905). 


THE   ELIMINATION    OF   METABOLIC   PRODUCTS.         587 

this  nature  made  under  quite  different  conditions  that  we  may  well 
assume  that  an  actual  secretion  of  uric  acid  takes  place,  and  its  separa- 
tion from  the  blood  is  probably  the  result  of  a  selective  action  of  the 
epithelium  of  the  above-mentioned  portions  of  the  uriniferous  tube.  We 
will  mention  in  addition  that  Hober  and  Konigsberg  l  have  proved  that 
the  epithelium  of  the  uriniferous  tube  is  not  only  able  to  take  up  colors 
which  are  soluble  in  lipoids,  but  also  those  which  are  insoluble  in  lipoids. 
Unfortunately,  it  has  up  to  the  present  not  been  found  possible  to  local- 
ize th«  secretion  of  urea  and  other  substances  in  the  same  way  as  in  the 
case  of  uric  acid. 

We  do  not  in  any  way  intend  to  suggest  that  the  secretion  of  the  urine 
is  a  perfectly  simple  and  uniform  process.  Unquestionably  a  great  num- 
ber of  different  processes  are  taking  place  side  by  side,  which  mutually 
assist  one  another.  On  one  side  constituents  of  the  urine  are  given  up 
through  the  Malpighian  bodies  to  the  capsules  of  Bowman,  and  evi- 
dently at  this  place  the  greater  part  of  the  water  is  sent  out,  while  the 
epithelium  of  the  uriniferous  tube  is  constantly  removing  definite  con- 
stituents from  the  blood,  accumulating  them  and  then  giving  them  up 
again  inward  to  the  lumen  of  the  tube.  If  we  consider  in  addition  that 
many  observations  indicate  that  there  is  more  or  less  absorption  in  the 
uriniferous  tube  of  some  of  the  substances  which  have  previously  been 
secreted,  of  water  especially,  then  we  shall  begin  to  understand  that 
diuretics  can  find  a  number  of  different  points  of  attack,  and  cause,  in  a 
number  of  different  ways,  disturbances  in  the  secretion  of  the  urine. 

We  must  come  back  once  more  to  the  fact  that  under  normal  condi- 
tions there  is  no  sugar  in  the  urine.  As  we  have  said,  it  has  been  sug- 
gested that  this  was  because  the  glucose  did  not  circulate  as  such  in  the 
blood,  but  combined  in  some  way  with  colloidal  substances,  although 
direct  experiments2  have  shown  that  this  representation  is  in  no  way 
justifiable.  Sugar  is  present  as  such  in  the  blood.  Evidently  the  vas- 
cular endothelia  of  the  kidneys  are  adjusted  to  a  certain  definite  sugar 
content  of  the  blood.  When  more  than  this  is  present  the  sugar  passes 
over  into  the  urine.  Now  it  seems  probable  that  certain  substances  cause 
sugar  to  pass  into  the  urine  even  when  there  is  no  glucohemia.  Such, 
for  example,  is  phloridzin,  which,  according  to  many  observers,  acts 
directly  upon  the  kidneys,  or  indeed  at  first  upon  the  vascular  endo- 
thelia.3 Recently  Underbill  and  Closson  4  have  stated  that  those  forms 
of  glucosuria,  which  appear  when  common  salt  is  introduced  into  the 
circulation,  are  in  some  cases  to  be  regarded  as  due  to  a  direct  influence 

1  Hober  and  Konigsberg:   Pfluger's  Arch.  108,  323  (1905). 

2  Leon  Asher  and  R.  Rosenfeld:  Zentr.  Physiol.  19,  449  (1905).  See  Lecture  II,  p.  30. 
8  See  Lecture  V,  p.  81. 

4  Am.  J.  Physiol.  15,  321  (1906). 


588  LECTURE  XXV. 

upon  the  kidneys.  They  found  that  a  great  deal  depended  upon  the 
place  in  which  the  salt  solution  was  introduced.  If  it  was  an  artery  of 
the  brain,  glucohemia  ensued,  and  consequently  glucosuria,  but  no  poly- 
uria.1  When,  however,  they  injected  the  salt  solution  into  one  of  the 
veins  of  the  body,  polyuria  soon  resulted,  and  at  the  same  time  an  elimi- 
nation of  sugar  took  place,  but,  instead  of  the  amount  of  sugar  present 
in  the  blood  increasing,  it  decreased.  This  case  of  glucosuria,  therefore, 
must  arise  from  another  cause,  and  may  be  attributed  to  an  action  upon 
the  endothelia  of  the  kidneys. 

If  we  consider  that  the  kidneys  have  the  function  of  removing  all 
abnormal  substances  from  the  blood,  and  any  excess  of  normal  ones,  then  it 
is  self-evident  that  definite  statements  cannot  be  made  concerning  the 
composition  of  the  urine.  It  is  dependent  first  of  all  upon  the  nature  of 
the  nourishment  and  upon  the  intensity  of  the  metabolism  of  the  cells. 
There  is  nothing  uniform  concerning  the  amount  of  urine  eliminated  in  a 
day,  nor  concerning  its  reaction  or  other  behavior.  The  individual 
products  which  are  eliminated  in  urine  we  have  already  discussed,  and, 
in  each  separate  case,  traced  the  product  to  its  source.  The  end-products 
of  metabolism  are  always  eliminated  with  a  greater  or  less  quantity  of 
salts.  These  originate,  to  be  sure,  partly  from  decomposition  and  partly 
from  destruction  of  tissue,  but  for  the  most  part  they  may  be  traced  to 
the  food  itself.  The  amount  of  water  in  urine  does  not  depend  entirely 
upon  the  amount  that  is  drunk,  but  is  materially  affected  by  the  amount 
that  is  utilized  in  the  organism.  We  shall  soon  see  that  by  the  evapora- 
tion of  water  from  the  surface  of  the  body,  the  animal  organism  has  a 
very  efficient  means  of  regulating  its  temperature.  We  may  expect 
that  one  and  the  same  individual,  under  conditions  remaining  constant 
and  a  diet  which  is  qualitatively  and  quantitatively  the  same  each  day, 
would  eliminate  a  urine  which  would  show  a  constant  composition  within 
narrow  limits.  It  is  remarkable  that  but  few  exact  and  complete  analy- 
ses of  urine  have  ever  been  made.  Usually  the  composition  of  the 
food  that  is  eaten  is  entirely  disregarded.  It  is  clear  that  such  analyses 
are  useless  for  drawing  any  conclusions  or  for  future  inquiry.  The  great 
gap  in  our  knowledge  is  thus  made  more  apparent,  for  we  would  unques- 
tionably be  able  to  draw  certain  conclusions  as  to  the  metabolism  of  the 
cells  if  there  were  exact  analyses  which  took  into  consideration  all  the 
substances  present  in  urine,  and  such  investigations  would  be  of  great 
help  in  the  case  of  pathological  processes.  Quite  recently  Otto  Folin  2 
has  undertaken  the  analysis  of  urine  from  a  single  individual  during 
several  days  in  which  the  diet  remained  the  same.  We  regret  that  we 
cannot  give  all  the  values  he  obtained  in  his  work,  but  we  have  to  be 

1  See  Lecture  V,  p.  81. 

2  Am.  J.  Physiol.  13,  No.  1,  45  and  66  (1905). 


THE  ELIMINATION   OF  METABOLIC   PRODUCTS. 


589 


satisfied  here  with  certain  parts  of  it  which  are  shown  in  the  following 
summary.  The  nourishment  consisted  of  500  c.c.  milk,  300  c.c.  cream 
with  a  fat-content  of  18  to  22  per  cent,  450  grams  egg,  200  grams  Hor- 
lick's  Malted  Milk,  20  grams  sugar,  6  grams  salt.  This  mixture  con- 
tained about  two  liters  of  water,  and  in  addition  900  c.c.  were  drunk. 
In  this  food  there  was  contained  119  grams  albumin,  about  148  grams 
fat,  and  225  grams  carbohydrate.  The  mixture  was  shown  to  have  a 
constant  composition  by  the  determination  of  the  chlorine  from  day  to 
day  (about  6.1  grams),  of  the  sulphuric  acid  (about  3.7  grams),  of  the 
phosphoric  acid  (about  5.8  grams),  and  of  the  nitrogen  (about  19.0  grams). 

ANALYSIS  OF  THE   URINE  OF  A  NORMAL   INDIVIDUAL. 


Body 
Weight. 

Date. 

Volume 
of  Urine. 

Total  Ni- 
trogen. 

Nitrogen 
as  Urea. 

Nitrogen 
as  Am- 
monia. 

Nitrogen 
as  Great  i- 

nine. 

Nitrogen 
as  Uric 
Acid. 

Nitrogen 
in  Other 
Com- 

pounds. 

kg. 

c.c. 

70.8 

Sept.  21 

1520 

15.9 

13.7 

0.64 

0.61 

0.08 

0.81 

Sept.  22 

1530 

16.6 

14.5 

0.72 

0.58 

0.10 

0.80 

Sept.  23 

1460 

16.6 

14.4 

0.73 

0.56 

0.11 

0.83 

Sept.  24 

1430 

16.5 

14.2 

0.75 

0.52 

0.12 

0.90 

70.1 

Sept.  25 

1380 

16.6 

14.5 

0.86 

0.54 

0.11 

0.85 

Each  100  grams  of  the  total  nitrogen  were  distributed  as  follows: 


t)ate. 

Urea. 

Ammonia. 

Urea  and 
Ammonia. 

Creatinine. 

Uric  Acid. 

Nitrogen 
in  Other 
Com- 
pounds. 

September  21 

85  9 

4   1 

90  0 

3  8 

0  5 

5  7 

September  22   

86  9 

4  3 

91  2 

3  6 

0  6 

4  6 

September  23   

86.5 

4.4 

90.9 

3.4 

0  7 

5  0 

September  24   

86.1 

4.5 

90.6 

3.2 

0  7 

5  5 

September  25   

85.7 

5.2 

90.9 

3.3 

0.7 

5  1 

Neutral 

Total  Sul- 

Inorganic 

Ether-sul- 

Sulphur 

phur  De- 

Sulphuric 

phuric 

Deter- 

Date. 

termined 

Acid. 

Acid. 

mined 

as  Sul- 

as Sul- 

phate. 

(s,) 

(S2) 

phate. 

(S3) 

September  21   

3.31 

2  85 

0  25 

0  21 

September  22 

3  00 

0  25 

September  23                   ... 

3  35 

2  89 

0  28 

0  18 

September  24   

3  20 

2  73 

0  24 

0  13 

September  25   

3.25 

2.92 

0  21 

0  12 

590 


LECTURE  XXV. 


Date. 

In  Per  cent  of  the  Total 
Sulphur. 

Acidity  in  c.c.  of   —  Solution. 

S, 

S2 

S3 

Total. 

Inorganic. 

Organic. 

September  21   

86.1 

86^3 
85.3 
89.8 

7.6 

8^3 
7.5 
6.5 

6.3 

5^4 
4.1 
3.7 

589 
630 
625 
617 
646 

219 
299 
432 

276 

370 
331 
193 

370 

September  22  

September  23   .    .    .    .    . 

September  24 

September  25   . 

Date. 

Total 
Phosphate 
asP205 

Chlorine 
in  Grams. 

Indican 
(Fehling's 
Solution 
=  100). 

September  21 

3  98 

6  3 

140 

September  22 

4  16 

5  7 

150 

September  23                                             .    . 

3  84 

5  8 

140 

September  24 

3  68 

5  7 

140 

September  25                         

3  85 

5.2 

130 

It  is  evident  from  these  values  that  the  urine  during  these  five  days 
showed  a  very  constant  composition.  It  would  be  very  interesting  to 
carry  out  such  experiments  with  a  uniform  diet,  and  especially  with  the 
same  kind  and  amount  of  albumin,  also  on  a  large  scale  during  patho- 
logical conditions.  In  such  a  way  we  should  obtain  an  insight  into  the 
cell-metabolism  under  different  conditions.  At  the  same  time  it  is  not 
true  that  we  can  draw  very  far-reaching  conclusions  in  all  cases  as  to  the 
cell-metabolism  from  the  composition  of  the  urine.  We  must  always 
remember  how  little  we  know  concerning  cell-metabolism  and  of  the 
dependence  of  one  organ  upon  another.  It  is  indeed  possible  that 
there  is  an  exchange  of  material  in  such  a  way  that  the  decomposi- 
tion-products from  one  organ  are  utilized  by  another.  Thus  there  may 
be  a  considerable  destruction  of  tissue  of  certain  specific  composition, 
which  would  not  show  any  indication  in  such  an  analysis,  because  there 
might  not  be  any  of  the  products  from  the  destruction  of  this  tissue, 
in  the  urine.  The  kidney  may  be  an  economizing  organ  of  the  animal. 
It  is  perfectly  possible  that  the  constituents  which  it  receives  that 
are  useful  in  the  organism  are  in  some  way  transformed  and  given 
back  to  the  circulation.  We  will  recall  the  fact  that  the  kidneys  are 
capable  of  effecting  syntheses.  Their  cells  conjugate  benzoic  acid  with 
glycocoll.  Is  there  any  reason  for  believing  that  this  is  the  only  syn- 
thesis which  the  kidneys  are  capable  of  effecting?  We  will  also  mention 
the  fact  that  the  animal  organism  is  exceedingly  economical  with  its 


THE   ELIMINATION   OF   METABOLIC   PRODUCTS.        591 

supply  of  phosphoric  acid.  In  increased  diuresis  the  amount  of  urea 
and  of  common  salt  in  the  urine  increases  considerably,  but  the  amount 
of  phosphoric  acid  present  remains  remarkably  constant. 

The  reaction  of  the  urine  depends,  as  we  have  already  said,  upon  the 
nature  of  the  food.  The  urine  of  herbivora  is  neutral  or  alkaline,  while 
that  of  the  carnivora  is  acid  as  a  rule.  The  direct  connection  which 
this  has  with  the  food  may  be  indicated  theoretically  by  compar- 
ing the  ash  of  plants  with  that  of  animals.  That  it  is  not  any  par- 
ticular difference  in  the  metabolism  taking  place  in  different  classes  of 
animals  which  causes  the  different  reaction  of  the  urine,  may  be  shown 
by  feeding  vegetables  to  the  carnivora.  The  urine  then  becomes  neutral 
or  alkaline.  Conversely,  herbivora  may  be  forced  to  become  carnivora 
by  starvation.  The  animal  is  then  obliged  to  live  upon  its  own  tissue, 
and  the  urine  then  has  an  acid  reaction.  Alkaline  urine,  especially  in 
herbivora,  is  usually  turbid  on  account  of  the  precipitation  of  alka- 
line earth  salts.  The  urine  of  a  normal  man  with  a  mixed  diet  shows  an 
acid  reaction.  The  acid  reaction  is  caused  by  the  fact  that  during  meta- 
bolism acid  products  are  formed  by  the  combustion  of  neutral  substances 
such  as  albumin  and  lecithin  for  example.  The  sulphur  contained  in 
albumin  is  largely  converted  into  sulphuric  acid,  the  phosphorus  of  leci- 
thin and  of  the  nucleic  acids  is  oxidized  to  phosphoric  acid.  Further- 
more, organic  acids,  as,  for  example,  hippuric  acid,  uric  acid,  oxalic  acid, 
and  aromatic  oxyacids,  are  also  formed.  The  organism,  moreover,  pos- 
sesses ways  and  means  for  keeping  the  acidity  within  certain  limits. 
For  one  thing,  the  acid  formed  may  be  neutralized  by  means  of  alkali 
carbonate;  and  if  there  is  not  enough  of  this  present,  then  the  ammonia 
which  is  set  free  by  the  decomposition  of  proteins  comes  into  play. 

It  is  perhaps  well  here  to  make  a  few  general  observations  concerning 
the  conception  of  acidity.  An  acid  may  be  denned  from  two  stand- 
points.1 The  chemist  understands  by  an  acid  a  substance  whose  hydro- 
gen atom,  or  atoms,  may  be  replaced  by  metals.  When  the  metal  enters 
the  molecule  the  acid  character  is  neutralized.  Thus  the  acidity  of  a 
solution  may  be  estimated  by  measuring  the  amount  of  alkali  which  is 
necessary  to  replace  all  of  the  acid  hydrogen.  Our  discussion  of  the  acidity 
of  the  urine  was  from  this  point  of  view.  The  physi co-chemist,  on  the 
other  hand,  defines  an  acid  as  a  chemical  compound  which  when  dis- 
solved in  water  is  dissociated,  yielding  positively  charged  hydrogen  atoms 
(H+).  According  to  the  degree  of  dissociation,  we  characterize  an  acid 
as  strong  or  weak.  A  weak  acid,  for  example,  is  one  which  at  a  given 
concentration  is  less  dissociated  than  a  strong  acid.  The  difference 
between  these  two  points  of  view  may  be  perhaps  best  illustrated  by  an 

1  Cf.  R.  Hoeber:  Hofmeister's  Beitrage,  3,  525  (1903). 


592  LECTURE  XXV. 

example.  Suppose  we  have  a  solution  of  ^  normal  hydrochloric  acid, 
and  one  of  acetic  acid  which  is  also  •£$  normal.  From  the  purely  chemi- 
cal standpoint  these  solutions  are  of  the  same  strength,  because  we  shall 
have  to  use  as  much  alkali  to  neutralize  a  liter  of  the  acetic  acid  as  would 
be  necessary  for  a  liter  of  the  hydrochloric  acid.  On  the  other  hand, 
from  the  point  of  view  taken  by  the  physico-chemist,  the  acidity  of  the 
3*2-  normal  hydrochloric  acid  is  about  40  times  as  great  as  that  of  the  3^ 
normal  acetic  acid.  Thus  the  hydrochloric  acid  of  the  above  concentra- 
tion is  about  97  per  cent  dissociated,  while  the  acetic  acid  is  only  disso- 
ciated to  an  extent  of  2.4  per  cent.  Now  in  our  ordinary  chemical 
methods  we  neutralize  all  of  the  hydrogen  of  the  acid,  because  there  is 
always  a  fraction  of  the  whole  molecule  that  is  dissociated,  the  value  of 
the  fraction  increasing  with  the  dilution;  and  as  fast  as  some  of  the 
ions  are  neutralized  more  of  the  molecule  dissociates,  so  that  eventually 
not  only  the  hydrogen  ions  originally  present,  what  we  may  designate  as 
the  active  hydrogen  ions,  but  also  those  which  were  originally  undissoci- 
ated,  the  potential  hydrogen  ions,  are  neutralized.  The  physico-chemist 
in  his  determination  of  the  acidity  takes  into  consideration  only  the 
former  kind  of  hydrogen.  From  his  point  of  view  the  urine  is  usually 
neutral.  There  seems  to  be  no  definite  relations  between  the  acidity 
determined  by  the  tit  ration  of  urine  and  the  so-called  ion-acidity.  It 
is  desirable  that  in  all  cases  both  values  should  be  known. 

In  general,  not  much  is  known  concerning  the  way  in  which  the  dif- 
ferent substances  proved  to  be  present  in  urine  are  combined  there.  The 
analysis  of  the  ash  as  such  teaches  us  but  little.  It  gives  us  considerable 
information  in  tracing  the  course  of  the  non-volatile  material,  but  in  this 
case  the  intestinal  elimination  must  not  be  disregarded.  The  fact  that 
the  inorganic  substances  are,  at  least  to  some  extent,  eliminated  by  the 
intestines,  complicates  our  understanding  of  the  general  metabolism,  and 
especially  because  of  the  fact  that  in  every  case  it  is  impossible  to  decide 
what  part  of  the  constituents  of  the  ash  of  the  faeces  is  to  be  re- 
garded as  unabsorbed  material  and  what  part  was  eliminated  from  the 
intestinal  walls  after  absorption  had  taken  place.  The  value  of  mineral 
substances  for  the  whole  organism  and  their  absolute  indispensability 
have  been  repeatedly  mentioned,  and  we  are  convinced  that  exact  investi- 
gations concerning  metabolism  on  as  broad  a  basis  as  possible,  taking 
into  consideration  the  inorganic  material  introduced  and  that  eliminated, 
will  give  us  considerable  information  as  to  the  nature  of  cell-metabolism. 

We  must  also  consider  a  phenomenon  which  is  frequently  met  with  in 
human  urine.  Fresh  urine  is  usually  clear  and  shows  no  sediment.  After 
the  urine  has  stood  for  some  time  a  sediment  often  forms,  sometimes  as 
a  reddish,  crystalline  powder,  sometimes  as  a  reddish-gray  precipitate, 
resembling  brick-dust.  The  latter  is  called  Sedimentum  lateritium.  It 


THE  ELIMINATION   OF   METABOLIC   PRODUCTS.        593 

dissolves  completely  on  heating,  and  appears  again  on  cooling.  On  stand- 
ing for  some  time,  crystals  often  appear  in  the  sediment,  which  will  not 
dissolve  on  heating  the  urine.  These  crystals  are  free  uric  acid,  while  the 
sediment  was  monosodium  urate.  The  precipitation  of  the  latter  is, 
partly  at  least,  due  to  the  cooling  of  the  urine,  for  it  is  much  more  soluble 
in  hot  water  than  in  cold.  As  the  crystals  form,  the  acidity  of  the  urine 
decreases.  The  question  arises  whether  the  change  in  the  reaction  of  the 
urine  has  any  connection  with  the  deposition  of  the  urate  precipitate.  We 
have  at  a  previous  place  mentioned  the  insolubility  of  uric  acid;1  it  requires 
at  18°  C.,  39,000  parts  of  water  to  dissolve  one  part  of  the  acid.  The 
values  given  in  the  literature  are  often  widely  different  from  the  above 
value  which  is  taken  from  the  work  of  His.  This  is  partly  explained  by 
the  fact  that  it  is  usually  disregarded  that  glass,  especially  common  glass, 
contains  alkali,  which  it  gives  up  to  water  which  is  in  contact  with  it,  and 
this  affects  the  analysis.  His,  again,  has  called  attention  to  the  great 
tendency  of  uric  acid  to  form  supersaturated  solutions.  The  acid  urate 
of  sodium,  also  called  the  mono-urate,  is  far  more  soluble  in  water  than 
uric  acid  itself.  Now  this  urate  is  deposited  frequently  in  urine,  and  of 
other  cases  free  uric  acid  is  found  in  the  sediment,  and,  in  fact,  so  much  in 
it  that  it  is  hard  for  us  to  believe  that  it  was  present  as  such  in  the  urine. 
Camerer  2  compared  the  solution  of  uric  acid  in  the  urine  with  the  following 
experiments.  He  mixed  a  saturated  solution  of  acid  urate  of  sodium, 
which  reacted  alkaline  toward  litmus,  with  a  solution  of  acid  phosphate 
of  sodium.  The  mixed  solution  showed  an  acid  reaction  and  was  perfectly 
clear  at  37°  C.  On  cooling  the  mixture,  the  reaction  toward  litmus 
changed.  The  solution  became  alkaline  and  uric  acid  was  precipitated. 
A  chemical  decomposition  had  taken  place.  From  the  acid  phosphate  of 
sodium  (NaH2PO4),  and  at  the  cost  of  the  sodium  in  the  monosodium 
urate,  disodium  phosphate  (Na2HPO4)  had  been  formed,  and  uric  acid 
had  been  set  free;  which,  on  account  of  its  insolubility,  was  precipitated. 
On  heating  the  solution,  tjie  reverse  process  took  place,  and  the  reaction 
of  the  urine  became  acid.  In  the  urine  there  is  always  more  or  less  alkali 
phosphate  present,  which  may  have  the  same  effect  as  in  the  above  test- 
tube  experiment.  Naturally,  according  to  this  explanation,  it  must  be 
assumed  that  the  uric  acid  is  originally  present  as  the  monosodium  salt. 
There  is  no  question  that  part  pf  the  uric  acid  is  actually  present  in  this 
form;  but,  on  the  other  hand,  it  is  certain  that  a  part  of  the  uric  acid 
is  present,  combined  in  some  other  way.  This  is  evident  from  the  fact 
that  from  a  simple  solution  of  alkali  urate,  the  whole  of  the  uric  acid  may 
be  precipitated  by  the  addition  of  acid,  while  this  is  not  the  case  with 
urine.  A  part  of  the  uric  acid  remains  in  solution  after  the  urine  has 


1  Cf.  T.  Paul:  Pharm.  Ztg.  1900,  also  Lecture  XIII,  p.  298. 

2  Deut.  med.  Wochschr.  17,  No.  10,  p.  356  (1896). 


594  LECTURE  XXV. 

been  acidified.  Now  urea  is  a  good  solvent  for  uric  acid.  It  is  an  open 
question  whether  we  are  justified  in  assuming  with  Rudel 1  that  there  is  a 
chemical  combination  between  the  urea  and  the  uric  acid  in  this  case, 
and  it  is  equally  uncertain  whether  the  urea  alone  affects  the  solubility  of 
the  uric  acid,  or  whether  there  are  other  compounds  present  in  urine  which 
have  the  same  action. 

We  have  already  said  that  the  epithelia  of  the  blood-vessels  and  of  the 
uriniferous  tubes  can  only  cause  the  elimination  of  those  substances  which 
do  not  belong  to  the  plasma,  or  which  are  present  in  more  than  the  normal 
amount.  Thus  the  kidneys,  for  example,  are  very  sensitive  to  an  increase 
in  the  sugar-content  of  the  blood.  Albumin  does  not  pass  through  the 
kidneys  when  they  are  acting  normally,  except  when  albumins  foreign 
to  the  body  evade  the  alimentary  canal,  and  get  into  the  circulation. 
It  is  a  well-known  fact  that  under  pathological  conditions,  in  diseases  of 
the  kidneys,  albumin  passes  from  the  blood-capillaries,  and  enters  through 
the  epithelium  of  the  uriniferous  tubes.  The  presence  of  albumin  in  the 
urine  is  a  symptom  which  may  arise  from  a  number  of  different  processes. 
There  is  no  question  that  a  study  of  the  nature  of  the  eliminated  albumin 
could  be  used  as  a  basis  for  further  inquiry.  To  be  sure,  in  many  cases 
there  is  a  mere  appearance  of  serum-albumin,  but  we  can  well  imagine 
that  in  other  cases  the  tissue-cells  for  some  reason  or  another  produce  an 
albumin,  and  give  it  up  to  the  plasma,  of  a  nature  which  in  its  entire  con- 
struction is  foreign  to  the  plasma,  and  that  it  is  accordingly  eliminated  by 
the  kidneys.  This  is  not  the  place  to  discuss  at  any  length  such  questions, 
which  are  closely  related  to  the  pathology  of  metabolism. 

As  we  have  already  mentioned,  the  organism  can  under  certain  condi- 
tions eliminate  the  constituents  of  the  urine  through  other  glands,  especially 
through  the  skin.  Thus  in  many  cases  of  uraemia,  urea  may  be  secreted 
in  such  quantities  by  the  sweat-glands,  that  crystals  deposit  upon  the  skin. 
By  uraemia  we  understand  a  very  serious  complex  of  symptoms,  occurring 
when  the  kidneys  to  a  greater  or  less  extent  ha,ve  ceased  to  exercise  their 
functions.  The  organism  seeks  by  every  means  in  its  power  to  get  rid  of 
the  constituents  of  urine  which  are  circulating  in  the  blood.  If  it  does 
not  succeed  in  accomplishing  this,  symptoms  appear  which  are  similar  to 
intoxication.  The  attempt  has  often  been  made  to  trace  the  cause  of  the 
disease  to  some  constituent  of  the  urine,  and  in  this  connection  urea  has 
been  principally  considered.  On  the  other  hand,  there  are  quite  a  number 
of  observations  which  indicate  that  the  urine  itself  exerts  a  poisonous  action. 
Thus  if  human  urine  is  injected  into  the  veins  of  a  rabbit,  it  will  produce 
acute  poisoning,  which  will  result  in  the  death  of  the  animal.  The  urine 
from  different  animals  shows  different  degrees  of  poisonous  properties. 

1  Arch.exper.  Path.  Pharm.  30,  469  (1892).  Cf.T.  J.  Zerner:  Wiener  klin.  Wochschr. 
6,  No.  15,  p.  272  (1893).  A.  Hitter:  Z.  Biol.  35,  155  (1897). 


THE  ELIMINATION  OF  METABOLIC  PRODUCTS.         595 

From  the  material  at  hand  it  is  hard  to  decide  as  to  the  significance  of  the 
phenomenon,  and  there  is  no  indication  of  what  substances  in  the  urine 
exert  this  poisonous  action.  In  the  case  of  uraemia  we  have  no  reason 
for  attributing  any  one  substance  as  causing  the  whole  complex  of 
symptoms.  It  is  self-evident  that  all  sorts  of  different  substances  may 
come  into  play  here,  and  furthermore  it  must  never  be  forgotten  that  an 
abnormal  composition  of  the  plasma  will  immediately  have  an  effect  upon 
all  the  processes  of  metabolism  in  the  cells,  and  result  in  the  production 
of  incompletely  formed  products,  or  of  those  which  are  built  up  in  an 
unsuitable  way.  Here,  as  in  all  physiological  and  pathological  processes, 
an  organ  should  not  be  considered  by  itself,  but  we  must  trace  the 
damages  which  start  from  it  in  a  continuous  line  from  organ  to  organ, 
from  tissue  to  tissue,  and  finally  from  cell  to  cell. 

The  animal  organism  is  also  normally  eliminating  substances  constantly 
through  the  skin.  We  find  in  mammals  essentially  two  kinds  of  glands 
in  the  skin,  the  sweat-glands  and  the  sebaceous  glands.  The  former 
eliminate  a  secretion  which  consists  almost  entirely  of  water.  The  amount 
of  sweat  secreted  in  the  course  of  a  day  varies  tremendously,  and  is  depend- 
ent upon  certain  conditions,  and  especially  upon  the  demands  for  a  regu- 
lation of  the  body  temperature.  In  the  evaporation  of  water  from  the 
surface  of  the  body  the  animal  organism  finds  its  most  important  means 
for  preventing  the  body  from  being  overheated.  A  large  amount  of  heat 
is  required  to  transform  water  from  the  liquid  to  the  gaseous  state.  This 
causes  the  body  to  be  cooled.  It  is  interesting  to  find  that  the  activity  of 
the  sweat-glands  is  influenced  by  the  central  nervous  system.  A  secretion 
may  be  produced  directly  by  nervous  stimulation. 

The  sebaceous  glands  have  a  different  and  more  local  function.  Corre- 
sponding to  this  fact,  their  secretion  has  a  quite  different  composition. 
In  a  fresh  condition  it  is  an  oily,  semi-liquid  mass,  which,  on  standing  in 
the  air,  solidifies  on  the  surface  of  the  skin  to  a  greasy  tallow.  It  contains 
fat,  albumin  and  cholesterol.  Its  most  important  function  is  to  lubricate 
the  skin.  We  will  here  mention  again  that  a  modified  sebaceous  gland, 
the  oil-bag  of  birds,  contains  octadecyl  alcohol  CisHagO,1  and  finally  that 
the  mammary  glands  likewise  may  be  considered  as  related  to  the  sebaceous 
glands. 


1  Rohmann:  Hofmeister's  Beitr,  6,  110  (1904). 


LECTURE   XXVI. 

THE  RELATIONS  OF  THE  ORGANS  TO  ONE  ANOTHER. 

AT  the  close  of  the  last  lecture  we  referred  briefly  to  the  mammary 
glands.  These  glands  exercise  their  function  only  under  certain  definite 
conditions.  The  period  of  lactation  does  not  begin  until  about  the  time 
the  secretion  is  required  by  the  suckling.  Long  before  the  birth,  however, 
external  changes  may  be  noticed  showing  that  the  glands,  then  at  rest,  are 
developing  in  such  a  way  that  they  will  be  able  to  meet  the  demands  that 
are  to  be  laid  upon  them.  We  have  here  an  interesting  example  of  the 
relation  of  widely  different  organs  to  one  another.  The  function  of  the 
mammary  glands  is  dependent  directly  upon  the  generative  apparatus  of 
the  female.  There  must  be  an  intimate  connection  between  the  two 
organs.  Just  what  this  is,  we  cannot  tell.  It  is  generally  assumed  that 
nervous  influences  cause  the  coincidence  in  the  development  of  the  preg- 
nant uterus  and  that  of  the  mammary  glands.  It  is  perfectly  conceivable 
that  this  assumption  is  correct,  although  in  recent  years  it  has  been  shown 
that  many  apparently  reflex  nervous  processes  may  be  traced  to  chemical 
reactions.  We  would  recall  in  this  connection  the  influence  of  the  hydro- 
chloric acid  from  the  stomach  upon  the  secretion  of  the  pancreas.  The 
secretion  of  the  latter  is  accelerated  as  soon  as  the  hydrochloric  acid  enters 
the  intestine.  The  simplest  assumption  was  that  the  hydrochloric  acid 
irritated  the  end-apparatus  of  the  nerves  in  the  intestinal  membrane,  and 
thus  reflexively  stimulated  the  pancreas  into  increased  activity.  It  has 
been  shown,  however,  that  the  mucous  membrane  of  the  intestine  contains 
an  antecedent,  the  prosecretin,  which  is  set  free  by  the  hydrochloric  acid, 
and  as  secretin  is  carried  by  the  blood-passages  into  the  pancreas.  Accord- 
ing to  this,  the  alimentary  tract,  or  at  least  that  portion  which  produces 
the  prosecretin,  falls  into  line  with  those  organs  which  are  said  to  produce 
internal  secretions.  It  is  not  right  to  give  a  particular  position  to  an  organ 
shown  to  produce  internal  secretions.  There  is  no  reason  why  an  organ 
which  gives  up  its  secretion  directly  to  the  blood  should  be  considered  as 
essentially  different  from  the  ordinary  glands  which  send  out  their  secre- 
tion through  ducts.  Numerous  observations  in  physiology  and  in  pathology 
compel  us  to  assume  that  all  the  organs  are  in  some  way  related  to  one 
another.  We  must  not  be  satisfied  by  merely  saying  that  this  connection 
is  made  by  means  of  the  nerves.  It  is  far  more  probable  that  the  separate 
cells  of  the  body  not  only  give  up  the  metabolic  end-products  to  the  lymph 
and  blood,  but  secretions  as  well.  This  view  seems  in  accordance  with 

596 


RELATIONS    OF   THE   ORGANS   TO    ONE   ANOTHER.     597 

the  entire    anatomical  construction    of  the  animal  tissue  and    with  our 
ideas  of  metabolism. 

It  would  be,  in  fact,  hard  to  understand  why  the  separate  tissues 
should  be  so  much  differentiated  if  the  essential  part  of  metabolic  pro- 
cesses consisted  merely  in  enabling  the  cells  already  formed  to  retain  their 
constituents  and  in  furnishing  them  merely  with  sufficient  heat  units  for 
the  exercise  of  their  functions.  If  even  the  digestive  process,  which 
a  priori  appears  so  simple,  requires  such  a  fullness  of  chemical  processes, 
utilizes  so  many  organs,  and  reacts  so  sensitively  to  the  different  condi- 
tions which  prevail,  we  may  conclude  at  once  that  the  cell-metabolism 
certainly  cannot  proceed  along  altogether  simple  lines,  but  that  here 
also  secretions  from  certain  groups  of  cells  must  be  of  considerable  sig- 
nificance. We  hold  that  it  is  not  entirely  impossible  that  every  indi- 
vidual cell  of  the  body  takes  part  in  secretory  work,  and  thus  has  in  some 
way  a  favorable  effect  upon  the  general  metabolism.  Perhaps  this  point 
of  view  may  give  us  some  idea  of  the  reason  why  organisms  constantly 
require  a  certain  amount  of  albumin.  Unquestionably  the  proteins 
occupy  a  quite  different  position  in  metabolism  from  that  taken  by  the 
nitrogen-free  foodstuffs.  We  can  well  imagine  that  they  are  required 
chiefly  for  the  formation  of  secretions.  We  do  not  overlook  by  any  means 
the  fact  that  the  large  requirement  of  albumin  is  even  then  only  partly 
explained  unless  one  is  ready  to  assume  that  in  the  formation  of  the  secre- 
tions a  large  number  of  cells  are  disintegrated  and  therefore  must  be 
built  up  anew.1  It  seems  to  us  very  important  to  state  that  there  is  no 
essential  difference  between  the  glands  with  an  excretory  duct  and  thosa 
in  which  there  is  no  duct.  It  is  especially  doubtful  whether  we  are  justi- 
fied in  assuming  that  only  cells  arranged  in  the  shape  of  a  gland  are 
active  in  the  formation  of  secretions.  Many  facts  indicate  that  the 
contrary  is  true.  Moreover,  there  are  many  intermediate  stages  between 
glands  with  ducts  and  those  with  none.  The  mucous  membrane  of  the 
intestine  secretes  intestinal  juice,  enterokinase  externally  and  secretin 
internally.  The  pancreas  secretes  externally  the  digestive  juice,  and  also 
probably  secretes  substances  internally  which  take  part  in  the  metabolism 
of  carbohydrates.  Again,  the  liver  undoubtedly  has  several  secretory 
functions.  On  the  one  hand,  it  yields  the  bile  which,  in  its  formation 
and  the  method  of  giving  it  up,  corresponds  to  an  external  secretion. 
Now  we  know,  for  example,  that  the  liver  is  constantly  storing  away 
sugar  and  assimilating  it  as  glycogen  in  order  that,  at  the  right  moment, 
fermentation  may  cause  the  reverse  process  to  take  place, — i.e.  sugar  be 
given  up  to  the  blood.  Certainly  this  is  an  internal  secretion  just  as 
much  as  the  formation  of  any  other  substance  under  the  influence  of  the 
cells.  To  be  sure,  in  this  case  we  know  just  what  this  secretion  is, 


1  Cf.  Lecture  XI,  p.  221  et  seq. 


598  LECTURE   XXVI. 

namely,  d-glucose.  The  cells  of  the  liver  take  part  in  its  formation, 
inasmuch  as  they  furnish  the  ferment  which  hydrolyzes  glycogen.  We 
have  already  indicated  that  we  must  not  regard  these  fermentation  pro- 
cesses as  simple  in  their  nature.  Wherever  it  has  been  possible  to  follow 
a  fermentation  closely,  it  has  been  found  invariably  that  it  consists  of  a 
whole  chain  of  separate  processes.  The  ferment  itself  does  not  origi- 
nally exist  as  such,  but  in  a  precursory  stage,  which  is  changed  to  the 
active  condition  by  the  aid  of  a  product  obtained  from  other  cells.  We 
cannot  be  wrong  in  assuming  that  such  relations  take  part  in  the  breaking 
down  of  glycogen. 

We  have  mentioned  these  processes  particularly  because  they  seem 
to  be  the  most  suitable  for  demonstrating  how  the  different  cells  of  the 
body  work  together.  It  is  certain  that  greater  clearness  would  prevail 
with  regard  to  pathological  processes  if  such  relations  were  kept  more  in 
the  foreground  in  each  instance  and  the  diseased  organ  itself  not  so  much 
regarded  as  representing  the  whole  "  case."  If  we  study  all  of  the  com- 
plicated processes  which  take  part  in  a  single  fermentation  from  the 
beginning  to  the  end,  we  shall  realize  at  how  many  different  places  dis- 
turbances in  the  normal  course  of  metabolism  may  arise. 

Let  us  now  return  to  the  functions  of  the  mammary  glands.  These 
may  very  likely  be  excited  into  lactation  by  means  of  a  secretion  pro- 
duced by  the  pregnant  uterus,  or  its  accessories.  The  transformations 
taking  place  in  the  dormant  mammary  gland  from  the  beginning  of  its 
preparatory  period  to  the  time  when  it  enters  into  the  full  exercise  of  its 
functions,  are  profound.  There  is  an  extensive  formation  of  new  cells. 
The  cells  of  these  glands,  which,  like  all  other  cells  of  the  body,  receive 
their  nutriment  from  the  blood,  suddenly  make  new  demands  upon 
it.  They  abstract  a  great  deal  of  material  from  the  blood,  which  they 
transform  considerably.  They  form  casein  from  the  albumins  of  serum, 
and  lactose  from  d-glucose.  Again  the  salts  are  removed  in  definite 
amounts  and  quite  independently  of  the  ratio  in  which  they  are  present 
in  the  blood.  We  have  previously  gone  into  these  details.  How  the 
cells  of  the  mammary  glands  accomplish  these  changes  is  not  known. 
We  do  not  know  of  any  intermediate  stages  between  the  serum-albumins 
and  casein,  nor  between  grape-sugar  and  milk-sugar.  We  can  merely 
imagine  that  maltose  is  formed  in  the  production  of  the  latter.  Before 
much  was  known  concerning  the  composition  of  the  various  different 
proteins,  the  transformation  of  serum-albumin  into  casein  did  not  appear 
to  be  a  very  complicated  process.  To-day  we  are  already  compelled  to 
assume  that  before  casein  can  be  formed,  the  serum-albumin  must  be 
decomposed  to  a  considerable  extent,  after  which  a  synthesis  is  effected. 
The  cells  of  the  mammary  gland  do  not  in  principle  assume  any  extraor- 
dinary position.  Their  chemism  is  merely  an  individual  and  a  specific 


RELATIONS    OF   THE   ORGANS   TO   ONE   ANOTHER.     599 

one,  and  consequently  the  products  which  they  form  are  typical,  just 
the  same  as  the  salivary  glands  yield  one  specific  secretion  and  the  pan- 
creas another.  There  are  not  any  essential  differences  between  these 
processes.  We  should  be  making  a  sad  mistake  if  we  were  to  consider 
the  function  of  the  cells  of  the  mammary  glands  by  itself.  We  are 
able  to  understand  it  only  when  we  trace  its  phases  from  a  general  stand- 
point. The  cells  of  the  mammary  glands  take  up  from  the  blood,  or 
more  directly  from  the  lymph,  certain  substances  which  evidently  must 
be  transformed  completely,  and  to  a  certain  extent  assimilated,  in  order 
to  form  the  product  which  it  will  subsequently  give  up.  Recent  inves- 
tigations indicate  that  even  the  actual  process  of  secretion  is  not  different 
from  that  of  other  glands,  for  here  also,  after  the  secretion  has  been  given 
up  by  the  cells,  a  residue  of  protoplasm  and  nucleus  remains,  and  a  new 
formation  of  the  same  secretion  again  ensues. 

It  is  not  alone  the  mammary  glands  that  are  dependent  upon  the  sexual 
apparatus.  More  and  more  we  become  cognizant  of  the  fact  that  the 
different  parts  of  the  latter  stand  in  a  number  of  different  relations  to 
other  organs,  though  we  are  not  able  to  discover  the  nature  of  the  active 
principle  any  more  definitely.  We  know  at  present  merely  of  isolated 
facts  which  we  cannot  explain  satisfactorily.  The  different  female  sexual 
organs  are,  in  the  first  place,  related  to  one  another.  As  an  example  of 
this,  we  need  only  cite  the  influence  of  the  ovaries,  when  they  are  exerting 
their  normal  function,  upon  the  uterus,  and  especially  upon  the  mucous 
membrane  of  the  uterus  at  the  time  of  menstruation.  Here  again  we 
frequently  find  this  attributed  to  nervous  excitement,  although  there  is 
no  definite  proof  that  such  is  the  case.  The  experiments  of  Halban  l 
have  shown  that  the  ovaries  can  exercise  their  function  when  there  is  no 
connection  with  the  nervous  system.  He  showed  that  if  he  extirpated 
the  ovaries  from  young  guinea  pigs  and  inserted  them  at  another  part  of 
the  body,  the  development  of  the  external  genitals  took  place  exactly  as  if 
the  ovaries  had  remained  in  their  original  position.  On  the  other  hand, 
in  immature  animals  in  which  the  ovaries  had  been  completely  removed 
from  the  body,  there  was  a  halt  in  the  development  of  the  external  organs 
of  generation.  It  is  also  well  known  that  when  the  function  of  the 
ovaries  ceases,  whether  due  to  their  ablation  in  a  mature  condition,  or  to 
the  fact  that  they  have  reached  the  end  of  the  period  of  their  activity, 
changes  take  place  in  the  uterus  corresponding  to  a  retrogression. 

Similarly  the  male  organs  of  generation  stand  in  relation  to  one  another. 
This  is  already  evident  from  the  way  the  cells  of  the  testes  work  together 
with  those  of  the  prostate  gland,  although  this  may  be  explained  as  a 
result  of  a  common  stimulation.  There  are  observations  according  to 
which  the  prostate  atrophies  after  the  removal  of  the  testes. 

1  Monatschr.  f.  Geburtshilfe  u.  Gynakol,  12,  496  (1900). 


600  LECTURE   XXVI. 

The  relations  of  the  sexual  organs  to  the  entire  organism  are  very  inter- 
esting. By  numerous  experiments  on  men  and  animals,  it  has  become 
well  recognized  that  extirpation,  the  so-called  castration,  before  sexual 
ripening  has  taken  place,  tends  to  prevent  the  formation  of  the  secondary 
sexual  character.  This  is  well  illustrated  in  cocks,  which,  as  we  all  know, 
when  fully  developed  sexually  may  be  recognized  by  their  wattles  and 
combs.  These  remain  undeveloped,  or  at  least  are  but  scanty,  if  the  testes 
are  removed  before  the  sexual  development  is  complete.  It  is  interesting 
also  to  find  that  a  secondary  sexual  character  develops  if  the  extirpated 
testes  are  transplanted  after  their  removal  from  the  fowl.1 

One  of  the  most  prominent  results  of  the  removal  of  the  sexual  glands 
is  an  abnormal  growth  of  the  bones.  In  castrates  it  is  frequently  found 
that  especially  the  tibia  and  the  femur  are  prolonged.  The  cause  of  this 
has  been  traced  to  a  faulty  ossification  of  the  epiphysis  cartilage  such  that 
there  is  no  limit  placed  upon  the  growth  of  the  bone.  Apparently  castra- 
tion affects  the  general  metabolism.  The  great  tendency  of  castrates 
towards  obesity  is  well  known.  It  has  never  been  positively  established 
whether  this  results  primarily  from  the  loss  of  the  sexual  glands  or  whether 
it  is  a  secondary  effect. 

Although  there  is  undoubtedly  a  connection  between  the  sexual  organs 
and  the  other  organs  of  the  body,  still  at  present  we  are  unable  to  identify 
any  definite  product  of  their  secretion  as  the  active  principle.  We  know 
of  glands,  however,  which  are  ductless,  but  do  not  give  rise  to  such 
secretions.  We  refer  to  the  suprarenal  bodies  and  the  thyroid  gland. 

The  extirpation  of  the  two  suprarenal  capsules  has  been  made  by  Brown- 
Sequard,2  whom  we  have  to  thank  for  many  investigations  in  this  line  of 
research.  He  found  that  their  removal  caused  death  in  a  short  time.  He 
was  able  to  keep  the  animal  alive,  if  a  part  of  one  of  the  capsules  was  allowed 
to  remain.  The  animal  soon  lost  in  weight  and  showed  a  peculiar  behavior. 
It  was  lazy,  and  if  compelled  to  work  soon  became  very  tired.  One 
of  the  pronounced  effects  was  that  the  blood-pressure  fell  immediately 
after  the  operation.  The  fact  that  the  blood  from  such  animals  had  toxic 
properties,  and  when  injected  into  normal  animals  led  to  similar  symp- 
toms, as  in  the  animal  which  had  undergone  the  operation,  gave  rise 
to  the  assumption  that  the  suprarenal  capsules  served  to  destroy  those 
products  formed  by  metabolism  which  are  injurious.  According  to  this 
view,  the  suprarenal  bodies  serve  merely  as  a  means  of  protection.  There 
is  no  conclusive  proof  of  the  correctness  of  this  assumption.  It  is  clear 
that  the  extirpation  of  these  capsules  may  influence  metabolism  in  such 
a  way  that  when  they  are  removed  from  the  body  some  product  circu- 
lates through  the  body  in  an  abnormal  condition,  and  the  toxic  properties 


1  Foges:  Pfliiger's  Arch.  93,  39  (1903). 

2  Compt.  rend.  43,  422  and  542  (1856) ;  ibid.  45,  1036  (1857). 


RELATIONS   OF  THE   ORGANS   TO  ONE   ANOTHER.     601 

of  the  blood  may  be  due  to  this  fact.  It  is  perfectly  unjustifiable  to 
assume  that  substances  appearing  after  the  extirpation  of  an  organ  are 
in  any  way  to  be  regarded  as  normal  products,  and  that  they  are  simply 
not  removed  because  a  certain  organ  is  missing.  It  is  possible  that  such 
an  assumption  does  represent  the  truth,  but  at  the  same  time  it  is  equally 
probable  that  the  injurious  substances  are  formed  because  the  organ  is 
not  present. 

It  has  only  quite  recently  been  shown  that  the  suprarenal  bodies  do 
actually  give  up  to  the  blood  a  specific  substance.  It  has  been  found 
possible  to  isolate  this  substance  and  crystallize  it.  Oliver  and  Schafer1  had 
observed  that  extracts  of  the  suprarenal  capsules  when  injected  into  the 
veins  gave  rise  to  a  marked  increase  in  the  blood-pressure.  These  investi- 
gators traced  this  increase  of  pressure  to  a  strong  contraction  of  the  blood- 
vessels, and  also  to  the  fact  that  the  suprarenal  extract  had  an  action  upon 
the  heart.  Long  before  this,  in  1856,  Vulpian  2  had  his  hands  upon  this 
active  principle.  He  found  that  the  suprarenal  bodies  contained  a  sub- 
stance, the  so-called  chromogen  substance,  which  turned  dark  on  exposure 
to  the  air,  and  gave  with  ferric  chloride  solution  a  green  coloration.  It 
is  only  recently,  however,  that  it  was  found  possible  to  prepare  this  active 
principle  in  a  pure  state.  Its  discovery  was  not  alone  of  physiological 
interest,  but  at  the  same  time  a  remedy  was  added  to  our  store,  which 
met  with  a  favorable  reception  such  as  is  but  seldom  accorded  to  a  new 
preparation.  It  is  used  especially  to  prevent  bleeding  in  surgical  opera- 
tions. The  composition  of  the  substance  corresponds  to  the  formula 
C9H13N03.3 

According  to  E.  Friedmann  4  it  has  the  following  structure: 

H 
C 

HOC        C  -  CH(OH)  .  CH2  .  NH  .  CH3 

I          II 
HOC        CH 

^    / 

C 
H 

1  J.  Physiol.  16  (1894);  17,  IX  (1894-95). 

2  Compt.  rend.  43,  663  (1856). 

3  Cf.  von  Fiirth:  Z.  physiol.  Chem.  24,  142  (1898);  26, 15  (1898-99);  29,  105  (1900); 
Hofmeister's  Beitrage,  1,  243  (1901);   Sitzber.  kais.  Akad.  Wissensch.  in  Wien.  Math.- 
natur.  Klasse  112,  Abt.  3  (March  5,  1903).     Abel  and  Crawford:  Johns  Hopkins  Hosp. 
Bull.,  No.  76  (1897).     J.  Abel:   ibid.  No.  90-91  (1898);  Am.  J.  Physiol.  March,  1899; 
Z.  physiol.  Chem.  28,  318  (1899);   Johns  Hopkins,  Bull.,  No.  120  (March,  1901);   No. 
128  (Nov.   1901);    No.   130,   131   (Feb.-March,   1902);    Am.  J.  Physiol.  8,  2  (1903); 
Ber.  36,  1839  (1903).    J.  Takamine:  Am.  J.  Pharm.  73  (1901).    H.  Pauly:    Ber.  36, 
2944  (1903).     Abderhalden  and  Bergell:   ibid.  37,  2022  (1904). 

4  Hofmeister's  Beitrage,  8,  94  and  118  (1906). 


602  LECTURE   XXVI. 

Several  names  have  been  assigned  to  the  substance,  but  that  of  adrenalin 
seems  most  suitable.  By  fusing  it  with  caustic  potash,  protocatechuic 
acid  is  obtained.  By  the  action  of  mineral  acids,  methylamine  is  split  off. 
Among  the  other  cleavage-products,  pyrrole,  methyl  indole,  and  pyridine 
have  also  been  observed.  We  are  not  much  better  informed  concerning 
the  formation  of  adrenalin  than  we  are  concerning  its  constitution.  We 
do  not  know  its  source,  although  it  is  possibly  derived  from  the  proteins 
and  their  disintegration  products. 

As  little  as  0.0013  milligram  of  adrenalin  will  cause  a  noticeable  increase 
of  the  blood-pressure  when  introduced  into  the  circulation.  At  the  same 
time  it  strengthens  the  heart-action.  The  peripheral  vessels  become 
strongly  contracted.  Mucous  membranes  appear  nearly  white  on  account 
of  the  almost  complete  absence  of  blood  in  them.  Adrenalin  also  acts 
upon  the  dilatator  pupillce,  retractor  membrana  nictitans,  and  the  smooth 
muscles  of  the  eyelids.1  These  muscles  contract  when  under  its  influence. 
The  movements  of  the  stomach,  the  gall-bladder,  and  the  urinary-bladder 
on  the  other  hand  are  possibly  restricted.2 

How  shall  we  imagine  that  the  suprarenal  capsules  act  in  the  economy 
of  the  animal  organism?  Evidently  they  are  constantly  giving  up  adrena- 
lin to  the  blood  either  as  adrenalin  or  perhaps  in  some  kind  of  combination 
such  that  all  the  organs  innervated  by  the  Sympatheticus  are  affected 
by  it.  It  is  certainly  interesting  in  this  connection  that  neither  their 
development  nor  anatomical  structure  indicates  that  these  capsules  are 
homogeneous  organs.  There  are  two  distinct  parts  of  the  capsule,  one  of 
which  is  derived  from  a  collection  of  mesenchymatous  cells  in  the  vicinity 
of  the  inferior  vena  cava  and  gives  rise  to  the  cortex,  while  the  other  origi- 
nates from  the  abdominal  sympathetic  ganglia  and  forms  the  medulla. 
There  is  considerable  evidence  which  points  to  the  fact  that  adrenalin  is 
produced  by  the  cells  of  the  medulla.  We  have,  therefore,  in  a  wide 
sense  an  innervation  process  before  us  which  is  brought  about  by  the  aid 
of  a  chemical  product.  It  is  certainly  not  without  significance  that  the 
Sympatheticus,  or  rather  an  organ  derived  from  it,  produces  a  substance 
which  acts  upon  it  and  the  organs  innervated  by  it.  At  present  there  is 
nothing  definitely  known  as  to  whether  the  sympathetic  nerve  influences 
this  internal  secretion,  but  there  is  some  evidence  which  indicates  that 
such  is  the  case. 

We  have  already  mentioned  that  there  has  been  ascribed  to  the  supra- 
renal bodies  an  action  in  combating  poisons.  Although  we  do  not  doubt 
in  any  way  that  these  organs  may  have  other  functions  than  that  of  pro- 
ducing an  internal  secretion,  still  there  is  nothing  positively  known  as  to 


1  M.  Lewandowski:  Zentr.  Physiol.  12,  599  (1898). 

2  Boruttau:   Pfliiger's  Arch.  78,  97  (1899). 


RELATIONS   OF  THE   ORGANS   TO   ONE   ANOTHER.     603 

the  nature  of  such  functions.  It  may  be  mentioned  that  large  doses  of 
adrenalin  produce  glucosuria.  It  results  from  a  glucohemia  the  cause  of 
which  is  still  obscure. 

We  may  also  mention  that  a  disease  is  known  to  pathology  which  is 
related  to  the  suprarenal  glands.  It  is  named  after  its  discoverer,  being 
known  as  Addison's  disease.1  The  most  important  symptoms  are  as 
follows:  There  is  an  external  pigmentation  upon  the  skin.  The  mucous 
membrane  also  shows  dark-colored  patches,  and  there  is  a  marked  anaemia 
and  extreme  asthenia.  Great  muscular  weakness  characterizes  the  whole 
course  of  the  disease.  It  is  shown  not  alone  in  the  inability  of  the  muscles 
to  perform  work,  but  by  the  fact  that  they  quickly  become  tired.  We 
remember  that  these  same  symptoms  were  observed  in  animals  with 
ablated  suprarenals.  All  of  the  other  symptoms  in  Addison's  disease  are 
of  a  secondary  nature,  and  are  due  especially  to  the  marked  anaemia.  A 
post-mortem  examination  shows  that  the  suprarenal  bodies  are  more  or 
less  destroyed  by  tumors,  and  usually  as  a  result  of  tuberculosis.  We  must 
not  fail  to  mention,  however,  that  cases  of  the  disease  are  known,  in  which 
the  suprarenal  capsules  remain  anatomically  "  normal."  We  have  repeat- 
edly laid  stress  upon  the  fact  that  the  anatomical  appearance  of  an  organ 
does  not  always  indicate  whether  the  organ  is  exerting  its  normal  function 
or  not.  Only  when  it  has  been  found  possible  to  show  that  the  complex  of 
symptoms  of  Morbus  Addisonii  can  exist  without  there  being  any  change 
in  the  functions  of  the  suprarenal  bodies,  shall  we  be  justified  in  questioning 
the  connection  of  the  above-mentioned  disease  with  the  suprarenal  bodies. 
There  has  been  a  great  deal  of  discussion  as  to  the  origin  and  significance 
of  the  bronze-colored  patches  upon  the  skin.  The  nature  of  the  deposited 
pigment  is  not  known.  It  is  possible  that  it  has  some  relation  to  the 
formation  of  the  secretion  by  the  suprarenals,  and  that  it  may  perhaps 
represent  an  antecedent  of  adrenalin,  which  is  deposited  because  in  that 
condition  it  is  of  no  benefit  to  the  system.  On  the  other  hand,  we 
must  guard  against  putting  the  secretion  of  adrenalin  too  much  in  the 
foreground,  simply  because  it  is  the  only  secretion  of  the  glands  of  which 
we  now  know.  It  is  pretty  certain  that  the  suprarenals  have  other  func- 
tions, and  it  is  perfectly  possible  that  when  these  functions  disappear  the 
results  are  more  serious  than  when  the  known  secretion  alone  is  wanting. 
Our  knowledge  is  still  far  too  limited  for  us  to  attempt  to  discuss  the 
relations  of  the  individual  symptoms  of  the  disease  to  the  suprarenal 
bodies.  Above  all,  the  cause  of  the  extreme  lassitude  of  the  patients 
remains  unexplained. 

Another  very  important  organ  is  the  thyroid  gland.  Its  functions  were 
investigated  constantly  for  years,  without  its  being  possible  to  ascertain 


1  T.  Addison  :     On  the  Constitutional  and  Local  Effects  of  Disease  of  the  Suprarenal 
Capsules.     London,  1855. 


604  LECTURE   XXVI. 

what  they  were,  and  the  attempts  to  isolate  the  active  principle  contained 
in  the  organ  were  fruitless.  Here  again  we  have  observations  from  the 
fields  of  physiology  and  of  pathology  at  our  disposal.  We  shall  begin 
with  the  latter.  The  thyroid  gland  frequently  shows  signs  of  degenera- 
tion, and  this  apparently  takes  place  in  a  definite  manner,  and  is  most 
common  in  definite  localities.  These  are  the  so-called  goitre  regions;  i.e., 
regions  in  which  there  is  frequently  a  cystic  deformity  producing  an 
enlargement  of  the  thyroid.  The  nature  of  the  soil,  and  especially  of 
the  drinking-water,  has  been  assumed  to  be  the  cause  of  the  disease,  with- 
out any  one  being  able  to  show  this  conclusively.  Frequently  other 
severe  derangements  accompany  the  deformity  of  the  gland.  The  mental 
development  of  those  afflicted  with  the  disease  is  slight.  Such  individuals 
are  known  as  cretins.  There  is  a  derangement  of  their  entire  metabolism. 
Scholz  1  in  particular,  who  studied  a  case  very  carefully,  showed  this  to  be 
true  of  the  metabolism  of  albumin  and  salts.  We  are  justified  in  assum- 
ing, as  we  shall  soon  see,  that  the  thyroid  gland  has  not  ceased  entirely 
to  exercise  its  function.  It  seems  highly  probable  that  we  shall  realize 
more  closely  the  part  taken  by  the  thyroid  gland  in  metabolism,  if  we 
assume  that  it  has  different  functions.  We  can  well  imagine  that  in 
cretinism  it  is  possible  for  the  thyroid  to  retain  certain  of  its  functions 
while  others  are  missing. 

An  idea  as  to  the  complete  function  of  the  thyroid  gland  is  probably  to 
be  obtained  best  by  studying  an  organism  after  the  complete  ablation  of 
the  organ.  The  operation  has  been  performed  upon  man  as  well  as  upon 
animals;  in  the  first  case,  however,  only  at  a  time  when  we  were  not  yet 
ready  to  study  the  whole  consequence  of  the  interference.  To-day  it  is 
well  recognized  that  the  organ  is  quite  essential,  so  that  care  is  taken  not 
to  remove  it  completely.  We  may  say,  in  this  connection,  that  a  small 
portion  of  the  gland  left  in  the  body  is  usually  sufficient  for  the  retaining 
of  all  the  functions  of  the  organ.  This  fact  should  be  well  borne  in  mind, 
for  it  gives  us  the  key  to  the  cause  of  many  contradictions  which  are  to  be 
found  in  the  literature.  The  thyroid  gland  itself  is  an  unpaired  organ. 
Anatomically  it  is  usually  homogeneous.  Embryologically  it  arises  from 
clefts  or  bronchial  arches  at  the  lower  part  of  the  epithelium  of  the 
pharynx.  Often,  however,  we  find  near  the  main  gland  isolated  fragments 
of  similar  material  in  the  surrounding  tissue,  and  frequently  these  are 
quite  far  from  the  main  gland.  In  the  ablation  of  the  latter,  they  may 
assume  its  functions,  so  that  the  typical  results  of  the  operation  are  not 
felt.  Entirely  distinct  from  the  thyroid  gland  are  the  parathyroid  glands. 
They  are  paired,  and  originate  from  the  last  pair  of  clefts  of  the  pharyn- 
geal  epithelium.  We  shall  find,  later  on,  that  their  position  relatively  to 


1  Z.  exper.  Path.  u.  Therap.  2,  271  (1905). 


RELATIONS   OF   THE   ORGANS  TO   ONE   ANOTHER.     605 

the  main  thyroid  gland  varies  in  different  animals.  Their  significance  has 
only  very  recently  been  realized. 

If  the  thyroid  gland  is  completely  removed  from  the  body,  or  its  functions 
fail  for  any  reason,  peculiar  changes  result.  They  were  first  observed 
and  described  by  William  Gull l  in  1874.  The  most  prominent  symptom 
is  a  thickening  of  the  skin.  It  appears,  on  account  of  the  increased 
amount  of  mucin  in  the  subcutaneous  connective  tissue,  as  an  edematous 
swelling.  For  this  reason  Ord  2  gave  to  the  disease  the  name,  myxedema. 
Subsequently  the  swelling  goes  down,  and  the  skin  then  appears  more 
atrophied.  The  secretion  of  the  glands  in  the  skin  ceases,  and  the  latter 
becomes  hard  and  dry.  Metabolism  is  disturbed,  and  so  is  the  temperature 
of  the  body,  and  the  mechanism  for  regulating  the  body-temperature. 
The  most  striking  disturbances  are  those  of  the  muscular  and  nervous 
systems.  They  are  of  various  kinds.  Sometimes  there  is  evidence  of 
increased  sensitiveness,  while  in  other  cases  the  change  is  entirely  in  the 
other  direction.  The  various  effects,  which  also  change  as  the  disease 
progresses,  may  be  due  to  the  more  or  less  complete  failure  of  the  functions 
of  the  gland. 

J.  L.  Reverdin,  A.  Reverdin,3  and  afterwards  Theodor  Kocher,4  had 
considerable  opportunity  to  study  the  effects  of  the  total  extirpation  of 
the  organ  in  man.  They  found  on  the  whole  the  same  symptoms  as  in 
myxedema.  Kocher  embraced  the  whole  complex  of  symptoms  under 
the  name  of  Cachexia  strumipriva.  It  is  not  a  simple  disease.  In  general 
the  same  characteristics  are  manifest.  In  individuals  which  have  not 
attained  full  growth,  extirpation  of  the  organ  causes  a  tardy  develop- 
ment of  the  length  of  the  bones.  We  find  here  reminiscences  of  cretinism. 
It  is  specially  noteworthy  that  individuals  quickly  lose  the  ability  to 
reason.  Finally  idiocy  may  result. 

After  J.  L.  Reverdin  had  published  his  first  results,  physiologists  recalled 
the  experiments  of  Moritz  Schiff  5  made  in  1859,  with  regard  to  the  total 
extirpation  of  the  thyroid  gland  in  animals.  Schiff  showed  that  dogs 
did  not  long  survive  the  operation.  They  died  within  from  4  to  27 
days.  There  is  to-day  no  doubt  prevailing  as  to  the  correctness  of 
his  observations,  although  the  cause  of  the  different  behavior  of  vari- 
ous classes  of  animals  has  been  much  disputed.  With  dogs  and  cats 
death  results  quickly  and  usually  in  a  convulsive  attack  (tetany).  Muscu- 


1  Trans.  Clin.  Soc.  London,  1874. 

2  On  Myxoedema.     Medic-chirurgical  Transactions,  Second  Series,  43,  57  (1878). 

3  J.  L.  Reverdin:  Revue  medicale  de  la  Suisse  romande,  2ieme  anne"e,  539  (1882), 
and  3ieme  ann6e,  p.  47  (1883).      J.  L.  Reverdin  and  Aug.  Reverdin:  ibid.  3ieme  ann6e, 
No.  4,  pp.  169,  233,  309,  and  686  (1883). 

4  Arch.  Clin.  Chir.  29,  254  (1883). 

6  Arch,  exper.  Path.  Pharm.  18,  25  (1884). 


606  LECTURE   XXVI. 

lar  tremors  first  appear,  which  gradually  pass  into  clonic  spasms,  finally 
resulting  in  tetanus.  The  muscular  tremors  are  not  of  peripheral  origin, 
for  they  disappear  on  section  of  the  peripheral  nerves.  Apparently  the 
thyroid  gland  in  some  way  influences  the  higher  nerve  centers.  It  is 
evident,  however,  that  the  lower  nerve  centers  are  also  affected,  for  the 
tremors  continue  after  the  removal  of  the  cortical  brain  area  concerned 
with  the  movement  of  the  part.  In  the  case  of  herbivora,  the  ruminants, 
rodents,  and  monkeys,  tetany  does  not  as  a  rule  take  place.  Instead, 
cachexia  becomes  a  prominent  symptom.  This  contrast  of  symptoms  in 
the  two  classes  of  animals,  which  was  made  more  puzzling  by  reason  of 
the  fact  that  with  the  herbivora  sometimes  tetany  appears  and  sometimes 
does  not,  has  recently  been  offered  an  explanation.  We  have  already 
mentioned  the  presence  of  the  parathyroid  glands.  In  the  carnivora 
these  are  included  in  the  main  gland,  whereas  in  the  herbivora  they  are 
separated  from  it.  For  this  reason  the  parathyroid  glands  are  always 
removed  from  carnivora  in  cases  of  complete  ablation  of  the  thyroid 
gland,  whereas  in  the  herbivora  this  is  rarely  the  case.  In  fact,  it  has 
usually  been  found  that  tetany  in  herbivora  results  when  these  parathy- 
roid glands  are  removed.1  According  to  this  discovery,  it  would  seem 
that  the  parathyroid  glands  and.  the  main  gland  have  different  functions. 
It  seems  highly  desirable  that  clinical  observations  should  receive  renewed 
study  with  regard  to  this  point. 

It  might  be  objected  with  regard  to  the  experiments  in  the  ablation  of 
the  thyroid  gland  that  the  operation  itself  may  be  such  a  severe  one  that 
other  injuries  can  produce  some,  at  least,  of  the  observed  symptom  com- 
plex. This  objection,  however,  has  been  successfully  refuted  by  means 
of  a  great  many  experiments.  In  the  first  place,  the  entire  operation 
may  be  performed,  except  that  the  gland  is  allowed  to  remain  in  place, 
without  any  of  the  symptoms  occurring.  Again,  if  a  part  of  the  organ 
is  allowed  to  remain  in  the  body,  the  symptoms  do  not  appear;  and, 
finally,  if  a  part  of  the  organ  is  transplanted  to  another  part  of  the  body, 
the  whole  operation  may  then  be  carried  out  without  fatal  results.  Such 
experiments  were  performed  by  Schiff  and  have  been  repeated  by  Eisels- 
berg  2  in  a  particularly  convincing  manner.  The  latter  extirpated  half  of 
the  thyroid  gland  from  a  cat  and  grafted  it  in  the  wound  between  the 
abdominal  fascia  and  the  peritoneum.  Then,  after  this  had  been  accom- 
plished, the  other  half  of  the  organ  was  carefully  removed.  The  animal 
was  kept  under  observation  for  two  months  without  its  showing  any 


1  Cf.  E.  Gley:  Compt.  rend.  soc.  biol.  Paris  (9),  841  (1891).     Vassale  et  General!: 
Arch.  ital.  biol.  25,  459  (1896);  26,  61  (1896).     Biedl:  Innere  Sekretion,  Berlin,  1904. 
MacCallum:   Zentr.  allg.  Path.  u.  path.  Anat.  16,  No.  10  (1905). 

2  A.  Freiherr  von  Eiselsberg,  Wiener  klin.  Wochschr.  5,  81  (1892). 


RELATIONS   OF   THE    ORGANS   TO   ONE   ANOTHER.     607 

indication  of  a  cessation  in  the  functions  of  the  gland.  Then  the  grafted 
piece  of  thyroid,  which  showed  normal  gland-tissue,  was  removed.  The 
very  next  day  tetany  resulted,  and  the  animal  died  at  the  end  of  the 
third  day. 

It  is  also  important  to  learn  that  it  is  possible  to  prevent  the  severe 
disturbances  resulting  from  the  ablation  of  the  organ,  by  injecting  thyroid 
juice  into  a  vein  or  under  the  skin,  and  even  by  feeding  it,  or  raw  thyroid, 
directly.  In  fact,  it  is  even  possible  to  improve  the  condition  of  the 
patient  who  has  already  begun  to  feel  the  effects  of  the  operation.  It  is 
seldom  that  a  therapeutic  conception  can  be  demonstrated  so  clearly 
and  so  strikingly  as  in  the  treatment  of  Cachexia  strumipriva,  and  true 
myxedema,  by  means  of  thyroid  preparations.  The  swelling  of  the  skin 
goes  down,  and  the  mental  faculties  are  noticeably  improved.  In  a  short 
time  the  habits  of  the  patient  are  so  changed  that  almost  nothing  remains 
to  indicate  the  original  severe  disease. 

As  soon  as  the  action  of  the  thyroid  gland  became  understood,  attempts 
were  made  to  isolate  the  active  principle;  but,  up  to  the  present  time, 
such  attempts  have  been  in  vain.  It  was  indeed  believed,  for  a 
short  time,  that  the  goal  had  been  reached  when  E.  Baumann,1  after 
making  the  important  discovery  that  the  thyroid  glands  of  many  animals 
contain  iodine,  succeeded  in  isolating  an  amorphous  substance,  the  so-called 
iodo-thyrin  (or  thyro-iodine).  To-day  the  relation  of  this  substance  to 
the  organ  is  still  very  vague.  It  contains  phosphorus  and  about  nine 
per  cent  of  iodine.  Now  there  is  no  doubt  that  iodine  itself  has  an 
effect  upon  the  thyroid  gland,  and,  in  fact,  even  when  it  is  administered, 
not  in  the  form  of  an  organic  compound,  but  as  free  iodine.  Often  an 
existing  swelling  of  the  gland  subsides.  It  is  still  an  open  question  how 
the  iodine  acts,  but  we  are  aware  that  it  has  a  favorable  effect  upon 
various  other  nitration  processes  and  facilitates,  for  example,  the  absorp- 
tion of  exudates.  To  be  sure,  iodine  apparently  has  a  quite  specific 
action  upon  the  thyroid  gland.  The  fact,  however,  that  iodine  may  be 
absent  from  a  normal  organ,  makes  it  seem  doubtful  whether  one  is  on 
the  right  road  in  assuming  that  iodo-thyrin  is  the  active  principle  of  the 
gland.  It  seems  that  possibly  too  much  attention  has  been  paid  to  the 
iodine  constituent.  It  also  must  not  be  forgotten  that  we  have  no 
guarantee  for  assuming  that  iodo-thyrin  is  itself  a  simple  substance.  It 
is  more  probably  a  mixture  of  several  different  products.  At  all  events, 
it  is  certain  that  the  gland  itself  is  more  active  than  iodo-thyrin,  and  so 
are  all  the  preparations  which  contain  as  many  glandular  constituents 
as  possible. 


1  E.  Baumann:  Z.  physiol.  Chem.  21,  319  (1895-96).  Baumann  and  Roos:  ibid. 
21,  481  (1895-96).  E.  Baumann:  ibid.  22,  1  (1896-97).  E.  Roos:  ibid.  22,  16 
(1896-97);  25,  1  and  242  (1898).  A.  Oswald:  ibid.  23,  265  (1897). 


608  LECTURE   XXVI. 

We  are  still  very  far  from  being  able  to  trace  the  functions  of  the  thyroid 
gland  to  definite  chemical  processes.  We  merely  understand  the  effect 
of  its  extirpation,  and  know,  furthermore,  that  it  stands  in  some  relation 
to  the  sexual  organs.  It  has  been  observed  that  at  the  time  of  menstru- 
ation, during  pregnancy  and  lactation,  there  is  frequently  a  swelling  of  the 
gland.  To  be  sure,  processes  may  be  involved  here  which  have  nothing 
whatever  to  do  with  the  cell-functions  of  this  organ,  but  may  be  caused  by 
vascular  influences.  Again,  the  observation  that  in  cretins  the  sexual 
organs  frequently  remain  undeveloped,  does  not  necessarily  prove  that 
there  is  a  direct  relation  between  the  thyroid  gland  and  the  sexual  organs. 
It  is  certainly  not  remarkable  that  in  the  general  metabolic  disturbance 
even  the  sexual  organs,  which  as  a  rule  require  a  constant  supply  of  mate- 
rial as  they  in  a  certain  sense  are  constantly  growing,  will  likewise  suffer 
to  a  marked  extent.  At  present  it  is  impossible  for  us  to  distinguish  here 
between  primary  and  secondary  phenomena. 

That  the  thyroid  gland  yields  a  secretion,  cannot  be  doubted.  This  is 
evident  alone  from  its  histological  structure.  Apparently  the  follicular 
cells  produce  the  specific  secretion.  It  then  passes  through  openings  in 
the  follicular  walls  into  the  lymph,  and  is  then  given  up  to  the  blood.1 
We  will  merely  mention  the  fact  that  Oswald  isolated  from  the  secretion 
of  the  follicles  (the  so-called  colloid)  two  proteins,  the  so-called  thyreo- 
globulin  and  a  nucleoproteid.  The  former  alone  contains  iodine.2 

Our  limited  knowledge  concerning  the  chemical  processes  taking  place 
in  the  thyroid  gland  makes  it  impossible  for  us  to  in  any  way  give  a  precise 
description  of  the  nature  of  the  function  of  this  very  important  organ. 
Everything  is  hypothetical.  According  to  the  autotoxication  theory,  it  is 
the  purpose  of  the  thyroid  gland  to  remove,  or  render  innocuous,  one  or 
more  toxic  substances  which  would  otherwise  accumulate  in  the  blood. 
There  is  no  ground  for  this  assumption,  but  it  is  perfectly  conceivable  that 
the  organ  can  secrete  substances  which  are  capable  of  combining  with  other 
products.  It  is  possible  that  the  iodine  content  of  the  thyroid  gland 
serves  such  a  purpose  and  perhaps  indicates  the  presence  of  easily  replace- 
able substances.  It  is,  however,  also  very  probable  that  the  thyroid 
gland  secretes  substances  that  take  part  in  the  general  metabolism  and 
regulate  chiefly  the  transformations  which  albumin  undergoes.  It  is  not 
at  all  difficult  to  formulate  assumptions  in  this  direction,  particularly  after 
repeatedly  meeting  with  facts  which  show  that  in  order  to  accomplish 
fermentation,  a  number  of  different  body-cells  act  together.  One  cell 
yields  an  activator  of  the  ferment,  and  another  the  ferment  itself.  It  is 
perfectly  conceivable  that  the  thyroid  gland  is  active  in  this  sense,  and 


1  Hiirthle:  Pfliiger's  Arch.  56,  1  (1894). 

2  Z.  physiol.  Chem.  27,  14  (1899).     Hofmeister's  Beitrage,  2,  545  (1902).     Z.  physiol. 
Chem.  32,  123  (1901). 


RELATIONS   OF   THE   ORGANS  TO   ONE   ANOTHER.     609 

that  it  perhaps  secretes  a  kinase  which  is  for  the  good  of  all  the  body-cells. 
But  all  this  is  speculation,  and  drawing  inferences  from  analogy  without 
any  real  foundation.  We  must  not  fail  to  repeat  here  that  the  functions 
of  the  thyroid  gland  are  not  all  of  the  same  kind.  It  may  also  serve  to 
start  certain  processes. 

We  must  now  consider  an  action  of  the  thyroid  gland  bearing  a  certain 
analogy  to  a  disease,  which,  to  a  certain  extent,  is  the  exact  opposite  to 
Cachexia  strumipriva.  We  refer  to  Basedow's  disease.  If  too  much  thyroid 
gland  is  administered,  there  results  an  abnormal  destruction  of  albumin. 
The  elimination  of  nitrogen  in  the  urine  increases  considerably.  Further- 
more, there  is  an  apparent  intoxication,  with  increased  pulse  frequency, 
polyphagia,  polydipsia  and  polyuria.  In  Basedow's  disease  similar  symp- 
toms appear,  especially  the  increased  destruction  of  albumin.  This 
disease  has  been  traced  to  an  increased  activity  of  the  follicular  epi- 
thelium of  the  thyroid  gland.  Quite  recently  the  parathyroids  have 
also  been  held  to  be  partly  responsible.  There  are  many  observations 
which  indicate  such  a  connection,1  but  it  has  been  by  no  means  positively 
established. 

The  hypophysis,  or  pituitary  gland,  is  always  mentioned  in  connection 
with  the  thyroid.  It  is  a  compound  organ.  The  anterior  lobe  is  glandular 
and  resembles  somewhat  the  thyroid  body,  while  the  posterior  portion 
consists  chiefly  of  fibrous  tissue.  Between  the  two  lobes  there  is  a 
hollow  space  rich  in  vessels  and  lined  with  ciliated  epithelium.  The 
function  of  this  body,  which  was  once  considered  to  be  a  rudimentary 
organ,  is  still  unknown  to  us.  In  cases  of  myxedema  there  has  frequently 
been  hypertrophy  of  the  pituitary  gland,  while  extirpation  of  the  thyroid 
tends  to  produce  the  same  effect.  In  cases  of  hypertrophy  and  enlarge- 
ment of  the  pituitary  body  peculiar  symptoms  often  develop,  especially 
an  abnormal  growth  of  the  bones  at  the  end  of  the  extremities,  the 
phalanges  of  the  fingers  and  toes,  although  the  softer  parts,  as  the  hands, 
feet,  lips,  tongue,  and  nose,  are  also  affected.  It  is  quite  natural  to 
compare  this  increased  development  with  the  retarded  growth  which  takes 
place  after  the  cessation  of  the  functions  of  the  thyroid  gland.  Yet  we  do 
not  positively  know  that  there  is  a  direct  connection  with  this  disease, 
known  as  acromegaly,  and  the  changes  in  the  functions  of  the  pituitary 
gland.  Experiments  carried  out  to  determine  the  functions  of  this  organ, 
by  studying  the  effects  of  its  removal,  have  not  led  to  conclusive  results. 
Pituitary  extracts  have  also  been  administered  and  found  to  cause  an 
increased  elimination  of  nitrogen.2  We  are  not  justified  in  drawing  any 
conclusion  from  this  observation  as  to  any  existing  analogy  with  the  thyroid 

1  L.  Humphry:  The  Parathyroid  Glands  in  Grave's  Disease.     Lancet,  11  (1905). 

2  T.  Malcolm:  J.  Physiol.  30, 270  (1904).  Thompson  and  Johnston:  ibid,  33, 189  (1905). 


610  LECTURE   XXVI. 

gland.  The  increased  elimination  of  nitrogen  may  be  caused  in  many 
ways.  We  shall  not  be  in  a  position  to  decide  such  questions  until  it  has 
been  found  possible  to  isolate  the  active  principles  from  each  of  the 
organs. 

We  now  turn  to  two  other  organs  for  which  a  specific  function  has 
been  suggested.  These  are  the  spleen  and  the  thymus.  The  latter  is  a 
temporary  organ,  being  a  true  organ  in  the  case  of  man  only  during  infancy. 
After  the  child  is  two  or  three  years  old  it  no  longer  develops,  but  slowly 
and  steadily  atrophies,  and  has  nearly  disappeared  by  the  fifteenth  year, 
though  traces  of  it  remain  in  old  age.  It  can  be  completely  extirpated 
without  causing  death.  It  is,  therefore,  not  to  be  classed  with  the 
organs  that  are  essential  to  life.  Its  ablation  is  said  to  result  in  disturb- 
ances in  the  general  health  and  in  metabolism;  but  from  the  data  at  hand, 
it  is  not  possible  for  us  to  obtain  a  very  clear  conception  of  the  func- 
tions of  the  thymus  gland.  Similarly,  its  anatomical  construction  is  not 
instructive.1 

We  are  almost  as  much  at  sea  concerning  the  significance  of  the  spleen 
in  the  economy  of  the  animal  organism.  All  sorts  of  different  functions 
have  been  ascribed  to  it.  It  has  been  said  to  influence  the  activity  of  the 
pancreas,  an  assumption  which  is  not  well  founded.  It  has  also  been 
assumed  that  it  plays  a  part  in  the  production  and  destruction  of  the 
red  corpuscles,  and  furthermore  that  it  is  able  to  remove  and  store  up  waste 
material  from  the  blood  and  lymph.  This  much  is  certain,  however:  the 
spleen  can  be  extirpated  completely  without  any  severe  consequences. 
It  would  be  of  course  unjustifiable  to  conclude  from  this  that  the  spleen  is 
an  organ  of  subordinate  importance.  Everything  depends  upon  the  con- 
ditions under  which  the  functions  of  an  organ  are  tested.  It  is  perfectly 
possible  that  under  certain  conditions  the  absence  of  the  spleen  might 
make  itself  felt.  It  may  be  mentioned,  in  this  connection,  that  great 
importance  has  been  ascribed  to  the  spleen  in  combating  disease  germs. 
In  the  case  of  infections,  the  spleen  sends  out  a  great  number  of  leucocytes. 
On  the  other  hand,  there  are  certain  indications  of  the  fact  that  the  spleen 
on  account  of  its  anatomical  construction  is  called  upon  to  regulate  the 
composition  of  the  blood  so  that  the  cellular  elements  are  kept  in  such  a 
condition  that  they  are  capable  of  exercising  their  functions.  Abnormal 
red  and  white  blood-corpuscles  are  held  back  and  destroyed.  It  is  possible 
that  the  proteolytic  ferment  found  in  spleen,  which  has  an  action  upon 
fibrin,  may  be  active  in  the  breaking  down  of  these  discarded  elements. 
On  the  other  hand,  the  high  iron  content  of  the  spleen,  to  which  our 
attention  has  been  called  repeatedly,  is  not  necessarily  to  be  regarded  as 


1  A.  Friedleben:  Die  Physiologie  der  Thymusdriise  (1858).     Cf.  J.  Aug.  Hammar: 
Pfliiger's  Arch.  110,  337  (1905).     Rudolf  Fischl:  Z.  exper.  Path.  Therap.  1,  388  (1904). 


RELATIONS   OF   THE   ORGANS   TO   ONE   ANOTHER.     611 

absolute  proof  of  the  destruction  of  blood-corpuscles,  for  it  collects  cellular 
decomposition  products  from  other  organs.1  Many  observations  make  it 
seem  probable  that  the  spleen  is  related  in  some  way  to  bone-marrow. 
These  two  substances  can  mutually  aid  one  another. 

In  discussing  the  individual  organs  we  have  lost  sight  of  the  chief  con- 
stituents of  the  entire  organism,  namely  the  muscles,  nerves,  and  the  con- 
nective-tissue group.  Of  the  latter,  especially  bone,  cartilage,  and  true 
connective-tissue,  we  scarcely  assume  any  intimate  relations  with  the  other 
organs,  although  undoubtedly  such  relations  do  exist.  We  are  accustomed  to 
consider  them  merely  as  mechanically-acting  structures,  and  for  this  reason 
but  little  attempt  has  been  made  to  ascertain  what  metabolic  changes  take 
place  within  this  group  of  tissues.  As  a  rule,  investigators  have  been  con- 
tent with  the  study  of  their  chemical  composition  without  attempting  to 
determine  positively  the  extent  to  which  they  take  part  in  the  general  metab- 
olism. Now  this  connective-tissue  group  of  substances  takes  part  quite 
extensively  in  building  up  the  organism,  and  its  functions  are  not  always 
the  same.  This  is  particularly  true  of  connective-tissue  itself,  which, 
according  to  its  histological  construction,  is  related  to  different  groups. 
For  one  thing  it  forms  the  fundamental  support  of  the  body-cells,  which, 
to  a  certain  extent,  are  embedded  in  it.  From  it  the  finer  and  coarser 
network,  in  which  the  lymph  passes  until  it  reaches  the  individual  cells, 
is  formed.  It  is  very  questionable  whether  one  is  justified  in  assuming 
that  the  cells  of  connective-tissue  play  a  passive  role  here,  or  whether  it  is 
not  more  probable  that  they  take  active  participation  in  the  exchange  of 
material  between  the  blood  and  the  lymph,  and  between  the  latter  and 
the  remaining  cells  of  the  body.  Its  adjustment  to  purely  mechanical 
requirements  is  evident  from  the  construction  of  the  individual  tissue; 
for  example,  in  the  segregation  of  elastic  fibers.  A  particularly  differen- 
tiated tissue,  and  one  which  also  belongs  in  this  group,  is  the  fatty  tissue; 
the  importance  of  which  we  have  already  considered. 

As  regards  the  physiological  functions  of  cartilage,  but  little  is  known 
beyond  its  purely  mechanical  properties.  It  is,  however,  not  to  be  doubted 
that  in  it,  as  well  as  in  body  tissue,  there  is  a  constant  occurrence  of  metabo- 
lism. Growth  never  really  ceases,  for  new  cells  are  constantly  being 
formed.  Numerous  observations  prove  to  us  the  dependence  of  the 
metabolism  in  these  organs  upon  the  requirements  placed  upon  them. 
Their  development  ceases  if  for  any  reason  there  are  no  demands  placed 
upon  them,  and  in  such  cases  they  retrogress  even  if  they  are  already 
well  developed.  The  influence  of  the  thyroid  gland  and  other  organs  upon 
growth,  we  have  already  mentioned.  Very  active  metabolic  processes 
unquestionably  take  place  in  cartilage  and  bony  tissue  of  the  growing 


1  Blumenreich  and  Jacoby :  Z.  Hygiene  u.  Infectionskrankh.,  29, 419  (1898).  G.  Jawein: 
Virchow's  Arch.  161,  461  (1900). 


612  LECTURE  XXVI. 

organism.  These  two  tissues  are  intimately  related  to  one  another.  The 
latter  can  act  for  the  former  within  certain  limits.  We  find  here  quite 
extensive  assimilation  processes,  and  at  the  same  time  there  is  a  consid- 
erable wearing  away.  It  is  seldom  that  we  obtain  such  a  deep  insight  into 
the  transformations  of  tissue  as  in  the  case  of  the  new  formation  of  bones. 
To  be  sure  our  knowledge  in  this  direction  is  almost  wholly  morphological. 
There  has  been  but  little  attempt  to  study  this  interesting  process  from  a 
physico-chemical  standpoint.  Even  the  fully-developed  bone  retains, 
especially  as  regards  its  periosteum  and  medulla,  its  embryonal  charac- 
ter. From  these,  new  bone  material  may  be  formed  continually.  Thus 
fractures  are  healed.  Even  under  normal  conditions,  however,  there  is 
continuously  taking  place  a  fusion  and  new  formation  of  bone-substance. 
Occasionally  we  notice  the  appearance  of  peculiar  cells,  the  so-called 
osteoclasts,  which  cause  the  dissolution  of  bony  tissue  at  the  place  where 
they  appear,  while  on  the  other  hand  we  meet  with  the  so-called  perforating 
fibers,  which  also  destroy  bones.  In  pathological  conditions  often  the 
real  disappearance  of  bony  tissue  is  preceded  by  decalcification  as  a  primary 
process.  It  is  interesting  to  trace  the  course  of  all  these  processes,  in 
order  to  ascertain  how,  in  each  separate  case,  the  breaking  down  of  the 
bony  substance  is  effected,  what  agents  are  active  in  the  process,  and  why 
it  is  necessary  that  this  fusing  together  of  bone  and  new  formation  of  such 
tissue  are  constantly  taking  place.  We  must  for  the  present  allow  all  these 
and  similar  questions  to  remain  unanswered.  We  mention  these  relations 
especially  because  we  are  indisputably  justified  in  assuming  that  if  in  a 
tissue  to  which  we  are  accustomed  to  assign  a  very  specific  function,  and 
in  which  we  would  scarcely  expect  a  priori  that  important  metabolic 
processes  would  take  place,  there  is  a  constant  exchange  of  material,  so 
much  more  will  this  be  true  of  all  the  other  tissues  which  are  intimately 
connected  with  active  metabolism  and  upon  which  great  demands  are 
placed,  and  that  they  will  likewise  participate  in  an  active  interchange  of 
cell-material. 

Such  an  assumption  appears  to  be  particularly  justifiable  for  those 
organs  whose  activity,  within  certain  limits,  is  a  continuous  one,  as  is  true 
especially  of  muscular  and  nervous  tissue.  The  latter,  as  we  well  know, 
is  never  at  rest.  Impulses  are  constantly  passing  along  the  nerve  fibers, 
partly  towards  the  central  nervous  system,  and  partly  from  this  to  the 
peripheral  organs.  The  nerves  are  very  intimately  connected  with  the  mus- 
cular tissue.  This  is  evident  even  from  the  entire  development  of  the 
organs,  for  they  early  enter  into  relations  with  one  another.  We  know 
also  that  if  the  innervation  ceases,  retrogression  soon  results,  bringing  on 
atrophy,  and,  in  fact,  this  is  evidently  due  in  part  to  the  inactivity  of  the 
muscles.  Unquestionably,  the  nerves  have  to  some  extent  a  direct  influ- 
ence upon  the  metabolic  processes  in  the  cells  of  the  muscles  themselves, 


RELATIONS    OF   THE   ORGANS   TO   ONE   ANOTHER.     613 

perhaps  in  the  same  way  as  we  found  in  the  formation  and  breaking  down 
of  glycogen  in  the  liver  that  there  was  an  indeterminable  dependence  upon 
the  nervous  system.  Unfortunately,  in  comparison  with  the  countless 
observations  of  pure  physiology  concerning  the  functions  of  the  entire 
nervous  system,  we  have  nothing  from  the  physiological-chemical  stand- 
point. In  fact,  aside  from  the  knowledge  of  a  few  constituents  of  the 
nerve  substance,  we  know  very  little  indeed  concerning  the  metabolism 
taking  place  in  nervous  tissue.  We  will  give  here  the  results  of  the  analysis 
of  the  gray  and  white  substances  of  the  brain.1 


White  Sub- 
stance. 

Gray  Sub- 
stance. 

Water         

695.35 

769  97 

Total  solids  

304.65 

230  .  03 

Protacron 

25  11 

10  80 

Insoluble  albumin  and  connective-tissue       

50  02 

60  79 

Cholesterol,  free         

18.19 

6  30 

Cholesterol   combined 

26  96 

17  51 

Nuclein 

2  94 

1  99 

Neurokeratin                                                                .    . 

18  93 

10  43 

Mineral  matter                                                             .    .    . 

5  23 

5  62 

The  most  striking  value  —  and  this  holds  also  for  the  composition  of  the 
peripheral  nervous  system  —  is  the  high  phosphorus  content  of  nervous 
tissue.  Phosphorus  is  evidently  found  in  very  different  states  of  combina- 
tion, at  one  time  as  nuclein,  again  in  the  form  of  a  substance  which  is 
known  as  protagon,2  and  at  other  times  as  lecithin.  The  latter  occurs 
partly  free,  and  partly  results  from  the  hydrolysis  of  different  products, 
which  have  been  isolated  from  nervous  tissue,  and  have  been  designated 
by  different  names;  thus  in  the  decomposition  of  protagon  among  the  fatty 
acids  and  other  cleavage-products,  the  so-called  cerebrin  has  been  found. 
Of  the  substances  which  have  been  isolated  directly  from  the  brain,  cere- 
bron  has  been  best  studied,  and  its  constitution  established  by  Thierfelder.3 
He  obtained  from  it,  by  hydrolysis,  cerebronic  acid,  sphingosine,  and  galac- 
tose in  the  following  proportions:  cerebronic  acid  48.13  per  cent,  sphin- 
gosine 34.46  per  cent,  galactose  21.77  per  cent. 

Cerebron  has  the  empirical  formula  C48Hg3NO9.  Its  hydrolysis  takes 
place  in  accordance  with  the  equation: 

2TT/^v  PTT/^iPTT      \m      _1_   P   TT      A 

Ll2\J   —   1^25^50^3     '     yl  7*135^^2   ~r     ^6^12^6 

Cerebronic  acid  Sphingosine     Galactose 


Cerebron 


1  F.  Baumstark:  Z.  physiol.  Chem.  9,  145  (1885). 

2  Liebreich:  Annal.  134,  29  (1865). 

3  H.  Thierfelder  and  Emil  Worner:  Z.  physiol.  Chem.  30,  542  (1900).     H.  Thierfelder: 
ibid.  43,  21  (1904),  and  44,  366  (1905). 


614  LECTURE   XXVI. 

A  number  of  other  products  containing  nitrogen,  and,  for  the  most  part, 
phosphorus  as  well,  have  been  isolated  from  the  brain  and  described  under 
different  names.  We  have  no  means  of  deciding  at  present  anything 
regarding  the  nature  of  these  substances  as  to  whether  they  are  simple 
substance  or  mixtures,  and  for  that  reason  will  not  stop  even  to  enumerate 
them.1 

Nervous  tissue  always  contains  cholesterol,  fat,  and  albumin,  and,  in 
fact,  besides  nucleoproteids  and  nucleoalbumins,  globulin  and  albumin. 
The  framework  of  the  tissue  is  formed  by  neurokeratin. 

If  we  compare  the  amounts  of  the  separate  constituents  present  in  100 
grams  of  organic  dry  substance,  we  note  especially  the  high  albumin  con- 
tent of  the  nervous  tissue.  Thus  Chevalier 2  analyzed  the  sciatic  nerve  of 
man  (the  central  organs  have  a  similar  composition),  and  obtained  the 
following  values: 

Protein      36 . 8    per  cent 

Lecithin         .    .    .  • .    .    .    .  33 . 57  per  cent 

Cholesterol 12.22  per  cent 

Cerebrin 1 1 . 30  per  cent 

Neurokeratin    . 3 . 07  per  cent 

Other  organic  substances 4 .       per  cent 

It  is  a  striking  fact  that  gray  brain  matter  contains  much  more 
water  than  white  brain  matter.  The  former  contains  about  77  per 
cent  of  water,  while  the  latter  has  but  70  per  cent.  The  proteins  occur 
chiefly  in  the  gray  matter,  and  amount  to  more  than  one-half  of  its  dry 
substance. 

The  metabolism  of  nervous  tissue  is  almost  entirely  unknown  to  us. 
Whereas  in  the  case  of  muscles  we  are  able  to  detect  purely  external 
changes  (shortening)  during  their  activity,  and  at  the  same  time  can  detect 
the  liberation  of  heat  and  consumption  of  glycogen,  this  is  impossible  in 
the  case  of  nervous  tissue.  In  the  ganglion  cells  alone  have  histological 
pictures  been  described  which  apparently  indicate  changes.  The  nature 
of  these  changes  is,  however,  very  obscure.  We  merely  know  that  nervous 


1  As  regards  the  chemical  constituents  of  brain,  see  J.  L.  W.  Thudichum:  Die  chem- 
ische  Konstitution  des  Gehirns  des  Menschen  und  der  Tiere.   Tubingen,  1901.    Although 
the  investigations  of  Thudichum  are  in  certain  respects  valuable  as  a  basis  for  further 
physiological-chemical  investigation,  still  it  must  be  said  that  none  of  the  many  com- 
pounds described  by  him  was  proved  to  be  a  simple  substance,  nor  was  there  given  any 
proof  concerning  the  chemical  combination  of  the  substance.     There    is    an  almost 
unexplored  field  for  investigation  here.     The  article  by  W.  B.  Halliburton,  Die  Bio- 
chemie   der   peripheren    Nerven.    Ergeb.    Physiol.     (Asher   and   Spiro)  Jg.  4,  p.  23 
(1905),  is  a  valuable  summary  of  the  work  that  has  been  done. 

2  Z.  physiol.  Chem.  10,  97  (1886). 


RELATIONS   OF  THE   ORGANS  TO   ONE   ANOTHER.     615 

tissue  requires  oxygen  for  the  performance  of  its  functions.  This  may  be 
shown  very  prettily  by  means  of  methylene  blue.  As  we  have  seen,  this 
dyestuff  is  deprived  of  oxygen  by  the  tissues,  and  is  thereby  transformed 
into  the  colorless  reduction  product.  If  the  colorless  organ  is  subse- 
quently exposed  to  the  air  for  some  time,  gradually  the  blue  color  of 
methylene  blue  reappears.  In  the  case  of  narcotized  animals  in  which 
the  brain  has  been  made  inactive,  the  brain  substance  remains  blue,  so 
that  evidently  under  these  conditions  the  tissue  does  not  require  oxygen.1 
The  abundance  with  which  the  nerve-centers  are  supplied  with  blood- 
vessels is  an  indication  of  their  high  oxygen  requirement,  and  in  fact 
anaemia  in  these  places  causes  severe  disturbances,  eventually  leading 
to  the  loss  of  function. 

It  might  be  thought  that  some  idea  concerning  the  metabolism  of  nervous 
tissue  might  be  gained  by  seeking  the  end-products.  As  a  matter  of  fact, 
in  the  cerebro-spinal  fluid,  which  in  a  sense  may  be  regarded  as  the  lymph 
of  the  brain,  choline,  a  decomposition  product  of  lecithin,  has  been  found. 
This,  however,  does  not  give  us  much  information.  We  do  not  know 
whether  choline  is  to  be  regarded  as  a  true  metabolic  end-product,  or 
whether  it  is  not  more  probably  produced  by  the  destruction  of  nerve- 
tissue,  and  is  far  from  being  concerned  in  true  metabolism.  Its  detection 
has  usually  been  an  indirect  one  and  not  quantitative.  The  fact  that  an 
increased  amount  of  choline  appears  in  degenerative  processes  indicates 
that  its  formation  corresponds  to  a  destruction  of  nervous  tissue,  so  that 
it  is  not  to  be  considered  as  a  normal  metabolic  product.  We  do  not  wish 
to  place  any  great  weight  upon  this  discovery  of  the  presence  of  choline, 
and  would  rather  take  the  attitude  that  at  present  we  know  nothing  what- 
ever concerning  the  metabolism  in  nervous  tissue.  It  is  also  hardly  to  be 
expected  that  there  will  be  much  progress  in  this  direction  for  a  long  time. 
There  is  no  foundation  for  research.  Even  our  knowledge  of  the  compo- 
sition of  nervous  tissue  is  extremely  faulty.  We  have  only  to  remember 
that,  with  few  exceptions,  we  know  but  little  concerning  the  metabolism 
of  those  cells  of  the  body  which  are  much  more  readily  accessible.  We 
recognize  only  the  total  results  of  metabolism,  and  are,  as  a  rule,  ignorant 
as  regards  the  part  taken  by  the  separate  organs.  We  shall  soon  come 
back  to  the  fact  that  it  is  impossible  to  detect  any  effect  of  intense  mental 
effort  in  metabolism  experiments. 

We  might  perhaps  expect  that  pathology  would  tell  us  something 
concerning  the  metabolism  in  nervous  tissue.  We  know  that  there  exist  the 
so-called  functional  nervous  diseases,  i.e.,  diseases  which,  according  to  the 
general  assumption,  are  not  caused  by  any  anatomical  change  of  the 


1  C.  A.  Herter  and  A.  N.  Richards:  Am.  J.  Physiol.  12,  207  (1904).  Cf.  H.  von 
Bayer:  Z.  allg.  Physiol.  2,  169  (1902).  Frohlich:  ibid.  3,  131  (1903).  Frohlich  and  Tait: 
ibid.  4,  105  (1904).  K.  H.  Baas:  Pfliiger's  Arch.  103,  276  (1904). 


616  LECTURE   XXVI. 

nerve-tissue.  We  observe  all  sorts  of  different  symptoms,  one  of  the  most 
characteristic  being  the  readiness  with  which  the  patient  becomes  fatigued. 
One  gets  the  impression  that  the  nerve-centers  have  but  a  limited  supply 
of  material  at  hand,  or  that  the  combustible  material  is  consumed  rapidly 
without  a  sufficient  regulation.  This,  however,  is  merely  supposition 
and  rests  upon  no  foundation.  In  the  case  of  organic  nervous  diseases, 
the  symptoms  of  which  are  characteristic  according  to  the  nerves  and 
nerve-centers  that  are  affected,  we  find  degeneration.  The  nerve-cells 
and  their  processes  are  destroyed.  We  may  say  that  the  experiment 
has  been  tried,  to  trace  some  relation  between  the  selection  which  certain 
poisons,  e.g.  lead  and  "  syphilis  poison,"  show  toward  the  various  nerve- 
paths  and  the  activity  of  the  metabolic  processes  in  special  regions. 
Those  nerve-paths  and  nerve-centers  are  assumed  to  show  soonest  the 
action  of  the  poison  which  are  most  affected  because  they  have  the  most 
work  to  do.  As  interesting  as  this  hypothesis  of  Edinger  *  may  be,  we 
must  state  that  there  is  absolutely  no  direct  proof  possible  at  present. 
As  long  as  the  physiological  course  of  metabolism  remains  so  obscure,  it 
is  very  difficult  indeed  for  us  to  get  any  clear  idea  from  pathological 
deviations.  We  can,  it  is  true,  imagine  that  cells  which  are  in  constant 
activity  and  are  constantly  being  used  up  and  reconstructed,  will  feel  the 
effects  of  a  given  poison  much  more  rapidly  than  those  which  are  fairly 
stable.  This,  however,  does  not  necessarily  imply  that  there  is  an  exhaus- 
tion in  the  sense  meant  by  Edinger,  but  rather  it  may  be  that  there  is  an 
effect  upon  the  more  active  supply  of  new  material  and  increased  con- 
sumption which  is  necessary  for  the  exercise  of  the  enlarged  function. 
We  know  that  there  are  certain  cells,  e.g.,  of  infusoria,  algae,  etc.,  which 
have  a  particular  power  of  attracting  certain  metals,  even  when  the  latter 
are  present  in  extremely  slight  amount.  They  take  up  these  substances 
even  from  very  dilute  solutions  and  store  them  up.  This  may  very  easily 
cause  the  destruction  of  the  cells,  evidently  in  part,  at  least,  on  account  of 
the  fact  that  these  substances  combine  with  the  constituents  of  the  cell 
in  such  a  way  that  they  prevent  the  further  exercise  of  function  by  the 
cell-protoplasm,  and  to  some  extent  destroy  the  cell.  Similarly  it  is 
conceivable  that  the  interposition  of  the  above-mentioned  poisons  between 
the  separate  constituents  of  the  protoplasm  of  nerve-centers,  disturbs  the 
normal  construction  of  the  cells,  and,  therefore,  its  functions.  There  is 
not  necessarily  any  affinity  existing  between  the  nerve-cell  as  a  whole, 
and  the  poison  in  question,  for  it  is  perfectly  possible  that  in  the  breaking 
down  and  building  up  of  the  constituents  of  protoplasm,  the  products 
'resulting  combine  with  the  poison  and  consequently  place  a  limit  upon 

1  Eine  neue  Theorie  uber  die  Ursachen  einigen  Nervenkrankheiten  insbesondere  der 
Neuritis  und  Tabes,  Leipsic,  1899,  und  Deut.  med.  Wochsch.  Nos.  45,  49,  52  (1904) ; 
Nos.  1  and  4  (1905). 


RELATIONS  OF  THE  ORGANS  TO  ONE  ANOTHER.  617 

the  normal  composition  of  the  cell-protoplasm.  We  mention  these  ideas 
merely  to  show  that  we  are  able  to  get  along  perfectly  well  without  the 
conception  of  exhaustion.  On  the  other  hand,  we  must  remember  that 
the  various  nerve-cells  are  not  necessarily  all  of  uniform  nature.  It  is 
perfectly  possible  that  the  different  groups  of  nerve-cells,  which  serve  for 
the  exercise  of  definite  functions,  are  differently  constituted  chemically 
and  possess  a  perfectly  distinct  metabolism,  and  that  the  key  to  the 
cause  of  the  different  diseases  of  the  system  is  to  be  sought  in  this  fact. 
The  familiar  diseases  of  the  nervous  system  which  are  always,  within  quite 
narrow  limits,  localized  along  definite  paths  are  of  quite  particular  interest 
in  many  directions.  Here  the  close  connection  between  nervous  and 
muscular  tissue  becomes  very  evident.1 

We  have  repeatedly  spoken  of  the  direct  and  indirect  influence  of  the 
nervous  system  upon  all  the  organs  of  the  body.  It  is  quite  impossible  to 
define  this  more  closely,  i.e.,  we  cannot  in  any  way  explain  the  nature 
of  the  conveyance  of  sensation.  We  merely  know  that  the  nerve-fibers 
are  merely  outgrowths  of  the  nerve-cells  with  which  they  form  a  unit. 
The  former  are  in  contact  with  the  organs  usually  by  means  of  a  character- 
istic end-apparatus.  It  does  not  seem  at  all  impossible  that  physiological 
chemistry,  together  with  physical  chemistry,  will  eventually  throw  light 
upon  this  process.  It  can  hardly  be  doubted  that  definite  changes, 
whether  in  the  end-apparatus  or  in  the  nerve-cells,  give  rise  to  definite 
functional  expressions  of  the  nervous  tissue. 

Before  we  take  up  the  relations  of  the  musculature  to  the  other  organs, 
we  will  consider  briefly  a  reaction  which  is  common  to  both  muscle  and 
nervous  tissue,  namely  the  so-called  heat-rigor.2  If  a  muscle  is  gradually 
heated,  it  loses  at  a  definite  temperature  its  power  of  being  stimulated, 
and  contracts.  The  cause  of  this  heat-rigor  is  the  coagulation  of  the 
albumin,  and  it  may  be  shown  that  this  does  not  take  place  all  at  once,  but 
in  stages.  Different  albumins  present  in  the  muscle  coagulate  at  different 
temperatures.  The  nerves  behave  in  exactly  the  same  way.  They  also 
show  a  heat-rigor.  The  lowest  temperature  at  which  one  of  the  albumins 
coagulates,  corresponds  to  the  time  that  the  nerve  ceases  to  be  capable 
of  response  to  stimulation.  Here,  as  in  the  case  of  muscles,  there  is  a 
contraction. 

As  is  well  known,  the  albumins  in  muscles  coagulate  after  death.  Rigor 
mortis  results,  and  this  does  not  attack  all  the  different  muscles  at  one 
time.  Its  appearance  after  death  also  occurs  at  different  intervals  of 
time.  The  cause  of  death-rigor  has  been  much  studied.  It  is  certain 

1  Cf.  Robert  Bing:  Deut.  Arch.  klin.  Med.  86,  199  (1905);  and  Deut.  Z.  Nervenheilk. 
26,  163  (1904);  and  Ueber  angeborene  Muskeldefekte.  Inaug. -Dissert.  Basel  (1902). 

2  Brodie  and  Richardson:  Philos.  Trans.  London,  Series  B,  191,  127  (1899).     Vernon: 
J.  Physiol.  24,  239  (1899).     O.  von  Fiirth:  Z.  physiol.  Chem.  31,  338  (1900). 


618  LECTURE  XXVI. 

that  it  results  from  the  coagulation  of  the  protein  in  muscle,  and  in  fact 
it  is  believed  to  be  the  protein  known  as  myogen  which  takes  part  especially 
in  the  process.  This  is  supposed  to  pass  over  first  into  soluble  myogen- 
fibrin,  which  is  subsequently  transformed  into  the  coagulated  modification. 
The  other  protein,  myosin,  also  takes  part  in  the  formation  of  the  clot.1 
Although  the  assumption  that  death-rigor  results  from  a  coagulation  of 
the  protein  has  been  generally  accepted,  on  the  other  hand  the  manner 
in  which  the  coagulation  takes  place  has  been  variously  explained.  Con- 
siderable attention  has  always  been  paid  to  the  fact  that  an  acid  reaction 
appears.  This  is  apparently  brought  about  by  the  formation  of  lactic 
acid,  and  by  the  resulting  transformation  of  a  part  of  the  diphosphate 
contained  in  muscle  to  monophosphate.  Now  it  has  been  observed  that 
acid,  and  especially  lactic  acid,  accelerates  the  coagulation  process.  The 
early  appearance  of  death-rigor  after  previous  active  muscular  contraction, 
as,  for  example,  in  tetanus,  has  been  attributed  to  the  action  of  the  lactic 
acid,  which  is  in  such  cases  present  in  larger  amount  than  usual.  Further- 
more, it  has  been  assumed  that  a  ferment  assists  in  causing  the  coagulation. 
The  final  relaxation,  which  takes  place  after  an  indefinite  length  of  time, 
is  also  not  perfectly  understood.  Acids  have  been  supposed  to  take  part 
in  this  process  also,  while,  on  the  other  hand,  it  has  also  been  assumed 
that  autolytic  processes  come  into  play. 

In  certain  directions  we  are  well  informed  concerning  the  processes  of 
metabolism  which  take  place  in  muscles  during  the  exercise  of  their  func- 
tions. We  have  already  discussed  these  points.  We  also  know  that  the 
liver  is  apparently  in  direct  relation  to  the  muscles,  for,  by  means  of  its 
glycogen  store,  it  satisfies  their  nutritional  requirements.  It  is  not  neces- 
sary that  the  relation  between  the  liver  and  muscles  should  be  a  direct 
one.  It  may  be  brought  about  by  means  of  the  blood.  This  has,  as  we 
know,  a  sugar  content  which  is  very  constant  within  narrow  limits.  In 
case  the  sugar  in  the  blood  is  used  up  by  the  muscles,  it  receives  a  new 
supply  from  the  liver,  the  cells  of  which  in  such  cases  at  once  break  down 
glycogen  into  sugar.  There  must  also,  without  doubt,  be  relations  between 
the  general  metabolism  of  the  cells  and  that  of  the  muscles.  If,  for  example, 
it  is  desired  to  fatten  with  albumin,  this  can  be  accomplished  well  only 
when  there  is  muscular  effort  at  the  time  the  abundance  of  albumin  is  fed. 
This  may  be  explained  on  the  assumption  that  under  such  conditions 
albumin  is  assimilated  to  a  greater  extent  than  usual,  although  it  is  also 
possible  that  the  other  cells  of  the  body  are  in  some  way  stimulated  to 
take  up  more  albumin. 

This  finishes  all  that  we  have  to  say  here  with  regard  to  the  relations  of 
the  individual  organs  to  one  another.  They  are,  to  be  sure,  much  more 

1  O.  von  Fiirth:  Arch,  exper.  Path.  Phar.  36,  231  (1895). 


RELATIONS   OF   THE   ORGANS   TO   ONE    ANOTHER.     619 

diversified  than  we  have  here  represented,  and  are  of  great  importance  in 
the  study  of  the  processes  which  take  place  in  the  animal  organism.  It 
is  one  of  our  most  important  tasks  to  follow  these  problems  farther.  It 
is  only  when  we  shall  have  acquired  as  thorough  a  knowledge  as  possible 
in  this  direction,  that  we  shall  be  in  a  position  to  draw  a  clear  picture  of 
the  cell-metabolism  and  the  functions  of  the  organs.  The  dependence 
of  the  organs  upon  one  another  is,  as  a  rule,  too  little  emphasized. 


LECTURE  XXVII. 

GENERAL  METABOLISM. 

I. 

WE  have  so  far  considered  for  each  foodstuff  the  way  it  is  absorbed, 
assimilated,  and  finally  eliminated  from  the  animal  organism,  and  attempted, 
above  all  else,  to  follow  the  intimate  processes  of  metabolism  in  the  tissues 
and  especially  in  the  cells.  The  study  of  these  processes  separately  has 
to-day  become  the  particular  field  of  the  physiological  chemist.  We  should 
err  greatly,  however,  if  we  were  to  regard  the  chemical  decompositions  in 
the  animal  organism  solely  from  the  standpoint  of  the  individual  food- 
stuff. We  should  obtain  an  entirely  false  impression  of  the  general  meta- 
bolism, and  should  be  unable  to  answer  some  of  the  most  important 
questions.  We  have  up  to  this  time  studied  metabolism,  as  it  were,  from  a 
more  or  less  qualitative  standpoint.  There  remains  the  quantitative  side 
to  be  considered;  i.e.,  we  must  compare  the  total  income  and  the  total  outgo. 
We  have  already  touched  upon  this  problem  in  discussing  the  transforma- 
tion of  the  different  organic  foodstuffs  into  one  another,  and  in  considering 
their  mutual  replacement  according  to  their  calorific  value. 

It  is  particularly  important  for  the  study  of  metabolism  that  in  the 
economy  of  the  animal  organism  the  law  of  the  conservation  of  matter 
and  of  energy  holds  absolutely.  This  fact  forms  the  basis  of  all  experi- 
ments in  metabolism.  We  may  determine,  by  studying  as  accurately 
as  possible  the  income  and  outgo,  the  part  played  by  each  individual 
foodstuff  in  the  general  metabolism.  Only  by  comparing  the  income 
with  the  outgo  are  we  able  to  form  judgment  as  regards  the  condition  of 
the  system.  In  this  way  alone  is  it  possible  to  determine  whether  the 
animal  experimented  upon  increases  its  balance  of  nutrition,  is  in  nutritive 
equilibrium,  or  whether  there  is  a  deficit  such  that  the  organism  is  com- 
pelled to  draw  upon  its  reserve  stores  or  to  consume  its  own  tissue  in  order 
to  maintain  the  functions  of  its  organs.  The  study  of  the  body-weight 
alone  can  never  take  the  place  of  this  important  method  of  examination. 
An  increase  or  loss  in  weight  may  arise  from  a  number  of  different  causes. 
Such  deviations,  for  example,  may  be  brought  about  merely  by  a  retention 
or  an  elimination  of  considerable  water.  The  varied  natures  of  the 
problems  concerning  metabolism  have  led  to  different  methods  of  investi- 
gation. In  some  cases  it  is  sufficient  to  follow  the  course  of  a  single  food- 

620 


GENERAL   METABOLISM.  621 

stuff,  while  at  other  times  it  is  necessary,  in  order  to  draw  a  clear  picture, 
to  measure  the  total  intake  and  outgo.  A  simple  problem,  for  ex- 
ample, is  to  determine  whether  a  definite  substance  acts  as  an  albumin 
sparer.  Here,  in  most  cases,  it  is  sufficient  to  estimate  the  amount  of 
protein  in  the  food  without  introducing  any  serious  error,  by  merely  de- 
termining the  amount  of  nitrogen  contained  therein.  The  amount  of 
nitrogen  in  the  urine  and  in  the  faeces  then  shows  clearly  whether  the 
animal  experimented  upon  is  in  nitrogen  equilibrium  or  not.  If  the 
animal  is  once  found  to  be  in  such  equilibrium,  i.e.  eliminates  the  same 
quantity  of  nitrogen  that  it  receives  in  the  food,  then  by  feeding  the  given 
food  we  can  easily  determine  whether  the  elimination  of  nitrogen  is  in- 
creased, diminished,  or  remains  the  same.  The  experiment  in  this  case  is 
so  simple,  because  we  know  that  nitrogen  is  given  up  by  the  kidneys  and 
not  by  the  lungs  or  skin.  Such  an  experiment,  however,  is  not  perfectly 
satisfactory.  A  number  of  questions  always  arise  concerning  such  results. 
We  are  by  no  means  justified  in  assuming  that  the  appearance  of  nitrogen 
in  the  urine  is  a  sign  that  there  has  been  a  total  consumption  of  the  albu- 
min. We  know  that  in  all  cases  only  a  part  of  the  carbon  appears  com- 
bined with  nitrogen  in  urine.  The  rest  of  the  carbon  chains  from  the. 
cleavage-products  of  proteins  are  broken  down  in  a  different  manner. 
These  chains  may  remain  in  the  organism  long  after  all  of  the  nitrogen 
has  been  eliminated,  and  take  part  in  metabolism  in  a  way  which  is  not 
yet  clear  to  us.  At  all  events,  in  an  exact  investigation  it  would  be  neces- 
sary to  take  into  account  also  the  elimination  of  the  sulphur.  But  even 
here  we  cannot  be  entirely  satisfied.  Only  by  combining  the  examination 
of  the  urine  and  fseces  with  that  of  the  remaining  elimination  products, 
especially  the  gaseous  ones,  shall  we  obtain  an  exact  insight  into  the 
influence  upon  the  total  metabolism.  In  many  cases  even  with  such 
experiments  the  results  are  not  entirely  satisfactory.  We  should  know 
oftentimes  more  accurately  to  what  extent  kinetic  energy  has  been  changed 
into  potential  energy,  in  order  to  judge  correctly  the  physiological 
nutritional  value  of  the  individual  foodstuff. 

Before  considering  the  details  of  an  experiment  in  metabolism,  we 
must  bring  forward  the  fact  that  an  exact  insight  into  the  questions 
concerning  metabolism  can  only  be  expected  when  influences  which  have 
no  bearing  upon  the  problem  at  hand  are  excluded  as  completely  as 
possible.  Comparative  experiments  in  which  the  basal  conditions  are  as 
nearly  alike  as  possible,  should  be  carried  out  as  a  rule  upon  the 
same  animal.  Individual  peculiarities  which  sharply  influence  metabolism 
should  never  be  disregarded.  One  of  the  most  important  requirements  to 
be  satisfied  in  a  metabolism  experiment  is  that  the  test  should  be  carried 
out  for  a  considerable  length  of  time.  It  is  not  possible  to  draw  any 
exact  conclusions  from  observations  made  only  during  a  period  of  twenty- 


622  LECTURE  XXVII. 

four  hours  or  less.  The  metabolism  of  the  food  eaten  the  previous  day 
will  affect  the  results;  and,  moreover,  the  metabolism  of  the  food  taken 
during  the  day  of  the  experiment  will  not  be  complete  during  such  a 
short  time.  Atwater  1  showed  how  much  more  valuable  the  results  were 
when  the  experiment  was  continued  for  some  considerable  time.  A 
great  many  contradictions  and  differences  in  the  researches  concerning 
metabolism,  which  are  to  be  found  in  the  literature,  may  be  traced  to  the 
fact  that  this  requirement  has  not  been  satisfied.2 

As  a  foundation  for  a  metabolic  balance,  an  accurate  knowledge  of  the 
composition  of  the  income  and  of  the  outgo  is  essential.  As  regards  the 
income,  the  foods  are  to  be  considered  in  two  directions.  We  can,  on 
the  one  hand,  evaluate  them  according  to  their  chemical  composition, 
and,  on  the  other,  according  to  the  energy  which  they  contain.  We  obtain 
the  former  values  by  means  of  chemical  analysis.  We  have  the  organic 
and  inorganic  constituents  to  estimate.  In  the  former  the  carbon,  hydrogen, 
and  nitrogen  are  determined.  By  multiplying  the  nitrogen  found  by  6.25, 
the  amount  of  albumin  is  obtained.  Of  course  this  method  of  estimat- 
ing the  amount  of  albumin  is  not  an  exact  one.  It  is  perfectly  possible  that 
the  food  may  contain  nitrogen  in  some  other  form  than  as  albumin.  In 
general,  however,  the  amount  of  such  nitrogenous  matter  is  inconsiderable. 
The  fat  content  is  obtained  by  extracting  the  food  with  ether,  in  which 
connection  it  is  to  be  remembered  that  a  part  of  the  fat  will  go  into  solu- 
tion only  after  the  product  examined  has  been  "  opened  up  "  3  by  digestion 
with  pepsin-hydrochloric  acid,  or  with  two  per  cent  hydrochloric  acid. 
Then,  when  the  ash  is  known,  the  amount  of  carbohydrate  may  be 
determined  by  difference.  By  drying  an  aliquot  part  of  the  weighed 
mixture,  and  weighing  the  dry  residue,  the  amount  of  water  in  the  food  is 
determined.  Oxygen  is  naturally  also  to  be  considered  among  the  sub- 
stances taken  into  the  system.  Unfortunately,  up  to  the  present  it  has 
not  been  found  possible  to  measure  accurately  the  amount  of  this  gas 
that  is  utilized.  This  thwarts  the  exact  answering  of  many  questions 
in  the  field  of  metabolism.  The  potential  energy  of  the  food  may  be 
ascertained  by  the  heat  of  combustion.  In  exact  experiments  we  must 
naturally  also  take  into  consideration  the  temperature  of  the  food  and 
drink  as  it  is  taken  into  the  system. 

1  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  3,  497  (1904). 

2  Studies   of   metabolism   under   pathological   conditions   are   important.     Clinical 
investigation  and  experimental  pathology  are  closely  connected  with  the  progress  of 
the  knowledge  of  metabolism  under  normal  conditions.     By  such  means  many  new 
questions  have  arisen,  and  certain  disturbances  have  given  us  insight  into  this  or  that 
process.     It  would  be  beyond  the  scope  of  these  lectures  to  attempt  to  mention  the 
numerous  discoveries  which  have  been  made  in  this  way.     We  can  give  only  the  outline 
here  and  the  more  important  results.     The  physiology  of  metabolism  has  become  such 
an  important  branch  of  science  that  it  can  be  studied  only  upon  a  broad  basis. 

3  Cf.  Lecture  XIV,  p.  325. 


GENERAL   METABOLISM.  623 

The  income  is  to  be  contrasted  with  the  outgo.  There  are  three  prin- 
cipal ways  in  which  the  products  of  metabolism  leave  the  organism,  — 
through  the  kidneys,  the  intestine,  and  the  lungs.  The  fseces  contain 
not  only  products  of  metabolism,  but  also  the  unabsorbed  food.  The 
determination  of  the  nature  of  the  faces  is  highly  important.  It  gives  us 
an  idea  how  completely  the  nourishment  has  been  utilized.  In  the  urine, 
besides  the  inorganic  salts,  we  have  to  consider  the  nitrogen,  sulphur, 
phosphorus,  carbon  and  hydrogen  content.  The  first  three  elements  give 
us  information  concerning  the  decomposition  of  the  protein.  Usually  the 
nitrogen  is  alone  determined  and  the  amount  of  consumed  protein  is 
obtained  by  multiplying  the  nitrogen  value  by  6.25.  In  many  cases  the 
decomposition  of  the  protein  is  also  traced  qualitatively,  and  it  is  deter- 
mined how  much  nitrogen  is  present  as  urea,  and  how  much  in  the  form 
of  other  compounds.  In  order  to  get  an  idea  of  the  energy  economy,  the 
heat  of  combustion  of  the  entire  excreta  is  determined,  further  the  heat 
given  off  by  the  body,  and  the  amount  of  heat  equivalent  to  the  muscular 
work  performed. 

The  gas  metabolism  is  studied  with  the  help  of  apparatus  of  special 
construction,1  by  means  of  which  the  amounts  of  carbon  dioxide  and 
water  vapor  eliminated  are  determined.  From  the  amount  of  carbon 
dioxide  the  equivalent  weight  of  carbon  may  be  computed.  This,  together 
with  the  amount  of  carbon  contained  in  all  the  remaining  excreta,  gives  us, 
first  of  all,  an  idea  as  to  the  utilization  of  the  carbon  in  the  food  by  the 
organism.  The  question  then  arises  how  can  we  tell  from  the  total  amount 
of  carbon  the  amount  that  has  resulted  from  the  separate  foodstuffs, 
albumin,  carbohydrate,  and  fat.  To  estimate  this  we  start  with  the  total 
amount  of  nitrogen  eliminated,  and  from  that  compute  the  amount  of 
albumin  decomposed.  Since  the  average  carbon  content  of  protein  is 
known,  it  is  easy  to  compute  how  much  of  the  carbon  came  from  proteins. 
This  is  naturally  on  the  assumption  that  the  combustion  of  the  remaining 
protein  molecule  takes  place  simultaneously  with  the  elimination  of  the 
nitrogen.  As  a  rule,  the  relation  of  nitrogen  (16  per  cent)  to  carbon  (53 
per  cent)  in  protein  is  as  1  :  3.3.  If,  then,  we  multiply  the  nitrogen  value 
by  3.3  we  obtain  the  amount  of  carbon  which  was  obtained  from  protein; 
and  by  deducting  the  product  from  the  total  amount  of  carbon  in  the 
egesta,  the  amount  obtained  from  nitrogen-free  food  is  given.  If  there 
is  no  remainder,  then  only  protein  was  consumed.  By  comparing  the  total 
amount  of  carbon  and  the  remainder  after  deducting  the  carbon  from 


1  Descriptions  of  such  apparatus  may  be  found  as  follows:  Regnault  and  Reiset: 
Annal.  73,  92,  129,  257  (1850),  and  Ann.  chim.  et  phys.  (3)  26  (1849).  Hoppe-Seyler: 
Z.  physiol.  Chem.  19,  574  (1894).  Pettenkofer:  Annal.  II,  Suppl.-Band,  p.  1  (1862). 
Voit:  Z.  Biol.  11,  541  (1875).  Sonden  and  Tigerstedt:  Skand.  Arch.  Physiol.  6  (1895); 
and  Atwater:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  3,  498  (1904). 


624  LECTURE  XXVII. 

protein  in  the  egesta  with  that  in  the  ingest  a,  we  can  tell  whether  all  of 
the  carbon  has  been  eliminated  or  whether  more  or  less.  In  the  two  latter 
cases  we  can  tell  whether  the  organism  has  consumed  its  own  protein  or 
fat,  or  whether  it  has  added  to  its  supply  of  albumin  and  of  nitrogen-free 
substances. 

We  have  disregarded  the  losses  which  the  body  sustains  by  its  secretions, 
and  the  losses  of  epidermis  from  the  skin,  intestinal  canal,  and  other  mucous 
membranes.  These  losses  are  very  hard  to  estimate.  To  some  extent  they 
come  into  consideration  with  the  eliminations  from  the  alimentary  canal 
in  the  analysis  of  the  faeces.  They  may  be  disregarded,  or  not  be  estimated 
by  themselves,  because  they  are  so  small  in  amount  that  the  error  intro- 
duced does  not  assert  itself  in  the  nutrition  balance.  Particular  attention 
should  be  paid  to  the  nitrogen  content  of  the  faeces,  which  arises  largely 
from  intestinal  depositions.  The  faeces  of  man  contain  0.5  to  1.4  grams  of 
nitrogen,  even  when  the  food  contains  but  little  nitrogen  or  none.  Among 
the  nitrogen-free  products,  the  faeces  contain  principally  fat.  In  starvation 
man  eliminates  0 . 6  to  1.4  grams  of  fat  per  day.  With  nourishment  free 
from  fat,  3  to  7  grams  are  eliminated  daily. 

For  the  determination  of  the  heat  given  off  by  the  organism,  a  special 
apparatus  is  also  necessary.  A  calorimeter  which  permits  the  simultaneous 
determination  of  the  respiratory  exchange  and  the  amount  of  heat  liberated 
is  Atwater's  respiration  calorimeter.1  This  apparatus,  in  which  the  person, 
or  animal,  experimented  upon  may  remain  for  a  week,  consists  of  a  chamber 
which  is  large  enough  to  be  comfortable.  This  space  is  supplied  with  a 
ventilating  arrangement,  so  that  the  volume  of  the  air  can  be  accurately 
measured.  It  is  so  regulated  that  the  air  enters  and  leaves  at  exactly  the 
same  temperature.  Now  and  then  samples  of  air  are  taken  as  it  enters  and 
as  it  leaves  the  chamber,  whereby  the  amount  of  carbon  dioxide  and  water 
given  off  by  the  lungs  and  by  the  skin  is  determined.  Suitable  arrange- 
ments are  also  provided  for  the  introduction  of  food  and  drink,  and  for 
the  removal  of  the  solid  and  liquid  excretory  products.  The  amount  of 
heat  given  up  by  the  organism,  together  with  the  heat  equivalent 
of  the  external  muscular  work,  is  measured  at  the  same  time.  The  heat 
given  off  is  carried  away  by  a  stream  of  cold  water,  which  flows  in  tubes 
around  the  chamber.  By  carefully  regulating  the  temperature  of  the  water 
and  the  velocity  at  which  it  flows  through  the  tubes,  it  is  possible  to  carry 
away  the  heat  as  fast  as  it  is  produced,  thereby  keeping  the  temperature 
of  the  chamber  constant.  By  determining  the  amount  of  water  that  has 
flowed  through  the  tube,  and  the  change  in  temperature,  it  is  possible  to 
estimate  the  amount  of  heat  given  off  by  the  body. 

By  determining  the  amount  of  water  vapor  in  the  air  as  it  enters  and  as  it 
leaves  the  chamber,  it  is  possible  to  find  out  how  much  water  is  given  off  by 

1  Loc.  rit.  p.  499. 


GENERAL   METABOLISM. 


625 


the  body.  The  amount  of  heat  energy  required  for  its  evaporation  must  be 
added  to  the  amount  of  heat  energy  carried  away  by  the  water  current. 
Atwater  measured  the  heat  equivalent  of  the  external  work  performed  in 
a  very  interesting  manner.  He  provided  a  bicycle  which  was  connected 
with  a  dynamo.  The  electric  current  produced  was  led  through  an  incan- 
descent lamp,  and  there  transformed  into  heat  energy,  which  can  be  directly 
measured  as  such.  From  the  duration  of  the  experiment,  and  the  amount  of 
•electric  current  produced,  the  amount  of  work  performed  can  be  estimated. 

According  to  this  method  of  investigation,  the  kinetic  energy  of  the 
body  is  computed  from  three  factors.  First,  there  is  the  total  amount  of 
heat  carried  away  as  heat,  including  that  carried  away  by  the  air  current ; 
second,  the  latent  heat  of  the  water  vapor  which  is  carried  away  from  the 
body ;  and  third,  there  is  the  heat  equivalent  of  the  external  work.  The 
first  amount  of  heat  has  several  sources.  It  comprises  the  heat  given  off 
by  radiation  and  conduction  from  the  skin,  that  obtained  from  the  excreta 
on  their  being  cooled  to  the  room  temperature,  and  further  there  is 
the  cooling  of  the  expired  air  (carbon  dioxide  and  water  vapor)  to  the 
room  temperature. 

By  means  of  such  an  apparatus  not  only  the  influence  of  different  kinds 
of  nourishment  upon  metabolism  can  be  determined  exactly,  but  also 
their  relations  to  the  external  work.  As  we  have  already  seen,1  it  is  by 
the  help  of  such  experiments  that  we  have  been  able  to  prove  that  the 
fats,  in  order  to  be  utilized  for  muscular  work,  need  not  necessarily  be 
transformed  into  carbohydrate,  but  that  their  calorific  value  may  be 
applied  directly. 


Transformed  Energy. 

Excess 

Name,  Nature  of  the 
Experiment. 

Laboratory 
Number. 

Duration 
in  Days. 

Sum 

Energy  in 
Period  of 
Work  Over 
Period  of 

Heat 
Equiva- 
lent of  the 
External 

Utiliza- 
tion in 
Per  cent. 

Rest. 

Work. 

E.G. 

Rest  experiment     .    .    . 

13 

42 

2279 

Work  experiment   .    .    . 
J.  F.  S. 

3 

12 

3892 

ieis 

214 

13.3 

Rest  experiment     .    .    . 

4 

12 

2119 

Work  experiment   .    .    . 

6 

18 

3559 

1440 

233 

16.'2 

J.  C.W. 

Rest  experiment     .    .    . 

1 

4 

2357 

Work  experiment 

Minimum  work    .    .    . 

4 

16 

5056 

2699 

529 

19.6 

Maximum  work  .    .    . 

2 

8 

5332 

2975 

601 

20.2 

Average     .... 

14 

46 

5143 

2786 

546 

19.6 

See  Lecture  XV,  p.  338  et  seq. 


626  LECTURE  XXVII. 

Atwater  succeeded  in  solving  a  number  of  important  problems  concern- 
ing metabolism  with  the  help  of  his  apparatus.  If  we  consider  metabo- 
lism simply  from  the  standpoint  of  energetics,  i.e.,  consider  the  organism 
simply  as  a  machine,  then  one  of  the  first  questions  to  interest  us  is  as 
regards  the  utilization  of  the  food  for  the  performance  of  external  work. 
We  must  remember  that  an  ordinary  steam  engine  on  an  average  converts 
but  15  per  cent  of  the  energy  contained  in  the  fuel  into  work.  The  rest 
is  set  free  as  heat. 

The  table  on  page  625  shows  the  relation  of  the  external  muscular  work 
to  the  total  amount  of  transformed  energy,  from  which  the  efficiency  of 
the  human  body  as  a  machine  may  be  computed.1 

The  work  performed  in  these  experiments  was  measured  by  the  bicycle 
arrangement  described  above.  In  the  table  its  heat  equivalent  is  taken 
into  consideration.  The  objection  might  be  raised  that  it  is  hardly  possible 
to  distinguish  sharply  between  a  period  of  rest  and  one  of  work,  for  in  the 
latter  case  there  is  merely  additional  work  over  that  required  by  the 
organism  for  the  exercise  of  the  remaining  physiological  functions.  It  is 
difficult,  and  in  fact  entirely  impossible,  to  make  sure  that  the  mental  and 
nervous  expenditure  of  energy  will  be  exactly  the  same  in  two  experi- 
mental periods.  A  priori  it  is  conceivable  that  there  is  a  considerable 
transformation  of  energy  in  these  two  kinds  of  work.  To  meet  this  objec- 
tion Atwater  2  compared  the  results  obtained  where  the  person  experi- 
mented upon  was  resting  mentally  and  physically  as  completely  as  possible, 
with  results  obtained  in  a  period  where  the  person  was  engaged  in  severe 
mental  effort,  and  found  that  there  was  no  appreciable  increase  in  the 
transformations  of  matter  or  of  energy  in  the  latter  case.  This  does  not 
necessarily  mean  that  mental  activity  does  not  correspond  to  a  considerable 
consumption  of  energy.  It  is  entirely  impossible  to  stop  completely  at 
will  all  mental  effort.  The  mental  work  continues,  whether  the  person 
experimented  upon,  as  in  Atwater's  experiments  was  the  case,  is  busied 
with  the  results  of  experiments,  a  German  treatise,  or  the  study  of  physics; 
there  is  no  apparent  difference  from  the  results  obtained  in  metabolism 
when  the  brain  is  as  much  at  rest  as  is  possible  to  make  it  voluntarily. 
As  far  as  the  above  experiments  are  concerned,  therefore,  it  makes  no 
difference  to  what  extent  brain  and  nervous  activity  affect  the  total 
consumption  of  energy;  for,  as  Atwater  has  sKown,  the  consumption  of 
energy  from  these  causes  remains  the  same,  whether  mental  work  is  per- 
formed intentionally  or  unintentionally.  A  glance  at  the  above  table 
shows  that  all  human  organisms  do  not  work  with  the  same  degree  of  effi- 
ciency. That  of  E.  O.  was  less  efficient  than  that  of  J.  S.  F.  and  J.  C.  W. 
At  all  events,  however,  as  a  machine  the  human  organism  is  more  efficient 

1  Atwater:  loc.  cit.  p.  608. 

2  Atwater:  U.  S.  Dept.  Agr.  Office  of  Exper.  Stations.     Bull.  44. 


GENERAL   METABOLISM.  627 

than  an  ordinary  steam  engine.  We  must  admit,  on  the  other  hand, 
that  the  way  this  was  proved  by  Atwater's  experiments  is  not  altogether 
beyond  reproach.  It  is  not  an  exact  determination.  We  do  not  know 
just  how  much  effect  the  increased  muscular  work  had  upon  the  functions 
of  the  other  organs.  At  the  same  time  it  is  probable  that  the  values 
obtained  are  not  far  from  the  truth. 

While  the  advance  in  technique  and  in  methods  results  in  more  precise 
investigations,  still,  on  the  other  hand,  we  are  often  compelled  to  resort 
to  indirect  methods  with  all  their  sources  of  error  which  we  have  so  often 
mentioned.  This  is  true  in  many  cases  when  we  attempt  to  determine 
the  participation  of  nitrogen-free  foodstuffs  in  metabolism.  We  can,  it 
is  true,  get  some  idea  of  this  by  comparing  the  volumes  of  inspired  and 
expired  air.  In  normal  breathing  the  volume  of  the  expired  air  is  always 
greater  than  that  of  inspired  air.  This  is  due  to  the  fact  that  the  outer 
air  is  warmed  to  the  body  temperature  after  it  is  inspired,  and  at  the  same 
time  it  is  almost  completely  saturated  with  water  vapor.  In  order  to 
obtain  actually  comparable  figures  it  is  necessary  to  measure  the  two 
volumes  of  air  under  precisely  the  same  conditions.  Both  must  be  brought 
to  the  same  temperature  and  pressure;  and,  furthermore,  they  must  be 
dried.  When  this  is  done,  it  will  be  found  that  the  volume  of  the  expired 
air  is  almost  invariably  smaller  than  that  inspired.  This  is  due  to  the 
fact  that  in  the  combustion  of  the  foodstuffs,  the  carbohydrates  alone 
yield  a  volume  of  carbon  dioxide  equal  to  that  of  the  oxygen  consumed, 
while  in  the  combustion  of  protein  and  fat  this  is  not  the  case.  In  the  case 
of  the  latter,  a  part  of  the  inspired  oxygen  is  utilized  for  the  formation  of 
water,  sulphuric  acid,  and  other  substances.  The  amount  of  oxygen  con- 
sumed in  this  way  does  not  appear  in  the  volume  of  the  expired  air  when 
measured  as  above.  In  the  combustion  of  carbon,  one  volume  of  carbon 
dioxide  gas  is  formed  from  one  volume  of  oxygen.  In  this  case  the  ratio 

PO 

—x—  =  1.     This  relation  of  expired  carbon  dioxide  to  inspired  oxygen  is 
U2 

called  the  respiratory  quotient.  In  the  combustion  of  carbohydrates 
this  is  1.  A  diet  in  which  protein  predominates  causes  the  quotient  to 
fall  to  about  0 . 80,  while  if  fat  is  chiefly  concerned  in  the  metabolism,  the 
value  of  the  quotient  falls  to  0.70.  According  to  the  value  of  this  re- 
spiratory quotient,  therefore,  we  can  draw  some  conclusions  regarding  the 
nature  of  the  food  upon  which  the  subject  experimented  upon  is  working. 
If,  for  example,  a  dog  which  has  a  good  supply  of  glycogen  stored  up  is  made 
to  fast,  then  the  high  respiratory  quotient,  which  is  approximately  1, 
shows  that  at  the  given  moment  the  dog  is  maintaining  its  economy 
chiefly  by  drawing  upon  its  carbohydrate  stores.  When  the  value  of  the 
quotient  begins  to  fall,  it  shows  that  fat  is  being  consumed,  and  finally  it 
will  be  compelled  to  utilize  its  own  protein.  Naturally,  it  is  not,  in  general. 


628  LECTURE  XXVII. 

advisable  to  depend  upon  this  respiratory  quotient  alone,  but  we  should 
also  take  into  consideration  the  other  eliminations,  especially  that  of 
nitrogen. 

Now  that  we  have  roughly  sketched  the  outlines  of  the  methods  employed 
for  studying  metabolism,  we  will  briefly  discuss,  before  taking  up  the 
important  facts  that  have  been  ascertained  concerning  metabolism  under 
definite  conditions,  the  influence  of  the  conditions  created  by  the  subject 
experimented  upon  itself.  First  of  all,  there  is  the  question  of  size.  It 
is  perfectly  clear  that  the  total  metabolism  will  be  more  extensive  in  pro- 
portion to  the  size  of  the  organ  in  function.  Eventually  the  consumption 
of  material  is  to  be  traced  to  the  work  of  the  individual  cells,  and  the  more 
cells  there  are  the  greater  will  be  their  total  requirement.  Thus  a  small 
animal  will  require  absolutely  less  nourishment  than  a  larger  one.  Of 
course  individual  peculiarities  play  a  part  which  must  not  be  left  out  of 
consideration.  If,  on  the  other  hand,  instead  of  paying  attention  to  the 
absolute  amount  of  material  consumed,  we  consider  the  energy  trans- 
formed per  kilogram  of  body-weight,  provided  we  are  working  under 
otherwise  parallel  conditions,  we  shall  find  that  the  metabolism  of  the 
smaller  animal  is  greater  than  that  of  the  larger  one.  In  order  to  obtain 
values  which  shall  be  actually  comparable,  the  separate  experiments  upon 
metabolism  must  be  carried  out  with  the  animal  at  rest,  and  also  fasting. 
In  this  way  the  so-called  fasting  value  is  obtained.1  The  reason  that 
a  small  animal  decomposes  more  substance  in  proportion  to  its  own 
weight  lies  in  the  following:  —  The  smaller  an  animal  is,  the  larger  the 
surface  of  its  body  in  comparison  to  the  volume  and  weight  of  the  body. 
It  may  be  assumed  that  about  four-fifths  of  the  total  heat  given  off  by 
the  body  is  through  the  skin.  The  amount  of  heat  lost  by  the  skin  is  very 
nearly  proportional  to  the  amount  of  surface  covered  by  it,  so  that  the 
smaller  animal  with  its  relatively  larger  surface  loses  more  heat  than  the 
larger  animal.  Consequently  the  smaller  animal  requires  a  greater  supply 
of  heat  energy  than  the  larger  one,  as  otherwise  its  body  temperature, 
which  is  regulated  by  two  factors,  the  amount  of  heat  generated  and  that 
given  off,  will  not  be  maintained  at  the  proper  height. 

The  tables  on  the  following  page  show  how  the  amount  of  oxygen 
consumed  depends  upon  the  size  of  the  body,2  and  give  also  a  comparison 
of  the  metabolism  of  energy  in  animals  of  various  sizes  with  their  relative 
surface  development.3 

The  influence  of  the  greater  surface  becomes  apparent  when  we  compare 
the  metabolism  of  younger  and  older  individuals  of  the  same  species. 


1  Cf.  Max  Rubner:  Z.  Biol.  19,  535  (1883).     Slowtzoff :  Pfliiger's  Arch.  96, 158  (1903). 
Karl  Oppenheimer:  Z.  Biol.  42,  (1901). 

2  Max  Rubner:  Z.  Biol.  19,  536  (1883). 

3  Max  Rubner:  ibid.  p.  549. 


GENERAL   METABOLISM. 


629 


This,  however,  of  itself  does  not  by  any  means  explain  the  considerably 
more  active  metabolism  on  the  part  of  the  younger  individual.  This  is 
evident  when  we  compare  not  the  metabolism  of  the  whole  external  sur- 
face, but  rather  that  per  unit  of  surface.  On  comparing,  for  example, 
the  metabolism  per  square  meter  in  fully  developed  dogs  of  different  sizes, 
we  will  find  that  the  value  is  the  same  for  all  dogs  within  certain  narrow 
limits.  This  is,  however,  not  the  case  if  we  compare  the  metabolism  of 
young  dogs  with  that  of  older  ones.  In  the  case  of  the  former  the  metabo- 
lism is  greater  per  unit  of  surface  than  it  is  in  the  older  dogs. 

I. 

CONSUMPTION    OF    OXYGEN,    ARRANGED    IN    THE    ORDER    OF    THE 

ANIMAL'S  WEIGHT. 


Grams  Oxy- 

Grams Oxy- 

Species. 

Weight  in 
Kilograms. 

gen  Absorbed 
per  Kilogram 

Species. 

Weight  in 
Kilograms. 

gen  Absorbed 
per  Kilogram 

in  1  Hour. 

in  1  Hour. 

Male  calf     .    . 

115 

0.481 

Rabbit   .    .   . 

3.43 

0.735 

Male  calf     .    . 

115 

0.428 

Mountain  rat 

1.55 

1.198 

Sheep    .... 

70 

0.464 

Hen  

1.51 

0.846 

Sheep    .... 

66 

0.490 

Drake.    .    .    . 

1.22 

1.382 

Sheep    .... 

65 

0.400 

Cross-bill  .    . 

0.028 

10.974 

Hen-turkey    . 

6.2 

0.702 

Green-finch  . 

0.025 

13.000 

Dog   . 

5.59 

0.902 

Green-finch  . 

0  025 

9.742 

Goose    .... 

4.60 

0.677 

Sparrow.    .    . 

0.022 

9^595 

Rabbit     .    .    . 

3.58 

0.763 

II. 

COMPARISON  OF  THE  EXCHANGE  OF  ENERGY  IN  ANIMALS  (DOGS) 
OF  DIFFERENT  SIZES  WITH  THEIR  RELATIVE  SURFACE  DEVEL- 
OPMENT. 


Number. 

Weight  in 
Kg. 

Surface  in 
Cm2. 

Surface  in  Cm2. 
per  1  Kg.  Weight. 

Calories  per  1  Kg. 
in  24  Hours  at 
15°  C. 

Calories  per  1 
Cm2.  Surface. 

I. 

31.20 

10.750 

344 

35.68 

1036 

II. 

24.00 

8.805 

366 

40.91 

1112 

III. 

19.80 

7.500 

379 

45.87 

1207 

IV. 

18.20 

7.622 

421 

46.20 

1097 

V. 

9.61 

5.286 

550 

65.16 

1183 

VI. 

6.50 

3.724 

573 

66.07 

1153 

VII. 

3.19 

2.423 

726 

88.07 

1212 

In  the  case  of  sucklings  the  metabolism  per  kilogram   of  body-weight 
is  likewise  much  greater  than  it  is  with  fully  developed  dogs;  but,  on  the 


630  LECTURE  XXVII. 

other  hand,  that  per  square  meter  of  external  surface  is  smaller  than  in  the 
case  of  the  older  dogs.  This  is  not  remarkable.  The  suckling  performs 
as  a  rule  but  little  external  work.  It  sleeps  the  greater  part  of  the  time, 
so  that  the  consumption  of  material  is  not  so  extensive  as  during  latter 
periods. 

In  old  age,  the  metabolism  is  greatly  diminished,  even  when  we  compare 
the  amount  per  square  meter  of  external  surface  with  the  values  obtained 
in  the  same  way  at  middle  age.  In  human  beings  between  the  ages  of  22 
and  56  years  the  amount  of  carbon  dioxide  eliminated  in  an  hour  per  square 
meter  of  body  surface  is  about  11.2  grams,  while  in  old  age  (70  to  77  years) 
the  value  is  only  9.2  grams  in  the  case  of  males;  with  females  the  elimina- 
tion between  the  ages  of  17  and  40  years  is  about  11.75  grams,  while  at 
71  to  86  years  it  is  only  9.79  grams.1 

The  fact  that  the  extent  of  metabolism  in  different  periods  of  life  is 
of  different  intensity  need  not  surprise  us.  In  considering  metabolism 
as  a  whole,  we  must  not  forget  that  it  is  the  sum  of  the  metabolism 
of  innumerable  units,  the  cells.  In  the  developing  tissue  of  youth 
the  transformations  are  unquestionably  much  more  extensive  than  in 
the  adult  organism.  We  know  from  a  great  many  observations  that  the 
organism  soon  accustoms  itself  to  certain  functions,  and  usually  expends 
more  energy  the  first  time  that  a  demand  is  made,  whereas,  later  on, 
it  accomplishes  the  same  result  much  more  economically  and  with  the 
expenditure  of  far  less  effort.  It  is  indeed  conceivable  that  the  cells  of 
the  adult  organism  learn  to  work  more  and  more  economically.  At  pres- 
ent we  are  not  in  a  position  to  study  the  metabolism  of  the  individual  cells, 
i.e.,  that  of  the  protoplasm.  We  obtain  the  impression,  instinctively  rather 
than  as  a  result  of  scientific  investigation,  that  the  cells  of  the  individual 
are  not  all  equally  efficient.  This  hypothesis  gains  form  when  we  recall 
the  numerous  cases  of  pathology  whose  etiology  is  paraphrased  with  the 
conception  of  disposition.  There  is  no  doubt  that  the  various  diseases; 
of  metabolism,  such  as  diabetes,  gout,  rachitis,  etc.,  are  eventually  to 
be  traced  to  a  disturbance  in  the  metabolism  of  individual  cells.  This 
may  affect  a  larger  or  smaller  cell-complex,  and  the  whole  cell-work  of  the 
individual  may  be  affected  apparently  without  our  being  able  to  explain 
precisely  the  way  in  which  the  metabolism  of  such  a  weakened  or  weak 
individual  is  changed.  As  long  as  the  cell  itself  belongs  in  the  domain 
of  the  unknown,  we  cannot  expect  to  be  able  to  gain  precise  information' 
concerning  the  physiology  and  pathology  of  cells.  While  we  must  empha- 
size the  fact  that  at  present  the  designation  of  a  pathological  derange- 
ment of  a  cell-function,  or  of  the  metabolism  as  a  whole  of  individual 
cells,  only  represents  a  conception  in  accordance  with  our  present  knowl- 

1  Magnus-Levy  and  E.  Falk:  Arch.  Anat.  Physiol.  1899.     Suppl.  314. 


GENERAL   METABOLISM.  631 

edge,  still,  on  the  other  hand,  the  importance  of  cell-life,  of  the  metabolism 
of  the  cells  and  their  functions,  must  not  be  overlooked  in  considering 
the  metabolism  of  the  body  as  a  whole. 

Interesting  glimpses  into  the  course  of  general  metabolism  have  been 
obtained  by  studying  the  results  under  definite  conditions.  The  metabo- 
lism taking  place  after  the  complete  withdrawal  of  the  food  has  been 
studied  especially.  Under  this  condition  the  animal  lives  at  first  upon 
its  own  stored-up  material,  and  finally  attacks  its  own  tissues.  The 
duration  and  the  whole  course  of  the  metabolism  during  starvation  depends 
largely  upon  the  condition  of  the  body  at  the  beginning  of  the  experiment. 
As  soon  as  a  certain  definite  fraction  of  the  body-substance  has  been  used 
up,  death  takes  place.  Naturally  the  activity  of  the  metabolism  also 
affects  the  duration  of  starvation  period.  According  to  the  principles 
enunciated  above,  therefore,  we  should  expect,  a  priori,  that  young  in- 
dividuals would  suffer  from  the  withdrawal  of  nourishment  much  more 
quickly  than  adults.  Similarly  in  the  case  of  animals  which  in  general 
have  a  lower  metabolism,  as  with  cold-blooded  animals,  they  will  sur- 
vive starvation  longer  than  will  the  warm-blooded  animals.  Dogs  can 
live  without  food  for  six  weeks.  Birds  live  on  an  average  from  5  to 
20  days,  while  fish  and  reptiles  may  survive  for  from  6  months  to  a  year. 
Even  in  the  case  of  human  beings,  long  periods  of  fasting  have  been 
observed.1 

The  first  marked  change  that  results  from  the  withdrawal  of  all  nour- 
ishment is  the  loss  in  weight  of  the  body,  which  within  a  relatively  short 
time  is  followed  by  a  loss  in  muscular  power.  The  subject  sleeps  much; 
and  towards  the  end  of  the  period  of  starvation  is  in  a  somnolent  con- 
dition. The  whole  metabolism  of  the  animal  diminishes  simultaneously 
with  the  loss  in  weight.  If,  however,  the  amount  of  material  transformed 
is  compared  to  a  kilogram  of  body-weight,  it  will  be  found  that  the  metabo- 
lism is  only  slightly  changed  from  that  of  a  well-nourished  animal.  In 
a  short  time  the  fasting  animal  adjusts  itself  to  a  minimum  metabolism, 
which  remains  constant  for  quite  a  while.  First  of  all  the  animal  makes 
use  of  its  stores  of  carbohydrates  and  fat.  The  former  are  soon  exhausted. 
From  the  beginning  of  the  starvation  period,  albumin  is  continuously  being 
decomposed.  The  amount  of  albumin  which  the  fasting  organism  must 
decompose  in  order  to  accomplish  the  necessary  metabolism,  depends 
chiefly  upon  the  amount  of  nitrogen-free  substances  which  are  present. 
If  the  animal  is  able  to  consume  a  considerable  amount  of  the  latter,  then 

1  L.  Luciani:  Das  Hungern,  Hamburg-Leipzig,  1890.  J.  E.  Johannson,  E.  Lundgren, 
KlasSonde"n,  and  Robert  Tigerstedt:  Skand.  Arch.  Physiol.  7,  29  (1896).  C.  Lehman, 
F.  Miiller,  I.  Munk,  H.  Senator,  and  N.  Zuntz:  Virchow's  Arch.  131,  Suppl.  1  (1893). 
R.  Tigerstedt:  Nordisk,  Medic.  Arch.  No.  37  (1897).  C.  Voit:  Z.  Biol.  41,  113  (1901). 
Siegfried  Weber:  Ergeb.  Physiol.  (Asher  and  Spiro)  Jg.  1,  Abt.  1,  p.  702  (1902). 


632 


LECTURE  XXVII. 


the  albumin  in  the  organism  is  protected  to  a  certain  extent  from  con- 
sumption. On  the  very  first  day  of  fasting,  there  is  in  the  majority  of 
cases  a  noticeably  high  elimination  of  nitrogen,  and  especially  when  the 
food  has  been  rich  in  proteins.  The  rise  in  the  amount  of  nitrogen  elimi- 
nated, which  in  individual  cases,  as  with  rabbits,  for  example,  reaches  a 
maximum  on  the  third  to  the  fifth  day  from  the  beginning  of  the  fasting, 
is  taken  as  a  guide  for  determining  the  time  when  the  carbohydrate  stores 
have  been  exhausted;  i.e.,  when  the  albumin-sparing  factor  has  been 
eliminated.1  Moreover,  this  increase  in  the  decomposition  of  albumin  is 
not  a  constant  phenomenon,  and  evidently  depends  upon  the  species.  In 
the  case  of  rabbits,  especially,  it  is  hard  to  determine  the  exact  day  when 
the  starvation  period  begins.  These  animals  have  an  extremely  volumi- 
nous intestine,  and  particularly  in  the  caBcum  there  is  always  a  mass  of  only 
partly  utilized  material  upon  which  the  animal  may  subsist  for  some  time. 
In  the  case  of  dogs,  in  general  there  is  a  uniform,  slowly  diminishing  elimi- 
nation of  nitrogen.2  Voit  has  shown  the  influence  of  a  preliminary  diet, 
rich  in  protein,  upon  the  elimination  of  nitrogen  during  the  first  day  of 
fasting,  by  the  following  three  experiments.3  He  determined  the  amount 
of  nitrogen  eliminated  daily.  Before  beginning  the  experiment  the  first 
dog  was  fed  daily  with  2500  grams  of  meat,  the  second  dog  received  1500 
grams  of  meat,  while  the  third  dog  was  fed  with  a  mixed  diet,  poor  in 
proteins. 


Nitrogen  Eliminated  in  Grams  per  24  Hours. 


Experiment  I. 

Experiment  II. 

Experiment  III. 

First  day  of  fasting    

60.1 

26.5 

13.8 

Second  day  of  fasting    

24.9 

18.6 

11.5 

Third  day  of  fasting      
Fourth  day  of  fasting    
Fifth  day  of  fasting   

19.1 
17.3 
12.2 

15.7 
14.9 
14.8 

10.2 
12.2 
12.1 

Sixth  day  of  fasting   

13.3 

12.8 

12.6 

Seventh  day  of  fasting 

12.5 

12.9 

11.3 

Eighth  dav  of  fasting    . 

10.1 

12.1 

10.7 

A  summary  of  the  nitrogen  elimination  in  a  five-day  fasting  experiment 
with  men,  is  given  by  the  following  values  published  by  Tigerstedt: 4 

1  R.  May:  Z.  Biol.  30,  1  (1894). 

2  M.  Kumagawa  and  R.  Miura:  Arch.  Anat.  Physiol.  1898,  431. 

3  Voit:  Hermann's  Handbuch,  6,  1,  p.  89  (1881). 

4  Robert  Tigerstedt:  Lehrbuch  der  Physiologic  des  Menschen.  3  Aufl.  Bd.  1,  p.  Ill 
(Leipsic,  1905). 


GENERAL   METABOLISM. 


633 


Decomposed  in  Grams. 

Total 

Transfor- 

Total 

mation 

Body 
Weight  in 
Kilograms 

Nitrogen. 

Fat. 

Carbohy- 

Alco- 

Transfor- 
mation in 
Calories. 

per  Kilo- 
gram of 
Body 

drate. 

hol. 

Weight  in 

Calories. 

Last  day  of  eating 

67.8 

23.41 

87 

267 

28 

2705 

39.9 

First  day  of  fasting 
Seco'nd  day  of  fasting 

67.0 
65.7 

12.17 
12.85 

206 
192 

2220 
2102 

33.2 
32.0 

Third  day  of  fasting 

64.9 

13.61 

181 

2024 

31.2 

Fourth  day  of  fasting 

64.0 

13.69 

178 

. 

1992 

31.1 

Fifth  day  of  fasting 

63.1 

11.47 

181 

1970 

31.2 

First  day  of  eating 

64.0 

25.44 

64 

250 

22 

2437 

38.1 

Second  day  of  eating 

65.6 

18.07 

72 

248 

37 

2410 

36.8 

From  these  values  it  is  apparent  that  the  starving  man  quickly  adjusts 
himself  to  a  definite  minimum  consumption. 

In  the  further  duration  of  the  fasting  period  the  organism  lives  exclu- 
sively at  the  cost  of  its  protein  and  its  stores  of  fat.  The  carbohydrates 
are  quickly  consumed,  and  in  the  later  periods  come  scarcely  into 
consideration  at  all.  The  starving  organism  is  very  economical  with  its 
protein.  Of  the  total  calories  84  to  90  per  cent  come  from  the  fat,  and 
only  from  10  to  16  per  cent  from  protein.  This  holds  naturally  only  for  fat 
animals.  After  a  time  the  stores  of  fat  are  exhausted,  and  the  organism  is 
then  compelled  to  obtain  the  requisite  amount  of  energy  (calories)  at  the 
expense  of  its  own  protein.  At  this  time  there  is  a  rapid  increase  in  the 
elimination  of  nitrogen  through  the  urine.  This  was  observed  by  Voit,1 
and  has  subsequently  been  much  discussed.  As  a  matter  of  fact,  the 
animals  experimented  upon  were  found  to  be  not  entirely  free  from  fat  at 
the  time  when,  just  before  death,  there  was  an  increased  elimination  of  nitro- 
gen in  the  urine.  Often  quite  a  considerable  amount  of  fat  has  been 
found  to  be  present  at  such  a  time.  On  account  of  this  fact  the  conclusion 
has  been  drawn  that  the  increased  elimination  of  nitrogen  is  not 
altogether  due  to  the  fact  that  the  store  of  fat  has  been  entirely  con- 
sumed, but  that  there  must  be  other  causes.  F.  N.  Schulz  2  assumes 
that  the  increased  decomposition  of  protein  just  before  death  by  starvation 
is  to  be  attributed  to  the  sudden  destruction  of  numerous  cells  in  the  body. 
It  is  indeed  conceivable  that  the  cells,  whose  ability  is  taxed  to  the 
utmost  during  starvation,  in  order  to  provide  the  necessary  material  for 
the  general  metabolism,  at  last  disintegrate.  They  are  constantly  giving 


1  E.  Voit:  Z.  Biol.  41,  113,  502,  550  (1901). 

2  F.  N.  Schulz:  ibid.  41,  368  (1901),  and  Pfliiger's  Arch.  76,  379  (1899). 


634  LECTURE  XXVII. 

up  material  but  receive  nothing  from  without.  The  increase  in  the  elim- 
ination of  nitrogen  shortly  before  death  may  be  prevented  by  feeding 
cane-sugar.  Thus  Kaufmann  l  fed  starving  rabbits  with  25  to  30  grams 
of  sugar  daily,  and  when  they  died,  at  the  end  of  18  or  19  days,  it  was 
without  the  appearance  of  the  increased  nitrogen  elimination.  This  ex- 
periment does  not  permit  us  to  decide  satisfactorily  the  question  as  to 
the  cause  of  the  increased  decomposition  of  albumin  which  has  been  so 
often  observed  just  before  the  end  of  the  fasting  period.  It  is  possible 
that,  when  the  cane-sugar  is  fed  to  the  starved  animals,  the  destruction 
of  the  cells  is  prevented.  On  the  other  hand  naturally  the  carbohydrate 
acts  as  a  protein-sparer.  Perhaps  the  increased  elimination  of  nitrogen 
is  prevented  for  this  reason.  Furthermore,  it  must  not  be  left  out  of 
consideration  that,  as  we  have  already  frequently  mentioned,2  there 
is  no  question  but  that  fat  acts  as  a  solvent  for  many  substances,  and 
plays  an  important  part  in  this  direction,  besides  its  function  of  acting 
as  reserve  material.  Especially  in  the  extensive  transportation  of 
material  from  one  cell  to  another,  it  is  possible  that  the  fat  content 
of  the  tissues  may  play  an  important  part.  If  the  amount  of  fat 
present  has  been  reduced  to  a  minimum,  the  exchange  of  material 
will  necessarily  suffer,  and  thereby  the  entire  metabolism.  We  must 
also  not  forget  that  evidently  the  fat,  as  it  lies  deposited  in  the  fat- 
cells,  cannot  be  consumed  as  such  by  the  body.  It  must  first  be  removed 
from  the  cell.  It  is  very  probable  that  a  cleavage  into  fatty  acid  and 
glycerol  takes  place.  This  eventually  affects  cell  activity,  for  only  the  cell 
can  yield  the  required  ferment.  It  is  perfectly  clear  that  when  the  cells 
are  working  with  a  limited  supply  of  material,  the  formation  of  the 
ferment  will  finally  be  influenced.  It  might  be  thought,  a  priori,  that  the 
oxidation  power  of  the  starved  organism  would  likewise  become  consid- 
erably lessened.  This  is,  however,  not  the  case,  or  at  least  not  of  the 
oxidation  processes  as  a  whole.  M.  Nencki  and  N.  Sieber  3  injected  sub- 
cutaneously  one  gram  of  benzene  into  a  rabbit  weighing  2.517  kilograms. 
They  subsequently  found  0.307  gram  of  phenol  in  the  urine.  The  animal 
was  then  starved  for  three  days,  at  the  end  of  which  time  it  weighed  2.425 
kilograms.  Once  more  a  gram  of  benzene  was  injected,  and  this  caused 
the  elimination  of  0.334  gram  of  phenol.  Analogous  results  were  obtained 
in  experiments  with  dogs.  On  the  other  hand,  the  observation  that  in 
starvation  the  ratio  of  the  neutral  sulphur  to  the  oxidized  sulphur  increases 
in  value  indicates  a  lessened  oxidation  power  of  the  starving  organism. 
We  should  not  yet  attempt  to  draw  definite  conclusions  from  the  experi- 
ments at  hand.  It  is  perfectly  possible  that  the  power  of  oxidation  is 


1  M.  Kaufmann:  Z.  Biol.  41,  75  (1901). 

2  Cf.  Lecture  VI,  p.  112. 

3  Pfliiger's  Arch.  31,  319  (1883). 


GENERAL   METABOLISM. 


635 


lessened  only  in  certain  directions.  On  the  other  hand,  in  discussing 
animal  oxidations  we  called  attention  to  the  importance  of  the  preliminary 
cleavage  for  a  complete  combustion.1 

If  food  is  no  longer  withheld  from  the  animal,  it  recovers  rapidly. 
It  replaces  first  of  all  what  it  has  lost  of  its  own  body-substance,  and  seeks 
to  regain  its  former  condition. 

Now  it  is  very  interesting  to  find  that  during  starvation  the  animal 
organism  attacks  the  different  parts  of  its  own  body-material  to  quite 
different  extents.  It  might  have  been  expected,  a  priori,  that  those  organs 
would  suffer  most  upon  which  the  greatest  demands  are  placed.  On  the 
contrary,  there  is  a  constant  transference  of  material  to  those  organs  which 
are  most  useful  and  are  consequently  most  indispensable  to  life.  This  was 
shown  very  clearly  in  considering  the  life  and  development  of  the  salmon,2 
and  led  to  the  question  whether  we  must  not  assume  that  the  starving 
organism  is  obliged  to  effect  extensive  syntheses  from  the  building-stones 
of  the  less  important  cells.  We  can  easily  believe  that  the  heart,  whose 
function  is  so  essential  for  the  maintenance  of  life,  retains  its  material 
unchanged  and  carries  out  its  work  at  the  expense  of  other  tissue.  On 
the  other  hand,  it  is  also  possible  that  the  muscle-cells  of  the  heart  are 
constantly  being  broken  down  and  rebuilt.  At  present  we  have  no  means 
of  estimating  the  life  of  a  cell,  and  cannot  decide  how  long  it  can  retain  its 
corporate  existence,  or  whether  it  is  constantly  assimilating  and  giving  up 
material.  If  the  latter  is  the  case,  then  the  tissues  of  the  starving  organism 
must  be  the  scene  of  remarkable  transformations. 

Voit 3  gives  the  following  values  for  the  loss  of  body-weight  during  starva- 
tion in  the  case  of  doves  and  cats. 


Per  cent  of  Original 
Weight. 

Per  cent  of  Original 
Weight. 

Doves. 

Cats. 

Doves. 

Cats.  . 

Fat    
Spleen 

93 
71 
64 
52 
45 
42 
42 

97 
67 
17 
54 
3 
18 
31 

Testes  

33 
32 
22 
17 

2 

40 
21 
26 
18 
14 
3 

Skin 

Pancreas          .... 

Kidnevs     .... 

Liver     

Lungs     

Heart    
Intestine 

Bones     .    .  t.    .    ,    . 
Nervous  system  .    . 

Muscles    

1  Cf.  Lecture  XIX,  p.  451  et  seq. 

3  Cf.  Lecture  XVI,  p.  351. 

3  Handbuch  der  Physiologic  des  Gesamtstoffwechsels  und  der  Fortpflanzung.  Part  I. 
Physiologic  des  allgemeinen  Stoffwechsels  und  der  Ernahrung  by  C.  von  Voit,  Vol.  6, 
p.  96,  97  Leipsic  (1881). 


636  LECTURE  XXVII. 

It  is  evident  from  this  summary  that  the  organs  which  are  in  constant 
activity,  as  the  heart,  lungs,  kidneys,  and  nervous  system,  suffer  much  less 
loss  of  weight  than  the  other  organs.  Voit  also  tested  the  influence  of  the 
activity  of  an  organ  upon  keeping  its  composition  constant  by  feeding 
doves  with  food  which  was  deficient  in  lime,  but  contained  a  sufficient 
amount  of  other  materials.  A  post-mortem  examination  showed  that 
those  bones  which  were  in  constant  use  had  suffered  less  from  the  lack  of 
lime  than  relatively  inactive  bones,  such  as  the  breast-bone  and  the  bill. 
The  last  two  bones  had  become  perfectly  porous.  Evidently  the  composi- 
tion of  the  bones  which  were  used  most  was  maintained  at  the  expense  of 
the  others.  In  this  direction  the  observation  of  E.  Pfliiger  on  dogs  is 
worth  mentioning.  He  found,  as  has  already  been  mentioned,1  that  when 
the  pancreas  was  extirpated  the  liver  of  these  animals  tended  to  gain 
rather  than  lose  in  weight.  Evidently  the  liver  is  an  important  place  for 
transformations,  such  as  fat  into  sugar,  etc.2 

The  loss  in  weight  affects  all  the  different  substances  contained  in  the 
organs.  The  starving  animal  constantly  loses  water  even  when  it  is  given 
none  to  drink.  Water  is  formed  by  the  combustion  of  fat  and  albumin. 
Mineral  substances  are  likewise  being  eliminated  constantly.  The  organs 
maintain  their  functions  as  long  as  possible  even  in  those  cases  where,  as  far 
as  we  know,  the  organ  is  dispensable.  Thus  while  the  secretion  of  bile 
diminishes,  to  be  sure,  during  starvation,  still,  on  the  other  hand,  it  con- 
tinues to  form  for  quite  a  length  of  time.  Likewise  the  secretion  of  milk 
continues  for  a  time.  On  the  other  hand,  the  gastric  secretion  soon  ceases, 
as  was  shown  by  the  examination  of  the  contents  of  the  stomach  of  the 
fasting  professional,  Succi. 

A  very  important  result  of  these  starvation  experiments  is  that  the 
animal  organism  constantly  eliminates  nitrogen  under  all  conditions.  To 
be  sure,  the  amount  of  decomposed  albumin  may  become  quite  small,  but 
it  never  ceases  altogether.  Albumin  assumes,  as  we  have  already  shown 
in  discussing  the  Law  of  Isodynamics,3  a  peculiar  position  among  our 
organic  foodstuffs.  It  cannot  be  entirely  replaced  by  any  other  material. 
It  is  possible  to  nourish  a  dog  upon  albumin  alone,  and  even  to  fatten  it 
somewhat.  This  is  never  the  case,  however,  when  the  total  calorific 


1  Cf.  Lecture  V,  p.  85. 

2  The  observations  concerning  the  relative  loss  of  weight  for  the  different  parts  of 
the  body  are  as  a  rule  very  inadequate  and  unsatisfactory.     We  have  stated  above  the 
generally  accepted  view  concerning  these  relations,  but  we  must  say  that  the  field  has 
not  yet  been  well  covered.     There  is  no  question  but  that  a  careful  examination  of  the 
losses  of  the  different  organs  in  their  various  constituents,  naturally  referred  to  average 
values,  will  give  us  a  new  point  of  view  concerning  intermediate  metabolism  and  of  the 
relations  existing  between  the  individual   organs.     The  well-known  experiment  of 
Miescher  is  the  first  step  in  this  direction. 

8  Cf.  Lecture  XV,  p.  336. 


GENERAL   METABOLISM.  637 

requirement  is  met  with  nitrogen-free  food.  It  is  then  impossible  to  pre- 
vent the  animal  from  losing  weight  even  when  far  more  fat  and  carbo- 
hydrate are  fed  to  it  than  corresponds  to  the  calories  required  when  the 
dog  was  in  metabolic  equilibrium  with  albumin  present  in  its  food. 
As  soon  as  the  albumin  is  wanting  in  the  food  supply,  starvation 
metabolism  begins,  i.e.,  body  albumin  begins  to  be  decomposed.  It  is 
true  that  the  animal  lives  a  few  days  longer  than  if  it  were  absolutely 
starving  on  account  of  lack  of  all  food,  but  it  will  gradually  die  as  a  result 
of  albumin  starvation.  The  decomposition  of  albumin  shows  a  peculiar 
behavior  when  varying  amounts  of  albumin  are  present  in  the  food.  The 
more  albumin  the  animal  eats,  the  more  there  is  decomposed.  To  be  sure, 
by  greatly  increasing  the  amount  of  albumin  it  is  possible  for  the  organism 
to  store  away  material,  but  usually  not  in  the  form  of  albumin  itself.  The 
cells  of  the  body  evidently  strive  to  keep  the  albumin  content  of  the  organ- 
ism at  a  constant  level.  It  is  possible  to  bring  an  animal  into  so-called 
nitrogen  equilibrium  with  different  amounts  of  albumin.  Equilibrium  is 
reached  when  the  organism  experimented  upon  eliminates  the  same  amount 
of  nitrogen  that  it  receives.  This  relation  is  most  apparent  if  instead  of 
estimating  the  amount  of  nitrogen  eliminated  during  a  single  day,  a  period 
of  several  days  is  studied. 

The  fact  that  an  increase  in  the  albumin  income  also  causes  an  increase 
in  the  total  metabolism  apparently  helps  to  enable  us  to  decide  whether 
the  cell-material,  or  protoplasm,  itself  takes  part  directly  in  the  decompo- 
sitions and  combustions,  or  whether  we  have  to  distinguish  sharply  between 
the  cell-nutriment  and  the  cell-building-stones.  Here  we  meet  with  the 
most  important  problem  of  metabolism.  It  is  quite  generally  assumed  that 
in  animal  combustions  it  is  chiefly  the  albumin  in  the  nutriment,  also 
designated  as  circulating  albumin,  which  is  consumed,  while  the  living 
protoplasm  is  only  drawn  upon  for  the  outgo  when  there  is  a  deficiency  in 
the  supply  of  albumin.  There  are  a  number  of  observations  which  support 
this  assumption.  Above  all,  it  is  remarkable  how  quickly  the  albumin  is 
oxidized  after  its  introduction  into  the  organism.  Within  a  few  hours  the 
total  amount  of  nitrogen  reappears  in  the  urine.  It  is  hardly  absorbed 
before  its  elimination  begins.  Although  the  presence  of  fat  and  carbo- 
hydrate in  the  food  somewhat  diminishes  the  decomposition  of  albumin, 
still  on  the  whole  the  decomposition  of  the  albumin  is  about  the  same  as 
with  a  purely  meat  diet.  The  fact  that  the  extent  of  albumin  decomposi- 
tion is,  within  wide  limits,  independent  of  the  albumin  content  of  the  body 
itself,  has  also  been  cited  as  supporting  the  above  conception.  The 
assumption  that  the  tissue-cells  of  the  fully  developed  animal  organism 
are  in  a  relatively  stable  condition,  and  work  essentially  by  means  of  the 
energy  obtained  from  the  food,  is  an  attractive  one.  According  to  this, 
the  cell  takes  up  from  the  blood,  or  the  plasma,  the  substances  which  it 


638  LECTURE  XXVII. 

requires  for  the  exercise  of  its  functions.  It  retains  its  own  cell-material. 
The  fact  that  now  and  then  a  few  cells  are  broken  down  and  renewed, 
hardly  affects  the  metabolism  as  a  whole. 

This  very  simple  representation  of  metabolism  is,  however,  as  we  shall 
find  on  closer  examination,  not  entirely  in  accordance  with  certain  facts. 
As  we  have  already  repeatedly  stated,  it  has  become  recognized  during  the 
last  few  years  that  the  digestion  of  the  food  is  not  for  the  sole  purpose  of 
making  it  capable  of  absorption.  Unquestionably,  one  of  the  principal 
objects  is  to  make  the  material  which  is  obtained  from  different  sources 
conform  to  the  material  out  of  which  the  body  is  made  up.  The  substances 
contained  in  the  food  are,  by  means  of  the  various  ferments,  not  only  made 
capable  of  absorption,  but  of  assimilation  as  well.  Starch,  which  is  the 
glycogen  of  plants,  is  broken  down  into  molecules  of  d-glucose,  only  to  be 
changed  later  into  animal  glycogen.  We  do  not  yet  know  how  much  of 
the  absorbed  glucose  is  changed  into  the  latter  compound,  nor  whether 
the  glycogen  throughout  the  entire  animal  kingdom  is  all  of  the  same  nature, 
or  whether  perhaps  there  are  not  different  kinds  of  glycogen  corresponding 
to  the  different  species  of  animals.  Here  we  cannot  decide  definitely 
whether  the  preliminary  preparation  is  all-important  as  regards  assimilation, 
or  whether  it  merely  serves  the  purpose  of  making  the  material  capable  of 
absorption.  The  question  is  similar  in  the  case  of  the  fats.  In  this  case 
one  might  even  get  the  impression  that  the  nutriment  is  deposited  in  an 
unchanged  condition.  The  fat  is  split  by  the  digestive  ferments  into  its 
constituents,  fatty  acids  and  glycerol,  which,  however,  unite  again  in  the 
intestinal  wall.  It  has  been  found  possible  to  cause  foreign  fat  to  be 
deposited  in  the  body.  We  have  already  shown  that  the  fat  stores  occupy 
a  peculiar  position  in  animal  economy.  It  is  a  question  whether  the  animal 
organism  can  also  utilize  substances  foreign  to  it  for  physiological  functions 
in  cell-metabolism.  At  the  same  time  we  may  quite  safely  assume  that 
in  the  case  of  the  fats,  digestion  only  serves  to  prepare  it  for  absorption.  To 
be  sure,  we  must  confess  that  the  fat  stores  of  different  animals  under 
normal  conditions  are  not  homogeneous  as  regards  their  composition. 
How  far  these  differences  in  chemical  composition  depend  upon  differences 
in  the  nature  of  the  food,  remains  an  open  question.  In  general  we  may 
indeed  assume  that  the  fat  contained  in  the  stores  has  a  specific  composi- 
tion for  every  animal,  in  case  the  animal  is  not  deprived  of  the  power  to 
construct  its  own  fat  by  decomposition  and  selection,  on  account  of  being 
limited  to  fat  of  a  definite  kind. 

At  all  events,  it  is  very  remarkable  how  quickly  and  easily  the  animal 
organism  decomposes,  by  means  of  the  ferments,  the  fats  and  complicated 
carbohydrates  into  their  simple  components,  only  to  rapidly  reconstruct 
them  again,  and  eventually,  at  the  time  they  are  consumed,  carry  away 
the  resulting  products  equally  rapidly.  These  very  complicated  processes 


GENERAL   METABOLISM.  639 

become  still  more  remarkable  when  we  follow,  as  we  have  done,  the  behavior 
of  albumin  in  the  animal  organism.  We  find  that  in  the  alimentary  canal 
it  undergoes  a  far-reaching  decomposition.  Now  the  different  albumins 
are  very  similarly  constituted  in  respect  to  the  amino  acids  which  they 
contain.  With  few  exceptions  they  all  contain  the  same  building-stones. 
Their  chief  difference  lies  in  the  relative  amounts  which  they  contain  of 
these  acids.  In  spite  of  these  differences  the  serum  albumins  are,  as  far 
as  our  knowledge  goes,  of  the  same  composition,  no  matter  whether  the 
albumins  contained  in  the  food  are  closely  related  to  the  serum  bodies 
in  their  composition  or  not.1  Although  the  researches  in  this  direction 
have  only  just  begun,  still  a  number  of  observations  indicate  that  the 
albumin  in  the  food  is  so  transformed  before  it  reaches  the  circulation  and 
the  tissues  that  it  loses  its  original  character  and  becomes  of  a  nature 
corresponding  to  the  body  albumins,  first  of  all  to  the  serum  albumins. 
It  is,  in  fact,  not  the  albumins  of  the  food  that  circulate  in  the  blood  and 
tissues,  but  rather  those  of  the  body  itself.2  Possibly,  if  we  were  able  to 
trace  more  closely  the  transformations  of  the  albumias  on  their  path  of 
absorption  and  assimilation,  and  had  a  better  understanding  of  the  albu- 
min molecule,  the  decompositions  would  then  appear  to  be  very  simple 
ones.  At  present  it  appears  as  if  we  could  not  neglect  the  above-described 
relations  in  the  conception  of  albumin  metabolism.  According  to  them, 
the  decomposition  which  albumin  undergoes  does  not  appear  to  be  a  rela- 
tively simple  process.  It  is  certain  that  the  albumin  before  it  is  consumed 
must  be  decomposed  again  in  the  tissues  into  simpler  components.  The 
great  question  is  only  with  regard  to  the  reason  for  the  changes  in  the 
albumin  in  the  food,  so  that  it  becomes  like  the  albumin  of  the  body,  when 
it  is  to  be  consumed  so  quickly. 

It  seems  to  us  as  if  the  answer  to  this  question,  as  we  have  previously 
stated,3  will  give  the  solution  to  the  enigma  of  the  large  albumin  require- 
ment. To  be  sure,  the  animal  organism  effects  all  these  changes  chiefly 
in  order  that  nourishment  may  be  offered  to  the  cells  in  a  form  such 
that  they  are  able  to  utilize  it.  We  must  always  remember  that  the  cells 
eventually  accomplish  their  work  by  means  of  ferments,  and  that  these  are 
regulated  very  sensitively  so  that  they  will  react  only  with  certain  definitely 
constituted  compounds.  Undoubtedly  the  tissue-cells  cannot  break  down 
and  utilize  starch,  or  the  fat  and  albumin  of  the  food.  The  intestine 
works  over  these  materials  and  gives  to  the  cells  nutriment  of  quite  specific 
composition.  The  cells  are  capable  of  utilizing  these  definite  products  and 
only  these.  Their  whole  construction  corresponds  to  these  compounds. 


1  Emil  Abderhalden  and  Franz  Samuely:  Z.  physiol.  Chem.  46,  193  (1905). 

2  In  Lecture  XXIX  we  shall  discuss  a  biological  method  for  determining  whether 
the  albumin  nutriment  passes  directly  into  the  blood  and  lymph  circulation. 

3  Cf.  Lecture  XI,  p.  223  et  seq. 


640  LECTURE  XXVII. 

This  is  a  satisfactory  explanation  as  regards  the  carbohydrates  and  fats, 
which,  at  least  with  fully  developed  organisms,  can,  under  certain  con- 
ditions, be  regarded  solely  as  combustible  materials.  The  amount  of  these 
substances  consumed  is  determined  by  the  amount  of  energy  which  is  trans- 
formed in  the  body.  If  the  supply  of  carbohydrate  or  fat  is  greater  than 
the  organism  requires  at  a  given  time,  some  of  it  is  laid  aside.  It  is  quite 
different  with  albumin.  The  amount  at  hand  regulates  the  entire  metab- 
olism. The  more  there  is  present,  the  greater  the  metabolism.  Why  is 
so  much  albumin  required?  The  distinction  between  circulating  albumin, 
i.e.  albumin  which  is  to  be  used  as  fuel,  and  organized  albumin,  or  that 
which  is  used  for  the  construction  of  cell-material,  does  not  help  us  here.1 
As  a  matter  of  fact,  there  is  no  proof  that  there  is  any  justification  for  a 
sharp  distinction  between  these  two  kinds  of  albumin.  As  we  have  pre- 
viously stated,  we  prefer  to  consider  the  total  albumin  metabolism  from  a 
single  standpoint  and  to  trace  the  high  requirement  of  albumin  on  the  part 
of  the  animal  organism  to  the  fact  that  in  the  adaptation  of  the  albumin 
in  the  food  to  the  form  required  by  the  body  there  are  quite  a  number  of 
the  simpler  constituents  which  are  not  suitable  for  synthesizing  the  new 
albumin,  and  these  are  eliminated.  The  intestine  contains  a  mixture  of 
different  amino  acids  from  which  it  selects  those  which  suit  it  and  in  quite 
definite  porportions.  Here  again  the  Law  of  the  Minimum  holds.  The 
amount  of  amino  acid  which  is  utilized  in  the  synthesis  of  new  albumin  is 
governed  by  the  amount  of  that  amino  acid  which  is  present  to  the  slightest 
extent  relatively.  This  conception  holds  only  while  we  have  no  positive 
proof  that  the  animal  cell  is  capable  of  forming  one  amino  acid  from  another 
to  any  considerable  extent.  For  the  present  our  knowledge  of  the  rela- 
tions concerning  the  decompositions  in  the  tissues  makes  any  such  assump- 
tion appear  improbable.  Now  the  most  widely  different  cell  complexes 
likewise  possess  their  own  characteristic  albumin.  We  refer,  for  example, 
to  the  histones,  which  differ  again  from  the  albumin  of  their  nutriment, 
in  this  case  the  serum  albumin.  Here  again  the  nutriment  is  broken  down, 
and  again  the  cell  chooses  those  building-stones  which  it  can  utilize,  and 
rejects  the  others.  Thus  we  can  imagine  that  in  this  reconstruction  of  the 
cells,  which,  although  not  very  extensive  of  itself,  is  nevertheless  constantly 
taking  place,  a  considerable  supply  of  albumin  is  required.  When  the 
albumin  supply  is  large,  the  cell  is  assured  of  a  sufficient  supply  of  all  the 
most  varied  building-stones.  The  unutilized  amino  acids  are  at  once 
robbed  of  their  amino  group,  and  perhaps  the  nitrogen-free  chains  are 
further  utilized.  Even  in  starvation  metabolism  the  consumption  of 
albumin  must  be  remarkably  high,  for,  in  this  case  also,  the  albumin  trans- 


1  Cf.  Emil  Abderhalden:  Zentr.  gesamte  Physiol.  u.  Pathol.  des  Stoffwechsels,  N.  F. 
1  (1906). 


GENERAL   METABOLISM.  641 

ported  from  organs  of  minor  importance  cannot  be  utilized  directly.  Here 
again  there  is  a  preliminary  decomposition  and  selection  of  material. 

Now  the  only  other  striking  phenomenon  is  that  an  increased  supply  of 
albumin  increases  the  extent  of  the  entire  metabolism;  i.e.,  not  that  of 
albumin  alone.  Perhaps  this  discovery  may  be  accounted  for  by  the  fact 
that  the  animal  organism  evidently  has  no  depot  for  storing  up  the  excess 
of  albumin.  This  is  evident  because  it  is  so  difficult  under  normal  condi- 
tions of  nutrition  to  cause  a  deposition  of  albumin  in  the  fully  developed 
organism.  Under  these  circumstances  it  is  perfectly  conceivable  that  when 
there  is  an  increased  supply  of  albumin  there  is  a  greater  amount  of  cellular 
transformations  so  that  the  other  materials  are  also  required. 

In  this  explanation  we  wish  to  call  particular  attention  to  the  importance 
that  is  attached  to  the  maintenance  of  the  perfectly  specific  cell  construction 
in  the  case  of  each  species  of  animals  and  perhaps  of  every  single  individual. 
Here  unquestionably  the  proteins  play  the  most  important  part  by  virtue 
of  the  fact  that  they  offer  such  a  variety  of  forms.  The  abundant  supply  of 
albumin  guarantees  to  the  animal  organism  its  own  individuality  and  that 
of  its  cells  as  well  as  its  own  metabolism. 

We  must  at  this  place  once  more  mention  the  fact  that  albumin 
metabolism  has  been  studied  almost  entirely  from  a  single  point  of  view. 
The  rapidity  of  the  albumin  decomposition  has  been  identified  with  the 
rapidity  of  the  nitrogen  elimination.  We  have,  however,  no  precise  reason 
for  assuming  that  the  splitting-off  of  the  nitrogen  is,  as  a  matter  of  fact, 
the  signal  for  the  disruption  of  the  entire  molecule.  After  the  formation 
of  urea,  carbon  chains  remain  which  may  be  utilized  in  a  number  of  different 
ways.  It  is  possible  that  the  cells  prefer  to  have  so  much  albumin  because 
it  provides  them  with  all  the  different  materials  which  they  require.  It  is 
perfectly  thinkable  that  these  carbon  chains  can  be  used  to  form  sugars, 
or  they  might  equally  well  be  utilized  for  the  production  of  fat. 

It  is,  as  the  above  discussion  shows,  perfectly  impossible  to  give  an 
explanation  of  albumin  metabolism  which  shall  be  based  upon  exact 
experimentation.  We  can  indeed  formulate  hypotheses,  but  for  the 
present  there  is  no  preference  to  be  given  to  any  particular  one.  None  of 
the  present  hypotheses  satisfactorily  unites  all  the  known  facts,  in  such  a 
way  that  in  every  respect  all  the  results  of  experimentation  are  clearly 
accounted  for.  We  must  leave  these  questions  entirely  open,  and  suggest 
that  new  theories  and  new  experiments  can  alone  cause  progress,  and  con- 
sequently a  discussion  of  the  various  attempts  at  explanation  would  be 
scarcely  worth  our  while.  Again  and  again  in  the  questions  arising  from 
all  sorts  of  different  kinds  of  metabolism  we  run  against  the  metabolism  of 
the  cell,  and  cell  activity.  The  conception  of  intermediary  metabolism  is 
a  very  accessible  one.  We  are  constantly  coming  in  contact  with  it.  It 
is  here  the  place  to  state  that  contrary  to  what  one  might  expect  by  reading 


642  LECTURE  XXVII. 

the  literature,  as  far  as  we  are  concerned  it  is  an  unknown  quantity,  and 
at  present  we  have  practically  no  clear  insight  into  cell-metabolism.  For 
the  time  being  we  recognize  only  the  general  stages  of  metabolism  as  a 
whole.  There  is  here  a  vast  field  for  experimentation  which  has  scarcely 
been  touched  upon.  It  is  only  by  a  clear  recognition  of  this  fact  that  it 
will  be  possible  for  us  to  penetrate  fully  unprejudiced  into  this  obscurity, 
and  with  new  methods  and  new  resources  succeed  in  gradually  developing 
more  and  more  facts  which  will  replace  the  hypotheses.  We  have  gone 
into  albumin  metabolism  upon  a  somewhat  broad  basis,  because  eventually 
all  questions  concerning  metabolism,  no  matter  what  their  nature  may  be, 
directly  or  indirectly  •  penetrate  into  the  problem  of  albumin  metabolism 
in  the  animal  organism.  The  uncertainty  which  at  present  envelops  the 
latter  to  some  extent  affects  all  other  investigations  in  this  field,  and 
explains,  at  least  to  some  extent,  the  different  answers  which  have  been 
given  the  apparently  similar  questions  concerning  metabolism. 

In  this  connection  we  must  once  more  remember  that  it  is  exceedingly 
difficult  to  cause  a  deposition  of  albumin  in  the  animal  organism.  Muscular 
work  has  a  remarkably  favorable  action  in  this  direction.  The  significance 
of  work  for  accomplishing  an  albumin  "fattening"  has  been  recognized 
by  the  physician.  A  retention  of  nitrogen  has  alone  been  satisfactorily 
established  in  this  connection.  Less  nitrogen  appears  in  the  urine  than 
the  organism  receives.  We  do  not  know  what  becomes  of  this  nitrogen 
that  remains  in  the  body.  From  the  experiments  of  Schreuer l  we  know 
that  the  "albumin"  retained  in  the  body  is  not  equivalent  to  the  remaining 
albumin  in  the  body.  The  deposited  albumin  is  readily  lost  again,  for  when 
the  ordinary  diet  is  resorted  to,  the  organism  soon  returns  to  its  usual 
albumin  condition.  This  is  true  especially  of  the  nitrogen  retention  which 
is  brought  about  by  a  large  supply  of  albumin.  If,  at  the  same  time, 
demands  are  placed  upon  a  function  of  the  body,  e.g.,  that  of  the  muscles, 
we  can  easily  imagine  that  the  individual  cells  will  attempt  to  utilize  this 
for  increasing  their  cell  material. 

In  the  fully  developed  organism  there  is  also  some  occasion  for  albumin 
being  retained.  It  requires  constructive  material.  Direct  experiments 
teach  that  the  developed  organism  in  fact  constantly  acquires  nitrogen. 
The  adult  organism  during  pregnancy  finds  itself  placed  under  quite  similar 
conditions  as  during  youth.  Here  again  there  is  a  constant  formation  of 
new  tissue  to  an  unusual  extent.  Corresponding  to  this,  P.  Bar  and  R. 
Daunay2  showed  that  in  the  case  of  a  gravid  bitch,  nitrogen  was  constantly 
held  back  from  the  nourishment.  This  nitrogen  retention  was  also  notice- 
able when  the  food  was  the  same  as  that  with  which  the  animal  was  in 


1  Pfliiger's  Arch.  110,  227  (1905).     Cf.  Karl  Bornstein:  ibid.  106,  66  (1904). 
3  J.  physiol.  et  pathol.  general,  1,  832  (1905). 


GENERAL   METABOLISM.  643 

nitrogen  equilibrium  before  the  period  of  gestation.  From  this  fact  it 
follows  that  the  developing  fetus  does  not  live  at  the  expense  of  the  organ- 
ism of  the  mother,  but  to  a  certain  extent  is  included  in  the  general  nourish- 
ment. The  organism  of  the  pregnant  mother  utilizes  to  better  advantage 
than  usual  the  substances  contained  in  the  food  and  especially  the  protein. 

In  discussing  the  replacement  of  one  foodstuff  by  another  and  the  posi- 
tion of  each  in  animal  economy,  we  have  considered  the  suitability  of  each 
kind  of  food  for  definite  functions.  We  have  seen  that  the  carbohydrate 
decomposition  is  proportional  to  the  amount  of  muscular  work,  and  that 
fats  and  also  albumins,  can  replace  carbohydrates  as  sources  of  energy.1 

It  remains  for  us  to  mention  briefly  the  influence  of  certain  external 
conditions  upon  metabolism.  Above  all,  the  influence  of  the  surround- 
ings is  of  interest.  Up  to  the  present  time  the  effect  of  temperature  has 
alone  been  studied  to  any  extent.  In  this  respect  the  poikilothermous 
animals  are  very  different  from  the  homothermous  ones.  In  the  former, 
metabolism  runs  parallel  to  the  variations  in  temperature,  i.e.,  it  decreases 
with  a  fall  in  the  external  temperature  and  increases  with  a  rise  in  tem- 
perature. This  can  be  demonstrated  very  clearly  by  studying  the  respi- 
ratory exchange.  The  warm-blooded  animals,  on  the  other  hand, 
behave  quite  differently.  With  them  metabolism  increases  with  falling 
temperature  and  decreases  with  rising  temperature.  This  is  due  to  the 
fact  that  the  warm-blooded  animals  seek  to  keep  their  body-temperature 
the  same,  irrespective  of  the  external  conditions.  The  loss  of  heat  caused 
by  a  fall  in  the  external  temperature  is  compensated  by  an  increased 
metabolism.  The  muscles  are  the  principal  seat  of  this  change  in  the  extent 
of  the  metabolism.  If  the  muscular  activity  which  may  be  expressed 
by  movements,  by  shivering,  or  also  by  muscular  tensions,  is  prevented 
by  curare  poisoning  or  by  severing  the  spinal  cord  high  up,  the  heat 
regulation  ceases.  The  principle  that  the  metabolism  of  homothermous 
animals  increases  with  falling  temperature  and  conversely  diminishes  with 
rising  temperature  holds  only  in  part.  It  has  been  shown  that  a  consid- 
erable rise  of  temperature  also  has  a  similar  effect  upon  the  warm-blooded 
animals  as  upon  the  cold-blooded  ones;  the  metabolism  increases  so  that 
there  is  an  increased  production  of  heat  against  which  the  organism  seeks 
to  protect  itself  by  giving  off  more  heat.  The  chief  difference,  then, 
between  the  homothermous  animals  and  the  poikilothermous  ones  is  their 
opposite  behavior  with  regard  to  a  fall  in  temperature. 

1  There  are  a  great  many  experiments  concerning  metabolism  under  varying  condi- 
tions. We  cannot  consider  them  here,  because  in  most  cases  it  is  difficult  to  establish 
the  exact  effect  of  the  different  factors.  We  would  refer  to  the  influence  of  high  altitude 
upon  metabolism,  and  of  a  sea-shore  climate.  Cf.  N.  Zuntz,  A.  Loewy,  F.  Miiller,  and 
W.  Caspari:  Hohenklima  und  Bergwanderungen  in  ihrer  Wirkung  auf  den  Menschen. 
Bong  &  Cie,  1906.  A.  Jaquet  and  R.  Stahelin:  Arch,  exper.  Path.  Pharm.  46,  274 
(1901).  Loewy  and  Miiller:  Pfliiger's  Arch.  103,  1  (1904). 


LECTURE  XXVIII. 

GENERAL   METABOLISM. 

II. 

THE  human  and  animal  organism  requires  for  the  maintenance  of  its 
bodily  condition  and  for  the  exercise  of  its  functions  a  perfectly  definite 
amount  of  nutriment.  The  nutritional  requirement  depends,  naturally, 
upon  various  external  conditions.  Unquestionably  individual  peculiari- 
ties also  come  into  play  here,  at  least  to  some  extent.  One  very  important 
factor  is  the  amount  of  work  to  be  performed.  It  is  also  self-evident  that 
the  large  amount  of  new  tissue  which  is  being  formed  in  the  growing 
organism  also  influences  the  amount  of  food  required. 

There  are  a  number  of  different  ways  for  getting  an  idea  of  the  amount 
of  food  required  under  definite  conditions.  For  one  thing  we  can  ascertain 
the  diet  chosen  by  different  people  of  various  callings,  and  estimate  from 
'its  composition  the  calorific  value,  and  use  this  as  a  basis.  If  this  is  done 
with  a  number  of  different  individuals  for  each  class,  then  we  shall  obtain 
very  useful  average  values.  A  single  observation  does  not  give  a  reliable 
indication  of  the  food  requirement.  Certain  circumstances,  such  as  the 
nature  of  the  food  chosen,  its  utilization,  especially  in  individual  cases, 
lessen  the  value  of  the  calculated  amount  of  calories  from  a  single  observa- 
tion. The  greater  the  amount  of  material  worked  over,  and  the  more 
uniform  the  external  conditions  are,  the  less  influence  will  be  exerted  by 
individual  peculiarities.  It  is  perfectly  clear  that  all  such  estimations 
will  involve  more  or  less  error,  and  at  best  we  can  only  arrive  at  approxi- 
mations. 

It  is  usually  not  possible  to  determine  in  such  investigations  the  extent  to 
which  the  food  material  is  utilized.  Such  computations  must  be  based  upon 
exact  experiments  on  metabolism.  Nevertheless,  such  observations  have 
great  value  from  a  hygienic-sociological  standpoint.  The  physiology  of 
metabolism  has  become  epoch-making  in  this  direction.  By  means  of  it, 
attention  has  been  called  to  the  altogether  insufficient  nourishment  of 
certain  classes.  It  is  perfectly  clear  that  a  permanent  underfeeding  and 
too  low  standard  of  life  must  eventually  tend  to  weaken  the  individual. 
The  resistance  towards  injurious  external  influences,  towards  infectious 
diseases,  etc.,  becomes  lessened,  morbidity  and  mortality  increase,  the 
growth  of  children  becomes  retarded,  the  number  of  able-bodied  men  for 

644 


GENERAL   METABOLISM. 


645 


the  army  becomes  smaller,  and  before  long  the  inadequate  nourishment 
of  a  class  of  people  casts  its  shadow  in  many  directions.1 


Occupation. 

Protein. 

Fat. 

Carbohy- 
drate. 

Calories.2 

Laborer  at  moderate  work        

118 

56 

500 

3091 

Laborer  at  hard  work 

137 

173 

352 

3678 

W^ell-paid  craftsman 

151 

54 

479 

3148 

Cabinet-maker  (40  years  old) 

131 

68 

494 

3242 

Street  porter  (36  years  old)      

133 

95 

422 

3214 

Young  physician,  Munich      

127 

89 

362 

2890 

Lawyer   Munich           

80 

125 

222 

2437 

Carpenters,  coopers,  and  locksmiths  in  Ba- 
varia           •                                        « 

122 

34 

570 

3206 

University  professor,  Munich  

100 

100 

240 

2373 

Bavarian  woodsmen    

135 

208 

876 

6091 

Brewery  man  at  hard  work  

190 

73 

599 

3993 

Peasant  man  

143 

108 

788 

4848 

German  laborer  (mean  from  11  families)  .    . 
Miners  at  hard  work           

72 
133 

49 
113 

451 
634 

2608 
4240 

Weavers'  families  in  Saxony    

65 

49 

485 

2710 

Two  laborers'  families  in  Frankfurt  a.  M  .   . 
Laborer  in  Berlin 

68 
98 

49 
69 

419 
490 

2424 
3075 

Italian  brickmaker                 

167 

117 

675 

4605 

French  laborer                     

138 

80 

502 

3419 

English  laborer                    

140 

34 

435 

2733 

Scandinavian  laborer  

198 

109 

710 

4811 

Well-nourished  tailor,  England   

131 

39 

525 

3096 

Hard-working  weaver 

151 

43 

622 

3618 

Hard-working  blacksmith     
Seamstresses   London     

176 
54 

71 
29 

667 
292 

4179 
1699 

Students,  Japan    

83 

14 

622 

3019 

Salesman         

55 

6 

394 

1898 

Swedish  laborer  at  moderate  work     .... 
Swedish  laborer  at  hard  work      

134 

189 

79 
101 

485 
673 

3322 
4545 

Transylvanian  farm-hand      

182 

93 

968 

5217 

Factory  people  in  Central  Russia: 
Men  and  women 

132 

80 

584 

3708 

Boys 

98 

51 

487 

2896 

Country  folk  near  Moscow: 
Men                  

129 

33 

589 

3236 

Bovs 

102 

28 

471 

2637 

Fishermen  on  the  Wolga: 
Men                                 .    .           . 

319 

57 

486 

4369 

Women                        

219 

43 

563 

2909 

1  Cf.  Paul  Mombert:  Das  Nahrungswesen.  Gustav  Fischer.  Jena,  1904.     Here  unfor- 
tunately we  can  but  touch  upon  these  problems  which  are  so  very  important  as  regards 
the  common  people.     It  is  highly  important  that  these  relations  should  be  studied 
closely. 

2  These  values  should  be  at  least  8  per  cent  lower  to  correspond  to  the  calories  actually 
utilized  by  the  organism.     A  part  of  the  food  is  not  absorbed.     This  amount  varies  with 
different  food,  as  we  have  seen.     The  results  given  are  comparable  without  making  this 
deduction.     For  accurate  data  it  would  be  necessary  to  know  the  amount  utilized  from 
case  to  case.     The  above  table  is  from  a  summary  in  J.  Konig's  "  Die  menschliche 
Nahrungs-  und  Genussmittel,  ihrer  Herstellung,  Zusammensetzung  und  Beschaffenheit," 
Julius  Springer,  Berlin,  4th  edition,  Vol.  1,  p.  388  (1904). 


646 


LECTURE  XXVIII. 


In  the  table  on  page  645  are  given  the  results  of  a  few  observations 
with  regard  to  the  amount  of  nourishment  taken  by  different  classes  of 
people. 

Atwater  has  published  the  following  values  for  the  different  classes  in 
the  United  States.1 


Class  and  Occupation. 

Food  Pur- 
chased. 

Food  Eaten. 

Digestible  Nu- 
trients in  Food 
Eaten. 

Fuel  Value  in 
Calories. 

•-     W 

P 

1 
O 
g 

I 

8 

!! 

0° 

p 

•S     03 

'§     S3 

2  ° 

<§ 
ja 

Ii 

0° 

r 

465 
406 

437 
363 
432 

£    » 

II 

r 

88 
97 

99 
98 
99 

o 

d 

i 

117 
137 

124 
141 
96 

*|     TO 

%     1 

£o 

Si    C3 

s~ 

1 

I 

1 
p 

3305 
3295 

3305 
3170 
3030 

4190 

Farmers'  Families  (9)  2  .    . 
Mechanics'  Families  (9)     . 
Professional   Men's   Fami- 
lies (9)  

101 
113 

110 
127 
109 
180 
200 

128 
153 

136 
181 
102 
365 
304 

476 
420 

442 
402 
434 
1150 
365 

557 
502 

487 
349 

442 
396 

436 

465 
414 

97 
106 

107 

106 
108 

121 
142 

129 

146 
100 

453 
395 

426 
354 
422 

3560 
3605 

3530 
3880 
3175 
8850 
6905 

5740 
4462 

3975 

3435 
3420 

3430 
3305 
3145 

4335 

College  Students'  Clubs  (5) 
Laborer's  Family      .... 
Mason  .    .    i  at  hardest 
Blacksmith  j     work 
Man  in  Adirondacks  in  mid- 
winter 

200 

216 

367 

190 

209 

358 

Football  Player 

181 
244 

124 
111 

110 

98 

114 

105 
101 

292 
151 

158 
110 

136 
155 

170 

147 
139 

Sandow,  "The  Strong  Man" 
Teachers'  Families: 
Illinois 

101 
106 

107 
91 

105 

113 
102 

129 
145 

154 

441 
340 

437 
380 

407 

3275 

Indiana    
Officials'  Families  with   lit- 
tle work: 
Connecticut    
Pennsylvania 

2910 

3530 
3465 

3826 

3705 
3405 

2780 

3430 
3280 

3524 

... 

Mechanics'    Families   with 
little  work  (5)    .... 
Students'  Clubs: 
Young  Men  (16)    .... 
Young  Ladies  (4)      ... 

C.  Voit  and  Max  Rubner3  compute  the  total  food  consumption  per  day 
for  adults  to  be  per  head: 


1  W.  O.  Atwater:  Storr's  Agricul.  Experim.  Station,  Storr's  Conn.  Ann.  Report,  9, 152 
(1896)  (1891-1896). 

2  The  numbers  in  parenthesis  represent  the  number  of  dietary  studies  upon  which 
these  average  values  are  based.     In  several  cases  experiments  were  made  with  a  family 
in  the  fall  and  spring  of  the  year,  thus  making  two  dietary  studies  with  one  family.     Thus 
in  the  first  case  there  were  five  farmers'  families  which  were  under  observation.     (Trans- 
lator.) 

3  Cf.  M.  Rubner  in  "  Handbuch  der  Ernahrungstherapie  und  Diatetic,"  by  E.  von 
Leyden,  Part  1,  154  (1857),  and  Konig:  loc  ciL 


GENERAL   METABOLISM. 


647 


Place. 

Protein. 

Fat. 

Carbohy- 
drates. 

Calories. 

Konigsberff                    

Grams. 
84 

Grams. 
31 

Grams. 
414 

2350 

Munich                         

96 

65 

492 

3036 

Paris                         

98 

64 

465 

2929 

London 

98 

60 

416 

2696 

From  the  values  published  by  Atwater  it  is  apparent  that  the  diet 
chosen  by  people  of  various  callings  is  very  different  both  as  regards  the 
composition  and  calorific  value.  In  order  to  be  able  to  estimate  the  extent 
to  which  the  food  chosen  suffices  to  meet  the  requirements  which  are  placed 
upon  the  organism,  it  is  necessary  to  make  use  of  the  average  values 
obtained  by  direct  experiments  upon  metabolism.  In  order  to  establish 
the  minimum  requirement  of  the  human  organism,  the  metabolism  is 
studied  under  conditions  at  which  the  muscles  are  as  much  at  rest  as  possi- 
ble. In  twenty-four  hours  the  requirement  per  kilogram  of  body-weight 
has  been  found  to  amount  to  from  30  to  36  calories.  The  average  man 
may  be  assumed  to  weigh  about  70  kilograms,  and  on  this  basis  the  mini- 
mum requirement  per  twenty-four  hours  would  be  2100  to  2520  calories. 
This  value  does  not  hold  for  absolute  rest,  when  the  requirement  is  con- 
siderably less.  The  resting  organism  is  satisfied  with  considerably  less 
food,  as  has  been  shown  by  metabolism  experiments  with  a  woman  in 
hysterical  coma.1  The  minimum  requirement  was  then  only  1680  calories. 
It  is  impossible  for  the  muscles  to  be  in  such  a  state  of  rest  when  the  per- 
son is  awake.  Now  from  the  computed  values  for  a  person  resting  as 
much  as  possible,  we  may  pass  judgment  upon  the  values  given  in  the 
above  tables.  Unquestionably  some  of  the  above  individuals  were  under- 
fed. According  to  the  wide  experience  of  Voit,  the  daily  diet  of  an  adult 
engaged  during  nine  or  ten  hours  in  ordinary  work  should  be  about  2749 
calories.2  This  amount  may  be  distributed  among  the  different  nutrients 
as  follows:  Protein  118  grams,  fat  56.0  grams,  carbohydrates  500  grams. 
The  more  work  there  is  to  be  done,  the  more  calories  are  needed.  Thus 
Voit  estimates  that  soldiers  engaged  in  maneuvers  require  135  grams 
albumin,  80  grams  fat,  and  500  grams  carbohydrates,  amounting  to  3018 
calories.  In  time  of  war,  however,  the  requirement  he  states  to  be  145 
grams  protein,  100  grams  fat,  and  500  grams  carbohydrates,  which  is 
equivalent  to  3218  calories.  Working  women,  on  the  other  hand,  require 
but  2200  calories,  which  should  be  composed  of  94  grams  protein,  45  grams 
fat,  and  490  grams  carbohydrates. 

1  Sond&i  and  Tigerstedt:  Skand.  Arch.  Physiol.  6,  1  (1895).     J.  E.  Johansson,  E. 
Landgren,  K.  Sonden  and  R.  Tigerstedt:  ibid.  7,  29  (1896). 

2  After  subtracting  the  calories  lost  by  insufficient  utilization.     This  deduction  is 
not  made  in  the  case  of  the  values  given  for  the  separate  nutrients. 


648 


LECTURE  XXVIII. 


In  order  to  get  a  better  idea  of  what  these  values  mean,  we  will  state 

that1 

100  grams  of  protein  are  contained  in 
5000  grams  potatoes,  650  grams  fat  pork, 

4200  grams  human  milk,  620  grams  yolk  of  hens'  eggs, 

3000  grams  cabbage,  600  grams  fat  beef, 

3000  grams  cow's  milk,  500  grams  lean  beef, 

1250  grams  rice,  430  grams  peas. 

800  grams  wheat, 
For  each  100  grams  of  protein  there  is  present 


Carbohydrates. 

Fat. 

Cow's  milk 

140 

107 

Peas 

230 

21 

Human  milk 

270 

170 

Wheat    . 

580 

14 

Rice                                                        

990 

11 

Potatoes                                   .        

1000 

0 

There  has  been  much  discussion  as  to  whether  the  amounts  of  abumin 
given  above  as  representing  the  average  albumin  requirement  are  too  high 
or  not.  It  has  been  found  possible  under  certain  conditions  to  get  along 
with  less  protein.  It  is  a  question,  however,  whether  these  results 
obtained  in  single  experiments,  which,  moreover,  cover  as  a  rule  but  a  brief 
period  of  time,  should  be  used  for  determining  the  ordinary  requirement. 
Aside  from  individual  peculiarities  which  unquestionably  come  into  play 
here,  there  are  certain  external  conditions  which  are  to  be  considered  as 
exerting  an  influence  in  a  way  that  it  is  difficult  to  define  accurately. 
The  food  requirement  is  different  with  different  nations  according  to  the 
climate  in  which  they  live.  It  is  certain  that  habits  also  play  a  part. 
The  human  and  animal  organism  must  also  be  independent,  within  certain 
narrow  limits,  of  the  amount  of  protein  in  the  food.  The  amount  of 
protein  which  the  organism  receives  from  day  to  day  changes  considerably 
when  the  diet  is  a  varied  one.  The  amount  of  non-nitrogenous  material 
which  the  organism  receives,  and  which  is  almost  invariably  sufficient  in 
quantity,  enables  the  organism  to  be  satisfied  with  as  little  as  100  or  even 
90  grams  of  protein  per  day.  It  would  of  course  be  wrong  to  base  a  definite 
standard  of  the  food  requirement  upon  the  investigations  which  have  been 
made  up  to  the  present  time.  It  would  be  possible  to  formulate  this 
requirement  more  sharply  if  we  knew  more  precisely  the  conditions  under 
which  the  values  were  obtained  in  different  cases.  Even  the  body- weight 
as  such  is  not  an  exact  factor.  A  very  muscular  individual  will  require 


1  These  values  are  taken  from  Konig's  "  Die  menschliche  Nahrung-  und  Genussmittel, 
etc."     They  refer  to  the  food  in  its  natural  condition. 


GENERAL   METABOLISM.  649 

more  protein  than  a  bony  person  with  but  slight  muscular  development. 
On  the  other  hand,  we  are  at  present  unable  to  measure  the  actual  amount 
of  work  done  by  people  of  different  callings,  which  would  give  us  exact 
data  for  the  calorific  requirements.  At  all  events,  the  protein  content  of 
the  food  is  practically  of  chief  importance,  as  regards  a  definite  food 
requirement.  From  a  practical  standpoint,  furthermore,  it  is  hardly 
desirable  to  have  a  definite  minimum  established  as  regards  the  amount 
of  protein  required  by  the  organism.  If  it  should  be  attempted  to 
make  the  food  contain  such  an  amount,  it  would  be  very  easy  to  fall 
below  it  from  time  to  time,  and  this  would  lead  to  albumin  losses  from 
the  body.  There  is  absolutely  no  reason,  aside  from  the  expense,  of 
being  afraid  that  too  much  albumin  will  be  eaten.  The  body  easily 
assumes  a  state  of  equilibrium  with  a  larger  supply  of  protein.  We  have 
seen  that  it  is  very  difficult  indeed  to  cause  an  accumulation  of  albumin 
in  the  body. 

The  question  of  expense  is  the  most  important  factor  as  regards  the  best 
way  to  meet  the  calorific  requirements  with  non-nitrogenous  food  after 
the  organism  has  received  sufficient  albumin.  Carbohydrates  are  cheapest. 
The  amount  of  these  in  the  above-mentioned  diets  is  also  considerable. 
They  can  be  easily  taken  care  of  by  the  intestine.  Fat,  unfortunately,  is 
very  expensive,  although,  to  be  sure,  an  equal  weight  of  it  has  more  than 
twice  as  much  calorific  value  as  the  carbohydrates. 

In  this  connection  we  must  call  attention  to  a  peculiarity.  When  persons 
are  obliged  to  resort  to  a  definite  diet  which  is  about  the  same  from  day  to 
day,  they  often  lose  in  weight,  and  show  even  in  their  outward  appearance 
that  they  are  not  well-nourished,  even  although  there  may  have  been  enough 
calories  in  the  food.  We  can  to  some  extent  understand  that  a  diet  which 
is  absolutely  non-irritating,  and  remains  exactly  the  same  from  day  to  day, 
will  not  be  as  nutritious  as  one  of  different  composition  which  may  not 
have  any  greater  calorific  value.  We  have  seen  that  the  smell,  taste,  and 
other  sensations  play  an  important  part  in  the  preparation  of  the  digestive 
fluids.  Now  when  the  sensation  is  exactly  the  same  from  day  to  day, 
and  the  food  is  free  from  irritating  substances,  it  soon  fails  to  cause 
any  stimulation  of  these  sensations.  The  way  in  which  the  food  is  pre- 
pared also  exerts  an  important  effect.  This  governs  largely  the  extent  to 
which  the  smell  and  taste  nerves  are  stimulated,  and  moreover  provides 
for  a  greater  utilization  of  the  food  material. 

One  question  which  has  been  considerably  discussed  is  whether  the 
human  organism  should  obtain  its  food  preferably  from  the  vegetable 
kingdom  exclusively,  or  whether  a  mixed  diet  is  preferable.1  Certain 


1  Cf.  G.  vonBunge:  Der  Vegetarianismus,  2d  edition.  A.  Hirschwald  Berlin,  1901. 
Ferdinand  Hueppe:  Der  moderne  Vegetarianismus.  A.  Hirschwald,  Berlin,  1900.  W. 
Caspari:  Physiologische  Studien  iiber  Vegetarianismus.  Martin  Hager,  Bonn,  1905. 


650 


LECTURE  XXVIII. 


anatomical  observations  apparently  indicate  that  man  is  adjusted  to  take 
care  of  a  diet  containing  both  meat  and  vegetables.  The  intestine  is 
neither  as  short  as  in  the  case  of  the  pure  carnivora,  nor  as  long  as  that  of 
the  herbivora.  It  is  interesting  to  find  that  nations,  such  as  the  Chinese 
and  Japanese  for  example,  which  are  accustomed  to  a  diet  in  which  vege- 
tables predominate,  have  a  longer  intestine  than  individuals  of  a  nation 
which  is  accustomed  to  a  meat  diet.  As  regards  the  shape  of  the  teeth, 
it  is  not  possible  to  draw  any  definite  conclusions;  and  it  is  also  true  as 
regards  the  historical  development  of  the  human  race,  that  there  is  no  proof 
that  man  was  originally  accustomed  to  a  vegetable  diet.  Our  knowledge 
of  cookery  has  to  a  certain  extent  made  us  independent  of  the  nature  of 
the  raw  material.  This  is  particularly  so  with  regard  to  the  products  of 
the  vegetable  kingdom.  Cooking  enables  us  to  get  at  the  contents  of  the 
plant  cells  better,  which  were  originally  enveloped  by  cellulose;  and 
important  foods,  such  as  the  potato,  are  made  more  accessible  to  the  action 
of  diastase.  If  we  really  wish  to  make  a  definite  decision  with  regard  to 
the  relative  values  of  vegetables  and  meats,  we  must,  in  the  first  place, 
compare  the  extents  to  which  each  is  utilized.  This  may  be  ascertained 
by  the  analysis  of  the  faeces,  determining  the  amount  of  unabsorbed 
material.  Certain  factors  come  into  play  here  which  make  it  hard  for  us 
to  decide.  A  great  deal  depends  upon  the  nature  of  the  food.  A.  diet  rich 
in  starch  may  have  an  unfavorable  action  upon  the  absorption  of  the  other 
nutriment,  on  account  of  the  fermentation  processes  resulting  and  the 
formation  of  acid  (butyric  acid),  which  accelerates  the  peristalsis  of  the 
intestines,  thereby  causing  a  prompt  evacuation.  Food  rich  in  cellulose 
will  have  the  same  effect.  Individual  peculiarities  also  undoubtedly  come 
into  play  here.  At  the  same  time  it  is  perfectly  possible  for  us  to  obtain 
approximate  values  for  the  extent  to  which  the  various  foodstuffs  are 
utilized  in  the  human  organism.  Such  values  are  given  in  the  table  on 
the  following  page. 

The  more  incomplete  utilization  of  the  protein  in  vegetables  as  com- 
pared to  that  of  flesh  foods  is  also  shown  by  the  results  of  experiments  by 
Atwater  and  Langworth1  with  vegetable,  meat,  and  mixed  diets.  This  is 
shown  in  the  following  summary. 


Food. 

Experi- 
ment 
No. 

Nitrogen  in  Grams  per  Day. 

In  Food. 

In  Urine. 

In  Faeces. 

Nitrogen 
unutilized. 

Purely  vegetable 

55 
74 
56 

13.8 
19.4 
33.1 

13.9 
15.6 
24.5 

3.9 
2.4 
2.9 

28.3% 
12.6% 
8-9% 

Mixed  (  Average  amount  of  meat, 
diet  (  Large  amount  of  meat    . 

A  Digest  of  Metabolism  Experiments,  Washington,  1897. 


GENERAL   METABOLISM. 


651 


1.   AXIMAL  FOODS. 

Food.1 

Food  Absorbed  in  Per  cents  of  that  Eaten. 

Dry  Sub- 
stance. 

Nitro- 
genous 
Substance. 

Fat. 

Carbohy- 
drate. 

Mineral 
Matter. 

Milk  — 
Children                             .... 

96.0 
94.5 
92.0 
95.0 

95.5 
95.0 
90.0 

95.5 
93.5 
95.0 
97.0 

97.5 
97.0 
89.0 

97.0 
95.0 
90.0 
95.0 

94.0 
91.0 
92.0 

97.0 
96.5 
96.0 

99.0 
99.0 
98.0 

60.0 
50.0 
60.0 
80.0 

82.0 
77.5 
70.0 

Adults                     

Cheese                 

EfiTfiTS 

Flesh  — 
From  slaughtered  animals     .    . 
From  fish    
Slaughter-house  scraps 

Fat  — 
Butter   .                          

Oleomargarine  

Lard 

2.   VEGETABLES. 

Wheat  flour  or  wheat  bread  — 
Fine                            

95.0 
93.5 
90.0 

93.0 
88.5 
84.0 
96.0 
93.5 

81.5 
90.5 
93.0 
82.0 
80.0 

81.0 
75.0 
72.0 

73.0 
68.0 
60.0 
80.0 
83.0 

70.0 

84.5 
78.0 
72.0 
70.0 
41.5 

75.0 
60.0 
55.0 

93^0 
70.0 

30.0 
40.0 
97.5 
93.0 

94^5 

98.5 
97.5 
92.5 

95.8 
93.3 
90.0 
99.0 
96.5 

84.5 
95.0 
95.8 
83.5 

9s!o 

60.0 
70.0 
55.0 

50.0 
57.4 
38.0 
85.0 
70.0 

70.0 
63.0 
85.0 
73.5 

Medium               

Coarse  

Rye  meal  or  rye  flour  — 
Fine                             

Medium       

Coarse          .    .        

Rice 

Indian  meal 

Whole  as  meal  — 
Legumes                  

Peas,  beans     

Potatoes 

Green  vegetables 

Mushrooms                        

Cocoa        .        

3.   MIXED   DIET. 

Largely  animal      

95.0 
90.0 
94.0 
95.0 
91.0 

91.0 
78.0 
85.0 
88.0 
82.0 

95.0 
86.0 
92.0 
92.0 
92.0 

97.0 
93.0 
95.0 
96.0 
93.0 

... 

Largely  vegetable 

Average  diet  
The  same  with  white  bread  .    .    . 
The  same  with  rye  bread   .... 

Metabolism  experiments  with  purely  vegetable  diets  show  that  it  is  per- 
fectly possible  to  nourish  a  youthful,  vigorous  organism  with  vegetables 


Konig:  loc.  dt. 


652  LECTURE   XXVIII. 

alone  and  to  maintain  it  at  the  highest  stage  of  bodily  and  mental  vigor.1 
A  diet  consisting  entirely  of  vegetables  is  inadvisable  for  the  following 
reasons:  In  the  first  place,  vegetables  are  not  utilized  very  advantageously, 
as  the  above  tables  show;  this  is  particularly  true  of  the  protein  which  they 
contain.  It  must  be  stated,  however,  in  this  connection,  that  the  values 
in  the  tables  were  determined  solely  by  the  amount  of  nitrogen  in  the  food. 
This  is  not  quite  right,  for  meat  contains  nitrogenous  extractive  substances 
which  are  not  of  an  albuminous  nature.  For  this  reason  the  values  given 
for  the  protein  in  the  meat  were  a  little  too  high.  This,  however,  does  not 
materially  influence  the  comparison.  A  vegetable  diet  has  the  further 
disadvantage  that  it  lacks  savor.  To  be  sure,  this  may  be  remedied  by 
artificial  additions,  and  by  exercising  especial  care  in  the  preparation  of 
the  food.  A  vegetable  diet  is  especially  objectionable  on  account  of  the 
greater  volume  of  the  food. 

All  our  present  knowledge,  both  from  the  standpoint  of  experiments  on 
metabolism  and  practical  experience,  justify  us  in  assuming  that  a  mixed 
diet  is  to  be  preferred  as  food  for  a  people.  There  is  no  reason  why  we 
should  attempt  to  eliminate  animal  food  from  our  rations. 

It  has  never  been  positively  proved  that  a  flesh  diet,  even  when  it  pre- 
ponderates, is  harmful.  All  statements  with  regard  to  the  injurious  effects 
of  a  meat  diet  are  based  upon  indirect  conclusions,  which  are  capable  of 
two  interpretations.  We  must  admit  that  the  human  organism  is  capable 
of  deriving  sufficient  nourishment  from  a  vegetable  diet,  if  it  is  provided  in 
sufficient  quantity.  It  does  not  seem  true,  from  the  above  experiments, 
that  the  organism  accustoms  itself  to  vegetable  food  in  the  sense  that  the 
vegetable  material  is  consumed  to  better  advantage  after  a  time.  It  would 
not  be  at  all  advisable,  on  the  other  hand,  to  restrict  the  diet  for  any  length 
of  time  to  meat,  and  chiefly  because  of  the  fact  that  there  is  then  a  lack 
of  material  which  tends  to  promote  the  peristalsis  of  the  intestines.  In 
the  case  of  the  carnivora,  the  same  effect  as  that  produced  by  cellulose  is 
obtained  from  the  fragments  of  bone  and  other  difficultly-digestible  material 
which  the  animal  swallows  with  its  food. 

The  whole  question  concerning  the  relative  advantages  of  vegetable, 
meat,  or  mixed  diets  rests  largely  upon  one  important  point,  namely,  which 
kinds  of  material  are  utilized  in  the  body  to  the  best  advantage.  We  have 
again  and  again  stated  that  the  food  does  not,  under  normal  conditions, 
become  part  of  our  bodies  in  the  form  that  it  is  eaten,  but  it  is  the  con- 
stituents which  result  from  a  complete  disintegration  of  the  food  that  are 
suitable  for  the  body.  All  nourishment  is  eventually  assimilated  in  our 
tissues.  If  we  hold  to  the  standpoint  that  the  tissue  cells  —  of  course  in 
a  restricted  sense  —  are  quite  independent  of  the  nature  of  the  food  which 


1  Cf.  Caspar!:  loc.  cit.  p.  122. 


GENERAL   METABOLISM. 


653 


is  eaten,  and  are  affected  solely  by  the  nutriment  which  they  receive  from 
the  circulation,  and  which  has  already  been  assimilated,  then  we  can  formu- 
late the  whole  question  regarding  the  value  of  animal  or  vegetable  food  in 
such  a  way  that  we  shall  have  to  know  merely  which  of  the  two  contains 
the  building-stones  of  protein  in  the  proportions  corresponding  more  closely 
to  the  albumins  of  the  body.  As  regards  the  assimilation  of  the  albumin- 
ous substances  in  the  animal  organism,  the  first  thing  to  consider  is  whether 
the  protein  introduced  can  be  decomposed  into  its  constituents  by  means 
of  the  ferments  contained  in  the  intestine,  and  then  whether  these  build- 
ing-stones are  present  in  the  right  proportions.  If  we  examine  the  pro- 
teins contained  in  vegetable  and  animal  food  from  this  point  of  view,  we 
shall  find  that  the  latter  correspond  more  closely  to  the  composition  of  the 
protein  contained  in  our  own  tissues.  This  is  shown  particularly  plainly 
in  the  case  of  glutamic  acid,  as  is  shown  by  the  values  given  in  the  follow- 
ing table: l 

One  hundred  grams  of  the  protein  contain  of  glutamic  acid  in  grams : 


Gliadin  from  wheat        .    .    . 

37  17 

Conglutin  from  Lupinus  luteus 

20  96 

Gliadin  from  rve  

33.81 

Casein             .        

10.7 

Hordein  from  barley      .... 
Zein  from  Indian  meal  .... 
Glutein 

36.35 

16.87 
23  42 

Egg-albumin     
Albumin  from  fish-muscle    .    . 
Albumin  from  ox-muscle 

8.0 
8.9 
11  9 

Legumin 

16  6 

Serum-albumin    .        

7  7 

Vignin  from  peas 

16  89 

Serum-globulin    

8.5 

Unquestionably  our  present  knowledge  indicates  that  the  albumin  from 
vegetable  foods  gives  rise  to  more  waste  products  in  the  intestine  than  that 
from  flesh  foods.  On  the  other  hand,  it  is  perfectly  conceivable  that  a  mix- 
ture of  animal  and  vegetable  proteins  would  enable  the  animal  organism 
to  utilize  certain  constituents  of  the  latter  in  common  with  the  former 
which  might  otherwise  be  worthless  perhaps  on  account  of  a  deficiency  in 
glutamic  acid.  This  is,  at  present,  merely  a  suggestion.  It  is  well,  how- 
ever, to  consider  such  questions  from  all  possible  points  of  view. 

The  fact  that  vegetarians  are  often  under-nourished  is  worthy  of  men- 
tion. They  are  then  obliged  to  draw  upon  their  own  albumin,  and  live, 
so  to  speak,  upon  animal  protein.  They  are  then  false  to  their  own 
doctrine! 

In  order  to  determine  the  nutritive  value  of  a  foodstuff,  we  must  in  the 
first  place  know  its  composition.  In  the  following  table  the  composition  of 
one  of  the  most  important  foods  is  given.  In  infancy  milk  is  the  chief,  if 
not  the  only,  form  of  nourishment.  We  have  already  discussed  the  compo- 
sition of  its  ash,  and  have  found  that  it  is  characteristic  of  the  milk  of  every 


'  Cf.  Lecture  IX,  p.  172  et  seq.t  and  T.  B.  Osborne  and  R.  D.  Gilbert:  Am.  J.  Physiol. 
15,  303  (1906). 


654 


LECTURE   XXVIII. 


species  of  animals.     This  is  also  true  of  the  organic  constituents,  especially 
protein,  fat  and  carbohydrate,  as  the  following  table  shows: 
One  hundred  parts  by  weight  of  milk  contain:  1 


Species. 

Casein. 

Albumin. 

Total 
Protein. 

Fat. 

Sugar. 

Dog  I 

4  80 

2  64 

7  44 

11  62 

3  24 

Dog  II    . 

4  84 

2  43 

7  27 

12  19 

3  23 

Pig  I   

3  76 

1  45 

'   5  21 

9  54 

3  30 

Pig  II     

3  26 

1  55 

4  81 

7  09 

3  44 

Pig  III    . 

3  71 

1  65 

5  36 

6  32 

3  19 

Sheep 

4  08 

0  80 

4  88 

9  29 

5  04 

Goat 

2  91 

0  76 

3  67 

4  33 

3  61 

Guinea  pig  I     ... 

4  60 

0  49 

5  09 

7  31 

2  31 

Guinea  pig  II  ... 

4  79 

0  61 

5  40 

6  96 

2  02 

Rabbit    

8  17 

2  21 

10  38 

16  71 

1  98 

Cat  I  ... 

3  79 

3  30 

7  09 

4  49 

4  79 

Cat  II. 

3.79 

3  11 

6.90 

4  80 

4  80 

Cat  III  . 

3  69 

3  29 

6  98 

4  98 

4  71 

Cat  IV 

3  59 

3  49 

7  08 

4  76 

4  82 

Cow  

2  90 

0  50 

3  40 

3  70 

4  95 

Buffalo  2     

4  26 

0  46 

4  72 

7  51 

4  77 

Zebra  2    .    . 

3  03 

4  80 

5  34 

Camel  2  

3  49 

0  38 

3  87 

2  87 

5  39 

Lama  2   

3  00 

0.90 

3.90 

3  15 

5  60 

Reindeer  2 

8  38 

1  51 

9  89 

17  09 

2  82 

Horse2   .... 

1  30 

0  75 

2  05 

1  14 

5  87 

Ass2   

0  79 

1  06 

1  85 

1  37 

6  19 

Mule2  

2  63 

1  92 

5  69 

Elephant  2     
Caaing-whale  2     
Hippopotamus  2 

... 

3.45 

20.58 
43.76 
4  51 

7.18 

Human  milk  differs  from  all  of  the  above  varieties  except  ass's  milk,  in 
containing  more  albumin  than  casein.  One  hundred  parts  by  weight  of 
human  milk  contain:3 


Casein. 

Albumin. 

Total  Protein. 

Fat. 

Milk-sugar. 

0.80 

1.21 

2.01 

3.74 

6.37 

Milk,  besides  containing  casein  and  albumin,  also  contains  a  small 
amount  of  globulin.4  The  composition  of  the  milk  with  a  uniform  diet 
varies  but  slightly  during  the  nursing  period,  with  the  exception  of  that 

*  Cf.  Emil  Abderhalden:  Z.  physiol.  Chem.  26,  487  (1899);  27,  408  (1899). 

2  Computed  from  several  analyses.     Cf.  Konig:  loc.  cit.  pp.  661,  663,  and  664. 

3  Average  values  from  Konig:  loc.  cit.  p.  598. 

4  Wroblewski  [Z.  physiol.  Chem.  26,  308  (1898-99)]  also  believes  that  a  different  pro- 
tein which  he  calls  opalisin  is  present,  but  its  isolation  and  description  are  not  very 
convincing. 


GENERAL   METABOLISM. 


655 


which  flows  shortly  after  birth.  This  contains  far  more  protein,  and  is 
called  the  colostrum.  Human  colostrum  contains  in  100  parts  by  weight 
in  grams: 


Nitrogenous 
Substances. 

Fat. 

Milk-sugar. 

3.07 

3.34 

0.40 

The  colostrum  is  found  in  all  species  of  mammals.  With  the  cow  the 
relations  are  as  follows:  100  parts  by  weight  of  milk  contain  2.90  grams 
casein,  0.50  gram  albumin,  3.70  grams  fat,  and  4.95  grams  milk-sugar. 
One  hundred  parts  by  weight  of  colostrum  contain  4.19  grams  casein, 
12.99  grams  albumin  and  globulin,  3.97  grams  fat,  and  2.28  grams  milk- 
sugar.  The  exact  significance  of  the  colostrum  is  not  known.  We  can 
indeed  imagine  that  the  tissues  and  cells  of  the  new-born,  which  now  exer- 
cise certain  functions  for  the  first  time,  require  a  considerable  supply  of 
protein. 

The  composition  of  the  milk  is  dependent  upon  a  number  of  external 
conditions.1  Cow's  milk,  especially,  has  been  much  studied  as  regards 
the  influence  of  various  factors  upon  the  composition  and  amount  pro- 
duced per  day.  One  of  the  chief  factors  is  the  breed,  and  another  the 
nature  of  the  nourishment  the  animal  receives.  Moving  about  and  work 
have  an  effect. 

The  variations  in  the  composition  of  the  milk  are  not  great  under 
normal  conditions.  This  is  very  important.  The  fact  that  the  milk  of 
different  species  of  animals  varies  greatly  is  of  much  significance.  The 
composition  of  the  milk  evidently  has  an  effect  upon  the  rate  of  devel- 
opment of  the  suckling.2  It  is  natural  to  expect  that  the  richer  the  milk 
is  in  its  organic  and  inorganic  constituents,  the  more  rapidly  the  suckling 
is  able  to  build  up  its  tissues.  If  the  milk  of  different  species  of  animals 
all  had  the  same  composition,  then  the  desired  effect  could  be  produced 
only  by  means  of  a  much  greater  production  of  milk,  and  similarly  a  corre- 
spondingly greater  quantity  would  have  to  be  taken  into  the  system  of  the 
suckling.  The  question  arises  whether  the  milk  of  one  species  of  animals 
can  be  substituted  for  that  of  another.  Our  experience  concerning  meta- 
bolism does  not  show  us  a  priori  any  reason  why  this  could  not  be  done, 
provided  of  course  that  the  suckling  should  receive  the  same  amounts  of 
nutriment,  both  qualitatively  and  quantitatively.3  It  is,  to  be  sure,  con- 


1  Cf.  Konig:  loc.  cit.  p.  601. 

2  Cf.  Lecture  XVII,  p.  404. 

3  Cf.  Max  Rubner  and  Otto  Heubner:    Z.  exper.  Path.  Therap.  1  (1905).      Franz 
Tangl:  Pfluger's  Arch.  104,  453  (1905).     Camerer:  Z.  Biol.  16,  24  (1880);  20,  566  (1884). 


656  LECTURE   XXVIII. 

ceivable  that  the  albumin  of  one  kind  of  milk  may  be  differently  constituted 
from  that  of  another  in  a  quite  specific  way.  In  the  case  of  sucklings  the 
most  important  function  of  the  food  is  to  build  up  the  cells.  Within  a 
short  time  the  animal  doubles  its  original  weight.  We  can  imagine  that 
some  kinds  of  protein  are  not  suitable  for  being  introduced  into  the  cell. 
Such  ideas  were  very  well  justified  at  the  time  when  it  was  assumed  that 
the  protein  was  decomposed  in  the  intestine  only  to  the  peptone  stage  and 
that  these  products  were  absorbed,  and  when  there  was  no  evidence  at 
hand  concerning  the  composition  of  the  different  proteins  of  the  body. 
After  it  was  ascertained,  however,  that  the  suckling  was  able  from  the 
protein  in  its  food  to  construct  all  the  different  proteins  contained  in  the 
various  fluids  of  the  body  and  in  the  tissues,  the  composition  of  which  is 
quite  different  from  that  of  casein,1  it  hardly  seemed  right  for  us  to  lay  too 
much  stress  upon  the  quantitative  composition  of  the  protein  in  the  food. 
Even  casein  is  decomposed  while  it  is  in  the  alimentary  canal.  Outside 
the  intestine  the  various  cleavage-products  unite  in  various  ways  to  form 
new  proteins.  Even  the  albumin  contained  in  milk  is  made  capable  of 
absorption  by  means  of  changes  which  take  place  while  it  is  in  the  intes- 
tine. This  does  not  imply  by  any  means  that  the  chemical  composition 
of  the  various  proteins  is  entirely  a  matter  of  indifference.  There  are 
no  grounds  for  any  such  assumption.  It  is  also  conceivable  that  the 
caseins  from  different  varieties  of  milk  contain  certain  specific  groups.  At 
present,  to  be  sure,  we  do  not  know  of  any  such.  All  that  we  do  know  is 
that  up  to  the  present  time  the  different  kinds  of  casein  which  have  been 
studied  all  contain  the  same  building-stones  and  apparently  in  about  the 
same  quantitative  relations.2  We  would,  however,  far  exceed  the  present 
state  of  our  knowledge  if  we  were  to  conclude  definitely  that  all  the  different 
varieties  are  identical  because  they  are  composed  of  the  same  constituents. 
It  is  perfectly  clear  that  the  same  amino  acids  may  be  combined  in  a  num- 
ber of  different  ways  in  the  complex  molecule.  The  number  of  possible 
isomers  is  very  large.  We  have  already  seen  in  studying  fermentations 
that  very  slight  differences  in  the  construction  of  the  molecule  are  of  much 
biological  significance. 

The  casein  of  human  milk  differs  from  that  of  cow's  milk  in  that  rennin 
throws  it  down  in  the  form  of  a  much  finer  flock.  It  is  also  easier  to  pre- 
cipitate casein  from  cow's  milk  by  slightly  acidifying  it  with  acetic  acid. 
From  human  milk  it  is  very  difficult  to  precipitate  the  casein  by  means  of 
acetic  acid.  At  ordinary  temperatures  the  precipitation  is  at  best  very 
incomplete,  and  in  most  cases  no  precipitate  at  all  is  formed.  In  order  to 
throw  down  completely  the  casein  from  human  milk,  it  is  necessary  to 
carefully  acidify  it  slightly,  dilute  it  with  water,  and  keep  it  at  37°  C.  for 

*  Cf.  Lecture  X,  p.  211. 

2  Emil  Abderhalden  and  Alfred  Schittenhelm :  Z.  physiol.  Chem.  47  (1906). 


GENERAL   METABOLISM.  657 

some  time.  In  spite  of  this  different  behavior  of  the  casein  from  the  two 
kinds  of  milk,  which  may  be  due  to  several  causes,  we  are  not  justified  in 
assuming  that  there  is  any  great  difference  in  the  nature  of  the  casein. 

On  the  other  hand,  just  as  we  cannot  safely  assume  from  our  present 
chemical  knowledge  that  the  composition  and  nature  of  the  protein  from 
different  kinds  of  milk  are  dissimilar,  so  we  are  not  justified  in  assuming 
that  the  milk  of  the  different  species  of  animals  is  quantitatively  but  not 
qualitatively  different.  The  present  state  of  our  knowledge  concerning 
the  composition  and  nature  of  the  different  constituents  of  milk  does  not 
tell  us  how  completely  the  milk  of  one  species  may  be  replaced  by  another. 
This  does  not  by  any  means  imply  that  it  is  impossible  to  effect  a  satis- 
factory replacement.  We  only  wish  to  emphasize  at  this  place  how  far 
our  present  knowledge  is  from  the  desired  goal,  and  how  far  the  present 
demands  and  concessions  have  stretched  beyond  the  boundaries  of  our 
actual  knowledge.  At  present  we  are  obliged  to  depend  almost  entirely 
upon  practical  experience  which  receives  but  slight  support  in  the  ana- 
lytical values  obtained  from  the  investigation  of  milk.  We  must  emphasize 
the  fact  that  our  present  methods  of  examining  milk,  particularly  the 
analysis  of  the  ash,  show  us  merely  what  elements  are  present  and  in 
what  proportions.  The  presence  of  sulphuric  acid  in  the  ash  may  be 
accounted  for  in  several  ways.  It  may  occur  in  the  milk  as  such,  or  the 
sulphur  may  be  present  in  some  state  of  combination  other  than  that  of 
sulphate.  On  the  other  hand,  the  old  idea  that  the  intestine  is  only  able 
to  bring  about  certain  slight  changes  in  the  food,  which  is  then  absorbed 
after  having  been  reconstructed  as  little  as  possible,  is  more  and  more  to 
be  discarded.  As  a  matter  of  fact,  the  changes  which  take  place  while 
the  food  is  in  the  intestine  are  quite  considerable.  The  assimilation  begins 
in  the  intestinal  canal.  The  synthetic  capabilities  of  the  animal  organism 
are  much  greater  than  was  formerly  assumed.  It  is  far  less  dependent 
upon  the  nature  of  the  food  which  it  receives  than  was  once  believed  to 
be  the  case. 

Practical  experience  has  shown  that  it  is  not  possible  to  replace  entirely 
satisfactorily  the  mother's  milk  with  that  of  some  other  species,  or  by  means 
of  a  milk  substitute.  The  mortality  of  infants  nourished  at  the  breast  is 
much  less  than  that  of  infants  brought  up  in  some  other  way.  It  is  an 
open  question,  however,  whether  this  increased  mortality  is  wholly  due 
to  insufficient  nourishment.  In  many  cases  it  is  perfectly  true  that  the 
children  of  women  who  are  not  able  to  nurse  their  children,  or  at  least  only 
for  a  short  time,  are  in  many  cases  not  as  strong  as  the  children  of  normal 
women.  Statistics  in  this  direction,  therefore,  to  be  useful  must  take  into 
account  not  merely  whether  the  child  was  brought  up  on  mother's  milk, 
or  upon  a  milk  substitute,  but  it  should  also  be  stated  why  the  mother's 
milk  was  abandoned.  It  is  perfectly  clear  that  if  a  sickly  child  is  placed 


658  LECTURE   XXVIII. 

upon  artificial  feeding,  it  will  be  hard  for  it  to  utilize  the  nutriment  to  best 
advantage.  The  child  has  at  the  start  a  defective  circulation.  It  is  hard 
for  the  weakened  cells  to  carry  out  a  thorough  assimilation  and  trans- 
formation of  the  food  materials.  They  tend  to  become  weaker  and  weaker, 
and  lose  more  and  more  the  ability  of  reconstructing  the  material.  Numer- 
ous complications  lessen  the  value  of  the  artificial  nourishment  which  the 
child  receives.  If  milk  from  an  animal  is  used,  large  amounts  of  micro- 
organisms are  invariably  present  which  cause  unfavorable  effects  in  the 
bowels  of  the  child.  These  organisms  may  be  killed  by  sterilization,  and 
then  their  harmful  effects  will  not  be  felt,  but  on  the  other  hand  it  has  been 
found  that  in  sterilization  changes  are  produced  in  the  milk  itself  which 
make  it  more  difficultly  digestible.  Perhaps  it  serves  to  "denaturize" 
the  proteins  in  the  milk,  so  that  it  is  harder  for  the  ferments  to  act  upon 
them.  It  has  been  found  possible  to  carry  out  the  sterilization  process 
in  such  a  way  that  this  injury  to  the  milk  itself  is  reduced  to  a  minimum. 
One  great  danger  to  be  feared  in  the  artificial  feeding  of  infants  is  the  over- 
loading of  the  alimentary  canal.  Under  normal  conditions  the  infant  has 
to  work  pretty  hard  to  get  its  food.  In  sucking  out  the  milk  the  child 
becomes  tired,  so  that  after  a  time  it  stops  feeding. 

Social  relations  undoubtedly  exert  a  great  influence  upon  the  prevailing 
conditions.  Many  people  resort  to  artificial  feeding  because  they  believe 
the  conditions  are  unfavorable,  and  even  when  the  mother's  milk  is  given, 
it  is  so  seldom  in  accordance  with  natural  conditions,  that  even  these 
infants  do  not  develop  normally.  It  should  be  our  task  to  educate  people 
to  believe  that  mother's  milk  is  the  proper  food  for  the  child,  and  that  it 
alone  affords  a  positive  guarantee  for  the  normal  development  of  the 
infant.  At  the  same  time  it  should  also  be  our  aim  to  carry  out  researches 
in  the  hope  of  discovering  more  satisfactory  substitutes  for  the  mother's 
milk  when  it  is  not  available.  As  we  have  said  before,  the  nourishment 
of  the  child  should  in  no  case  be  regulated  solely  with  Yegard  to  the  fuel 
value  of  the  food.  The  most  important  thing  is  to  make  sure  that  it  will 
serve  for  the  construction  of  tissue.  A  milk  substitute  may  be  absolutely 
worthless  in  spite  of  the  fact  that  it  has  a  high  calorific  value.  Especially 
at  this  time  of  rapid  development  the  Law  of  the  Minimum  holds  in  its 
entirety.  By  no  means  should  the  nature  of  the  organic  constituents 
alone  come  into  consideration.  It  is  equally  important  that  the  inorganic 
requirements  should  be  satisfied.  Furthermore,  it  is  not  even  sufficient 
to  know  the  total  amount  of  the  inorganic  material. 

In  the  case  of  mammals  the  milk  nourishment  continues  only  during 
the  lactation  period,  and  is  then  abandoned  entirely  within  a  relatively 
short  time.  We  have  already  seen  in  studying  the  iron  content 1  that 

1  Cf.  Lecture  XVII,  p.  386. 


GENERAL   METABOLISM. 


659 


it  would  be  dangerous  to  continue  milk  as  the  sole  food  for  too  long  a 
time.  In  the  case  of  the  human  race,  milk  plays  a  more  or  less  important 
function  as  food  during  the  whole  period  of  growth  and  even  for  adults. 
The  utilization  of  the  material  in  milk  is  somewhat  greater  on  the  part 
of  the  infant  than  is  the  case  with  the  adult,  but  even  then  it  remains 
very  satisfactory.  Cow's  milk  is  utilized  to  good  advantage  by  the  human 
offspring. 

One  very  important  food  for  the  growing  organism,  as  well  as  for  the 
adult,  is  the  egg.  In  the  raw  state,  as  well  as  when  hard  boiled,  the  egg  is 
equally  well  utilized.  As  far  as  we  are  concerned,  the  eggs  of  birds  alone 
come  into  consideration,  and  especially  those  of  hens. 

In  100  grams  of  fresh  eggs  there  are  present  :  73.7  grams  water,  12.6 
grams  nitrogenous  matter,  12.0  grams  fat,  0.7  gram  nitrogen-free  extrac- 
tive substances,  and  1.07  grams  of  ash.  The  percentage  composition  of 
the  last-mentioned  is  as  follows :  * 


Per  cent 

Ash  of 

the  Dry 

K20 

Na2° 

CaO 

MgO 

Fe203 

P205 

S03 

SiO2 

Cl 

Man-rial. 

Total  contents 

of  hen's  eggs 
White    of    the 

3.48 

17.37 

22.87 

10.91 

1.14 

0.39 

37.62 

0.32 

0.31 

8.9 

eggs       .    .    . 

4.61 

31.41 

31.57 

2.78 

2.79 

0.57 

4.41 

2.12 

1.06 

23.3 

Yolk      of     the 

eggs       .    .    . 

2.91 

9.29 

5.87 

13.04 

2.13 

1.65 

65.46 

0.86 

1.9 

The  greater  part  of  the  phosphorus  contained  in  eggs  (about  80  per  cent) 
is  present  in  lecithin,  nuclein,  and  other  organic  compounds.  Only  a 
small  part  is  found  in  the  form  of  inorganic  salts. 

Flesh  foods  form  one  of  the  most  important  articles  of  diet  for  adults. 
The  amount  eaten  varies  with  different  nations  and  with  different  classes 
of  people.  According  to  Ostertag 2  the  consumption  per  head  in  different 
localities  is  as  follows: 


Australia. 

U.S.A. 

Great 
Britain. 

France. 

Belgium 
and 
Holland. 

Austria- 
Hungary. 

Russia. 

Spain. 

Italy. 

Per  year  in  kgms. 

111.6 

64.4 

47.6 

33.6 

31.3 

29.0 

21.8 

22.2 

10.4 

Per  day  in  gms. 

306 

149 

130 

92 

86 

79 

59 

61 

29 

In  China  even  less  meat  is  eaten  than  in  Italy.     Similarly  certain  negro 
races  live  almost  entirely  upon  vegetables.     The  composition  of  meat  as 


1  Konig:  loc.  cit.  p.  576. 

2  R.  Ostertag:  Handbuch  der  Fleischbeschau,  p.  4.     Stuttgart,  1899. 


660 


LECTURE   XXVIII. 


it  comes  upon  the  table  varies  greatly.  The  species  of  animal  from  which 
it  is  obtained,  the  amount  of  waste  (tendons,  bones,  etc.),  and  the  state  of 
nourishment  of  the  animal,  all  constitute  important  factors.  Meat  con- 
tains, besides  albumin,  other  nitrogenous  substances,  such  as  creatin, 
creatinin,  sarkosin,  xanthin,  and  carnin.  It  is  not  right,  therefore,  to 
estimate  the  amount  of  protein  present  by  the  nitrogen  content  alone. 
The  composition  of  the  flesh  of  fish  is  quite  similar  to  that  of  mammals. 
Fish  is,  as  a  rule,  utilized  by  the  human  organism  as  well  as  other  flesh 
foods. 

The  values  given  in  the  following  table  illustrate  the  composition  of  dif- 
ferent kinds  of  food: 


Water. 

Nitroge- 
nous 
Material. 

Fat. 

Ash. 

Meat  of  mammals   .    .               .    .        ....        .    . 

76  0 

21.5 

1  5 

1  0 

Salmon   

64  0 

21.1 

13.5 

1.2 

Pike    

79.6 

18.4 

0.5 

1.0 

Shellfish 

81  5 

16  9 

0  3 

1  3 

Sole 

82  7 

14  6 

0  5 

1  4 

Oysters                                                    ....           .    . 

80  5 

9  0 

2  0 

2  0 

Lobsters        .               

81.8 

14  5 

1  8 

1.7 

Fresh-river  crabs        

81.2 

16.0 

0.5 

1.3 

Edible  snails    

80.5 

16.3 

1.4 

1.3 

Meat  as  well  as  milk  is  used  in  the  manufacture  of  certain  prepared 
foods.  The  latter  is  used  to  make  butter  and  cheese;  the  former  in  the 
manufacture  of  sausages  and  other  cured  products.  It  may  be  said  that 
the  value  of  flesh  food  from  an  economic  standpoint  is  largely  dependent 
upon  the  amount  of  the  product  which  may  be  utilized.  With  fish,  for 
example,  there  is  a  relatively  large  amount  of  waste. 

Among  the  vegetable  foods  the  different  kinds  of  grain  are  very  impor- 
tant; these  are  used  in  the  form  of  meal  and  flour  in  a  number  of  different 
ways,  especially  in  bread-making.  They  also  serve,  as  well  as  potatoes, 
for  the  manufacture  of  starch.  Then  again  there  are  the  large  number  of 
green  vegetables  and  fruits.  As  regards  their  nutritive  value  and  utiliza- 
tion in  the  human  organism,  we  have  found  that  on  the  whole  they  are  not 
utilized  as  completely  as  the  flesh  foods.  A  vegetable  diet  gives  rise  to  a 
large  amount  of  excreta.  In  the  case  of  the  different  grains  it  makes  con- 
siderable difference  whether  the  whole  grain  is  used  in  the  flour,  or  only 
that  which  has  been  freed  from  the  hulls.  The  more  of  the  hull  there  is 
present,  the  less  the  percentage  utilization.  We  cannot  include  within 
the  scope  of  these  lectures  all  the  different  data  which  have  been  acquired 
concerning  these  relations,  and  which  are  so  important  in  considering  the 
food-supply  of  a  people.  We  shall  have  to  refer  to  the  special  works  on 
the  subject.  Here  we  only  desire  to  point  out  the  great  importance  of  the 


GENERAL   METABOLISM. 


661 


study  of  such  problems  for  the  complete  understanding  of  the  principles  of 
practical  nutrition. 

It  is  very  significant  that  even  the  adult  organism  requires  nutriment 
not  only  as  fuel,  but  also  for  the  constant  construction  and  renewal  of  the 
cells.  It  must  never  be  forgotten  that  the  organism  is  adjusted  for  a 
mixed  diet,  and  that  certain  kinds  of  stimulation  are  necessary  for  the 
production  of  the  digestive  juices.  It  is  not  at  all  practical  to  consider 
replacing  our  food  with  chemical  products.  Our  knowledge  regarding 
the  necessary  nourishment  for  the  organism  is  far  too  limited  for  us  to 
attack  such  problems.  The  attempt  has  been  made  quite  recently  to 
provide  albumin  in  as  pure  a  form  as  possible  for  the  use  of  the  sick.  Our 
understanding  of  metabolism  is  not  such  that  we  can  approve  of  such 
experiments  unreservedly.  In  paying  a  good  deal  of  attention  to  a  par- 
ticular nutriment  we  are  pretty  sure  to  neglect  something  else.  We  have 
seen  from  the  Law  of  Isodynamics  that  the  carbohydrates  and  fats  replace 
one  another  in  accordance  with  their  calorific  values,  and  that  protein  may 
be  replaced  by  these  two  foodstuffs  to  a  certain  extent.  There  is  always 
danger,  in  making  use  of  chemically -pure  foods,  that  too  little  attention 
will  be  paid  to  the  amount  of  inorganic  salts  which  are  required.  The 
knowledge  of  the  calorific  requirements  for  the  performance  of  a  definite 
amount  of  work  is  very  important  for  the  establishment  of  a  ration.  The 
calorific  requirement  forms  a  foundation.  It  must  not,  however,  be  re- 
garded as  the  sole  requirement.  The  composition  of  the  ration  is  by  no 
means  a  matter  of  absolute  indifference. 

In  the  following  table  the  calorific  values  of  a  few  foodstuffs  are  given: l 
one  gram  of  substance  yields  the  following  number  of  heat  units,  expressed 
in  small  calories : 

(A)  PROTEINS. 


Stohmann. 

Berthelot. 

Stohmann. 

Berthelot. 

Plant-fibrin  .... 

Serum-albumin  .  . 
Hemoglobin  .... 
Milk  casein  .... 

Yolk  of  eggs  .  .  . 

5941.6 

5917.8 
5885.1 
5867.0 

5840  .  9 

5832.3 

5910.0 
5626.4 

Flesh  fibers  (with  fat 
removed)    
Flesh  (with  fat  rem'd) 
Blood-fibrin    .... 
Peptone    from   blood- 
fibrin     
Chondrin     

5720.5 
5662.6 
5637.1 

5298.8 
5130.6 

5728.4 
5529.1 

5342.4 

Le^umins 

5793  1 

Vitellin  .  . 

5745  1 

5780  6 

Egg-albumin  .  .  . 

5735.2 

5687.4 

(B)    FATS. 


Tissue  fat 
Butter  . 


9484.5 
9231.3 


Linseed  oil . 
Olive  oil 


9623.0 
9328.0 


Cf.  Konig:  loc.  cit.  p.  283  et  seq. 


662 


LECTURE   XXVIII. 


(C)    CARBOHYDRATES. 


Grape-sugar 

3742  6 

Maltose                  

3949  3 

Fruit-sugar     

3755.0 

Starch    

4182  8 

Galactose     .    .        

3721.5 

Dextrin      

4112.5 

Cane-sugar 

3955  2 

Cellulose 

4185  4 

Milk-sugar  

3951.5 

(D)    ORGANIC   ACIDS. 


Oxalic  acid. 
Tartaric  acid 


571 

1745 


Citric  acid     . 
Benzoic  acid 


2397 
6281 


This  is  all  that  we  care  to  mention  with  regard  to  metabolism  as  a  whole. 
We  realize  that  we  have  merely  touched  upon  most  of  the  questions 
without  attempting  to  consider  them  from  all  the  different  points  of  view. 
Metabolism  physiology  has  during  recent  years  developed  a  field  of  its 
own.  In  pathology  it  finds  much  that  is  kindred  in  nature.  Both  fields 
are  intimately  connected  with  one  another,  and  this  is  largely  the  result 
of  recent  efforts.  Without  going  into  clinical  experience  in  detail,  it  would 
be  hardly  possible  to  give  a  complete  picture  of  general  metabolism 
from  all  directions.  We  shall,  therefore,  be  obliged  to  refer  the  reader  to 
the  special  works  on  the  pathology  and  physiology  of  metabolism.  Our 
discussion  has  been  only  to  bring  out  the  more  important  principles,  and 
will,  it  is  to  be  hoped,  prove  an  incentive  to  further  studies. 


LECTURE    XXIX. 
OUTLOOK. 
I. 

WE  have  not  even  approximately  exhausted  the  large  domain  of 
physiological-chemical  investigation  in  the  discussion  of  our  knowledge 
concerning  the  chemical  processes  which  take  place  in  plant  and  animal 
organisms.  We  have  merely  been  able  to  touch  upon  the  fundamental 
principles  upon  which  the  science  rests.  To  be  sure,  our  knowledge  is  still 
incomplete,  and  the  explanation  of  many  phenomena  has  resulted  solely 
from  the  play  of  the  imagination.  On  the  other  hand,  the  progress  of 
the  exact  sciences  is  constantly  bringing  new  methods  to  the  aid  of  physi- 
ological chemistry,  and  in  this  way  we  are  being  led  to  more  definite  prob- 
lems, so  that  we  are  hopefully  looking  forward  to  the  further  development 
of  the  field.  Little  by  little  the  unknown  becomes  the  known.  Direct 
proofs  gradually  replace  the  indirect  conclusions.  The  physiological 
chemist  is  gradually  breaking  away  from  the  observation  of  a  single 
individual.  It  is  becoming  very  evident  that  satisfactory  results  can 
be  obtained  only  when  the  investigation  is  carried  out  with  as  many  dif- 
ferent organisms  as  possible.  The  broader  the  foundations,  the  greater 
the  scope  of  observation,  and  the  more  varied  the  conditions  are  under 
which  certain  physiological  processes  are  studied,  the  less  danger  there 
is  in  arriving  at  biased  conclusions.  Just  as  morphology  developed  into 
an  independent  science  only  by  extensive  comparative  investigations 
and  by  the  careful  consideration  of  the  anthropogeny  of  each  individ- 
ual species,  so  we  shall  expect  to  obtain  from  comparative  physio- 
logical-chemical investigation  the  answer  to  many  problems  and  to 
receive  new  impulses  for  further  inquiry.  Just  as  an  organ  which  is 
functionally  unimportant  —  e.g.,  an  apparently  superfluous  bone  —  may 
be  in  the  eyes  of  a  zoologist  an  eloquent  proof  of  a  common  origin  with 
a  certain  class  of  animals,  and  just  as  the  botanist  is  able  to  conclude 
from  the  similarity  of  the  flora  of  our  highest  Alpine  peaks  and  that  of 
the  Far  North  that  there  is  an  intimate  relation  between  these  two 
regions,  so  we  may  certainly  hope  to  meet  here  and  there  with  chemical 
processes  which  will  lead  us  from  the  present  into  the  far-distant  past. 
What  an  infinite  perspective  is  opened  to  us  by  a  glimpse  at  the  wonderful 
flower  tapestry  of  the  Alpine  heights,  this  so  foreign  and  so  characteristic 

663 


664  LECTURE   XXIX. 

witness  of  long-forgotten  ages !  We  also  find  many  insects  which  are  sharply 
confined  to  the  Alps  and  to  the  Far  North.  Many  a  paleontologic  discovery 
serves  to  form  a  bridge  between  two  apparently  foreign  fields,  and  at  one 
stroke  changes  assumptions  to  indisputable  proofs.  The  bottoms  of  our 
Alpine  lakes  are  covered  with  forms  of  life  which  we  encounter  again  only 
in  the  arctic  regions.1  How  interesting  it  would  be  to  turn  our  physiologi- 
cal chemistry  into  similar  channels!  We  have  hardly  begun  to  advance 
in  this  direction,  for  our  present  methods  are  still  unable  to  follow  the  flight 
of  thought,  and  our  understanding  of  the  chemical  processes  taking  place 
in  the  different  organisms  is  still  too  limited  for  us  to  make  comparative 
studies.  Nevertheless  this  goal  should  be  regarded  as  most  worthy  of 
attaining.  To  be  sure,  there  are  a  great  many  isolated  facts  and  a  multi- 
tude of  observations  concerning  the  organisms  of  different  kinds  of  plants 
and  animals,  but  they  are  far  from  being  of  equal  value,  and  it  remains  to 
unite  our  knowledge  of  certain  processes  into  a  continuous  chain.  We 
can,  however,  call  attention  to  certain  facts  which  indicate  that  not  only 
every  species  of  animal  but  even  each  individual  is  to  be  regarded  as  one 
which  is  characteristic  and  limited  in  its  general  metabolism.2 

Let  us  consider  for  the  moment  the  great  multiplicity  of  forms  in  the 
animal  kingdom.  In  what  a  contrast  the  tissues  of  these  morphologically 
so  different  beings  must  stand!  Consider  the  vertebrates.  Everywhere 
we  find  the  same  physiological  function,  the  same  tissue,  the  same  organ. 
Not  only  is  this  true  of  the  external  appearance,  but  even  the  finer  struc- 
ture shows  a  great  similarity.  In  spite  of  this  fact,  the  same  organs  of 
different  species  of  animals  are  very  different  in  their  metabolism,  and 
again  the  chemical  composition  of  these  organs  and  tissues  must  be  char- 
acteristic for  each  species  of  animals  and  perhaps  for  every  individual. 
Herein  lies  the  reason  for  the  differences  in  their  metabolism.  Let  us  see 
what  right  we  have  to  compare  the  purely  morphological  differentiation 
of  the  various  kinds  of  life  into  classes,  families,  and  species  with 
physiological-chemical  limitations,  especially  as  regards  the  species.  If 
we  consider  physiological-chemical  investigation  as  a  whole,  we  shall  find 
that  it  extends  in  two  directions.  On  the  one  hand  many  apparently 
dissimilar  elements  are  united  by  a  common  band  to  form  a  large  whole, 
and  on  the  other  hand  many  functions  which  were  apparently  identical 
have,  after  careful  study  of  the  individual  processes,  been  found  to  be 
different  in  nature,  and  thus  limitations  have  been  found  to  exist  where 
none  were  suspected.  Thus  it  was  formerly  believed  that  there  was  a 

1  Cf.  F.  Zschokke:  Die  Tierwelt  der  Schweiz  in  ihren  Beziehung  zur  Eiszeit,  Basel, 
1901. 

2  Cf.  Huppert:  Ueber  die  Erhaltung  der  Arteigenschaften,  Frag,  1896.     Franz  Ham- 
burger: Arteigenheit  und  Assimilation,  Leipsic  and  Vienna,  1903.     Emil  Abderhalden: 
Naturwissenschaftliche  Rundschau,  19,  No.  44  (1904). 


OUTLOOK.  665 

great  gulf  between  the  animal  and  vegetable  worlds.  There  was  not 
supposed  to  be  anything  in  common  between  them  as  regards  their 
chemical  processes  and  their  metabolism.  The  plant  cells  were  alone 
assumed  to  build  up  organic  substances,  or,  in  other  words,  effect  syntheses, 
whereas  the  animal  cells  were  assumed  to  break  down  only.  Wohler's 
discovery  that  benzoic  acid  is  changed  to  hippuric  acid  in  the  animal 
organism  made  the  first  breach  in  the  wall  separating  the  two  kingdoms. 
Then  in  rapid  succession  bridge  after  bridge  has  been  built  between  these 
apparently  so  distinct  fields,  so  that  to-day  a  common  band  unites  the 
animal  and  vegetable  worlds.  With  this  knowledge  as  a  basis,  it  was 
then  desirable  to  study  more  closely  the  differences  between  these  two 
kingdoms,  and  also  to  unite  them  more  closely  by  numerous  intermediate 
stages. 

A  few  examples  may  illustrate  the  significance  which,  from  a  physio- 
logical-chemical standpoint,  governs  the  conception  of  the  species. 

The  characteristic  mark  of  distinction  of  mammals,  the  mammary 
glands,  deliver  a  secretion,  the  milk,  which  is  quite  uniform  in  nature. 
The  milk  from  an  animal  almost  always  has  a  very  similar  qualitative 
composition,  although  it  varies  quantitatively  somewhat.  Each  species, 
however,  has  its  own  characteristic  milk,  and  this  is  true  not  only  of  the 
mineral  constituents,  but  of  the  organic  matter  contained  in  it  as  well.1 
In  fact,  we  have  reason  to  believe  that  even  qualitatively  the  different  kinds 
of  milk  differ  from  one  another.  Although  our  present  knowledge  does 
not  suffice  to  characterize  these  differences  more  precisely,  —  and  indeed 
the  different  kinds  of  casein  appear  to  us  as  identical,  —  we  must  not  forget 
that  we  are  never  justified  in  deciding  from  the  qualitative  and  quantita- 
tive composition  of  the  cleavage-products  whether  the  original  proteins 
under  investigation  are  identical.  In  the  arrangement  of  these  constit- 
uents in  the  original  molecule,  to  say  nothing  of  the  other  kinds  of  isomer- 
ism,  there  are  countless  possibilities. 

Furthermore,  let  us  consider  the  blood  of  different  animals.  In  every 
case  it  has  the  same  function,  the  same  physiological  significance,  and  mor- 
phologically the  most  far-reaching  similarity.  We  always  find  blood- 
corpuscles  and  plasma.  What  a  remarkable  similarity  there  is  between 
human  blood  and  sheep's  blood,  and  yet  the  sad  experiences  which  have 
resulted  from  the  attempts  at  substituting  the  latter  for  the  former  have 
proved  that  deep-seated  differences  must  exist.  The  blood-corpuscles  of 
mammals  all  contain  hemoglobin  as  a  characteristic  constituent.  Its 
function  is  invariably  the  same,  and  yet  the  hemoglobin  is  specific  for 
each  different  species,  as  is  apparent  from  the  external  relations  alone, 
such  as  the  crystalline  form  and  solubility.  Thus  the  hemoglobin  of  the 

1  Emil  Abderhalden:  Z.  physiol.  Chem.  26,  487  (1899);  27,  408,  594  (1899).  Cf. 
Lecture  XVII,  p.  404. 


666  LECTURE   XXIX. 

squirrel  crystallizes  in  the  hexagonal  system,  and  that  of  the  mouse  in  the 
orthorhombic.  From  a  mixture  of  these  two  kinds  of  blood,  each  crys- 
tallizes in  its  own  specific  form,  and  to  the  same  extent  as  corresponds  to 
the  original  mixture. 

Comparative  quantitative  analyses  of  different  kinds  of  blood  l  indicate 
that,  within  fairly  narrow  limits,  there  is  a  definite  composition  of  the 
blood  for  every  species.  In  closely  related  animals  the  relative  amounts 
of  the  individual  constituents  are  similar,  while  in  unrelated  ones  the  differ- 
ences may  be  very  marked.  It  is  noteworthy  that  the  serum  appears  to 
be  of  very  similar  composition  in  the  case  of  all  mammals.  The  product 
in  this  case  is  apparently  identical  when  prepared  from  various  classes  of 
different  animals.  We  must  not  forget,  however,  that  the  examination 
of  the  ash  can  give  us  at  best  only  a  rough  idea  of  the  composition  of  the 
serum.  It  only  serves  to  tell  us  what  elements  are  present,  and  nothing 
at  all  concerning  the  manner  in  which  they  are  contained  in  the  circulating 
blood.  But  even  if  it  were  possible  to  prove  that  the  inorganic  and  simple 
organic  constituents  were  qualitatively  and  quantitatively  the  same  in 
the  sera  of  widely  different  species,  there  still  remains  the  far  more  difficult 
problem  of  determining  the  identity  of  the  proteins.  It  is  perfectly  possible 
that  the  different  proteins  in  the  blood  contain  groupings  which  are  char- 
acteristic of  each  species  of  animals. 

Let  us  return  to  the  oft-discussed  observations  concerning  digestion. 
We  have  seen  that  the  nature  of  the  proteins  contained  in  serum 2  is  evi- 
dently independent  of  the  kind  of  food  that  is  eaten.  This  is  probably 
true  for  all  the  other  substances,  or  at  least  for  the  more  complicated 
organic  ones.  The  cells  of  the  body  never  know  what  the  nature  is  of  the 
food  eaten.  They  always  receive  a  modified  nutriment.  The  ferments 
of  the  intestine  and  the  accessory  glands  have  the  function  of  .resolving 
the  complicated  organic  constituents  of  the  food  into  cleavage-products 
and,  on  the  other  hand,  the  cells  of  the  intestine  have  the  property  of  effect- 
ing a  chemical  reorganization  of  these  building-stones  into  new  products 
which  are  suitable  for  the  cells  of  the  body.  The  intestine  thus  regulates  to 
a  certain  extent  the  general  metabolism  and  guarantees  the  maintenance 
of  a  constant  composition  of  our  tissues.  It  is,  therefore,  perfectly  clear 
that  the  entire  course  of  the  metabolism  in  the  cells  of  our  organs  is  depend- 
ent upon  their  composition.  The  composition  of  the  protein  molecule, 
or  perhaps  better  the  protein  molecules,  is  particularly  influential  in  impart- 
ing to  each  individual  cell  its  characteristics.  The  cells  of  the  body  pro- 
duce the  ferments,  and  these  are  probably  transformation  products  of 
the  proteins.  We  can  easily  understand  that  their  finer  construction  is 

1  Emil  Abderhalden:  Z.  physiol.  Chem.  23,  521  (1897);  25,  65  (1898). 

2  Emil  Abderhalden  and  Franz  Samuely:  Z.  physiol.  Chem.  46,   193  (1905).     Cf. 
Lecture  X,  p.  212. 


OUTLOOK.  667 

dependent  upon  that  of  the  cell  proteins.  Thus  their  activity  is  regulated 
very  delicately,  and  the  foundation  is  laid  for  a  specific  cell-metabolism. 
The  original  structure  of  the  cell  determines  its  characterization  for  the 
whole  of  its  existence.  Although  we  do  not  doubt  that  the  various  tissues 
possess,  corresponding  to  their  functions,  variously  constituted  cells,  the 
differences  of  which  are  apparent  not  only  in  the  metabolic  end-products, 
but  especially  in  the  nature  of  the  secreted  substances,  we  can,  on  the 
other  hand,  imagine  that  all  the  cells  of  one  and  the  same  nature  have  com- 
mon outlines  along  certain  lines,  so  that  a  common  character  marks  the 
whole  cell  structure  of  an  individual. 

Now  an  individual  results  from  the  union  of  two  cells,  the  egg  and  sperm- 
cells  of  the  same  nature.  Each  must  contain  within  itself  the  common 
form  of  cell  composition,  and  thereby  possess  the  kind  of  cell-metabolism 
which  is  characteristic  of  this  particular  species.  All  the  cells  which  result 
in  rapid  succession  from  the  fertilized  egg-cell  can  only  assume  these  char- 
acteristic tendencies,  and  thus  the  chemical  unity  of  the  original  cell  guar- 
antees the  maintenance  of  the  species.  This  is  subsequently  maintained 
by  the  activity  of  the  intestine,  which  only  permits  such  material  to  reach 
the  tissues  as  has  been  previously  prepared  in  a  definite  manner  for  the 
entrance  into  cell-metabolism  and  into  the  cells  themselves.  We  do  not 
mean  to  assert  that  the  body  cells  have  lost  the  ability  themselves  to  trans- 
form and  adjust  to  their  composition  and  to  their  metabolism  any  foreign 
nutriment,  or  especially  any  foreign  protein.  The  unicellular  organisms 
must  be  able  to  cause  all  these  processes  to  take  place  side  by  side.  With 
the  higher  animals,  the  function  of  transforming  the  foodstuffs  is  relegated 
almost  exclusively  to  the  intestine.  There  is  here  a  division  of  labor.1 
We  can  easily  imagine  that  by  reason  of  an  imperfect  function  of  the  intes- 
tine, an  insufficient  amount  of  prepared  material  may  be  carried  to  the 
tissues,  and  that  under  some  circumstances  the  entire  chemism  of  the 
cells,  their  structure  and  at  the  same  time  their  metabolism,  may  become 
altered  so  that  finally  degenerations  result  which  are  apparently 
inexplicable. 

In  mammals  the  individuality  of  the  cells  of  the  species  is  in  a  very  great 
measure  guaranteed  by  the  longer  or  shorter  period  during  which  the  new 
being  remains  associated  with  the  organism  of  the  mother.  The  foetus 
obtains  its  nourishment  from  the  blood  of  the  maternal  organism;  the 
suckling  from  her  milk. 

We  have  thus  arrived  at  a  purely  chemical  explanation  for  the  concep- 
tion of  species  and  its  maintenance.  We  admit  that  we  are  reasoning 
from  a  limited  number  of  observations,  and  are  not  yet  in  a  position  to 
demonstrate  experimentally  the  truth  of  our  conception.  We  realize  fully 

1  Cf.  Ulrich  Friedemann  and  S.  Isaac:  Z.  exper.  Path.  u.  Therapie,  1,  513  (1904). 


668  LECTURE   XXIX. 

that  we  are  now  only  constructing  as  it  were  a  scaffolding  which  will  per- 
haps serve  to  lead  future  investigation  into  definite  channels. 

We  are  not  alone  in  this  idea.  Franz  Hamburger,1  starting  from  entirely 
different  experimental  results,  has  likewise  traced  in  a  most  interesting 
manner  the  individuality  of  a  species  and  its  maintenance  to  a  definite 
composition  of  the  cells  and  body  fluids.  This  idea  is  closely  related  to  the 
so-called  biological  reaction,  which  we  shall  discuss  briefly.  Its  discovery 
is  associated  with  the  names  of  Bordet,  Tchistowitsch,  and  Nolf.2  It  rep- 
resents merely  a  generalization  of  the  Law  of  Immunity,  and  depends  upon 
the  formation  of  very  specific  substances  after  the  introduction  of  products 
foreign  to  the  species.  The  knowledge  of  this  principle  is  of  great  signifi- 
cance for  the  further  development  of  physiological  chemistry.  It  forms  a 
bridge  to  the  domain  of  pathology;  and  we  become  more  and  more  con- 
vinced that  pathological  processes  are  not  sharply  distinct  from  physio- 
logical ones,  but  are  common  manifestations  of  body  cells  under  definite 
conditions.  The  limitations  of  purely  physiological-chemical  investiga- 
tion are  thus  being  more  and  more  eliminated.  By  the  improvement  of 
methods,  it  continually  enters  new  fields,  and  on  the  other  hand  other 
fields  constantly  attach  themselves  to  it,  and  await  new  impulses  for 
further  fruitful  work.  Here  we  must  introduce  the  name  of  an  investigator 
to  whom,  more  than  any  one  else,  our  thanks  are  due  for  the  expression 
of  this  unity  between  physiological  and  pathological  processes,  namely, 
Paul  Ehrlich.  We  shall  return  to  his  theory,  which  has  served  as  a  founda- 
tion for  important  investigations  in  this  domain.  In  this  connection  also 
we  must  call  attention  to  the  great  importance  of  Pawlow's  work.3  He 
likewise  clearly  recognized  the  numerous  transition  stages  between  physio- 
logical and  pathological  processes,  from  his  observations  on  the  functions 
of  the  alimentary  tract  under  varying  conditions. 

It  is  quite  out  of  the  question  for  us  to  give  here  even  a  brief  summary 
of  all  the  investigations  which  are  based  upon  the  conception  of  the  "bio- 
logical reaction."  In  a  very  short  time  it  has  developed  into  an  important, 
independent  branch  of  biological  science.  We  shall  here  very  briefly  call 
attention  to  a  few  fundamental  experiments.  If  we  inject,  for  example, 
horse-blood  into  a  rabbit,  the  serum  of  this  animal  soon  shows  characteristic 
new  properties  towards  the  injected  blood.  It  dissolves  the  blood-corpuscles 
and  forms  a  precipitate  with  the  new  serum,  called  the  precipitin-formation. 
This  reaction  is  a  specific  one.  The  serum  of  the  rabbit  which  has  been 


1  Loc.  cit. 

2  Jules   Bordet:   Annales  de  ITnstitute   Pasteur,  1899,  240.     Tchistowitsch:   Ibid. 
1899,  413.   Nolf:  Ibid.  1900,  299.   Cf.  Rostoski:  Zur  Kenntnis  der  Prazipitine.   Wiirz- 
burg,  1902. 

3  Pawlow-Walther:  Das  Experiment  als  zeitgemasse  und  einheitliche  Methode  medi- 
zinischer  Forschung.     Bergmann,  Wiesbaden,  1900. 


OUTLOOK.  669 

treated  previously  with  horse's  blood  will  not  react,  for  example,  upon 
the  blood  of  the  ox,  sheep,  or  goat.  We  may  add  that  the  formation  of  such 
specific  products  is  not  peculiar  to  the  blood  and  its  serum.  The  property 
is  common  to  all  the  cells,  body-fluids,  and  secretions.  If  we  inject  the 
spermatozoa  of  the  sheep  into  a  rabbit,  the  blood-serum  of  this  animal 
when  added  to  the  living,  motile  spermatozoa  of  the  sheep  will  restrict  their 
activity.  And  this  serum  also  has  a  solvent  action  upon  the  blood-corpus- 
cles of  the  sheep's  blood;  i.e.,  the  effect  of  the  spermatozoa  is  the  same  as 
if  sheep-blood  itself  had  been  injected.  Hamburger  assumes  that  every 
cell,  and  all  the  other  substances  which  circulate  in  the  body-fluids,  possess 
definite  atomic  groupings,  which  we  must  regard  as  imparting  the  specific 
nature  to  these  products.  Consider  the  ferments!  These  are  substances 
of  which  we  know  merely  the  effect.  Emil  Fischer  has,  as  we  have  often 
mentioned,  called  our  attention  to  their  very  specific  action,  and  indicated 
clearly  their  dependence  upon  the  configuration  of  the  different  compounds 
with  which  they  react.  The  ferment  molecule  must  possess  certain  definite 
groups  by  reason  of  which  it  can  react  with  certain  other  molecules, 
and  only  these.  Fischer  has  aptly  compared  the  relation  between  the 
ferment  and  the  compound  with  which  it  reacts  as  that  of  a  key,  and  the 
lock  which  it  fits.  Just  as  a  given  key  fits  only  a  certain  kind  of  lock,  and 
conversely  the  lock  can  only  be  opened  by  just  such  a  key,  so  the  specific 
atomic  grouping  of  the  ferment  molecule  probably  harmonizes  exactly 
with  the  compound  to  be  acted  upon.  We  can  easily  imagine  that  slight 
changes  in  the  arrangement  of  the  atoms  in  the  ferment  molecule  will  be 
sufficient  to  modify  the  efficiency  of  the  ferment.  On  the  other  hand,  we 
can  also  believe  that  when  this  characteristic  group  is  in  combination  with 
some  other  substance,  the  ferment  will  be  prevented  from  exercising  its 
function.  It  is  possible  that  the  zymogen  stage  of  the  ferment  is  brought 
about  by  some  such  combination  or  different  arrangement  of  the  atoms 
in  the  ferment  molecule.  These  views  are  advanced  merely  to  indicate 
that  just  as  the  individual  cells  can  produce  ferments,  they  them- 
selves may  be  endowed  with  specific  atomic  groups,  which,  as  Ehrlich 
has  suggested,  may  perhaps  stand  in  certain  relation  to  the  assimilation 
of  the  food.  In  this  case  there  would  be  a  certain  analogy  between  fer- 
mentation and  cell-activity.  We  know  of  the  formation  of  anti-ferments 
when  the  ferments  are  introduced  into  the  circulation.  These  anti- 
ferments  are  also  specific  in  their  action.  We  may  look  upon  the  forma- 
tion of  the  precipitins,  and  related  bodies,  as  taking  place  in  a  perfectly 
analogous  manner.  We  introduce  into  the  blood  and  cells  of  a  foreign 
species  of  animals  a  certain  atomic  grouping  which  is  peculiar  to  a  different 
species,  and  which  is  perfectly  foreign  to  the  first  animal.  The  animal 
organism  reacts  towards  this  exactly  in  the  same  way  as  towards  the 
toxines  which  result  from  micro-organisms.  Substances  are  evidently 


670  LECTURE   XXIX. 

produced  which  are  so  constituted  that  they  exactly  correspond  to  the 
structure  of  the  foreign  product.  In  this  way  the  active  groups  which 
would  be  injurious  to  the  body-cells  are  rendered  harmless.  The  " bio- 
logical reaction"  of  the  animal  organism  is,  from  this  point  of  view,  to 
be  regarded  merely  as  a  means  of  protection. 

Let  us  see  what  subsequent  investigation  has  done  for  us  in  this  direc- 
tion towards  establishing  our  conception  of  species.  In  the  first  place 
it  could  be  shown  that  the  formation  of  precipitins  was  not  confined  to 
one  species,  but  that  the  specific  result  of  the  reaction  was  limited  to 
related  animals  within  such  narrow  limitations  that  the  relationship 
between  animals  which  from  morphological  and  other  similarities  are 
usually  grouped  together  could  be  confirmed  by  means  of  the  "biological 
reaction."  Nuttal 1  found,  for  example,  that  the  serum  of  a  rabbit  into 
which  the  serum  from  dog's  blood  had  been  injected  would  give  a  pre- 
cipitate with  the  blood  of  eight  different  kinds  of  Canidce,  but  not  with 
the  blood  of  any  other  species.  Friedenthal 2  showed,  furthermore,  that 
only  the  anthropoid  apes  showed  a  marked  blood-relation  to  man, 
whereas  the  lower  apes  showed  but  slight  indication  of  a  common 
origin.  We  may  add  that  the  different  kinds  of  birds  have  also  been 
compared  in  this  way,  and  that  recently  Uhlenhut 3  has  succeeded  in  so 
perfecting  the  method  of  carrying  out  the  biological  reaction  that  it  has 
become  possible  to  differentiate  and  distinguish  between  closely  related 
kinds  of  blood.  The  reaction  has  become  of  considerable  importance  in 
forensic  blood  determinations. 

It  would  be,  of  course,  desirable  to  ascertain  what  compounds  the  cells 
and  body-fluids  make  use  of  for  carrying  out  this  specific  reaction.  We 
would  naturally  think  of  the  proteins  in  this  connection,  for,  on  account  of 
their  extremely  complicated  composition,  they  are  most  suited  to  serve  as 
carriers  of  specific  groups  of  atoms.  As  a  matter  of  fact,  it  has  been  found 
possible  to  prove  that  after  the  injection  of  protein,  e.g.,  serum-albumin, 
perfectly  specific  precipitins  are  formed;4  and,  indeed,  it  was  even  found 
possible  to  distinguish  by  this  means  between  the  casein  of  different  kinds 
of  milk.  We  do  not  yet  know  whether  in  such  cases  the  individual  protein 
substances  come  into  consideration,  or  whether  the  effect  is  produced  by 
impurities  which  adhere  to  them.  At  all  events,  it  is  of  great  interest  to 


1  Cf.  Nuttal:  Proc.  Roy.  Soc.  69,  150   (1901).     Blood  Immunity  and  Blood  Rela- 
tionship.    Clay  &  Sons,  London,  1901. 

2  Arch.  Anat.  Physiol.  1900,  494.     Sitzsber.  Berliner  Akad.  1902.     Verhandl.  Ber- 
liner physiol.  Gesell.  1904.     Uhlenhut:  Arch.  Rassen-   und  Gesellschaftsbiologie,  1,  682 
(1904). 

3  Uhlenhut:  Deut.  med.  Wochschr.  1905,  42. 

4  Cf.  among  others,  L.  Michaelis:  Deut.  med.  Wochschr.  1902,  41.     L.  Michaelis  and 
Carl  Oppenheimer:  Arch.  Anat.  Physiol.  Sup.  1902,  336.     F.  Obermayer  and  E.  P.  Pick: 
Wien.  klin.  Wochschr.  1904,  10.     Andrew  Hunter:  J.  Physiol.  32,  327  (1905). 


OUTLOOK.  671 

find  that  if  the  proteins  enter  metabolism  in  any  other  way  than  through 
the  intestines,  i.e.,  in  such  a  way  that  the  substances  have  not  lost  their 
identity  by  the  activity  of  the  intestine  and  changed  so  that  they  are 
suited  to  the  body-albumin,  then  the  only  effect  to  be  observed  is  the  for- 
mation of  these  specific  products.  This  result  supports  our  views  regarding 
the  great  importance  of  the  digestion  processes  and  assimilation  in  the 
intestine  for  the  maintenance  of  the  species. 

With  the  assumption  of  atomic  groups  of  specific  nature  in  the  individual 
cells,  and  thus  in  the  egg  and  sperm,  new  aspects  are  given  to  the  problem 
of  heredity.  Although  it  has  not  yet  been  found  possible  to  cause  mor- 
phological changes  that  have  been  artificially  produced  to  be  inherited, 
still  there  remains  the  possibility  of  effecting  hereditary  variations  by 
influencing  the  chemical  composition.  We  may  mention  the  interesting 
experiments  of  Engelmann  and  Gaidukow  l  who  succeeded  for  the  first 
time  in  proving  satisfactorily  that  a  property  which  had  been  acquired 
could  be  inherited.  If  cultures  of  Oscillaria  sancta,  a  kind  of  alga,  are  kept 
for  months  at  a  time  in  light  of  a  definite  color,  then  the  single  threads  of  the 
alga  gradually  assume  a  complementary  color,  i.e.,  a  shade  which  is  favor- 
able to  the  assimilation  in  such  light.  The  change  of  color  takes  place  only 
with  the  living  organism.  Aqueous  solutions  of  the  dye  do  not  show  any 
such  change  in  shade  under  the  same  conditions.  We  have,  therefore,  a 
case  of  a  vital,  physiological  adjustment.  Engelmann  designates  it  as 
chromatic  adaptation.  Now,  strange  to  state,  this  acquired  change  of  color 
is  retained  when  the  Oscillaria  are  placed  in  ordinary  light.  In  the  case 
of  rapid  propagation,  the  new  color  prevails,  so  that  the  assumption  may 
be  made  safely  that  there  is  a  new  formation  of  chromophyll  in  the  younger 
generations  of  cells.  In  reality  we  have  here  a  case  of  the  inheritance 
of  a. change  in  chemical  composition,  and  in  fact  in  the  formation  of  a 
pigment,  the  synthesis  of  which  remains  the  same  as  formerly  in  the  new 
environment. 

It  might  have  been  thought  that  by  feeding  compounds  of  quite  definite 
composition  it  would  be  possible  to  effect  a  change  in  the  chemical  compo- 
sition, and  thereby  in  the  cell-metabolism.  Such  experiments  must  be 
without  much  prospect  of  success,  because  of  the  fact  that,  as  we  have 
seen,  the  intestinal  wall  frustrates  the  entrance  of  such  foreign  substances. 
The  unicellular  beings  are  likewise  unsuitable  for  deciding  such  questions, 
because  they  are  also  provided  with  the  necessary  means  for  maintaining 
their  constancy  of  chemical  composition.  At  best,  the  only  way  we  can 
conceive  of  any  such  experiment  being  successful  would  be  to  continue  for 
a  long  time  the  introduction  of  such  substances  to  the  body-cells  in  some 
other  way  than  through  the  alimentary  canal,  for  it  would  be  expected  that 

1  T.  W.  Engelmann:  Arch.  Anat.  Physiol.  1902,  Suppl.  333.  Sitzsber.  Berliner  Akad. 
Wissensch.  1902.  Arch.  Anat.  Physiol.  1903,  214. 


672  LECTURE   XXIX. 

in  the  course  of  time  the  cells  would  lose  to  some  extent  the  ability  of  trans- 
forming rapidly  the  substances  which  are  brought  to  them.  At  all  events, 
this  is  the  only  way  in  which  the  metabolism  of  more  highly  organized 
beings  could  be  affected. 

It  is  almost  generally  assumed  that  in  the  inheritance  of  certain  proper- 
ties the  nucleus  of  the  cell  plays  a  particularly  important  part,  and  in  fact 
it  is  usually  assumed  that  it  alone  is  able  to  transmit  the  characteristics  of 
the  parents.  This  is  certainly  not  justifiable,  for  although  the  protoplasm 
represents  an  apparently  homogeneous  mass,  which  is  but  slightly  differ- 
entiated and  excites  but  little  the  interest  of  the  histologist,  it  is  not  at  all 
apparent  why,  with  its  infinitely  complicated  composition,  it  should  not  be 
capable  of  at  least  taking  part  in  the  processes  named.  In  this  direction  the 
following  experiment  of  Godlewski l  is  interesting.  He  fertilized  nucleus- 
free  fragments  of  Echinus  eggs  with  spermatozoa  of  Antedon  rosacea.  It 
was  found  possible  in  some  cases  to  effect  a  development.  Even  these 
nucleus-free  pieces  did  not  develop  to  be  of  the  Antedon  type.  In  order 
to  understand  this  experiment  better,  we  should  recall  the  investigations 
of  Loeb,2  which  we  have  previously  mentioned,  who  succeeded  in  a  great 
number  of  cases  in  bringing  eggs  to  spontaneous  segmentation  by  the 
action  of  certain  salts  in  definite  concentrations.  Of  great  interest  is  his 
discovery  that  under  certain  definite  conditions  the  egg  of  a  definite  species, 
e.g.,  that  of  a  star-fish,  could  be  fertilized  by  the  spermatozoa  of  an  entirely 
different  nature.  We  shall  not  go  into  the  significance  of  these  discoveries 
any  more  deeply,  but  will  briefly  consider  the  outlook  which  Loeb  himself 
obtained  from  his  experiments.  He  believes  it  is  not  at  all  improbable 
that  the  greater  part  of  the  many  different  forms  of  life,  particularly  those 
of  deep  sea,  may  have  resulted  from  conditions  which  are  not  at  all  unlike 
those  of  his  experiments.  It  is  indeed  conceivable  that  in  the  course  of 
time  the  composition  of  the  sea-water  in  certain  localities  may  change  so 
that  the  conditions  for  the  fertilization  of  one  species  are  replaced  by  those 
corresponding  to  a  different  one.  We  mention  these  experiments  merely 
to  illustrate  in  what  widely  different  ways  biology  seeks  to  penetrate  the 
mystery  of  life.  To  be  sure,  we  are  not  justified  in  considering  the  inter- 
esting results  of  Loeb's  experiments  as  by  any  means  solving  the  problem  of 
egg  development,  or  even  in  hoping  that  by  such  a  way  we  shall  obtain  an 
insight  into  the  laws  of  heredity.  Loeb's  experiments  merely  show  that  it 
is  possible,  by  changing  the  concentration  of  a  salt  solution  in  which  the 
unfertilized  egg  is  placed,  to  bring  about  cell-division.  They  do  not  tell 
us  anything  at  all  about  the  causes  of  cell-multiplication,  and  the  reason 

1  Anzeigen  der  Akad.  Wissensch.  Krakau,  1905,  501. 

2  University  of  California  Publications,  1,  No.  1,  p.  1  (1903);  1,  39  (1903);  1,  83  (1904); 
2,  5  (1904).     Pfliiger's  Arch.  99,  323  (1903);  ibid.  104,  325  (1904).     Cf.  Emil  Abder- 
halden:  Arch.  Rassen-  und  Gesellschaftsbiologie,  1,  656  (1904). 


OUTLOOK.  673 

for  the  regular  arrangement  and  the  gradual  differentiation  of  their 
functions. 

Similarly,  Godlewski's  investigation  fails  to  shed  light  upon  the 
problem  of  heredity  itself.  It  shows  us,  on  the  other  hand,  quite  clearly 
and  definitely  that  it  is  not  right  to  regard  the  process  of  cell-division  as  a 
function  of  the  nucleus  alone,  and  consider  that  the  protoplasm  plays  a 
passive  part.  The  cell  of  the  egg,  in  its  entirety  and  according  to  its  chem- 
ical composition,  must  have,  more  than  any  other  cells  of  the  body,  the 
ability  to  subdivide  and  increase.  The  entire  nature  of  cell  propagation, 
in  all  its  particulars,  has  been  found  to  be  bound  up  with  it. 

Loeb's  experiments  have  shown  that  the  egg-cells  of  various  species  of 
animals  may  be  easily  induced  to  take  part  in  such  a  process  of  cell-division. 
The  cells  of  one  kind  develop  up  to  a  certain  stage  apparently  of  their  own 
accord,  others  require  a  slight  stimulation,  while  others  need  quite  a  con- 
siderable impulse.  The  entire  development  of  the  individual  is  bound  up 
with  countless  problems.  When  we  remember  that  we  have  before  us  a 
mode  of  development  which  has  been  inherited  for  ages  and  has  been 
taking  place  over  and  over  again  in  paths  which  have  been  well  defined, 
the  wonderful  thing  is  that  there  is  apparently  no  limitation  to  it.  We 
can  understand  perhaps  how,  in  the  case  of  the  mature  organism,  lost 
tissues  may  be  regenerated;  and,  again,  it  does  not  appear  so  remarkable 
to  us  that  from  the  cells  of  a  certain  tissue  others  may  be  produced  with 
the  same  function  and  the  same  chemical  composition,  so  that  the  whole 
corresponds  to  a  morphological  and  functional  unit.  On  the  basis  of  our 
present  knowledge,  however,  it  is  a  mystery  how  all  the  different  tissues 
can  develop  from  a  single  cell,  and  how  in  each  kind  of  tissue  chemical 
processes  will  take  place  which  are  peculiar  to  that  particular  tissue,  as  is 
evident  from  a  study  of  the  secretions  and  of  the  end-products  of  their 
metabolism.  The  complicated  picture  of  the  morphological  development 
of  the  individual  seems  to  us  far  less  remarkable  than  the  much  more 
intricate  and  more  involved  differentiation  of  the  chemical  construction 
and  the  chemical  processes  which  take  place  in  the  individual  cells. 

Now  we  know  that  the  individual,  in  the  case  of  the  more  highly  organ- 
ized animals  especially,  shows  not  only  a  development  of  species,  but  in 
its  beginnings  there  are  stages  of  development  to  be  detected  which  we 
can  understand  only  from  the  history  of  the  ancestry  of  the  animal  organ- 
ism. We  need  recall  merely  the  formation  of  the  gill-clefts  or  gill-slits,  a 
stage  of  development  which  even  the  human  foetus  passes  through.  Is  it 
not  probable  that  there  are  differences  in  the  chemical  composition  of  the 
tissues  during  the  separate  stages  of  its  being,  which  are  likewise  suited 
for  tracing  the  entire  group  of  vertebrates  back  to  a  common  ground 
plan?  We  must  thank  G.  von  Bunge  for  an  answer  to  this  question.1 

1  Z.  physiol.  Chem.  28,  452  (1899). 


674  LECTURE   XXIX. 

He  pointed  out  that  the1  land  vertebrates  are  richer  in  sodium  chloride 
in  proportion  as  the  stage  of  development  is  young.  This  fact  was  illus- 
trated particularly  clearly  by  comparing  the  sodium  chloride  content  of 
the  cartilage  of  embryo  and  that  of  later  stages  of  development  of  the 
same  species.  The  older  the  animal,  the  lower  sinks  the  content  of 
sodium  and  chlorine.  There  must  be  some  reason  why  the  cartilage  of 
the  embryo  is  so  rich  in  common  salt.  This  fact  is  all  the  more  striking 
because  the  land  is  poor  in  this  salt,  potassium  salts  preponder- 
ating. Typical  inhabitants  of  the  land,  such  as  insects,  have  in 
their  bodies  the  elements  sodium  and  potassium  in  about  the  same 
proportion  as  that  in  their  food.  The  remarkably  high  content  of  sodium 
chloride  in  the  cartilage  of  the  early  stages  of  development  of  verte- 
brates which  inhabit  the  land  may  be  regarded,  like  the  appearance 
of  the  gill-slits  and  other  similar  phenomena,  as  an  ancestral  reminis- 
cence. It  is  not  at  all  strange  that  even  the  chemical  composition 
should  indicate  long-forgotten  conditions. 

Not  alone  the  development  of  the  individual  leads  to  such  various 
problems,  but  in  later  life  also  we  meet  with  processes  the  nature  of  which 
we  can  understand  only  very  imperfectly.  We  usually  assume  that  the 
development  of  the  entire  organism  can  be  traced  back  eventually  to  three 
germ-layers.  We  can  indeed  distinguish  these  as  regards  their  chemical 
function  and  their  construction  even  although  one  and  the  same  layer, 
as  the  ectoderm,  may  be  of  very  heterogeneous  construction.  We  can 
imagine  that  the  cells  of  each  of  these  three  germ-layers  among  themselves 
have  certain  common  characters  so  that  eventually  each  individual  cell 
is  in  a  position  of  replacing  other  cells  which  have  resulted  from  the 
same  germ-layer  and  even  to  form  these  anew.  It  is  not  sufficient,  how- 
ever, to  conceive  that  these  three  germ-layers  correspond  to  three  great 
classes  of  different  cells.  They  must,  as  we  have  already  suggested, 
all  show  common  characteristics.  To  what  extent  the  body-cells  of 
even  adult  organisms  have  the  ability  of  changing  their  composition, 
and  thereby  their  function,  is  shown  by  the  following  experiment.1  If 
the  crystalline  lens  is  entirely  extirpated  from  a  water  salamander,  after 
a  short  time  there  will  be  found  in  its  place  a  newly  formed  transparent 
structure  which  perfectly  corresponds  to  the  original  lens.  It  is  very 
interesting  to  find  that  the  new  formation  of  the  lens  starts  from  the 
epithelial  cells  of  the  iris.  Now  the  cells  of  the  latter  are  normally  as 
opaque  as  possible.  Nevertheless  these  cells  multiply  after  the  removal 
of  the  lens,  and  the  pigment,  which  causes  the  opacity,  disappears.  In 
this  process  comprehensive  chemical  processes  must  take  place.  The  cells 


1  Cf.  Vincenzo  L.  Colucci:  Memor.  della  R.  accad.  delle  scienze  dell'  inst.  di  Bologna, 
Serie  5,  T.  1,  p.  593  (1890).  Also  G.  Wolff:  Arch.  Entwicklungsmechanik  der  Organis- 
men,  1,  380  (1896). 


OUTLOOK.  675 

of  the  crystalline  lens  and  of  the  iris  have  unquestionably  quite  different 
construction  corresponding  to  their  different  functions.  Certainly  their 
metabolism  is  different. 

Thus  when  we  find  that  from  one  tissue  another  of  entirely  different 
characteristics  may  be  formed,  with  a  quite  different  function,  we  can- 
not help  asking  whether  pathological  new  formations  do  not  arise  from 
similar  processes.  Certainly  the  cells  of  the  newly-formed  crystalline  lens 
of  the  Triton  renew  themselves  and  form  cells  of  the  same  kind,  and  show 
hardly  any  tendency  to  form  the  pigment  which  is  required  by  the  cells  in 
the  iris.  Similarly  it  is  possible  that  a  body-cell  may  retain  its  individual 
nature  only  with  difficulty  if  for  any  reason  its  chemical  nature  and  func- 
tion become  seriously  altered,  and  the  progeny  of  such  a  cell  will  possess 
the  characteristics  of  the  mother-cell  so  that  gradually  a  whole  cell-complex 
will  develop  which  is  of  a  nature  foreign  to  the  entire  organism  and  to  its 
metabolism,  and  in  fact  the  metabolic  end-products  of  this  new  cell-com- 
plex may  exert  a  disturbing  influence  upon  the  metabolism  of  the  remain- 
ing cells  of  the  body. 

Apparently  there  is  a  connection  between  these  cells  and  the  mother 
soil  —  we  refer  especially  to  sarcoma  and  carcinoma  —  for  it  has  been 
frequently  doubted  whether  such  cells  can  be  successfully  transmitted  to 
organisms  of  a  different  species.  We  are,  in  making  these  suggestions, 
very  far  from  explaining  the  formation  of  these  peculiar,  atypical 
tissues.  We  only  wish  to  bring  forth  the  fact  that  with  the  further 
development  of  our  physiological-chemical  knowledge  new 'tasks  will  be 
set,  and  that  even  problems  of  purely  morphological  investigations  will, 
in  the  course  of  time,  become  closely  allied  to  those  of  physiological 
chemistry.  If  it  is  once  found  possible  to  compare  the  metabolism  of  the 
cells  of  a  cancer,  or  other  malignant  growth,  with  normal  cells,  we  may 
certainly  expect  to  obtain  a  more  accurate  insight  into  the  nature  of  such 
mysterious  processes. 

Taking  into  consideration  all  that  we  know  concerning  metabolism, 
and  what  we  have  deduced  indirectly,  it  does  not  appear  to  us  impossible 
that,  among  the  more  complicated  processes,  here  and  there  a  link  in  the 
chain  of  separate  processes  may  be  missing,  or  react  in  a  faulty  manner, 
thus  giving  rise  to  degenerations  which  eventually  may  be  inherited,  or  at 
least  there  may  be  indications  of  the  transmission  to  several  members  of  a 
family.  We  would  recall  certain  anomalies,1  such  as  cystinuria,  alcap- 
tonuria,  and  albinoism,  and  finally  familiar  types  of  degenerations  in  the 
nervous  system.  Gout  and  diabetes  may  also  be  caused  by  disturbances 
in  some  phase  of  the  functions  of  cell-metabolism  which  are  partly 
inherited  and  partly  acquired.  Although  we  may  imagine  that,  for 
example,  an  anomaly  in  the  composition  of  the  body-albumin  is  inherited 

1  Cf.  A.  E.  Garrod:  Pfliiger's  Arch.  97,  410  (1903). 


676  LECTURE   XXIX. 

in  such  a  way  that  the  egg-cell,  as  a  part  of  the  mother's  organism,  is 
affected  by  the  disturbance,  still  this  will  not  hold  for  the  transmission  of 
many  other  properties.  In  this  direction  we  have  the  peculiarity  in  the 
inheritance  of  hemophilia,  as  we  have  already  indicated. 

If  we  consider  the  cells  in  their  entire  chemical  construction,  and  con- 
stantly bear  in  mind  that  herein  lies  their  entire  function,  we  can  indeed 
imagine  that  a  faulty  organization  of  the  cell  will  have  an  influence  upon 
the  general  metabolism.  The  conception  of  the  disposition  which  plays 
such  an  important  part  in  pathology  is  certainly  well  founded,  and  the 
cause  of  it  is  to  be  sought  in  the  state  of  the  function  of  certain  groups  of 
cells,  or  the  whole  cell  state  of  the  body  may  be  affected  in  such  a  way  that 
the  individual  appears  to  be  functionally  deficient.  Naturally  such  spec- 
ulations, which  have  no  experimental  justification,  do  not  penetrate  at  all 
into  the  nature  of  a  disposition;  but,  nevertheless,  it  seems  fitting  to  sug- 
gest that  an  alteration  in  the  chemical  processes  of  the  cells  themselves 
may  come  into  consideration  here. 

Let  us  now  turn  back  to  the  limitations  of  the  concept  of  species  on 
a  basis  of  physiological-chemical  investigation.  We  have  mentioned  only 
a  few  of  the  species  which  have  been  most  thoroughly  studied.  We  might 
multiply  these  examples,  but  a  few  suggestions  should  prove  sufficient. 
We  know  that  the  general  metabolism  of  different  animals  is  unlike. 
This  is  partly  due  to  the  different  kinds  of  nourishment  which  they  receive. 
Thus  we  can  readily  understand  that  the  urine  of  herbivora  will  be  of 
quite  different  composition  from  that  of  pure  carnivora,  and  that  of 
the  latter  will  likewise  be  different  from  that  of  omnivora.  We  even 
find  differences  in  the  same  animal  species.  We  recall  in  particular  the 
amount  of  kynurenic  acid  present  in  the  urine  of  dogs.  We  encounter 
other  characteristics  which  indicate  that  each  species  of  animal  has  a 
peculiar  cell-metabolism.  We  do  not  doubt  at  all  that  there  are  also 
individual  differences.  The  fact  that  there  is  a  perfectly  definite  endogenic 
uric  acid  value  for  each  individual  points  in  this  direction.  Also  the  pecul- 
iar characteristic  color  of  the  skin,  hair,  eyes,  etc.,  gives  one  the  impression 
that  it  is  the  expression  of  a  specialized  individual  metabolism  of  certain 
definite  cell-complexes.  Each  individual  possesses  its  own  characteristic 
smell.  This  is  usually  not  observed  by  human  beings,  but  that  there  are 
such  distinctions  is  evident  from  the  ability  of  certain  animals,  such  as  the 
dog,  to  trace  a  person  by  the  scent. 

The  differentiation  of  the  species  increases  infinitely  in  the  case  of  lower 
animals,  especially  the  anthropods.  What  a  richness  of  coloring,  and  what 
splendor  in  the  groups  of  butterflies  and  beetles!  Each  separate  color  is  an 
expression  of  the  chemism  of  the  cells  producing  it.  We  meet  with  the 
same  phenomena  in  the  plant  world,  where  the  beautifully  colored  flowers 
indicate  an  unsuspected  variety  of  peculiarly  modified  chemical  processes. 


OUTLOOK.  677 

To  be  sure  there  are  certain  relations  between  the  pigments  that  the  vege- 
table kingdom  produces  and  those  of  the  living  animal  organism,  which 
find  expression  particularly  when  it  is  a  case  of  assuming  a  color  for  pur- 
poses of  protection.  It  would  be  interesting  to  compare  the  pigment  used 
in  mimicry  with  that  of  the  plants  upon  which  the  animals  feed.  We 
would  also  refer  to  the  large  number  of  poisonous  substances  which  animals 
produce  partly  as  weapons  of  attack  and  partly  for  other  purposes. 

The  specific  character  of  cell-metabolism  does  not  by  any  means  stop  at 
causing  differentiated  individuals.  It  also  concerns  the  individual  cell. 
We  shall  refer  in  this  connection  merely  to  the  specific  metabolic  sub- 
stances, especially  the  toxines,  which  the  cells  produce  to  combat  every 
kind  of  bacteria. 

The  intricate,  specific  organization  of  the  cells  of  certain  kinds  of  animals 
is  also  indicated  indirectly,  as,  for  example,  by  their  behavior  towards  certain 
poisons.  Thus  we  know  that  a  man  who  is  not  accustomed  to  morphia 
will  usually  sleep  after  taking  two  centigrams,  whereas  with  dogs,  ten  times 
this  amount  does  not  have  the  slightest  effect  toward  producing  sleep.  A 
goat  will  stand  twenty  grams  of  morphine  hydrochloride  without  showing 
any  desire  to  sleep,  although  other  indications  of  poisoning  appear. 
Whereas  atropine  is  a  violent  poison  for  man,  rabbits  are  perfectly  immune 
toward  it.  They  can  feed  unharmed  upon  leaves  of  belladonna*.  It  is 
also  known  that  all  kinds  of  animals  do  not  furnish  equally  good  fostering 
soil  for  pathogenic  bacteria,  and  that  different  organisms  react  differently 
toward  certain  infections. 

If  we  summarize  all  these  details,  we  shall  recognize  how  manifold  the 
processes  are  which  stamp  their  outlines  upon  every  kind  of  species  and 
every  individual.  Here  lies  before  us  an  immeasurable,  almost  unculti- 
vated field  of  investigation.  New  problems  and  new  methods  become 
more  and  more  intricate,  and  the  demarcations  of  the  conception  of  species 
become  more  and  more  exact.  The.  purely  morphological  boundaries  of 
species,  families,  and  classes  will  pass  away.  Comparative  physiological- 
chemical  investigation  will,  in  the  future,  take  the  lead  and  control  the 
results  of  purely  morphological  investigation. 

We  must  consider  one  other  field  which  is  gradually  coming  into  more 
intimate  contact  with  physiological  chemistry.  We  refer  to  pharmacology. 
We  are  no  longer  satisfied  with  determining  the  effect  of  individual 
drugs.  We  desire  to  determine,  by  comparative  experiments,  whether 
it  is  this  or  that  group  which  represents  the  active  principle,  and 
whether  the  compound  exerts  its  effect  as  such,  or  whether  it  first  under- 
goes a  transformation.1  Finally,  we  are  interested  to  know  how  the 


1  Cf.  S.  Fraenkel:  Die  Arzneimittelsynthese  auf  Grundlage  der  Beziehungen  zwischen 
chemischen  Aufbau  und  Wirkung,  Berlin,  J.  Springer,  1906.  H.  Bechold  and  P.  Ehrlich* 
Z.  physiol.  Chem.  47,  173  (1906). 


678  LECTURE   XXIX. 

substance  introduced  is  broken  down,  and  in  what  form  it  leaves  the  body. 
Conversely  our  interest  is  fastened  upon  the  way  in  which  the  body  reacts 
toward  the  influence  of  certain  compounds.  Here  also  innumerable  specific 
cell  reactions  come  into  play,  and  we  constantly  meet  with  indications  of 
the  functional  differences  of  the  cell-complexes  of  different  organs.  Investi- 
gation in  this  field  is  only  just  beginning.  We  lack  methods  for  tracing 
the  course  of  each  individual  substance  in  the  body  from  cell  to  cell.  We 
should  like  to  know  whether  the  different  body-cells  have  a  different 
affinity  for  certain  products  which  are  introduced,  and  whether  perhaps 
the  specific  reaction  of  the  organism  is  not  the  expression  of  the  ability  for 
selection  on  the  part  of  certain  particular  tissue-cells.  On  the  other  hand, 
we  are  interested,  in  every  case,  to  know  how  the  animal  organism 
wards  off  the  action  of  all  the  different  substances  which  are  introduced 
into  the  body  and  are  foreign  to  it.  In  considering  the  functions  of  the 
cells  we  constantly  met  with  such  problems  and  have  seen  in  how  many 
different  ways  the  organism  protects  its  cells  from  the  action  of  such  sub- 
stances. Sometimes  the  substance  which  is  introduced  is  oxidized,  some- 
times it  is  reduced,  and  at  other  times  it  is  conjugated  either  directly, 
or  after  certain  preparatory  attacks,  with  different  substances  which 
are  produced  in  the  intermediate  metabolism.  Thus  we  have  seen  how 
the  aniihal  organism  behaves  toward  glycocoll,  sulphuric  acid,  urea,  and 
glucuronic  acid.1  We  know  that  the  proteins  themselves  play  an  impor- 
tant part  in  these  processes.  They  combine  with  many  of  these  harmful 
substances  which  are  introduced  into  the  body  and  form  insoluble  com- 
pounds. Often  this  combination  involves  the  breaking  down  of  the 
cell.  The  cell-albumin  becomes  incapable  of  exerting  its  function.  The 
effect  of  a  great  many  poisons  is  due  to  their  affinity  to  the  proteins  of  the 
cells  and  tissues.  Here  again  we  meet  with  certain  specific  differences 
according  to  the  nature  of  the  cell  and  the  proteins  which  have  taken  part 
in  their  construction.  In  this  connection  we  would  recall  the  different 
coloring  of  the  cells,  the  cause  of  which  is  likewise  attributed  to  a  different 
chemical  construction  of  the  cells.  It  is  this  which  lies  at  the  root  of 
the  various  functions  of  the  different  kinds  of  cells,  and  the  separate 
organs,  and  upon  it  depend  also  all  of  the  various  reactions  which  have 
been  mentioned,  whether  the  cell  plays  an  active  part,  or  whether  a 
mere  passive  one. 


1  Cf.  E.  Fromm:   Die  chemischen  Schutzmittel  des  Tierkorpers  bei  Vergiftungen. 
K.  J.  Triibner,  Strassburg,  1903. 


LECTURE   XXX. 

OUTLOOK. 

II. 

WE  have  seen  in  discussing  the  boundaries  of  physiological-chemical 
investigation,  that  such  exist  only  artificially,  and  that  the  domain  is 
immensurable.  The  tendency  is  becoming  more  and  more  marked  to  refer 
sciences  which  were  formerly  sharply  defined  to  a  common  basis.  This  is 
particularly  true  in  the  domain  of  pathology,  which  is  becoming  more  and 
more  closely  related  to  physiology.  In  fact,  pathological  processes  in  a 
certain  sense  are  nothing  else  than  physiological  processes  of  our  body- 
cells  under  specific  conditions.  This  applies  particularly  to  a  group  of 
processes,  interesting  alike  to  pathologists  and  physiologists,  namely,  the 
formation  of  certain  substances  in  response  to  the  action  of  other  products 
on  the  body -cells.  We  have  already  encountered  these  processes  at  various 
times.  We  have  seen  that  the  animal  organism  responds  to  the  intro- 
duction of  ferments  by  the  formation  of  anti-ferments;  that  is,  the  cells 
produce  substances  which  prevent  the  activity  of  the  ferments.  We  again 
met  this  problem  in  considering  the  so-called  "  biological  reaction. " 
Here  also,  it  was  a  case  of  the  formation  of  distinct  metabolic  products. 
The  most  significant  thing  about  these  processes  is  the  fact  that  the 
products  formed  act  in  a  very  specific  manner.  We  thus  involuntarily 
return  to  an  analogous  process  which  we  have  already  mentioned.  It  is 
known  that  the  human  and  animal  organism  is  capable,  not  only  of 
withstanding  the  infection  of  specific  pathogenic  bacteria,  but  also,  that 
it  possesses  peculiar  characteristics,  which  prevent  a  second  attack  of  the 
same  bacteria  for  a  long  time  after  their  first  repulse.  This,  of  course, 
only  applies  to  certain  infectious  diseases.  Other  diseases  do  not  leave 
such  a  condition  of  affairs  behind  them.  This  is  evident  from  the  fact 
that  one  may  be  afflicted  several  times  with  the  same  disease,  —  e.g., 
pneumonia,  —  whereas  other  sicknesses,  such  as  typhoid  or  scarlet  fever, 
usually  occur  but  once. 

The  far-reaching  specificity  is  also  noticeable  in  these  cases.  This  is 
best  demonstrated  by  the  following  example.  We  can  determine,  by 
experiment,  the  quantity  of  cholera  bacteria  necessary  to  cause  the  death 
of  a  guinea  pig  of  a  given  age  and  weight.  If  we  take  a  smaller  quantity, 
the  animal  will  only  become  sick,  and  will  gradually  recover.  This  guinea 

679 


680  LECTURE   XXX. 

pig  has  now  obtained  an  entirely  new  property,  which  sharply  differen- 
tiates it  from  the  other  animals  of  the  same  class,  which  have  not  been 
treated  in  the  same  manner.  We  usually  speak  of  this  as  an  acquired 
immunity.  This  is  evident  from  the  following.  The  immunized  animal  can 
then  be  infected  with  an  amount  of  cholera  bacteria  which  would  formerly 
have  produced  death,  and  it  now  does  not  even  cause  illness.  If  we 
inject  these  bacteria  into  the  abdominal  cavity,  and  after  a  time  withdraw 
some  of  the  fluid,  we  shall  observe  a  very  characteristic  picture  under  the 
microscope.  The  cholera  bacteria  have  lost  their  activity,  and  form  small 
balls,  which  are  sometimes  collected  into  "  clumps."  A  control  animal,  inoc- 
ulated for  the  first  time  with  these  cholera  bacteria,  will  show  an  entirely 
different  picture.  The  organisms  in  this  case  are  endowed  with  great 
activity.  We  find  it  necessary  to  assume  that  the  immunized  animal 
possesses  substances  in  its  organism  which  injure  the  cholera  bacteria, 
and  restrict  their  activity.  This  belief  is  strengthened  by  the  investigations 
of  R.  Pfeiffer.1  If,  together  with  the  cholera  bacteria,  serum  from  an 
immunized  animal  is  injected  into  the  abdominal  cavity  of  another  animal 
which  has  not  been  previously  treated,  we  shall  observe  the  same  phenom- 
ena which  were  characteristic  of  an  animal  which  had  already  been  infected 
with  cholera  bacteria.  The  latter  become  non-motile,  and  form  balls  or 
clumps.  M.  Gruber2  has  shown  that  this  phenomenon  may  be  verified 
in  a  test-tube,  by  bringing  cholera  bacteria  into  contact  with  serum  from 
an  animal  infected  with  cholera.  We  immediately  observe  under  the 
microscope,  that  the  cholera  bacteria  lose  their  mobility,  and  unite  in 
clumps.  This  is  spoken  of  as  an  "agglutination."  Its  appearance  is  indi- 
cated by  the  turbid  liquid  becoming  clear,  and  a  precipitate  forming  on 
the  bottom  of  the  vessel.  It  is  interesting  to  find  that  a  specific  reaction 
is  taking  place  here,  for  it  is  not  possible  to  detect  an  influence  upon  the 
cholera  bacteria  by  the  serum  of  an  animal  which  has  withstood  some  other 
infection.  Thus  an  animal  which  has  become  immune  against  typhoid 
bacteria  does  not  possess  a  serum  which  acts  upon  cholera  bacteria,  and 
conversely  the  serum  of  an  animal  which  has  been  immunized  against 
cholera  does  not  have  the  slightest  effect  upon  typhoid  bacteria. 

The  animal  organism  not  only  produces  a  specific  protecting  material 
against  bacteria,  but  also  against  their  poisons.  Thus,  the  medium  on 
which  diphtheria  bacteria  have  been  cultivated  shows  toxic  properties 
after  the  bacteria  have  been  filtered  off.  Diphtheria  toxine  acts  even  in 

1  R.  Pfeiffer:  Z.  Hygiene,  15,  268  (1894);  20,  217  (1895);  Deut.  med.  Wochsch.  Nos. 
7  and  8,  pp.  97,  119  (1896).     R.  Pfeiffer  and  Kolle:  Z.  Hygiene,  21,  203  (1896).     R. 
Pfeiffer  and  Wassermann:  Ibid.   14,  46   (1893).     R.  Pfeiffer  and  Marx:  Deut.  med. 
Wochschr.  1898,  47,  489;  Z.  Hygiene,  27,  272  (1898). 

2  M.  Gruber:  Miinchener  med.  Wochschr.  1896,  206.     M.  Gruber  and  H.  E.  Durham: 
Ibid.  1896,  285.     M.  Gruber:  Ibid.  1899,  1329.     Cf.  R.  Kraus:  Wiener  klin.  Wochsch. 
1897,  32. 


OUTLOOK.  681 

small  doses.  By  gradually  increasing  the  dose  of  this  poison  to  an  animal 
under  experiment,  we  can  immunize  it,  so  that  it  is  able  to  stand  relatively 
large  amounts  of  it.1  We  cannot  here  go  into  all  the  developments 
arising  from  these  observations,  which  are  so  interesting  from  a  biological 
standpoint.  We  can  state  merely  that  bacteria  yield  to  the  body  sub- 
stances which  we  call  toxines.  They  have  a  harmful  effect  upon  the  normal 
cell-metabolism.  They  are,  in  part,  constantly  given  up  by  the  bacteria, 
while  to  some  extent  the  toxines  are  retained  by  the  bacteria  in  their  cell 
structure.  In  the  latter  case  these  poisons  only  become  active  on  the 
death  of  the  micro-organism.  It  is  questionable  whether  we  are  justified 
in  looking  upon  these  two  groups  of  poisons  as  being  unlike.  It  is  possible 
that  the  eliminated  toxines  are  the  end-products  of  metabolism.  It  is  just 
as  plausible  to  believe  that  we  have  here  a  phenomenon  which  more  closely 
resembles  a  secretion  process.  From  this  point  of  view  it  is  easier  to  under- 
stand why  the  micro-organisms  eliminate  such  highly  complicated  sub- 
stances; while,  on  the  other  hand,  the  conception  that  the  toxines  are 
end-products  of  metabolism  seems  doubtful,  because  we  usually  find  that 
such  substances  require  but  little  expenditure  of  energy  for  their  formation; 
i.e.,  they  are  lower  decomposition  products.  The  strictly  specific  nature  of 
the  toxines  also  harmonizes  more  readily  with  the  idea  of  a  typical  secretion 
process.  In  such  a  case  we  have  to  deal  with  products  which  are  analogous 
to  the  ferments.  The  toxines  given  off  would  then  correspond  to  the 
"unorganized"  ferments;  those  remaining  in  the  cells,  to  the  "organized"' 
ferments. 

Just  as  this  classification  of  the  ferments  is  a  purely  superficial  one,  and 
has  nothing  to  do  with  their  nature  and  their  manner  of  action,  so  it  is 
perfectly  possible  that  the  toxines  which  are  given  up  freely  by  the  cells 
and  those  which  are  firmly  attached  to  the  cells  are  essentially  identical. 
Again,  the  comparison  of  the  toxines  and  ferments  is  also  superficial,  and 
should  not  prejudice  us  with  regard  to  the  toxines.  We  do  not  know 
anything  definite  about  their  nature.  They  are  classed  with  the  proteins, 
and  justly  so,  for  only  to  this  class  of  chemical  compounds  can  we 
imagine  that  such  complicated  bodies  belong.  For  the  same  reason  we 
have  concluded  that  the  ferments  belong  to  the  protein  group,  being 
probably  transformation  products  of  the  cell-proteins.  Just  as  the  fer- 
ments exert  a  specific  action,  so  the  bacterial  poisons  have  well-defined 
characteristics.  We  know  of  poisonous  substances  which  are  produced 
by  highly  organized  plants  and  by  animals  the  action  of  which  is  quite 
similar  to  that  of  the  toxines.  Thus  we  have  ricin  from  the  castor-oil 
plant  (Ricinus  communis),  and  abrin  from  the  seeds  of  Jequirity  (Abrus 
precatorius) .  Both  are  extremely  poisonous,  and  an  immunity  may  be 


1  E.  Behring:  Deut.  med.  Wochsch.  1890.     E.  Behring  and  Kitasato:  Ibid.  1890. 


682  LECTURE   XXX. 

established  to  offset  their  action.1  Snake  venom  also  belong  to  this  class. 
The  skin  and  blood  of  toads  likewise  contain  such  poisons,  and  they  are 
also  found  in  the  garden-spider.  The  blood  of  the  eel  contains  a  toxine 
belonging  to  this  group.  Indeed  the  number  of  plant  and  animal  poisons 
which  have  been  studied  is  far  greater  and  the  poisons  are  of  a  more  varied 
nature  than  we  can  attempt  to  describe.  We  are  not  yet  ready  to  discuss 
their  constitution,  and  in  fact  none  of  these  poisons  has  been  obtained  in 
a  .perfectly  pure  state.  It  is  perfectly  clear  that  this  fact  affects  investi- 
gation in  the  whole  field  of  toxines  and  antitoxines.  To-day  we  cannot 
depict,  as  sharply  as  we  should  like,  the  effect  of  the  toxines  and  the  cause 
of  the  formation  of  antitoxines.  At  present  we  must  resort  to  hypotheses, 
and  a  state  of  certainty  will  prevail  only  when  it  is  found  possible  to 
establish  the  constitution  of  at  least  one  of  the  toxines.  From  our  study 
of  the  ferments,  we  can  readily  believe  that  the  antitoxines  are  similarly 
constituted  to  the  toxines.  This  seems  probable  from  the  specific  relations 
between  these  two  products.  It  is  important  as  regards  the  development 
of  the  modern  conception  of  toxines  and  antitoxines  that  we  should 
recognize  clearly  where  the  facts  end  and  speculation  begins,  for  nowhere 
has  this  been  forgotten  more  than  in  this  particular  field.  Perfect  clear- 
ness in  this  respect  is  essential  for  the  sound  development  of  this  branch  of 
knowledge,  because  one  of  the  most  fruitful  and  most  beneficial  hypotheses 
of  the  age  governs  our  conception  of  the  nature  of  toxine  action  and  the 
formation  of  antitoxines.  We  have  in  mind  the  theory  to  which  Paul 
Ehrlich  refers  all  the  investigations  in  this  field,  and  which  with  unexpected 
rapidity  has  been  confirmed  by  observation  after  observation,  and  discovery 
after  discovery. 

This  hypothesis  is  quite  generally  known  under  the  name  of  Ehrlich's 
side-chain  theory.2  Ehrlich  attempted  with  his  theory,  which  is  closely 
related  to  chemical  representations,  to  bridge  over  the  gaps  in  our  inadequate 
knowledge  concerning  the  chemical  structure  of  the  toxines.  He  makes 
certain  assumptions  concerning  the  nature  of  the  active  groups.  In  place 
of  the  chemical  composition,  he  uses  certain  names  which  may  be  replaced 
by  definite  chemical  radicals  with  the  advance  of  our  knowledge.  Paul 
Ehrlich  has  not  only  succeeded  in  correlating  by  means  of  his  ingenious 
theory  many  processes  in  this  large  field  which  apparently  took  place  side 
by  side  quite  independently  of  one  another,  but  his  theory  has,  moreover, 

1  Paul  Ehrlich:   Deut.  med.  Wochschr.  1891,  976,  1218.     Fortschritte  d.  Medizin, 
1897,  41. 

2  Cf.    Rostoski:  Zur  Kenntnis  der   Prazipitine.  A.  Stuber,  Wiirzburg,   1902.     Carl 
Oppenheimer:    Toxine  und  Antitoxine.     G.  Fischer,  Jena,  1904.     P.  T.  Muller:  Vor- 
lesungen  iiber  Infektion  und   Immunitat.     G.  Fischer,  Jena,  1897.     Ludwig  Aschoff: 
Ehrlich's  Seitenkettentheorie  und  ihre  Anwendung  auf  die  kiinstlichen  Immunisierungs- 
prozesse.     G.  Fischer,  Jena,  1902.     Paul  Romer:  Die  Ehrlichsche  Seitenkettentheorie 
und  ihre  Bedeutung  fiir  die  medizinischen  Wissenschaften.     A.  Holder,  Wien,  1904. 


OUTLOOK.  683 

the  great  advantage  that  upon  it  as  a  foundation  link  after  link  of  a  tangled 
chain  of  processes  has  been  disentangled,  so  that  as  a  result  we  have  before 
our  eyes  a  continuous  picture  of  separate  processes.  Problem  after  problem 
has  accumulated,  and  gradually  a  new  structure  has  been  built  which 
serves  to  bring  under  one  roof  all  the  various  processes  which  stand  in  any 
relation  to  the  formation  of  the  anti-bodies.  The  investigations  of  Ehrlich 
appear  especially  important  to  us,  because  they  are  the  first  to  bridge  over 
the  chasm  which  has  previously  been  assumed  to  exist  between  physio- 
logical and  pathological  processes  in  the  animal  kingdom,  so  that  to-day  a 
sharp  line  can  no  longer  be  drawn  between  these  two  fields.  Ehrlich  has 
pointed  out  that  the  formation  of  the  anti-bodies  stands  in  direct  relation 
to  the  cell-metabolism.  In  order  to  make  this  relation  clear,  we  shall  explain 
briefly  how  Ehrlich  represents  the  assimilation  of  the  nutriment  by  the  cell 
as  taking  place.  The  individual  cells  are  only  capable  of  taking  up  and 
uniting  with  their  structure  those  substances  which  correspond  to  their 
entire  composition.  The  substances  taken  up  must  fit  into  the  cells. 
The  protoplasm  possesses  groups  which  are  chemically  active,  and  these 
have  a  maximum  affinity  to  a  certain  arrangement  of  the  atoms  in  the 
nutriment,  which  it  unites  to  the  cell-body.  Paul  Ehrlich  calls  these  groups 
side-chains,  or  receptors.  On  the  basis  of  this  theory  we  can  easily  picture 
to  ourselves  why  certain  cells  reject  this  and  that  substance,  and  on 
the  other  hand  assimilate  other  products.  One  is  tempted  to  deduce  a 
purely  chemical  theory  for  the  process  of  assimilation,  though  by  doing  so 
we  may  be  making  a  grave  error.  We  can  easily  imagine  that  a  chemical 
compound,  for  instance  the  benzene  ring,  may  carry  side-chains,  and  that 
these  may  enter  into  reaction  with  other  complexes.  A  new  compound 
would  result,  but  such  a  reaction  is,  as  a  rule,  complete  when  this  has  been 
accomplished.  The  cell,  however,  behaves  in  an  entirely  different  manner. 
It  constantly  utilizes  material,  and  must  be  continually  forming  new  side- 
chains,  for  it  is  always  confronted  with  the  necessity  of  taking  up  nutrient 
substances ;  that  is,  the  new  groups  must  always  be  present  to  combine  with 
the  nutriment.  It  follows  from  this  assumption,  that  the  "side-chains," 
as  conceived  by  Ehrlich,  do  not  correspond  to  our  present  idea  of  a  purely 
chemical  phenomenon.  These  side-chains  are  only  hypothetical  as  yet, 
and  have  nothing  definite  to  substantiate  their  existence.  If  we  assume 
that  the  various  cells  have  differently  constituted  side-chains,  we  will  then 
have  reached  the  idea  of  the  specific  nature  of  the  cells.  This  also  permits 
us  to  venture  the  assumption  that  the  different  nutrients  are  completely 
disintegrated  during  digestion,  and  are  transformed  into  homogeneous 
products  in  the  intestines.  Ehrlich's  theory  is  only  completely  compre- 
hensible from  this  point  of  view.  The  specific  groups  of  the  cells  must 
exactly  correspond  to  those  of  the  nutrient  materials,  the  latter  being 
established  only  at  the  time  of  assimilation. 


684  LECTURE   XXX. 

With  the  above  in  mind,  let  us  apply  the  side-chain  theory  to  the  forma- 
tion of  antitoxines.  We  have  already  stated  that  the  bacterial  poisons 
are  probably  very  closely  related  to  the  proteins.  We  can  easily  imagine 
that  they  may  have  atomic  groupings  very  analogous  to  those  of  the  nutri- 
ents, and  that,  for  this  reason,  they  are  attached  to  distinct  cells.  The 
cell  immediately  loses  its  ability  to  assimilate  any  nutrient  material  at 
those  points  where  any  toxines  have  attached  themselves.  If  the  cell  has 
not  been  permanently  injured  by  the  poison,  it  will  try  to  repair  the  damage 
by  a  fresh  supply  of  side-chains.  Under  these  conditions  there  may  be  an 
over-production  of  side-chains,  to  such  an  extent  that  they  will  not  all  have 
room  to  attach  themselves  to  the  protoplasm;  they  will  consequently  be 
pushed  off,  and  circulate  in  the  blood.  We  must  not  forget  that  these  new 
side-chains  must  correspond  exactly  in  their  composition  to  those  to  which 
the  toxines  have  attached  themselves.  This  " first"  side-chain  must  cer- 
tainly have  had  a  definite  affinity  for  the  toxine  before  it  combined  with  it, 
in  its  transport  in  the  organism. 

Those  analogously  constituted  side-chains  which  circulate  in  the  blood 
must  also  have  the  ability  of  uniting  with  toxines,  thus  making  them 
harmless,  before  they  reach  the  cells.  According  to  this  view,  the  forma- 
tion of  antitoxines  is  not  a  new  process  —  the  free  side-chains  are  nothing 
more  than  antitoxines  —  but  merely  a  repetition  of  a  normal  function  of 
the  cell.  It  corresponds  to  the  secretion  of  the  individual  cells  to  which 
we  have  repeatedly  called  attention.  It  is  impossible  for  us  to  go  into  the 
details  of  the  facts  which  go  to  substantiate  Ehrlich's  assumption.  We 
only  wish  to  add  that  it  has  been  shown  that  definite  bacterial  poisons,  for 
instance  tetanus  poison,  enters  into  combination  with  tissue-cells,  and 
that,  on  the  other  hand,  we  are  acquainted  with  poisons  which  can  be  recog- 
nized as  having  very  distinct  affinity  for  specific  tissues.  Thus,  it  is 
known  that  abrin  possesses  very  close  relationship  to  the  components  of 
the  tissues  of  the  conjunctiva.  Ehrlich  designates  the  group  of  the  toxine 
molecule,  which  unites  with  the  side-chains  of  the  cells,  or  the  free  side- 
chains,  as  the  haptophor  group.  It  is  clear,  if  this  conception  of  the  com- 
bination of  toxines  and  antitoxines  is  correct,  that  only  a  definite  amount 
of  the  latter  can  combine  with  a  given  quantity  of  the  former.  The  whole 
process  must  evidently  correspond  to  a  neutralization. 

The  toxine  also  contains  a  toxophor  as  well  as  a  haptophor  group.  This 
is  the  carrier  of  the  specific  poisonous  effect  of  the  toxine.  That  this 
assumption  of  different  groups  in  the  toxine  molecule  is  well  founded  fol- 
lows from  the  fact  that  antitoxines  may  be  produced  even  after  the  toxophor 
group  itself  has  been  destroyed.  It  has,  itself,  nothing  to  do  with  the  im- 
munity reaction  of  the  organism.  In  the  latter  case  the  haptophor  group 
only  must  be  taken  into  consideration.  If  this  be  removed,  for  instance 
by  antitoxine,  then  the  toxine  will  be  rendered  valueless  for  immunization. 


OUTLOOK.  685 

According  to  this  conception,  every  body-cell  must  be  able  to  form  anti- 
toxines,  although  such  an  assumption  is  not  absolutely  necessary.  We 
can  also  imagine  that  individual  cell-complexes  possess  the  ability  of  pro- 
ducing toxines;  in  fact,  there  seems  to  be  evidence  of  a  selective  action 
within  certain  limits.  The  whole  subject  of  the  formation  of  antitoxines 
is  analogous  to  that  of  the  general  process  of  metabolism.  We  can 
easily  imagine  that  the  cell-metabolism  is  so  altered  by  the  introduction 
of  toxines  that  an  over-production  of  side-chains  results.  This  assumption 
only  serves  as  an  assistant  hypothesis,  which  is  to  act  as  a  prop  to  the  main 
idea  which  is  likewise  hypothetical  in  its  nature.  It  is  entirely  possible 
that  the  idea  of  such  an  enlarged  production  of  atomic  groups,  and  their 
expulsion  beyond  the  influence  of  the  cell,  is  not  at  all  necessary.  We 
must  call  attention  to  a  process  which  we  have  already  discussed  in 
detail.  We  have  repeatedly  remarked  how  from  the  carbon  dioxide  of 
the  air  products  of  entirely  different  properties  are  formed  as  soon  as  it 
comes  in  contact  with  the  plant  cells  containing  chlorophyll.  They  are  in 
the  first  place  optically  active,  and  contain  in  their  composition  hydrogen 
as  well  as  carbon  and  oxygen.  We  are  accustomed  to  assume  that  the 
first  product  formed  is  a  carbohydrate,  although  this  belief  has  no  sub- 
stantial foundation.  Other  compounds,  as  well  as  carbohydrates,  might 
be  formed  just  as  easily.  Why  is  an  optically  active,  very  specifically 
constituted  substance,  formed  from  carbon  dioxide  and  water?  We  are 
unable  to  answer  this  question.  We  must  assume  that  this  phenomenon 
is  mainly  dependent  on  the  composition  of  the  protoplasm  of  the  chromo- 
phyll-containing  cells.  This  is,  itself,  asymmetrically  constituted,  and  can 
consequently  only  produce  asymmetric  compounds.  When  we  consider 
the  question  why  the  cells  of  the  stomach  only  deliver  pepsin  or  hydro- 
chloric acid,  and  those  of  the  pancreas  likewise  give  a  very  specific 
secretion,  we  must  answer  that  in  this  case  also  the  constitution  of  the 
cells  is  the  fundamental  cause  of  the  individual  functions.  Every  body- 
cell  evidently  endeavors  to  maintain  its  composition,  for  its  permanency 
guarantees  that  its  function  remains  the  same  and  that  there  is  a  normal 
progress  of  its  metabolism.  The  whole  organization  of  the  animal  body 
is  so  adjusted  that  the  cells  shall  maintain  their  specific  composition.  This 
is  already  evident  from  our  consideration  of  the  subject  of  digestion.  We 
do  not  in  the  least  doubt  that  every  individual  body-cell  continually  forms 
a  definite  secretion,  thus  participating  in  the  general  metabolism.  But 
the  same  food  is  being  normally  presented  to  the  cells  by  the  blood. 
If  a  foreign  substance  passes  beyond  the  intestine,  manifold  assistance  is 
offered  as  quickly  as  possible  all  over  the  organism  to  forestall  any  damage. 
The  liver,  especially,  guarantees  the  constant  composition  of  the  blood. 
It  captures  material,  unites  it  with  other  products,  etc.  If  its  functions 
are  not  sufficient,  other  organs  come  to  assist,  while  the  different  glands 


686  LECTURE   XXX. 

finally  begin  to  participate  in  removing  the  foreign  substance  by  an  in- 
creased elimination  of  secretions.  The  animal  organism  under  normal 
circumstances  constitutes  a  well-protected  entity.  Nothing  foreign  can 
penetrate  into  the  cell-metabolism,  consequently  the  general  metabolism 
proceeds  along  its  usual  course.  It  becomes  an  entirely  different  matter 
when  material  is  presented  to  the  cells  which  can  turn  the  whole  organiza- 
tion toward  an  entirely  different  direction.  There  are  constantly  cells  in 
our  body  which  are  engaged  in  process  of  destruction,  and  others,  which 
here  and  there  renew  an  important  foundation  stone,  or  even  entirely 
reconstruct  it.  The  body-cells  have  become  adapted  to  a  definite  nutri- 
tion through  many  generations,  and  confine  themselves  to  material  which 
is  useful  to  the  whole  organism.  During  infection,  the  blood  will  trans- 
port substances  which  are  evidently  closely  related  to  normal  nutrient 
materials. 

This  assumption  seems  all  the  more  probable  when  we  suggest  that  we 
can  easily  imagine  how  in  the  preparation  of  the  building-stones  of  a  cell, 
not  only  the -cell  in  question  is  active,  together  with  its  neighboring  cells, 
but  there  must  be  an  intimate  exchange  of  the  products  of  metabolism  on 
the  part  of  the  separate  cells.  Now  the  toxines  are  merely  products  result- 
ing from  the  metabolism  of  cells.  If  these  products  become  a  part  of  a 
body-cell,  then  immediately  the  entire  function  of  such  a  cell  is  changed. 
It  will,  as  before,  receive  and  give  up  substances  to  the  fluids  of  the  body, 
but  the  substances  now  given  up  will  be  of  an  entirely  different  character, 
for  the  function  of  a  cell  is  a  result  of  its  own  composition.  We  can  easily 
understand  how,  if  a  single  constituent  of  a  cell  is  altered,  all  the  chemical 
processes  may  take  place  in  a  different  direction.  If  the  cell  is  not  badly 
injured  it  will  continue  to  function.  Naturally  the  subsequent  absorp- 
tion of  material  will  take  place  in  accordance  with  the  altered  conditions, 
and  thus  the  peculiar  nature  of  such  cells  will  gradually  make  itself  felt. 
Among  the  thousands  of  body-cells,  it  is  not  necessary  that  many  of  them 
should  be  attacked,  perhaps  only  those  which  were  in  the  process  of  under- 
going a  transformation.  We  know  that  in  chemical  processes  the  slightest 
deviation  in  the  conditions  may  cause  the  reaction  to  take  place  differently. 
How  much  more  must  a  continuous  change  in  the  nature  of  the  metabolic 
products  affect  the  normal  course  of  processes  which  take  part  in  the  cell 
construction!  We  wish  to  affiliate  this  conception  of  Ehrlich  concerning 
the  formation  of  antitoxines  more  closely  with  processes  of  metabolism, 
and  especially  in  order  to  avoid  leaving  the  impression  that  the  formation 
of  these  side-chains  is  an  abnormal  function  of  the  cells.  The  different 
toxines  are  naturally  differently  constituted,  and  it  does  not  seem  at  all 
strange  that  the  cells  of  the  various  tissues  should  take  up  these  toxines 
in  different  degree,  and  that,  for  instance,  the  cells  of  the  nerve  tissues 
should  be  peculiarly  adapted  to  unite  with  tetanus  poison.  This  toxine 


OUTLOOK.  687 

shows  very  clearly  that  Ehrlich  is  right  in  his  conception  of  the  production 
of  toxines  by  the  cells.  Wassermann  and  Takaki 1  carried  out  the  fol- 
lowing experiment.  They  triturated  the  spinal  cords  and  brains  of 
normal  guinea  pigs  with  a  physiological  salt  solution.  Into  this  emulsion 
they  introduced  a  single,  double,  treble,  and  ten  times  deadly  dose  of 
tetanus  poison  and  injected  these  mixtures  subcutaneously  into  mice. 
The  animals  did  not  die.  It  is  noteworthy  that  this  antitoxic  action  of 
tetanus  poison  is  confined  solely  to  the  nerve  tissues.  It  was  also  shown 
that  the  brain  and  spinal  cord  emulsions  likewise  act  antitoxically  if  they 
are  injected  subcutaneously  into  mice  and  then  the  various  lethal  doses 
afterward  administered.  Similarly  the  poisonous  effect  is  much  lessened  if 
the  emulsions  in  question  are  introduced  after  the  toxine  into  the  body. 
It  is  possible  that  we  shall  be  able  to  isolate  the  poisonous  group  in  tetanus 
poison  and  find  out  its  composition.  Centrifugalized  emulsions  of  nerve 
tissue  are  perfectly  inactive,  which  proves  that  we  are  not  concerned  with 
the  substances  in  the  surrounding  fluids  but  with  the  cells  themselves. 
The  discovery  that  the  antitoxine  from  the  brain  is  destroyed  by  boiling, 
and  that  the  protective  effect  of  the  emulsion  obtained  from  the  spinal 
medulla  or  brain  is  lost  in  the  same  way,  is  of  great  significance.  Blumen- 
thal2  has  at  last  succeeded  in  proving  that  the  tetanus  poison  combines 
with  the  brain  substance,  by  adding  the  tetanus  poison,  which  itself  can 
readily  pass  through  a  filter,  to  brain  substance  and  then  filtering.  The 
filtrate  contains  no  toxine.  It  might  be  thought  that  perhaps  the  solids 
of  the  nervous  tissue  had  held  it  back  merely  mechanically.  That  this  is 
not  the  case  is  shown  by  the  fact  that  the  mixture  of  tetanotoxine  and 
nerve  substance  no  longer  has  a  toxic  effect.  Finally  Blumenthal  suc- 
ceeded in  proving  that  the  protective  action  of  the  brain  and  cord  grew 
less  in  proportion  to  the  amount  of  toxine  which  had  been  administered 
to  the  animal  in  life.  It  is  easy  to  explain  why  this  is  true.  The  brain 
substance  cannot,  of  course,  combine  with  an  infinite  amount  of  toxine. 
The  amount  taken  up  naturally  depends  upon  the  number  of  the  reacting 
groups  that  are  present  which  have  an  affinity  to  tetanotoxine.  If  some 
of  these  groups  have  already  been  satisfied,  then  naturally  this  tissue 
will  be  capable  of  removing  only  a  fraction  of  the  amount  which  it  is 
otherwise  capable  of  uniting  with.  In  fact,  we  can  determine  quantita- 
tively how  much  antitoxine  is  present  in  a  certain  amount  of  nerve  sub- 
stance by  estimating  the  point  at  which  it  ceases  to  combine  with  more 
toxine. 

We  cannot  here  go  into  further  details  concerning  the  toxines  and  anti- 
toxines,  nor  discuss  the  development  of  Ehrlich 's  side-chain  theory  in 
this  direction  any  further.  It  is  sufficient  for  us  to  have  sketched  the 


1  Wassermann  and  T.  Takaki:  Berliner  klin.  Wochenschrift,  1,  5,  1898. 
3  F.  Blumenthal:  Dent.  med.  Wochschr.  No.  12,  p.  185  (1898). 


688  LECTURE   XXX. 

extent  of  the  investigation  in  this  field  and  to  have  shown  how  closely 
related  it  is  to  physiological  conceptions.  We  shall  now  turn  our  attention 
to  the  results  of  Ehrlich's  hypothesis  in  the  study  of  hemolysis,  which  is 
more  closely  related  to  our  subject. 

It  is  a  well-known  fact  that  the  sera  of  many  varieties  of  blood  are  able 
to  dissolve  the  red  corpuscles  of  other  species  of  animals.  This  fact  is  the 
cause  of  the  bad  results  which  have  resulted  from  the  attempts  at  the  trans- 
fusion of  blood  into  human  beings.  For  a  long  time  little  was  known 
concerning  the  nature  of  hemolysis.  Recently  Belfanti  and  Carbone1 
have  established  the  fact  that  the  serum  of  a  horse  into  which  the  red  cor- 
puscles from  rabbits  have  been  injected,  has  a  much  more  poisonous  effect 
upon  rabbits  than  does  normal  horse  serum.  Bordet,2  whom  we  have  to 
thank  for  developing  our  conception  of  hemolysis,  showed  that  the  serum 
of  guinea  pigs  into  which  there  had  been  repeated  intraperitoneal  injections 
of  from  three  to  five  cubic  centimeters  of  defibrinated  rabbit's  blood,  would, 
when  placed  in  a  test-tube,  rapidly  dissolve  the  red  corpuscles  of  the  rabbit, 
whereas  the  normal  serum  of  the  guinea  pig  either  did  not  have  this  property 
at  all,  or  showed  but  slight  evidence  of  it.  Here  again  we  are  dealing  with 
quite  specific  effects,  and  there  is  really  a  formation  of  anti-bodies  here. 
This  discovery  is  of  especial  interest  because  Bordet  has  shown  that  even 
cells  to  which  we  are  not  accustomed  to  ascribe  toxic  effects  have  a  quite 
similar  effect  to  that  of  the  bacteria.  The  phenomenon  is  not  remarkable. 
It  merely  shows  us  that  every  species  of  animal  has  its  own  peculiarly 
constituted  cells  and  thereby  its  own  specific  metabolism. 

We  must,  first  of  all,  consider  the  explanation  of  how  the  hemoglobin 
is  removed  from  the  red  corpuscles  under  the  action  of  the  serum  which 
is  employed.  It  cannot  be  a  question  of  variations  in  the  osmotic  pres- 
sure, for  even  a  fraction  of  a  milligram  of  the  serum  exerts  this  effect,  and 
again  the  specific  action  also  contradicts  any  such  assumption.  All  of  our 
knowledge  points  to  a  poisonous  effect  upon  the  red  corpuscles  them- 
selves. We  shall  now  try  to  apply  Ehrlich's  side-chain  theory,  as  far  as 
possible,  to  the  phenomenon  of  hemolysis.  Bordet  succeeded  in  proving 
that  a  hemolytic  serum  loses  its  effect  if  it  is  heated  to  55°  C.  The 
serum  is  then  designated  as  inactive  serum.  In  order  to  avoid  any  mis- 
conceptions, we  had  best  take  up  a  specific  example.  Let  us  assume  that 
we  have  a  guinea  pig  which  has  previously  been  treated  with  rabbit's 
blood.  If  the  serum  of  this  animal  is  allowed  to  fall  drop  by  drop  upon 
an  opaque  solution  of  red  corpuscles  from  a  rabbit,  contained  in  isotonic 


1  S.  Belfanti  and  P.  Carbone:  Giorn.  della  R.  Accad.  di  med.  di  Torino,  1898. 

2  J.  Bordet:  Ann.  inst.  Pasteur,  12,  688  (1898) ;  13,  273  (1899) ;  14,  257  (1900) ;  15,  303 
(1901).     Cf.  Von  Dungern:  Miinchener  med.  Wochschr.  Nos.  13  and  14,  pp.  405,  449 
(1899).     K.  Landsteiner:   Zentr.  Bacteriol.  25  (1899).     P.  Ehrlich  and  J.  Morgenroth: 
Berliner  klin.  Wochschr.  1899,  1900,  1901.     P.  Ehrlich  and  H.  Sachs:  1902. 


OUTLOOK.  689 

salt  solution,  we  shall  find  that  within  a  short  time  a  solution  of  the  red 
blood-corpuscles  takes  place.  The  solution  becomes  transparent  and  a 
clear  red.  If  exactly  the  same  experiment  is  carried  out  with  inactive 
serum,  the  red  corpuscles  will  remain  unaffected.  Now  if  in  a  third  test- 
tube  the  serum  of  a  normal  guinea  pig  is  added  to  the  suspension  of 
blood-corpuscles,  there  is  again  no  hemolysis.  On  the  other  hand,  the 
solvent  effect  is  obtained  if  the  normal  serum  from  normal  guinea  pigs  is 
added  to  the  inactivated  serum.  This  proves  that  at  least  two  substances 
are  necessary  for  bringing  about  hemolysis.  One  of  these  is  found 
already  formed  in  the  immune  serum  and  also  in  normal  serum,  and  the 
other  is  only  yielded  by  immunized  serum,  i.e.,  in  this  case  in  the  blood 
of  guinea  pigs  which  have  been  previously  treated  with  the  blood 
of  rabbits.  The  two  substances  are  different  as  regards  their  behavior 
toward  heat.  That  which  is  present  in  normal  serum  is  stable  towards 
heat,  while  that  present  in  the  other  is  unstable.  Quite  a  number  of  different 
names  have  been  given  to  these  substances.  We  shall  choose  for  the 
thermo-stable  substance  the  designation  amboceptor,  and  for  the  thermo- 
unstable  one  the  name  complement. 

Ehrlich's  theory  fits  in  at  this  point.  He  was  especially  interested  in 
explaining  why  the  different  sera  should  act  so  specifically,  and  what  the 
relations  of  amboceptor  and  complement  are  to  the  red  blood-corpuscles 
and  to  themselves.  For  simplicity's  sake  we  will  designate  the  two  com- 
ponents, amboceptor  and  complement,  which  produce  hemolysis,  by  the 
name  hemolysin.  This  must  have,  judging  from  its  analogy  to  the  toxines, 
a  very  distinct  affinity  to  some  constituent  of  the  red  corpuscles.  Ehrlich 
and  Morgenroth's  experiments  have  proved  this.  They  injected  sheep's 
blood  into  a  goat.  The  serum  from  this  animal  completely  dissolved  the 
sheep-blood  corpuscles,  although  it  lost  this  property  on  heating  to  55 
degrees.  The  complements  were  destroyed.  The  amboceptors  must 
have  remained  unchanged,  as  they  are  thermo-stable  at  this  temperature. 
The  above  investigators  then  added  sheep-blood  corpuscles,  and  centri- 
fugalized  the  mixture  after  standing  half  an  hour.  To  the  resulting  serum 
they  added  more  sheep-blood  corpuscles,  and  also  some  fresh  normal 
serum.  No  hemolysis  resulted.  When  the  previous  addition  of  sheep- 
blood  corpuscles  was  omitted,  and  normal  serum  added  to  the  inactivated 
serum,  the  solution  of  the  red  corpuscles  immediately  set  in.  It  follows 
from  these  experiments  that  the  sheep-blood  corpuscles  had  removed  one 
of  the  components  of  the  hemolysin  which  was,  in  fact,  the  amboceptor. 
That  this  assumption  is  correct,  is  evident  from  the  fact  that  the  blood- 
corpuscles,  centrifugalized  as  above,  immediately  went  into  solution  on 
the  addition  of  normal  serum  in  an  0.85  per  cent  salt  solution.  We  must 
also  mention  that  normal  goafs-blood  serum  does  not  attack  the  normal 
sheep-blood  corpuscles. 


690  LECTURE   XXX. 

One  phase  of  hemolysis  was,  therefore,  explained.  The  amboceptors 
present  in  immune  serum  unite  with  the  red  blood-corpuscles  of  that  species 
of  animals  to  which  they  are  suited.  No  other  kind  of  blood  is  able 
to  combine  with  the  amboceptors  which  react  so  readily  with  sheep's 
blood.  For  this  reason  alone  we  cannot  assume  that  it  is  a  case  of  mere 
absorption  of  the  blood  amboceptors  by  the  red  blood-corpuscles.  The 
combined  amboceptors  cannot  be  removed  by  washing,  and  in  fact  the 
affinity  of  these  for  the  red  corpuscles  may  be  determined.  It  has  been 
found  that  different  red  corpuscles  are  capable  of  combining  with  very 
different  amounts  of  amboceptors. 

We  must  now  attempt  to  explain  how  the  complement  stands  in  relation 
to  the  process  of  hemolysis.  In  the  first  place,  Ehrlich  and  Morgenroth 
have  proved  that  normal  red  corpuscles  do  not  unite  with  the  complements. 
The  simplest  explanation  is  that  the  amboceptors  possess  at  least  two 
differently  constituted  groups.  One  unites  with  the  blood-cell,  and  the 
other  with  the  complement.  This  effects  the  solution  of  the  blood-cor- 
puscles. The  complement  alone  cannot  act  upon  them.  The  groups 
which  are  adapted  to  act  upon  the  red  corpuscles  are  wanting.  Only  by 
the  aid  of  the  amboceptor  is  the  complement  able  to  react  with  the  erythro- 
cytes.  Just  what  this  influence  is  we  cannot  tell,  but  it  is  possible  that  a 
fermentation  takes  place.  We  may  state  that  hemolysin  has  been  con- 
sidered to  be  analogous  to  the  toxines.  It  is  in  a  sense  a  compound 
toxine.  The  haptophor  group  of  the  toxine  corresponds  to  the  ambo- 
ceptor, and  the  toxophor  group  to  the  complement.  The  comparison 
seems  even  more  justifiable  when  we  add  that  it  has  been  found  possible 
to  form  anti-bodies  to  the  hemolysins.  Certain  poisons  of  the  animal 
and  vegetable  kingdom  are  analogous  to  the  hemolysins.1  We  may 
mention  snake  venom,  garden-spider  poison  (Arachnolysiri) ,  and  toad 
poison  (Phrynolysin) .  It  is  also  possible  to  obtain  poisons  with  a  hemo- 
lytic  action  from  bacterial  cultures.  We  may  refer  to  stapholysin  which 
is  obtained  from  staphylococcus  cultures,  and  tetanolysin  from  tetanus 
bacteria. 

Here  at  this  point  we  may  also  refer  to  an  observation  which  we  have 
already  discussed  in  detail.2  One  of  the  many  poisonous  effects  of  snake 
venom  is  its  hemolytic  action.  If,  for  example,  we  add  the  poison  of  the 
cobra  to  blood,  hemolysis  soon  sets  in.  If  the  blood-corpuscles,  how- 
ever, are  well  washed,  i.e.  freed  as  completely  as  possible  from  every  trace 
of  serum,  and  then  placed  in  0.85  per  cent  sodium  chloride  solution,  no 

1  Cf.  Flexner  and  Noguchi:  J.  exper.  Med.  6,  No.  3  (1902).     H.  Sachs:  Hofmeister's 
Beitr.  2,  125  (1902).     F.  Proscher:  Ibid.  1,  575  (1901).     R.  Kraus  and  P.  Clairmont: 
Wiener  klin.  Wochschr.  1900,  No.  3,  and  1901,  1016.     M.  Neisser  and  F.  Wechsburg: 
Miinchener  med.  Wochschr.  48,  No.  18,  p.  697  (1901)  and  Z.  Hygiene,  36,  299  (1901). 

2  Cf.  Lecture  VI,  p.  115,  et  seq. 


OUTLOOK.  691 

hemolysis  takes  place  on  the  addition  of  cobra  poison.  The  addition  of 
a  little  serum,  or  of  lecithin,  now  suffices  to  cause  hemolysis.  It  is  natural 
to  designate  lecithin  as  the  amboceptor  which  enables  the  poison  of  the 
cobra  to  attack  the  erythrocytes.  It  is,  furthermore,  interesting  to  find 
that  cholesterol  can  prevent  this  action  of  the  lecithin.  We  mention 
these  interesting  discoveries  here  because  they  perhaps  explain  why  the 
two  compounds,  cholesterol  and  lecithin,  are  found  in  every  cell. 

There  is  no  doubt  that  red  blood-corpuscles  are  constantly  being  de- 
stroyed in  our  organisms.  Hemolysis  undoubtedly  takes  place.  It  may 
be  brought  about  by  changes  in  the  osmotic  pressure,  but  it  is  also  possible 
that  the  normal  destruction  of  the  red  corpuscles  results  from  a  process 
similar  to  that  just  described. 

We  may  add  that  the  formation  of  precipitins  may  also  be  explained  on 
the  basis  of  Ehrlich's  side-chain  theory,  and  many  other  discoveries  find 
their  proper  place  in  complicated  processes  by  means  of  the  same  theory. 

We  have  now  reached  the  end.  We  are  aware  that  we  have  just  placed 
considerable  stress  upon  a  mere  hypothesis,  and  realize  the  danger  that  may 
result  from  such  a  generalization.  On  the  other  hand,  we  are  able,  in  each 
particular  case,  to  decide  whether  we  are  justified  in  comparing  a  given 
process  with  those  which  have  been  just  described.  It  is  clear  that  the 
final  goal  of  our  investigation  in  the  field  of  immunization  is  never  to  be 
attained  by  the  mere  advancement  of  any  special  theory.  We  find  our- 
selves temporarily  in  a  region  which  is  not  accessible  to  chemical  or 
physical  investigation,  for  both  require  as  a  starting-point  the  employment 
of  chemically  pure  substances.  As  long  as  we  are  unable  to  prepare  any 
one  of  these  complicated  products  in  a  pure  state,  and  establish  its 
chemical  constitution,  we  must  not  expect  to  obtain  an  exact  insight  into 
all  the  complicated  processes  upon  which  the  actions  of  the  toxines  and 
related  substances  are  based. 


AUTHOR    INDEX. 


A. 

ABDERHALDEN,  EMIL,  protein  hydrolysis, 
126,  134,  172-176;  partial  hydrolysis  of 
silk,  186;  fermentation  hydrolysis,  152, 
166,  204;  pepsin  digestion,  165,  192; 
trypsin  digestion,  165-167;  purpose  of 
digestion,  61,  110,  579,  638;  formation 
and  decomposition  of  protein,  100,  164, 
204,  209,  212,  245,  304;  di-amino-tri- 
hydroxydodecoic  acid,  154,  318;cystine, 
159;  carbohydrate  group,  126,  161;  pro- 
tein derivative  in  urine,  49,  269,  270; 
Bence-Jones  albumin,  269;  albumin 
synthesis  in  the  animal  body,  213,  224, 
355;  protein  requirement,  640;  Asper- 
gillus  niger,  216;  cystinuria,  267,  268; 
alcaptonuria,  273;  phosphorus  poison- 
ing, 264 ;  decomposition  of  polypeptides, 
184,  185,  192,  228,  249,  474;  proteolytic 
ferments,  192,  506;  decomposition  of 
racemic  amino  acids,  452;  ammo  acids 
in  urine,  264,  266;  peptones  in  blood, 
211;  cholesterol,  117;  hemolysis,  115; 
hemoglobin,  125,  126,  382,  558;  analysis 
of  blood,  114,  116,  365,  368,  553,  556, 
666;  effect  of  high  altitudes  on  blood, 
435;  sodium  chloride  (table  salt),  364; 
the  iron  question,  382,  390,  392,  394; 
milk,  366,  654,  665;  casein,  171,  656; 
rate  of  development,  371,  404;  ash  of 
sucklings,  368;  oxidation  by  microbes, 
448;  parthogenesis,  360,  672;  adrenalin, 
601 ;  nucleic  acids,  288 ;  hemophilia,  543; 
conception  of  species,  664,  666. 

ABEL,  J.  JOHN,  carbamic  acid,  232,  602. 

ABELES,  M.,  92. 

ABELMANN,  106. 

ABELOUS,  J.  E.,  hippuric  acid,  247; 
oxydases,  447. 

ADDISON,  T.,  603. 

ADERS-PLIMMER,  R.  H.,  gelatin,  176; 
lactase,  323. 

ABLER,  O.,  29. 

ADLER,  R.,  29. 

AEBY,  428. 

AFONASSIEW,  409. 

ALBERT,  R.,  464. 

ALBERTONI,  P.,  acetone,  99;  coagulation 
of  blood,  546. 

ALDEHOFF,  83. 

ALFTHAN,  K.  v.,  48. 

ALSBERG,  C.,  266. 

ANDRE,  333. 

ANDRE,  586. 


ANTEN,  HENRI,  586. 

ARAKI,   T.,   metabolism  with  insufficient 

oxygen,   75,   237;  phosphorus,   arsenic, 

etc.,  poisoning,  81  ;hydroxy-butyric  acid, 

97;  blood  pigment,  561. 
ARMSTRONG,  F.  E.,  sugar,  38;  syntheses  by 

ferments,  480. 
ARNSCHINK,  105. 
ARON,  H.,  361. 
ARTHUS,  diastase,  71 ;  glucolysis,  87;  blood 

coagulation,  536,  538. 
ASCHOFF,  L.,  682. 
ASCOLI,  A.,  281. 
ASHER,  L.,  blood-sugar,  30,  587;  lymph, 

576. 

ASTASCHEWSKY,  75. 

ATHANSIU,  J.,  328. 

ATTERBERG,  A.,  306. 

ATWATER,  W.  O.,  metabolism,  335,  338, 

339,  340,  344,  345,  346,  622,  623,  626, 

646,  651. 
AUBERT,  H.,  437. 
AUTENRIETH,  W.,  444,  457. 
AUVERS,  K.,  15. 

B. 

BAAS,  K.  H.,  615. 

BABAK,  E.,  438. 

BABKIN,  B.,  legumins,  173;  breaking-down 
of  polypeptides,  228;  pancreatic  juice, 
522,  526,  530. 

BACH,  A.,  oxidation  ferments,  54,  449; 
carbonic  acid  assimilation,  57,  201. 

BAEYER,  ADOLF  v.,  carbonic  acid  assimila- 
tion, 15,  56;  uric  acid,  278. 

BAGLIONI,  S.,  225. 

BAISCH,  K.,  48. 

BALDI,  49. 

BALKE,  298. 

BAMBERGER,  M.,  200. 

BANG,  IVAR,  guanylic  acid,  22,  284; 
albumin,  135,  139;  parachymosin,  207. 

BAR,  P.,  642. 

BARBERA,  A.  G.,  salivary  glands,  486; 
bile,  513;  lymph,  576. 

BARBIERI,  J.,  amides,  151;  phenyl- 
alanine,  151;  allantoine,  296. 

BARCROFT,  J.  L.,  410,  584. 

BARFURTH,  351. 

BARFURTH,  DIETRICH,  glycogen,  46. 

BARKER,  L.  F.,  264. 

BARRAL,  73,  87. 

BARRESWIL,  44. 

BARTH,  H.,  444,  457. 


693 


694 


AUTHOR   INDEX. 


BARTOLLETI,  F.,  13,  39. 

BARY,  DE,  53. 

BASHFORD,  E.,  247. 

BATELLI,  F.,  449. 

BAUMANN,  E.,  mercapturic  acid,  158; 
putrefaction  of  protein,  169;  ethereal 
sulphuric  acids,  243,  250,  251,  252,  253, 
254,  457,  458 ;  crystine,  266 ;  cystinuria, 
266;  alcaptonuria,  271;  iodothyrin,  607. 

BAUMERT,  438. 

BAUMGARTEN,  O.,  94. 

BAUMSTARK,  F.,  613. 

BAYER,  H.,  plasteYn,  208;  oxygen  require- 
ment, 615. 

BAYLISS,  W.  M.,  secretin,  168,  527;  lymph, 
574. 

BEAUMONT,  W.,  203. 

BECHOLD,  H.,  677. 

BEDDARD,  A.  P.,  582. 

BEHRING,  E.,  681. 

BEIJERINCK,  M.,  53,  197,  217. 

BELFANTI,  S.,  688. 

BENDIX,  E.,  22,  294. 

BENECH,  B.,  156. 

BERDEZ,  J.,  145. 

BERGELL,  P.,  choline,  113;  carbohydrate 
group  of  proteins,  126,  161;  breaking- 
down  of  polypeptides,  184,  185,  474; 
phosphorus  poisoning,  264;  adrenalin, 
601. 

BERGMANN,  TOBERN,  277. 

BERGMANN,  v.,  248. 

BERMINZONE,  M.  R.,  247. 

BERNARD,  CLAUDE,  glycogen,  44,  45,  67; 
diastatic  ferments,  478;  glucosuria,  38, 
73,  81 ;  diabetic  puncture,  76;  formation 
of  glycogen,  319;  color  of  blood  in 
glands,  486. 

BERNHARDT,  M.,  77. 

BERT,  PAUL,  417,  435. 

BERTAGNINI,  243. 

BERTEL,  R.,  202,  273. 

BERTHELOT,  nitrogen  assimilation,  195; 
calorimetry,  333;  invertin,  461. 

BERTRAND,  G.,  lactase,  447,  450;  sorbose, 
448;  arsenic,  407. 

BIAL,  M.,  pentosuria,  23;  diastase,  73. 

BIARNES,  447. 

BlBERFELD,  J.,  584. 

BICKEL,  A.,  499. 
BIDDER,  203. 

BlEDERMANN,  W.,  123,  447. 
BlENSTOCK,  218. 

BIGELOW,  S.  L.,  468. 

BING,  B.,  49. 

BING,  ROBERT,  617. 

BIOT,  polarization,  15. 

BIOT,  463. 

BLACKMAN,  F.  F.,  51. 

BLENDERMANN,  H.,  255. 

BLUM,  L.,  249. 

BLUMENREICH,  L.,  611. 

BLUMENTHAL,  F.,  pentoses,  21,  23;  tetanus 

poison,  685. 
BOCKEL,  K.,  177. 


BODONG,  A.,  547. 

BODEKER,  270. 

BOHM,  30,  72. 

BOTTCHER,  25. 

BOGDANOW,  E.,  325. 

BOHR,  CHRISTIAN,  respiratory  exchange. 
415,  417,  419,  425,  426,  427,  430,  431, 
432,  433,  435,  441;  hemoglobin,  560. 

BOKORNY,  T.,  357. 

BOLDIEREFF,  512. 

BONDZYNSKI,  ST.,  117,  269. 

BONTROUX,  448. 

BORDET,  JULES,  545,  668,  688. 

BORNSTEIN,  KARL,  642. 

BORUTTAU,  602. 

BOUCHARD  AT,  39,  91. 

BOUILLAC,  R.,  57. 

BOULUD,  32. 

BOURQUELOT,  E.,  447,  449. 

BOUSSINGAULT,  56. 

BRACONNOT,  H.,  148. 
BRAHM,  C.,  252. 
BRANDENBURG,  K.,  422. 
BRANDT,  K.,  198. 
BREDIG,  G.,  467,  468. 
BRIEGER,  169,  251,  458. 
BRION,  A.,  452. 
BRODERSEN,  398. 
BRODIE,  T.  G.,  584,  617. 
BROWN,  477. 
BROWN,  H.  P.,  42,  59. 
BROWN-SEQUARD,  E.,  600. 
BRUCKE,  545. 
BRUNNER,  ARNOLD,  173. 
BRUYN,  C.  A.  LOBRY  DE,  67. 
BUCHANAN,  536. 

BUCHNER,  E.,  448,  463,  465,  482. 
BUCHNER,  H.,  463. 

BUGARSKY,  S.,   120. 
BULNHEIM,    515. 

BULNHEIM,  G.  v.,  hippuric  acid,  9,  246; 
oxygen  requirement,  74,  443 ;  table  salt, 
354,  362,  363,  366;  ash  of  suckling,  368; 
iron,  368,  380,  381,  384,  387,  399,  401; 
lime,  370,  372,  377;  blood,  553;  lymph 
formation,  575;  composition  of  foods, 
648 ;  vegetarianism,  649 ;  biogenetic  law, 
673. 

BUNTE,  KARL,  277. 

BURCKHARDT,  A.,  556. 

BURIAN,  RICHARD,  uric  acid,  10,  241; 
nucleic  acid,  282,  284,  285;  purine 
metabolism,  287,  291 ;  purine  bases,  290, 
291,  292. 

BUSCH,  F.  W.,  576. 

BUSSY,  461. 

BYK,  A.,  55. 

C. 

CAMERER,  W.,  290,  368,  593,  655. 
CANTANI,  A.,  94. 
CARBONE,  P.,  688. 
CARVALLO,  G.,  509. 
CASH,  104. 
CASPARI,  W.,  436,  643,  649,  651. 


AUTHOR   INDEX. 


695 


CAVAZZANI,  E.,  72. 
CBNTNERSWER,  M.,  468. 
CHANDELON,  T.,  68. 
CHANIEWSKI,  ST.,  309. 
CHAUVEAU,  A.,  338. 
CHEVALIER,  J.,  614. 
CHEVREUL,  90,  101. 
CHIGIN,  P.,  502. 
CHODAT,  R.,  54,  449. 
CHOSSAT,  T.,  375. 

ClENKOWSKI,  533. 

CLAIRMONT,  690. 

GLAUS,  R.,  89. 

CLAUTRIAN,  47. 

CLEMENS,  P.,  34. 

CLERGET,  15. 

CLEVE,  P.  T.,  515. 

CLOSSON,  O.  E.,  587. 

CLOWES,  G.  H.  A.,  374. 

COHN,  RUDOLPH,  leucinimide,  169;  conju- 
gated compounds,  234,  243,  244,  245, 
246,  457;  sugar  formation,  318. 

COHN,  THEODOR,  296. 

COHNHEIM,  OTTO,  carbohydrate  combus- 
tion, 89;  albumin,  131,  134;  erepsin,  167, 
209;  work  of  glands,  341;  mountain 
sickness,  436;  absorption  in  small  intes- 
tine, 532. 

COLE,  S.  W.,  152. 

COLUCCI,  V.  L.,  674. 

CONNSTEIN,  W.,  lipase,  103;  fat  absorption, 
105;  lipolytic  action  of  blood,  109; 
lymph,  574. 

CORANDA,  230. 

COR  vis  ART,  164. 

COURMONT,  586. 

CRAMER,  A.,  47. 

CRAMER,  E.,  149. 

CRAMER,  W.,  247. 

CRAWFORD,  A.,  601. 

CREMER,  MAX,  66,  81,  83,  314. 

CZAPEK,  F.,  51,  103,  118,  216,  273. 

CZERNY,  509. 

CZERNY,  F.,  73. 

D. 

DAKIN,  H.  D.,  135,  137,  175,  226,  475. 
DAMASKIN,  N.,  526. 
DANILEWSKY,  A.,  208. 
DAPPER,  CARL,  290. 
DASTRE,  A.,  107,  547. 
DAUNAY,  R.,  642. 
DAVY,  H.,  193. 

DELEZENNE,  C.,  539,  541,  547. 
DENIS,  537. 
DESPRETZ,  335. 
DHERE,  C.,  402, 
DIAKONOW,  112. 
DIAMARE,  V.,  83,  90,  225. 
DIELS,  OTTO,  117. 
DIETSCHY,  R.,  230,  211. 
DITTHORN,  FRITZ,  20. 
DOCK,  F.  W.,  77. 
DORPINHAUS,  T.,  126,  161,  17& 
DOMBROWSKI,  ST.,  269. 


DOMINICIS,  DE,  87. 
DORMEYER,  C.,  325. 
DOYON,  548. 

DRECHSEL,  E.,  jecorin,  49 ;  albumins,  123  ; 
lysine,  154 ;  urea,  226 ;  carbamic  acid,  232. 
DRESER,  H.,  583. 
DUBRUNFAUT,  38,  39. 
DULONG,  335. 
DUNGERN,  v.,  688. 
DUPETIT,  195. 
DURHAM,  H.  E.,  680. 
DURIG,  A.  E.,  436. 

E. 

EBERLE,  203. 
EBNER,  V.  v.,  123. 
EBSTEIN,  E.,  22. 
EBSTEIN,  W.,  cystinuria,  266;  elimination 

of  uric  acid,  586. 
ECKHARD,  C.,  78,  80. 
EDINGER,  L.,  616. 
EHENSTEIN,  W.  ALBERDA  VAN,  67. 
EHRLICH,  FELIX,  isoleucine,  148;  cleavage 

of  racemic  bodies,  470. 
EHRLICH,    PAUL,    oxidation,    411,    431; 

chemical  constitution  and  disinfecting 

effect,  677;  side-chain  theory,  682-691. 

ElSELSBERG,   A.   FREIH  V.,   607. 

ELLINGER,  ALEXANDER,  tryptophane,  153, 
258;  cadaverine,  154,  260;  putrescine, 
155,  260;  intestinal  putrefaction,  220; 
kynurenic  acid,  260;  Bence-Jones  pro- 
tein, 269;  lymph,  574. 

EMBDEN,  G.,  89,  264,  273,  319,  454. 

EMERSON,  R.  C.,  259. 

EMMERLING,  O.,  isomaltose,  37;  cystine, 
157;  papayotin,  168;  amino  acids  as 
nutriment  for  molds,  216;  oxidizing 
molds,  448. 

ENGELMANN,  T.  W.,  chromophyll,  52,  53; 
heredity  of  acquired  properties,  672. 

ENGLER,  C.,  449. 

ERDMANN,  J.,  42. 

ERLENMEYER,  Jr.,  158. 

ERMAN,  326. 

ERNST,  468. 

ERRERA,  47. 

ESCHERICH,  218. 

ESCHLE,  215. 

EULER,  ASTRID,  57. 

EULER,  HANS,  57. 

EWALD,  C.  A.,  105. 

F. 

FALK,  E.,  630. 
FALTA,  W.,  271,  273,  355. 
FANO,  546. 
FARKAS,  G.,  549. 
FEDER,  L.,  230. 
FEER,  E.,  221. 
FEHLING,  H.,  378. 
FICK,  A.,  69,  412. 

FlECHTER,  464. 
FlLEHNE,  W.,  584. 

FILIPPI,  FILIPPO  DE,  389,  402. 


696 


AUTHOR   INDEX. 


FISCHER,  EMIL,  carbohydrates,  13-17,  19, 
20,  26,  27,  31,  32,  35,  37,  38,  55,  58; 
protein,  amino  acids,  serine,  149;  pro- 
line,  151;  diamino-trihydroxy-dodecoic 
acid,  154,  318;  lysine,  155;  ornithine, 
156;  cystine,  159,  266;  breaking  down 
of  proteins,  149,  152,  171,  174,  176; 
partial  hydrolysis  of  silk,  187;  breaking 
down  of  polypeptides,  178-187;  fer- 
mentation of  proteins,  152,  165,  166, 
204;  of  polypeptides,  184,  185,  192,474; 
uric  acid  and  purine  bases,  277,  278, 
279,  281;  physiological  significance  of 
stereochemistry,  471 ;  fermentation  of 
sugar,  471  et  seq.;  sense  of  smell,  494; 
taste  of  the  amino  acids,  494. 

FISCHER,  MARTIN  H.,  80,  359. 

FISCHL,  R.,  610. 

FLAMMAND,  153. 

FLECHSIG,  E.,  62. 

FLEISSIG,  P.,  56. 

FLEITMANN,  157. 

FLEXNER,  S.,  115,  116,  690. 

FLORESCO,  547. 

FOA,  P.,  540. 

FOGES,  600. 

FOLIN,  OTTO,  266,  588. 

FONTANA,  547. 

FORSTER,  354,  375. 

FOURCROY,  277. 

FRAENKEL,  A.,  435. 

FRAENKEL,  P.,  549. 

FRAENKEL,  S.,  271,  677. 

FRAMM,  F.,  73. 

FRANCHIMONT,  42. 

FRANK,  OTTO,  105,  325,  326. 

FRANKFURT,  S.,  38. 

FRANZ,  547. 

FREDERICQ,  L.,  402,  421,  431,  537. 

FRENTZEL,  J.,  70,  123,  312. 

FRERICHS,  236,  242. 

FRERICHS,  F.  T.,  92,  99. 

FREUND,  545. 

FREY,  MAX  v.,  70. 

FRIEDEL,  J.,  54. 

FRIEDEMANN,  U.,  667. 

FRIEDENTHAL,  H.,  diastase,  60;  fat  absorp- 
tion, 108;  biological  reaction,  670. 

FRIEDLEBEN,  A.,  610. 

FRIEDMANN,  E.,  cystine,  157,  158;  mer- 
capturic  acid,  159;  thiolactic  acid,  169. 

FRISBIE,  W.  S.,  374. 

FROHLICH,  615. 

FROMM,  EMIL,  34,  35,  244,  458,  678. 

FROMME,  ALBERT,  104. 

FURTH,  OTTO  v.,  proteins,  146;  muscle 
protein,  133,  617,  618;  tyrosinase,  447; 
comparative  physiology,  402. 

FULD,  547. 

G. 

GABRIEL  S.,  215,  403. 
GAD,  J.,  103. 

GAIDUKOW,  N.,  chromophyll,  52;  heredity, 
672. 


GAMGEE,  203. 

GARNIER,  L.,  273. 

GARROD,  A.  E.,  alcaptonuria,  272;  chemical 

anomalies,  675. 
GATIN-GRUZEWSKA,  Z.,  45. 
GAULE,  J.,  390. 
GAUTIER,  A.,  407. 
GAYON,  195. 

GEELMUYDEN,  H.  C.,  97. 
GELPKE,  L.,  377. 
GENERALI,  607. 
GENGOU,  545. 
GENTZEN,  MAX,  258. 
GEPPERT,  J.,  413,  435. 
GERBER,  C.,  307. 
GERHARDT,  C.,  97. 
GERHARDT,  D.,  218. 
GERNGROSS,  OTTO,  281. 
GIACOSA,  P.,  243,  289. 
GIERKE,  E.,  46. 
GIES,  W.  J.,  576. 
GILBERT,  R.  D.,  653. 
GILSON,  E.,  112. 
GIRARD,  H.,  72. 

GlUSTINIANI,  57. 

GIZELT,  A.,  527. 
GLASSNER,  K.,  505. 
GLAUBER,  13. 
GLEY,  E.,  606. 
GODLEWSKI,  E.,  672. 
GOLDMAN,  E.,  249,  266. 

GOLDTHWAIT,  378. 

GONNERMANN,  M.,  273,  447. 

GOTO,  M.,  136. 

GOTTLIEB,  R.,  269,  389. 

GRAEBE,  21. 

GRAFE,  V.,  42. 

GRAHAM,  T.,  120. 

GREEN,  J.  REYNOLDS,  202. 

GRIESMAYER,  V.,  131. 

GRIFFITHS,  402. 

GRUBE,  K.,  66. 

GRUBE,  MAX,  680. 

GRUTZNER,  P.,  gastric  digestion,  60,  500; 

urea  formation,  583. 
GRUND,  G.,  22. 

GSCHEIDLEN,  R.,  250. 

GURBER,  A.,  albumin,  124;  alkali  of  the 

blood,  426. 
GURTLER,  Ff,  81. 
GULEWITSCH,  W.,  thymine,  281. 
GULL,  W.,  605. 

GUNDELACH,  C.,  514. 

GURWITSCH,  A.,  582. 
GUSSEROW,  A.,  295. 

H. 

HAUSERMANN,  EMIL,  380. 
HAHN,  M.,  231. 
HAHN,  MARTIN,  463. 
HALBAN,  J.,  599. 
HALDANE,  JOHN,  431. 
HALL,  WALKER,  285. 
HALL,  W.  S.,  389. 
HALLERVORDEN,  E.,  230. 


AUTHOR   INDEX. 


697 


HALLIBURTON,  W.  B.,  614. 
HAMBURGER,  60. 
HAMBURGER,  389. 
HAMBURGER,  FRANZ,  664,  668. 
HAMBURGER,  H.  J.,  361,  426;  blood,  532, 

550;  lymph,  574. 
HAMMAR,  J.  A.,  610. 
HAMMARSTEN,   OLOF,   nucleoproteids,   21, 

134;   mucins    and    mucoids,    142,    144; 

rennin,  205;  bile  acids,  225,  515,  516; 

blood  coagulation,  537,  538. 
HANNON,  401. 
HANSEN,  355. 
HANSEN,  A.,  51. 
HARDEN,  A.,  47. 
HARDY,  W.  B.,  361. 
HARLESS,  402. 
HARLEY,  V.,  73. 
HARNACK,  E.,  muscarine,   114;  albumin, 

128,  sulphhemoglobin,  561. 
HARRIES,  C.,  305,  312. 
HARRIS,  ISAAC  F.,  23,  139,  285. 
HARROY,  M.,  54. 
HART,  EDWIN,  174,  177. 
HARTIG,  T.,  122. 
HARKINS,  H.  D.,  233. 
HASSELBACH,  K.,  427. 
HAYCRAFT,  JOHN,  levulose,  67,  95;  hirudin, 

547. 

HEDON,  E.,  77,  83. 
HEFFTER,  A.,  75. 
HEIDENHAIN,  MARTIN,  532. 
HEIDENHAIN,  RUDOLF,  salivary  glands,  79, 

486,  487;  fat   absorption,    106;   lymph 

formation,    547,    574;    urine   secretion, 

582. 

HEINEMANN,  H.  N.,  312. 
HEINTZ,  515. 
HELE,  T.  S.,  272. 
HELLRIEGEL,  H.,  196. 
HENNEBERG,  W.,  62. 
HENRIQUES,  355. 
HENRIQUES,  V.,  431,  441. 
HEFNER,  E.,  116. 
HERAEUS,  W.,  193. 
HERMANN,  74. 
HERMANN,  A.,  352. 
HERMANN,  L.,  561. 
HERON,  JOHN,  42,  60. 
HERRIK,  J.  B.,  173. 
HERRMANN,  E.,  407. 
HERTER,  C.  A.,  411,  615. 
HERTER,  E.,  243,  252,  457. 
HERTWIG,  OSKAR,  53. 
HERZOG,  R.  O.,  54. 
HEUBNER,  OTTO,  655. 
HILBERT,  PAUL,  458. 
HILDEBRANDT,   HERMANN,  decomposition 

of  cyclic  compounds,  32,  34;  ferments, 

476. 

HILL,  ARTUR  CROFT,  37. 
HIRSCH,  A.,  507. 
His,  351. 

His,  W.  d.  J.,  298,  593. 
HOCHHAUS,  389. 


HOEBER,  RUDOLF,  532,  591 ;  effect  of  ions, 
361;  blood,  549;  kidneys,  587. 

HOESSLI,  A.,  543. 

HOFF,  J.  H.  VAN'T,  15,  16,  25. 

HOFFMANN,  A.,  247. 

HOFFMANN,  F.  A.,  30,  72. 

HOFMANN,  A.,  389,  395. 

HOFMANN,  FRANZ,  109,  326. 

HOFMEISTER,  FRANZ,  starvation  glucosuria, 
30,  91,  95;  lactosuria,  39;  assimilation 
limit  for  carbohydrates,  76;  cell  fer- 
ments, 88;  albumins,  124,  131;  albumin 
absorption,  208;  urea,  230. 

HOFMEISTER,  VIKTOR,  62. 

HOLLE,  56. 

HOPKINS,  F.  G.,  albumin,  124;  trypto- 
phane,  152. 

HOPPE-SEYLER,  FELIX,  cellulose  fermen- 
tation, 62;  metabolism  with  insufficient 
oxygen,  75,  81,  237;  respiratory  ex- 
change, 623;  hemoglobin,  125,  424, 
559,  561;  ozone,  442;  blood,  553;  urea, 
230. 

HOPPE-SEYLER,  G.,  398. 

HORABACZEWSKI,  J.,  10,  278,  289,  290. 

HORNBORG,  499. 

HOYER,  E.,  103. 

HUBER,  71. 

HUFNER,  G.,  hemoglobin,  125,  559,  560, 

561,  562;  nitric-oxide  hemoglobin,  561; 

carbonic-oxide    hemoglobin,   424,    561; 

oxygen  combination,  414,  419. 
HUNEFELD,  F.  L.,  124. 
HUEPPE,    F.,     nitrifying    bacteria,     193; 

vegetarianism,  649. 
HURTHLE,  608. 

HtJRTHLE,  K.,   116. 

HUGONNENQ,  L.,  ash  of  a  suckling,  369; 
absorption  of  salt  by  the  foetus,  375, 
385;  hematogen,  387. 

HUISKAMP,  W.,  histone,  139;  fibrin- 
globulin,  542. 

HUMNICKI,  V.,  117. 

HUMPHRY,  L.,  609. 

HUNDESHAGEN,  FRANZ,  112. 

HUNTER,  ANDREW,  671. 

HUPPERT,  664, 


IKEDA,  K.,  468. 
INGENHOUSZ,  51. 
INOKO,  Y.,  285. 
ISAAC,  S.,  667. 


J. 


JACKSON,  HENRY,  202. 

JACOBJ,  547. 

JACOBJ,  CARL,  92. 

JACOB  Y,   MARTIN,  oxydases,  447;  spleen, 

611. 

JADERHOLM,  AXEL,  125,  562. 
JAFFE,   MAX,   conjugated  acids  in  urine, 

34,  457,   458;  glycogen,  92;  ormithine, 

155;  indican,  220,  258. 


698 


AUTHOR   INDEX. 


JAKOBSTHAL,  H.,  326. 

JAKSCH,  R.  v.,  97. 

JAQUET,  ALFRED,  carbonic  acid  combina- 
tion, 421;  effect  of  high  altitudes,  436, 
643;  oxydases,  445;  hemoglobin,  559. 

JASTROWITZ,  21. 

JAWEIN,  GEORG,  611. 

JELINEK,  JOHN,  73. 

JOHANNSON,  J.  E.,  631,  647. 

JOHNSON,  TREAT  B.,  281. 

JOHNSTON,  H.  M.,  610. 

JOLIN,  SEVERIN,  515. 

JONES,  W.,  281. 

JOTEYKO,  459. 

K. 

KALANTHAR,  A.,  473. 
KALBERLAH,  F.,  454. 
KALTENBACH,  P.,  39. 
KAREFF,  N.,  548. 
KASSOWITZ,  M.,  309. 
KASTLE,  446. 

KATZENSTEIN,  A.,  241,  452. . 
KAUFFMANN,  M.,  215,  290. 
KAUFMANN,  M.,  634. 
KAUSCH,  W.,  83. 
KEKULE,  45. 
KELLER,  W.,  242. 
KELLNER,  O.,  70,  215. 
KIESEL,  K.,  168. 
KILIANI,  13,  18. 
KIRCHHOFF,  C.,  13,  39,  461. 
KIRK,  271. 

KlSCHENSKY,  106. 
KlTASATO,  681. 

KLETZINSKY,  401. 

KNIERIEM,  W.  v.,  cellulose,  62,  63;  urea, 
228,  230;  uric  acid,  237. 

KNOOP,  F.,  286,  454. 

KOBERT,  R.,  388. 

KOCHER,  T.,  605. 

KOCHS,  247. 

KOENIG,  376,  645,  646,  648,  651,  654,  655, 
659,  661. 

KOENIGS,  E.,  183. 

KONIGSBERG,  A.,  587. 

KOEPPE,  H.,  492,  550. 

KOLLE,  680. 

KOSSEL,  A.,  22;  proteins,  134,  135,  137, 
173,  175,  176;  histidine,  154;  arginase, 
226;  nucleic  acids,  22,  277,  258;uracil, 
281;  thymine,  281;  cytosine,  281;  for- 
mation of  purine  bases,  287;  gas  pump, 
413. 

KOWALEWSKI,  KATHARINA,  169,  238. 

KRATTER,  J.,  326. 

KRAUS,  421. 

KRAUS,  F.,  326,  328. 

KRAUS,  RUDOLF,  680,  690. 

KRAWKOW,  N.  P.,  49. 

KRIEGER,  H.  T.,  124. 

KROGH,  417,  427,  432,  437. 

KRONECKER,  459. 

KRUGER,  195. 

KHVGER,  ALBERT,  157. 


KRUGER,  F.,  125,  559. 

KRUGER,  M.,  choline,  113;  purine  bases  of 

the  faeces,   289;     purine   bases  in  the 

urine,  297,  298. 
KRUGER,  T.  R.,  177. 
KRUMMACHER,  O.,  70. 
KUHN,  J.,  196. 
KUHNE,  459. 

KUHNE,  W.,  sugar,  92;  digestion,  164. 
KULZ,     E.,     pentoses,     23;     conjugated 

glucuronic  acids,  34;  breaking-down  of 

sugar,  59,  71;  glycogen,  68,  73,  75,  80, 

92,  319;  diabetes,  95;  hydroxy-butyric 

acid,  97;cystine,  157. 
KULZ,  R.,  410,  424. 
KUSTER,  W.,  carbonic-oxide  hemoglobin, 

424,    561;    hematin,    563,    564,    565; 

bilirubin,  568. 
KULIABKO,  90. 
KUMAGAWA,  M.,  324,  632. 
KUNKEL,  iron,  389,  395;  arsenic,  407. 
KUPFFER,  411. 
KURAJEFF,  D.,  137,  208. 
KUTSCHER,  F.,  proteins,   135,   173,   176; 

arginine,  156;  digestion,  208. 
KYES,  PRESTON,  115,  116. 

L. 

LADENBURG,  154. 
LAMY,  29. 

LANDERGREN,  E.,  345,  631,  467. 
LANDOIS,  H.,  125. 
LANDOLT,  H.,  15. 
LANDSIEDL,  ANTON,  200. 
LANDSTEINER,  K.,  364,  688. 
LANDWEHR,  A.  H.,  48. 
LANG,  S.,  237. 
LANGE,  CORNELIA  DE,  369. 
LANGENBUCH,  509. 
LANGENDORFF,  478. 
LANGENDORFF,  O.,  81. 
LANGERHANS,  90. 
LANGSTEIN,  LEO,  160,  173,  271. 
LANGWORTH,  C.  F.,  650. 
LAPICQUE,  L.,  364,  389. 
LA  PLACE,  DE,  334. 
LASCHKEWITSCH,  438. 
LASSAR-COHN,  515. 
LAURENT,  EM.,  196. 
LAVES,  E.,  94. 
LAVOISIER,  70,  334. 
LAWROW,  M.,  208. 
LEA,  SHERIDAN,  71. 
LE  BEL,  15,  16,  25. 
LECLERC  DU  SABLON,  308. 
LE  COUNT,  E.  R.,  115,  176. 
LEDDERHOSE,  35. 
LEHMANN,  CURT,  394,  631. 
LEHMANN,  K.  B.,  326. 
LEHMANN,  K.  H.,  215. 
LEMAIRE,  F.  A.,  39. 
LEO,  H.,  94. 
LEONE,  S.,  81. 

LEPINE,  R.,   blood  sugar,  32;  glucolytic 
ferment,  73,  87. 


AUTHOR   INDEX. 


699 


LEUCHS,     HERMANN,     glucosamine,     35; 

amino-acids,  149,  151. 
LEVENE,   P.   A.,   nucleic   acid,   285;  glu- 

cothionic    acid,    49;    vagus    nerve,    77; 

gelatin,  176. 
LEWANDOWSKI,  N.,  602. 
LEWINSKI,  JOHANN,  556. 
LICKIERNIK,  A.,  lecithine,  115;  leucine,  148. 

LlEBERMANN,  21. 
LlEBERMANN,   LEO,   120. 

LIEBIQ,  JUSTUS  v.,  56,  69,  260,  277,  295, 
356,  461. 

LlEBREICH,    114,  613. 
LlLIENFELD,   L.,    135. 

LIPPMANN,  EDMUND  O.  v.,  13,  51,  90. 

LIST,  R.,  123. 

LOEB,  JACQUES,  358,  359,  672. 

LOEB,  WALTHER,  57,  70. 

LOEBISCH,  W.  F.,  266. 

LOEW,  O.,  162,  450,  456. 

LOEW,  R.  MANNAN,  67. 

LOEWI,  OTTO,  213,  585. 

LOEWY,  A.,  cystinuria,  266;  respiratory 
exchange,  417,  422;  blood  circulation, 
435;  high  altitudes,  436,  643. 

LORENZ,  N.  v.,  309. 

LUBARSCH,  123. 

LUBARSCH,  O.,  47. 

LUCA,  S.  DE,  490. 

LUCHSINGER,  B.,  81. 

LUCIANI,  L.,  631. 

.LUDWIG,  CARL,  70,  420,  486,  583. 

LUDECKE,  KARL,  113. 

LUTHJE,  H.,  314,  320,  321. 

LUKJANOW,  S.  M.,  352. 

LUNIN,  N.,  355. 

LUSK,  82. 

LUZZATO,  RICCARDO,  23. 

M. 

MAAR,  V.,  433,  434. 

MACALLUM,  A.,  389. 

MAC  CALLUM,  606. 

MACFAYDEN,  A.,  218. 

MACLEOD,  J.  J.  R.,  233. 

MAGENDIE,  71. 

MAGNUS,  G.,  409. 

MAGNUS-LEVY,  ADOLF,  coma  diabeticum, 
98;  Bence- Jones  protein,  269 ;  respiratory 
exchange  in  diabetes,  323 ;  formation  of 
carbohydrates  from  fat,  303;  metabo- 
lism, 630. 

MAIGNON,  F.,  97. 

MALCOLM,  JOHN,  metabolism  of  salts,  403; 
hypophysis,  610. 

MALENGREAU,  F.,  139. 

MANASSE,  PAUL,  49. 

MANCHE,  EDUARD,  68. 

MANDEL,  JOHN  A.,  49. 

MANGOLD,  ERNST,  507. 

MAQUENNE,  306. 

MARCHAL,  E.,  217. 

MARCHLEWSKI,  L.,  396,  566,  567. 

M \RCUSE,  W.,  glycogen,  68;  extirpation  of 
pancreas,  83,  87. 


MARES,  290. 

MARFORI,  Pio,  402. 

MARGGRAF,  13. 

MARK,  H.,  49. 

MARK,  W.  R.,  202. 

MARX,  680. 

MASCHKE,  O.,  123. 

MASSEN,  O.,  231. 

MATHEWS,  A.,  135,  140. 

MATTHAEI,  GABRIELLE  L.  C.,  51. 

MAUTHNER,  215. 

MAXWELL,  W.,  42. 

MAY,  R.,  632. 

MAYER,  A.,  389. 

MAYER,  HANS,  388,  392. 

MAYER,  ROBERT,  334. 

MAYS,  KARL,  168. 

MCCRUDDEN,  F.  H.,  378. 

MEINERTZ,  49. 

MEISENHEIMER,  J.,  448,  465,  482. 

MEISSL,  E.,  309. 

MENDEL,  LAFAYETTE  B.,  296. 

MERINO,  J.  v.,  conjugated  glucuronic  acids, 
34;  diastase,  60,  71;  absorption  of 
sugar,  61;  phloridzin  diabetes,  81,  82; 
extirpation  of  pancreas,  82,  83,  86; 
formation  of  glycogen,  92;  gastric  ac- 
tivity, 507. 

MESTER,  BRUNO,  266. 

METZNER,  RUDOLF,  587. 

MEYER,  H.,  237. 

MEYER,  HANS,  glucuronic  acid,  31;  impor- 
tance of  fat,  112.  . 

MEYER,  PAUL,  32. 

MICHAELIS,  109. 

MICHAELIS,  L.,  670. 

MICHEL,  A.,  124. 

MIESCHER,  FRIEDRICH,  metabolism  of  the 
salmon,  130,  287,  351,  636;  protein,  135; 
nucleins,  140,  276,  284,  287;  high 
altitudes,  436. 

MINKOWSKI,  extirpation  of  liver,  73;  of 
pancreas,  81,  82,  83,  86,  95,  321; 
hydroxy-butyric  acid,  97;  allantoine, 
296;  icterus,  570;  uric  acid,  237,  586. 

MlTSCHERLICH,  461. 

MIURA,  K.,  95. 

MIURA,  R.,  632. 

MOERNER,  CARL  T.,  49,  143. 

MOERNER,  K.  A.  H.,  protein,   126,   143; 

cystine,  157, 174,  176;  pyroracemic  acid, 

169;  a-thiolactic  acid,  169;  acetanilide, 

458;hemin,  565. 
MOERS,  378. 
MOHR,  L.,  290. 

MOLISCH,  HANS,  53,  125,  162. 
MOMBERT,  PAUL,  645. 
MONTUORI,  A.,  87. 
MOORE,  25. 
Moos,  79. 
MORAWITZ,  P.,  albumoses  in  blood,  211; 

blood  coagulation,  536,  541,  542,  547, 
MOREAU,  433. 
MOREL,  387. 
MOREL,  A.,  548. 


700 


AUTHOR   INDEX. 


MORGENROTH,     J.,      anti  ferments,     476; 

hemolysis,  688. 
MORITZ,  507. 
MORKOWIN,  N.,  137. 
MORO,  64. 

MOROCHOWETZ,  LEO,  131. 
MORRIS,  477. 
Mosso,  547. 
MUCK,  378. 

MULLER,   117. 

MULLER,  FRANZ,  iron,  389,  395;  estimation 

of  oxygen,  413;  high  altitudes,  436,  643; 

estimation  of  blood,  557. 
MULLER,     FRIEDRICH,    glucosamine,    20, 

142,  320;  fasting  experiments,  97,  394, 

631;  absorption  of  fat,  105;  indole,  258; 

intestinal  putrefaction,   220;  antolysis, 

265,  478. 

MULLER,  JOHANNES,  494. 
MULLER,  KARL,  41. 
MULLER,  PAUL  TH.,  682. 
MULLER  v.  BERNECK,  R.,  468. 
MUNZER,  E.,  230. 
MUIRHEAD,  ARCHIBALD,  232. 
MUNK,   IMMANUEL,   fat  absorption,    105, 

106,    108;   fat   assimilation,    110,    309; 

asparagine,     215;    urea,     230;    fasting 

experiments,  394,  631;  phenol,  458. 
MUSCULUS,     M.,     conjugated    glucuronic 

acids,  34,  37;  diastase,  59,  71. 
MYLIUS,  F.,  515. 

N. 

NAEGELI,  C.  v.,  483. 

NAGANO,  J.,  62. 

NASSE,  OTTO,  59,  71,  72,  73. 

NAUNYN,  B.,  diabetes,  77;  glycocoll  con- 
jugate, 243,  458;  icterus,  570. 

NEESEN,  F.,  413. 

NEISSER,  M.,  690. 

NENCKI,  MARCEL,  physiological  oxidation, 
93,  440,  634;  melanin,  145;  digestion  of 
albumin,  152;  glycocoll  conjugate,  243, 
244;  albumin  putrefaction,  153,  169; 
intestinal  bacteria,  218;  urea,  228,  229, 
230,  231;  lactic  acid,  378;  behavior  of 
aromatic  substances  in  the  body,  458; 
bile,  520;  hematin,  396,  553,  557;  gastric 
juice,  462;  urobilin,  572. 

NERKING,  JOSEF,  325. 

NEUBANER,  OTTO,  273. 

NEUBERG,  CARL,  pentoses,  22,  23,  24,  29; 
glucuronic  acid,  32,  33;  chpndroitin 
sulphuric  acid,  49,  143;  cystine,  158, 
266;  behavior  of  stereoisomers  in  the 
animal  organism,  452. 

NEUMANN,  A.,  281. 

NEUMEISTER,  R.,  152. 

NICKLES,  J.,  403. 

NICOLAIER,  ARTUR,  586. 

NIEMANN,  A.,  266. 

NOEGGERATH,  C.  T.,  355. 

NOEL-PATON,  71. 
NOGUCHI,  H.,  115,  116,  690. 


NOLF,   P.,  formation  of  fibrinogen,  548; 

biological  reaction,  668. 
NOLL,  A.,  487. 
NOORDEN,  C.  v.,  290. 
NUSSBAUM,  MORITZ,  lungs,  429;  kidneys, 

583. 

NUTTAL,  670. 
NUTTAL,  G.  H.  F.,  64,  255. 

O. 

OBERMAYER,  FRIEDRICH,  192,  670. 
ODDI,  R.,  49. 
OERTMANN,  E.,  409. 
ORUM,  H.  P.  T.,  514. 
OFNER,  RUDOLF,  29. 
OGATA,  104,  509. 
OKUNEW,  208. 
OLIVER,  G.,  601. 
OLLENDORFF,  GERHARD,  58. 
OPPENHEIMER,  CARL,  albumoses  in  blood, 

211;    ferments,     461,     481;    biological 

reaction,  670;  toxines,  682. 
OPPENHEIMER,  KARL,  628. 
ORD,  WILLIAM  M.,  605. 
ORFILA,  M.,  406. 
ORGLER,  A.,  49,  143. 
ORTWEILER,  219. 
OSBORNE,  T.  B.,  nucleic    acid,    23,  285; 

protein,  139,  653. 
OSBORNE,  W.  A.,  359. 
OSGOOD,  R.  B.,  378. 
OSTERTAG,  R.,  659. 
OSTWALD,  467. 

O'SULLIVAN,  C.,  467. 

OSWALD,  AD.,  132,  607. 

OTTO,  J.  C.,  oxyhemoglobin,  125,  559; 

methemoglobin,  562. 
OVERTON,  importance  of  fat,  112;  effect 

of  ions,  358. 

P. 

PACHON,  V.,  509. 

PAGES,  538. 

PAINTER,  C.  F.,  378. 

PANCERI,  P.,  490. 

PANEK,  269. 

PARASTSCHUK,  S.  W.,  205,  505,  512. 

PASTEUR,  15,  470. 

PATTEN,  A.  J.,  159. 

PAUL,  THEODOR,  298,  593. 

PAULY,  HERMANN,  histidine,  154;  adrena- 
lin, 601. 

PAVY,  F.  W.,  carbohydrates,  66,  71,  73; 
phloridzin  diabetes,  81 ;  diabetes,  84. 

PAWLOW,  J.  P.,  164,  478;  rennin,  205,  206; 
urea,  231 ;  digestion,  485,  489,  496,  498, 
499,  500,  501,  502,  505,  512,  520,  523; 
relation  of  physiology  to  pathology,  668. 

PA  YEN,  39. 

PEARSON,  277. 

PEKELHARING,  C.  A.,  462. 

PELIGOT,  91. 

PELLACINI,  P.,  540. 

PENZOLDT,  494. 

PEREWOZNIKOFF,  105. 


AUTHOR   INDEX. 


701 


PERLS,  389. 

PERSOZ,  39. 

PETTENKOFER,  MAX  v.,  metabolism  in 
diabetes,  93;  absorption  of  fat,  108; 
assimilation  of  fat,  109;  fat  formation, 
324 ;  metabolism,  623. 

PETTERS,  W.,  97. 

PFEFFER,  W.,  51. 

PFEIFFER,  R.,  680. 

PFLUGER,  EDUARD  F.  W.,  carbohydrates, 
6,  30,  44,  45,  46,  66,  78;  physiological 
combustion,  74,  459 ;  glucosuria,  82,  83, 
84,  85;  absorption  of  fat,  104,  107; 
formation  of  sugar,  314,  315,  316,  317, 
318,  324,  329,  353 ;  oxidation,  410;  gases 
of  the  saliva,  410;  gases  of  the  blood, 
413,  415,  422,  423;  source  of  muscular 
power,  337;  Alytes  obstetricans  (the 
nurse-frog),  353. 

PICCARD,  J.,  135,  277. 

PICK,  ERNST  P.,  192,  670. 

PlLOTY,  OSKAR,  31,  32. 

PINKUS,  S.  N.,  124. 

PODUSCHKA,  RUDOLF,  296. 

POHL,  J.,  230,  446. 

POHL,  JULIUS,  33. 

POLITIS,  215. 

POLLACK,  LEO,  168. 

POPIELSKI,  L.,  524,  528. 

PORCHER,  CH.,  39. 

POUCHET,  G.,  295. 

PREGL,  FRITZ,  egg-albumin,  172;  carbon- 
nitrogen  quotient  in  urine,  270;  albumin 
derivatives  in  urine,  49,  270;  bile  acids, 
515. 

PREUSSE,  C.,  158,  251. 

PREYER,  W.,  493. 

PROSCHER,  FRIEDRICH,  milk,  404;  toad's 
venom,  690. 

PROUT,  WILLIAM,  277. 

PRUTZ,  WOLFGANG,  220. 

PRYM,  OSKAR,  531. 


QUINCKE,  389. 


Q. 


R. 


RAASCHOON,  C.  A.,  284. 
RACIBORSKI,  M.,  446. 
RADIJEWSKI,  105. 
RADLKOFER,  L.,  122. 
RAMSDEN,  W.,  121. 
RANKE,  J.,  71. 
RAPP,  R.,  464. 
RAPS,  A.,  413. 
RAUDNITZ,  P.,  450. 
RAUDNITZ,  R.  W.,  392. 
RAUSCHENBACH,  540. 
REACH,  FELIX,  269,  312. 
REALE,  83. 

RECHENBERG,  v.,  308. 
RECOURA,  333. 
REESE,  HEINRICH,  264. 
REGNAULT,  V.,  623. 
REICHEL,  H.,  467. 


REICHERT,  B.,  124. 

REINBOLD,  BELA,  trypsin  digestion,  165, 
167;  edestin,  172;  nitric-oxide  hemo- 
globin, 561. 

REISET,  J.,  623. 

RENZI,  DE,  83. 

REVERDIN,  AUG.,  605. 

REVERDIN,  JACQUES  Louis,  605 

REY,  J.  G.,  373,  392. 

RIBAUT,  H.,  247. 

RIBBERT,  H.,  582. 

RICHARDS,  A.  N.,  411,  615. 

RICHARDSON,  S.  W.  F.,  617. 

RIES,  255. 

RUN,  J.  J.  L.  VAN,  21. 

RITTER,  A.,  phloridzin  diabetes,  81,  83; 
uric  acid,  594. 

RITTHAUSEN,  H.,  132,  169. 

ROCKWOOD,  ELBERT  W.,  290. 

ROEDER,  GEORG,  281. 

ROHMANN,  F.,  62,  73,  102,  446,  595. 

ROMER,  PAUL,  682. 

ROHDE,  ERWIN,  152. 

ROHRER,  LADISLAUS  v.,  492. 

ROLLET,  550. 

RONA,  PETER,  histon,  174;  breaking  down 
of  polypeptides,  185,  192;  albumin 
synthesis  in  animal  organisms,  213,  224, 
355;  AspergiUus  niger,  216;  proteolytic 
ferments,  192,  506. 

Roos,  E.,  607. 

ROSENFELD,  GEORG,  fat,  110,  328;  phlorid- 
zin glucosuria  (behavior  of  the  liver), 
322;  estimation  of  fat,  325. 

ROSENFELD,  R.,  30,  587. 

ROSENSTEIN,  WlLHELM,  81,  105,   108. 

ROSTOSKI,  OTTO,  protein,  134;  gastric 
digestion,  165,  192;  edestin,  172;Bence- 
Jones  protein,  269;  precipitin,  668,  682. 

ROTHERA,  C.  H.,  249. 

ROTSCHY,  A.,  563. 

ROUSSILLE,  A.,  308. 

RUBNER,  MAX,  utilization  of  fat,  108;  for- 
mation of  fat,  309 ;  ratio  N  :C  in  muscles, 
324;  isodynamics,  333,  335;  metabolism, 
628,  646,  655. 

RUDOLPH,  398. 

RUDZINSKI,  ALBIN  v.  RUDNO,  65. 

RUDEL,  G.,  lime,  392;  uric  acid,  594. 

RUFF,  OTTO,  58. 

S. 

SACHS,  FRITZ,  288. 
SACHS,  HANS,  115,  688,  690. 
SACHS,  J.,  51,  309. 
SAHLI,  H.,  543,  545. 
SALASKIN,   S.,   erepsin,   167;  leucinimide, 

169:  plastein,  208;  urea,  228;  uric  acid,  238. 
SALKOWSKI,    E.,    pentoses,    21,    22,    323; 

glucuronic   acid,   33;  diastase,    71,   72; 

putrefaction  of  protein,  153,  169,  243, 

259;  xantho-proteic  reaction,  162,  163; 

urea,  228,  230,  234 ;  sulphuric  acid,  249 ; 

uric  acid,  290;  allantoine, 295 ;  adipocere, 

326;  antolysis,  478. 


702 


AUTHOR   INDEX. 


SALKOWSKI,  H.,  putrefaction  of  protein, 
153,  169,  243. 

SALOMON,  GEORG,  purine  bases,  297, 
298. 

SALOMON,  H.,  319,  434. 

SALOMON,  MAX,  90. 

SALOMON,  W.,  248. 

SALVIOLI,  GAETANO,  208. 

SAMUELY,  FRANZ,  melanin,  145;  decom- 
position of  protein,  172;  gliadin,  173; 
breaking-down  of  polypeptides,  185, 
228,  249,  452 ;  building  up  and  breaking 
down  of  protein,  212,  245,  579,  639,  666. 

SANDMEYER,  W.,  83,  95,  106. 

SATTA,  GIUSEPPE,  98. 

SATTLER,  HUBERT,  389. 

SAUER,  586. 

SAUSSURE,  THEODORE  DE,  51. 

SAWITSCH,  W.,  522. 

SAWJALOW,  208. 

SCHAFER,  E.  A.,  601. 

SCHATTERNIKOFF,  440. 

SCHEELE,  KARL  W.,  277. 
SCHEERMESSER,  W.,  177. 
SCHENK,  FELIX,  69. 
SCHENK,  FR.,  73. 
SCHERMETJEWSKI,  94. 
SCHIERBECK,  N.  P.,  437. 
SCHIFF,  MORITZ,  77,  79,  606. 
SCHIMPER,  A.  F.  W.,  122. 

SCHINDLER,  S.,  285. 

SCHITTENHELM,  ALFRED,  casein,  174,  656; 
elastin,  176;  amino  acids  in  urine,  264, 
266,  452;  cystinuria,  266,  267;  nucleic 
acid,  288,  289 ;  breaking  down  of  purine 
bases,  290,  292;  uricolytic  ferment,  293, 
294;  uric  acid,  10,  241;  coagulation  of 
blood,  536. 

SCHLATTER,  C.,  509. 
SCHLOESING,  T.,  196. 

SCHLOSSBERGER,  402. 

SCHLOSSMANN,  ARTUR,  403. 

SCHMIDT,  ADOLF,  582. 

SCHMIDT,  ALEXANDER,  hydrochloric  acid 
in  the  stomach,  203;  oxidizable  sub- 
stances, 409;  blood  gases,  413;  coagula- 
tion of  blood,  536,  537. 

SCHMIDT,  C.,  42,  378. 

SCHMIDT,  FR.,  454. 

SCHMIDT-MULHEIM,  546. 

SCHMIEDEBERG,  O.,  hippuric  acid,  9,  246, 
247;  glucuronic  acid,  31;  chondroitin 
sulphuric  acid,  49,  143;  muscarin,  114; 
proteins,  123,  135,  140;  urea,  230,  234; 
nucleic  acid,  284,  285;  oxydases,  440, 
445;  ferratin,  402. 

SCHNEIDER,  H.,  447. 

SCHNEIDEWIND,  195. 
SCHOFFER,  420. 

SCHONBEIN,  CHRISTIAN  F.,  441,  461. 

SCHONDORFF,  BERNHARD,  30,  47. 

SCHOLZ,  W.,  604. 

SCHOTTELIUS,  64. 
SCHOTTEN,  G.,  516. 
SCHREIBER,  290. 


SCHREUER,  MAX,  642. 
SCHROEDER,  W.  v.,  urea,  225,  231;  uric 
acid,  237,  241. 

SCHROETER,  F.,  289. 

SCHROETER,  H.  v.,  435,  436. 

SCHULTZE,  MAX,  411. 

SCHULTZEN,  O.,  diabetes,  93;  urea,  228; 
glycocoll  conjugates,  243,  458;  phos- 
phorus poisoning,  255. 

SCHULZ,  F.  N.,  galactosamine,  20;  proteins, 
122,  124,  127,  141;  colloids,  128,  161; 
cystine,  157;  acid  snails,  490;  hemo- 
globin, 558 ;  metabolism,  633. 

SCHULZE,  B.,  62,  309. 

SCHULZE,  E.,  cane  sugar,  38;  hemi-cellu- 
lose,  42;  lecithin,  115;  amino  acids,  155, 
173;  leucine,  148;  phenylalanine,  151, 
156;  amides,  150,  151;  ornithine,  155; 
nitrogen  cycle,  198;  allantoine,  296. 

SCHULZE,  ERNST,  116. 

SCHUMOW-SlMANOWSKAJA,  E.  O.,  498. 

SCHUNCK,  E.,  567. 

SCHUR,  HEINRICH,  287,  290. 

SCHWALBE,  E.,  536. 

SCHWARZ,  HUGO,  176. 

SCHWARZ,  LEO,  99,  319. 

SCHWENDENER,  53. 

SCZELKOW,  70. 

SEEGEN,  J.,  diastase,  59,  72. 

SEEMANN,  J.,  208,  574. 

SEGUIN,  70. 

SEMON,  492. 

SENATOR,  H.,  394,  631. 

SENFF,  A.,  81. 

SENTER,  GEORGES,  450. 

SETSCHENOW,  421,  423. 

SHAFFER,  PHILIPP,  450. 

SHEDD,  446. 

SIAU,  R.  L.,  73. 

SIEBER,  N.,  physiological  oxidation,  93, 
440,  634;  melanin,  145;  intestinal 
bacteria,  218;  significance  of  hydro- 
chloric acid  in  the  stomach,  219 ;  lactic 
acid,  378;  gastric  juice,  462;  hematin, 
563;urobilin,  572. 

SIEGFRIED,  M.,  jecorin,  49;  kyrin,  177; 
carbamic  acids',  233,  242,  425. 

SIGMUND,  W.,  103. 

SIMON,  OSKAR,  318. 

SJOQVIST,  JOHN,  120. 

SKITA,  ALADAR,  176. 

SKRAUP,  ZD.  H.,  177. 

SLOWTZOW,  B.,  Stoffwechsel  pentosans,  65; 
metabolism,  628. 

SMITH,  J.  LORRAIN,  431. 

SOBIERANSKI,  W.  V.,  582. 

SOCIN,  C.  A.,  diabetes,  95;  iron,  355. 

SOLDNER,  368. 
S0RENSEN,    S.    P.    L.,    152. 
SOLLMANN,  TORALD,  584. 

SOMMER,  A.,  328. 

SONDEN,  KLAS,  70,  623,  631,  647. 
SOXHLET,  F.,  309. 
SPALLANZANI,  203,  219,  461. 
SPECK,  C.,  70. 


AUTHOR   INDEX. 


703 


SPIESS,  A.,  486. 

SPIRO,  K.,  467,  547. 

SPIRO,  P.,  75. 

SPITZER,  W.,  uric  acid,  10,  289;  oxydases, 

446. 

STADELMANN,  E.,  152,  571. 
STADELMANN,  ERNST,  99. 
STADTHAGEN, 266. 
STAHELIN,  RUDOLF,  643. 
STAHEL,  H.,  543. 
STARLING,  E.  H.,  secretin,  168,  527;  inner- 

vation  of  the  intestine,  507;  lymph,  574. 
STASS,  J.  S.,  30. 
STEIGER,  E.,  42,  155. 
STEIN,  GUSTAV,  117. 
STEINFELD,  WLADIMIR,  392. 
STERN,  HANS,  570. 
STERN,  L.,  449. 
STERNBERG,  WILHELM,  494. 
STEUDEL,  H.,  glucosamine,  35,  143;uracil, 

281 ;  thy  mine,  281 ;  cytosine,  281 ;  nucleic 

acid,  285;  behavior  of  pyrimidine  bases 

in  the  organism,  298. 
STOHMANN,  F.,  62,  333. 
STOKLASA,  JULIUS,  73. 
STONE,  W.  E.,  64. 
STRASSBURG,  G.,  435. 
STRAUB,  WALTER,  81. 
STRAUSS,  H.,  29. 
STRECKER,  ADOLF,  lecithine,  112;  creatine, 

235 ;  uric  acid,259,302 ;  bileacids,514,515. 
STROHMER,  F.,  309. 
SUTER,  169. 
SUZUKI,     UMETARO,    cystine,     159,    266, 

267,  291. 
SWIRSKI,  G.,  389. 

T. 

TAIT,  615. 

TAKAKI,  T.,  687. 

TAKAMINE,  J.,  601. 

TALLQUIST,  F.  W.,  344. 

TAMMANN,  G.,  403. 

TANGL,  FRANZ,  73,  655. 

TAPPEINER,  H.,  62,  63. 

TARCHANOFF,  JOHANNES  FURST,  570. 

TARTA.KOWSKY,  389. 

TAUBER,  253. 

TAYLOR,  328. 

TCHISTOWITSCH,  668. 

TEBB,  M.  C.,  60. 

TEICHMANN,  M.,  107. 

TENGSTROM,  STEPHAN,  515. 

TERUUCHI,  YUTAKA,  protein,  173;  decom- 
position of  polypeptides,  185,  192,  228. 

TESTI,  39. 

THANHOFFER,  L.  v.,  106. 

THENARD,  grape-sugar,  90;  H2O2,  450. 

THIEL,  ANDREAS,  82. 

THIELE,  O.,  270. 

THIERFELDER,  H.,  cerebron,  20,  613; 
glucuronic  acid,  31,  32,  34;  life  without 
bacteria,  64,  255*  fermentation  of 
sugars,  471. 

THIROLOIX,  J.,  83. 


THOMPSON,     W.     H.,     136;    urea,     228; 

hypophysis,   610. 
THUDICHUM,  J.  LUDWIG  W.,  614. 
TICHOMIROFF,  A.,  287. 
TIGERSTEDT,    ROBERT,    metabolism,    70, 

623,  631,  632,  647. 
TOBLER,  LUDWIG,  £07. 
TOLLENS,  B.,  13,  289. 
TOMPSON,  467. 
TORUP,  422. 
TRAUBE,  J.,  532. 
TRAUBE,    MORITZ,    oxidation,    444,    445; 

H2O2,  449. 
TREBOUX,  57. 
TROSCHEL,  490. 
TSCHERWINSKY,  N.,  310. 
TSUJI,  66. 

U. 

UDRANSKY,  L.  v.,  266. 
UHLENHUT,  670. 
UNDERBILL,  FRANK  P.,  587 

V. 

VALLISNERI,  39. 

VASSALE,  606. 

VAUDIN,  L.;  373. 

VAUQUELIN,  277. 

VERNON,  H.  M.,  erepsin,  168;  heat  rigor, 

617. 

VERWORN,  MAX,  459. 
VIELLE,  333. 
VIRCHOW,  RUDOLF,  569. 
VITEK,  EUGEN,  73. 
VOLTZ,  W.,  215. 
VOGEL,  J.,  196. 
VOGEL,  J,  23,  59,  71. 
VOISIN,  S.,  273. 
VOIT,  CARL,  glycogen,  66 ;  muscular  power, 

69,    70;    consumption    of   material    in 

diabetes,  93 ;  absorption  of  fat,  108,  309 ; 

asparagin,   215;  metabolism,  343,   352, 

623,    631,    632,    635,    636;    lime,    375; 

formation  of  fat,  324. 
VOIT,  ERWIN,  glycogen,  66;  estimation  of 

fat,    325;    adipocere,    326;    lime,    375; 

metabolism,  633. 
VOIT,  FRITZ,  sugar,  39,  61,  323;  galactose 

in  diabetes,  95. 
VOLHARD,  104. 

VOLHARD,  J.,  235. 

VOORNVELD,  H.  J.  A.  VAN,  436. 
Vossius,  ADOLF,  570. 

VULPIAN,  601. 

W. 

WAHLGREN,  V.,  514. 
WALDVOGEL,  290. 

WALTER,  FRIEDRICH,  100,  230,  241. 
WALTER,  G.,  388. 
WALTFER,  A.,  499,  525. 
WARBURG,  OTTO,  475,  494. 
WARREN,  J.  W.,  75. 
WARTENBURG,  H.,  103. 
WASSERMANN,  680,  687. 


704 


AUTHOR   INDEX. 


WEBER,  S.,  631. 

WECHSBERG,  F.,  690. 

WEIGERT,  FRITZ,  155. 

WEINLAND,  ERNST,  invertin,  61;  lactose, 

62,  323;  antiferments,  477. 
WEINMANN,  R.,  494. 
WEINTRAUD,  W.,  94,  98,  299. 
WEISKE,  A.,  cellulose,  62,  64;  asparagin, 

216;  formation  of  fat,  309. 
WEISS,  S.,  68. 
WELLS,  H.  G.,  176. 
WENZEL,  FRIEDRICH,  30. 
WERNER,  A.,  15. 
WERTHER,  MORITZ,  75. 
WHEELER,  HENRY  L.,  282. 
WHITE,  BENJAMIN,  296. 
WIECHOWSKI,  WILHELM,  242,  245,  246. 

WlEDERSHEIM,  R.,   106. 

WIENER,  HUGO,  10,  238,  290,  294,  299. 

WILD,  E.,  309. 

WILD,  W.,  449. 

WILL,  A.,  105. 

WILFARTH,  H.,  196. 

WILLIAMS,  FRANCIS,  388. 

WlLLSTADTER,  113. 

WINDAUS,  A.,  cholesterol,  117;  histidine, 

154;  imidazole,  286. 
WINDISCH,  KARL,  326. 
WINOGRADSKY,  S.,  193,  194,  195. 
WINTER,  C.,  470. 
WINTERNITZ,  R.,  438. 
WINTERSTEIN,    E.,    tunicin,    42;    protein 

cleavage  products,  154,  173;  ornithine, 

155;  arginine,  156. 
WISLICENUS,  515. 
WISLICENUS,  J.,  69,  412. 

WlTTICH,    V.,    71. 

WITZEL,  O.,  83. 

WOHLER,  F.,  hippuric  acid,  5,   50,  242, 

243,  479;  uric  acid,  236,  277;  allantoine, 

295;  emulsin,  461. 


WORNER,  EMIL,  613. 

WOHL,  A.,  58. 

WOHLGEMUTH,  J.,  pentoses  in  organs,  22; 

cystine,  249;  behavior  of  stereoisomers 

in  the  organism,  452. 
WOLFF,  E.,  62. 
WOLFF,  GUSTAV,  674. 
WOLFFBERG,  SlEGFRIED,  429. 
WOLKOW,  M.,  270,  271. 

WOLLASTON,   157. 

WOLTERING,  W.  F.  C.,  389,  401. 
WORM-MULLER,  95. 
WORTMANN,  J.,  63. 
WROBLEWSKI,  654. 
WURTZ,  A.,  113. 

Y. 

YOUNG,  WILLIAM  J.,  47. 


Z. 

ZALESKI,  J.,  urea,  231 ;  hematin,  396,  563, 

567;  urobilin,  572. 
ZANETTI,  C.  N.,  161. 
ZAWARKIN,  106. 
ZERNER,  THEODOR  J.,  594. 
ZEYNECK,  RICHARD  v.,  562. 
ZIEGLER,  E.,  458. 

ZlLLESEN,  75. 
ZlNOFFSKY,  O.,   125,  384. 

ZINNSER,  ADOLF,  104. 

ZSCHOKKE,  664. 

ZSIGMONDY,  R.,  128,  161,  361. 

ZUNTZ,  N.,  cellulose,  62;  muscular  power, 
70 ;  phloridzin  diabetes,  82 ;  gas  exchange, 
420,  428;  blood  gases,  422,  424,  426; 
high  altitudes,  436,  643 ;  fasting  experi- 
ments, 394,  631. 

ZWERGER,  R.,  177. 


SUBJECT    INDEX. 


A. 

Abrin,  681. 

Abrus  prsecatorius,  681. 

Absorption  of  carbohydrates,  65;  of  fat, 
107;  of  lime,  373;  of  iron,  388;  of 
gases,  413;  in  the  stomach,  508;  in 
the  intestine,  532. 

Absorption  coefficients  (of  the  blood  for 
O,  N  and  CO2),  415;  (of  serum  for 
CO2),  421. 

Absorption  spectrum  of  oxyhemoglobin 
and  its  derivatives,  560  et  seq. 

Acceptors.  See  Side-chain  theory. 

Acetal,  303. 

Acetanilid,  458. 

Acetic  acid,  formation  from  carbohy- 
drates in  the  intestine,  63;  in  the 
tissues,  74;  f rom  glycocoll,  170;  from 
bacterial  action,  465;  as  product  of 
alcoholic  fermentation,  483. 

Acetic  acid  bacteria,  448. 

Aceto-acetic  acid,  97. 

Acetone,  a  cause  of  glucosuria,  81 ;  elimi- 
nation, 97;  from  leucine,  454;  in 
preserved  yeasts,  464. 

Acetonuria,  97,  98. 

Acetone  bodies,  source  of,  97,  98,  99,  454. 

p-Acetyl-amido-phenol,  458. 

Achras  sapota,  39. 

Acid  albumins,  121,  203. 

Acidity  of  blood,  99;  of  urine,  591. 

Acidosis,  99,  242. 

Acid,  chemical  and  physico-chemical  con- 
ceptions, 591,  592;  secretion  of  by 
snails,  490. 

Acid  fuchsin,  583. 

Acipenser  stellatus,  137. 

Acipenserin,  137. 

Acromegaly,  609. 

Activation  of  muscle  ferment,  88. 

Activity,  optical,  15. 
hypertrophic,  350. 

Acrose,  15. 

Adaptability,  of  salivary  secretion,  489; 
of  gastric  secretion,  501. 

Adaptation,  chromatic,  160. 

Addison's  disease,  603. 

Adelomorphous  cells,  496. 

Adenine,  280,  297. 

Adhesion,  importance  in  blood  coagula- 
tion, 545. 

Adipocere,  326. 

Adiposity,  111. 

Adonis  vernalis,  29. 


Adonitol,  29. 

Adrenalin,  601  et  seq. 

Aerobic  bacteria,  412. 

Agar-agar,  42. 

Age,  influence  on  metabolism,  629. 

Agglutination,  680. 

Alanine,  148,  304;  action  on  muscles,  358; 
taste,  490. 

Alanine  anhydride,  228  et  seq.,  180,  186. 

Alanine  carbonate  of  calcium,  233. 

Alanyl-alanine,  179,  180,  185,  228,  474. 

Alanyl-glycine,  179,  180,  186,  474. 

Alanyl-glycine  anhydride,  186. 

Alanyl-glycyl-glycine,  474. 

Alanyl-leucine,  179,  184,  474. 

Alanyl-leucyl-glycine,  474. 

Albumin.    See  also  Protein. 

Albumin,  absorption  of,  208;  denatur- 
ization  of,  120,  121;  from  carbohy- 
drates, 304;  calorific  value  of,  333- 
336;  with  regard  to  isodynamics, 
336;  as  source  of  muscular  energy, 
337;  as  source  of  energy  for  gland- 
work,  341;  influence  upon  general 
metabolism,  347,  348;  circulating 
and  organized,  673  et  seq.;  content 
of  foodstuffs,  648. 

Albumin  bodies,  substituted,  127;  clas- 
sification of,  129  et  seq.;  size  of 
molecules,  127,  128;  simple,  131; 
compound,  131;  true,  131. 

Albumin  crystals,  121,  122,  125;  fatten- 
ing, 618,  642. 

Albumin  decomposition,  in  Coma  dia- 
beticum,  100;  by  ferments,  166  et 
seq.;  in  phosphorus  poisoning,  328; 
computation  of  extent  of,  622,  627. 

Albumin  derivatives  in  urine,  270,  271 ; 
requirement,  221  et  seq.,  342,  343, 
639  et  seq.;  with  carbohydrates  or 
fats,  342  et  seq.;  with  mixed  diet, 
342,  343. 

Albumin  metabolism,  621,  637. 

Albumin  synthesis,  in  the  intestine,  208; 
in  animal  body,  213;  by  fungi,  216; 
in  plants,  193,  201  et  seq. 

Albumin  putrefaction,  169,  170,  217,  218, 
253. 

Albuminous  glands,  485. 

Albumins,  131,  172.  See  also  the  vari- 
ous albumins. 

Albuminates,  422. 

Abuminoids,  131,  176. 

Albumoids,  138. 


705 


706 


SUBJECT  INDEX. 


Albuminous  bodies.     See  Proteins. 

Albuminuria,  268. 

Albumoses,  164. 

Alcapton,  270. 

Alcaptonuria,  270. 

Alcohol,  formation  from  carbohydrates  in 
the  intestines,  63;  influence  upon 
gastric  secretion,  500;  upon  pan- 
creatic secretion,  527. 

Alcoholic  fermentation,  27,  461,  469,  482, 
483. 

Alcoholic  poisoning,  327. 

Alcohols,  in  the  tissues,  74;  of  sugars,  27. 

Aldoses,  19. 

Aleuron  grains,  122. 

Algae,  fresh  water,  52 ;  salt  water,  52. 

Alimentary  glucosuria,  30,  76. 

Aliphatic  amino  acids,  147. 

Alizarin,  21. 

Alkali  albuminates,  121. 

Alkali  salts,  part  played  in  CO2  combina- 
tion, 421-424 ;  migration  in  the  blood, 
426. 

Alkalinity,  influence  upon  oxidation,  440. 

Alkalinity  of  blood,  421. 

Alkaloids,  201,  305. 

Allantoine,  277,  295. 

Allantoic  fluid,  277. 

Alloxan,  277,  279. 

Alloxuric  bases,  297. 

Alloxyproteic  acid,  270. 

Almonds,  133,  308,  381. 

Alveolar  air,  composition,  428,  429;  gas 
tension,  414;  carbon  dioxide  ten- 
sion, 429. 

Alytes  obstetricans,  353. 

Amanita  muscaria,  114. 

Amanitine,  114. 

Amaryllidacese,  45. 

Amboceptor,  689. 

Amides,  150. 

p-Amido  phenol,  252,  458. 

Amino  acids,  129,  146  et  seq.;  cleavage 
of  inactive  acids  into  optically  active 
components,  181 ;  part  assumed  in 
CO2  union,  233,  425;  transformation 
into  sugars,  317  et  seq. 

Amino  acid  chloride,  180. 

Amino-acetic  acid.     See  Glycocoll. 

Amino-benzoic  acids,  234. 

Amino-butyric  acid,  148. 

Amino-butyryl-amino-butyric  acid  A  and 
B,  474. 

Amino-butyryl-glycine,  474. 

Amino-caproic  acid.     See  Leucine. 

Amino-ethyl  sulphonic  acid.     See  Taurine. 

Amino-glutaric  acid.     See  Glutamic  acid. 

Amino-jS-hydroxypropionic  acid.  -  See 
Serine. 

Amino-hydrpxy-valeric  acid,  152. 

Amino-/3-imidazol-propionic  acid.  See 
Histidine. 

Amino-isobutyl-acetic  acid.     See  Leucine. 

Amino-iso valeric  acid,  148,  454,  494. 

Amino-isovaleryl-glycine,  474. 


Amino-methyl-ethyl-propionic  acid.      See 

Isoleucine. 

Amino-,  6-,  oxypurine,  2-.     See  Guanine. 
Amino-,  2-,  oxypyrimidine,  6-.      See  Cy- 

tosine. 

Amino  propionic  acid.     See  Alanine. 
Amino   pyrotartaric   acid.     See  Glutamic 

acid. 

Amino  purine,  6-.     See  Adenine. 
Amino  salicylic  acids,  0-  and  p-,  234. 
Amino-succinic  acid.     See  Aspartic  acid. 
Amino-thiolactic  acid.     See  Cystine. 
Amino-valeric  acids,  148,  170,  454,  494. 
Amino  sugar.     See  Glucosamine. 
Ammonia,  99,  146,  193,  231,  237. 
Ammonium  carbonate,  229,  231. 

chloride,  action  upon  blood  corpuscles, 
550. 

cyanate,  231. 

formate,  231. 

lactate,  238. 

oxalate,  217. 
Amniotic  fluid,  236. 
Amoeba,  47,  459. 
Amorphophallus  Konjako,  29. 
Amphibia,  cutaneous  respiration  of,  432. 
Amygdalin,  20,  480. 
Amyl  alcohol,  148,  470. 
Amylan,  44. 

Amyl  nitrite,  cause  of  glucosuria,  81. 
Amylodextrin,  43. 
Amyloid,  49,  138. 
Amylolytic  ferment,  59,  60. 
Amylum,  42. 
Anaemia,  386. 
Anaerobic  bacteria,  412. 
Anchylostomum  caninum,  547. 
Animal  foods,  value  of,  650  et  seq. 
Anions,  358  et  seq. 
Annelida,  360. 
Anodons,  567. 
Anthrax  bacillus,  153. 
Anti-catalyzers,  468. 
Anti-ferments,  476. 
Anti-rennin,  476. 
Antimony  poisoning,  327. 
Antitoxins,  476,  684  et  seq. 
Antodon  rosacea,  672. 
Antoxyproteic  acid,  270. 
Apiin,  36. 
Apiose,  36. 

Appetite,  effect  on  gastric  secretion,  498. 
Araban,  65. 

Arabinose,  23,  24,  44,  452. 
Arabite,  28. 
Arabonic  acid,  28. 
Arachidic  acid,  102. 
Arachnolysin,  690. 
Arbacia  pustulosa,  140. 
Arginase,  228. 
Arginine,  154,  226,  259. 
Arginyl-arginine,  179. 
Argon,  414. 

Aromatic  amino  acids,  151. 
Arsenic,  81,  406. 


SUBJECT  INDEX. 


707 


Arsenious  acid,  446. 
Arsenic  acid,  446. 
Arsenic  poisoning,  327. 
Arseniureted  hydrogen,  570. 
Arsine.     See  Arseniureted  hydrogen. 
Ash  of  milk,  395. 

of  sucklings,  367,  368. 
of  foods,  369. 

Asparagine,  150,  202,  215,  358. 
Asparagus,  asparagine,  150;  iron,  381. 
Asparagyl-dialanine,  182. 
Asparagyl-monoglycine,  182. 
Aspartic  acid,  149,  304,  470. 
Aspergillus  oryzae,  37. 
Aspergillus  niger,  217. 
Assimilation  of  fats,  105;  of  iron,  392;  of 

lime,  466  et  seq.;    of  sugar  (direct), 

55;  of  carbonic  acid,  51. 
Assimilation  limit  for  carbohydrates,  76, 

88. 

Assimilation  product  of  CO2,  54. 
Ass's  milk,  404,  655. 
Asymmetric  carbon,  16. 
Asymmetric    cleavage    of    polypeptides, 

184,    185;    of    racemic   amino    acids, 

228,  443. 

Asymmetric  synthesis,  54  et  seq. 
Atractylis,  29. 
Atriplex,  362. 
Autolysis,  265,  266,  479. 

B. 

Bacillus  Dellbriicki  (Leichmann),  465. 

Bacillus  putrificus,  218. 

Bacteria,  as  reagent  for  oxygen,  53. 

aerobic  and  anaerobic,  412. 
Bacterial  action  upon  nucleins,  289. 
Bacterial  poisons,  680  et  seq. 
Bacterium  coli,  153,  218. 
Bacterium  denitrificans,  195. 
Bacterium  lactis,  27. 
Bacterium  lactis  aerogenes,  218. 
Bacterium  radicicola,  197. 
Bacterium  thermo,  63. 
Bacterium  xylinum,  448. 
Barley,  gliadin,  133;  iron,  380. 
Bathing  sponge.     See  Sponge. 
Balloon  ascension,  436. 
Beans,  iron  content  of,  380. 
Beaker  cells.     See  Goblet  cells. 
Beef,  366,  370,  377,  381 ;  ash  of,  369,  370, 

371 ;  extract  of,  500. 
Beef-blood,  366. 
Beer-acetic-acid-bacteria,  465. 
Beeswax,  102. 
Beggiatoa,  194. 
Bence-Jones  protein,  269. 
Benzaldehyde,  20. 
Benzamide,  244. 
Benzene,  93,  252. 
Benzidine,  446. 
Benzoic  acid,  5,  229,  440,  446. 
Benzyl  alcohol,  440,  446. 
Bertholletia,  123. 
Betain,  114. 


Betulase,  20. 

Bile,  513;  influence  on  digestion  of  fats, 
104,  107,  519 ;  antiseptic  action,  220, 
519;  composition,  516,  517;  influ- 
ence on  peristalsis,  519;  influence  on 
lipase,  520. 

Bile-acids,  514  et  seq. 

Bile  concretions,  572. 

Bile  pigments,  513,  569  et  seq. 

Bilianic  acid,  515. 

Biliary  fistula,  520. 

Bilirubin,  569. 

Biliverdin,  569. 

Biological  reaction,  668  et  seq. 

Birch,  cane-sugar  in,  38. 

Birds,  pancreas  extirpation,  583;  dia- 
betic puncture,  77;  oil  bags  of,  102, 
595. 

Bismuth,  392. 

Biuret  base  (Curtius'),  474. 

Biuret  reaction,  163. 

Bladder-stones,  297. 

Blood,  sugar  in,  29,  30;  jecorin,  49;  glu- 
colytic  ferment,  73;  fat,  109;  urea,, 
225;  creatine,  235;  impoverished, 
386;  gases  of,  413  et  seq.;  defibri- 
nated  and  clotted,  536;  analysis  of,. 
553  et  seq. ;  amount  of,  556. 

Blood  clot,  535. 

Blood  coagulation,  535  et  seq. 

Blood-corpuscles,  possible  presence  of  his- 
ton,  135;  presence  of  nucleo-proteid, 
140,  141;  formation  of,  401;  union 
with  CO2,  423  et  seq. ;  behavior  in  high 
altitudes,  436;  red  and  white,  535; 
red,  549,  550,  556;  white,  551,  556. 

Blood  extravasations,  569. 

Blood  gases,  408  et  seq. 

Blood,  laked,  550. 

Blood-leech.     See  Leech. 

Blood-pigments,  124. 

Blood  pressure,  effect  on  secretion  of 
urine,  584;  influenced  by  adrenalin, 
600  et  seq. 

Blood  plates,  535,  552. 

Blood-vessels,  glycogen  content  of,  47. 

Blood  relationship,  670  et  seq. 

Boar,  spermatozoa  from,  285. 

Bog  iron  ore  deposits,  193. 

Bones,  mucoid  in,  143;  in  rachitis,  371; 
in  osteomalacia,  377;  marrow  of, 
395,  573;  influence  of  castration,  600; 
influence  of  thyroid  gland,  605 ;  tissue 
of,  611. 

Bottcher's  sugar  test,  25. 

Bowman-Muller's  capsule,  581. 

Boyle's  law,  413. 

Brain,  glycogen  in,  47;  phosphorus,  403; 
creatine,  236. 

Brain  substance,  affinity  to  tetanus  toxin, 
687. 

Bread,  iron  and  lime  content,  370,  377, 
380;  influence  on  gastric  secretion, 
502,  503;  upon  pancreatic  secretion, 
531. 


708 


SUBJECT  INDEX. 


Brom-capronyl-glycine-chloride,  181. 
Brom-iso-capronyl-chloride,  -,  181. 
Bromine  water,  reagent  for  tryptophane, 

15.2. 

Brom-phenyl-mercapturic  acid,  158. 
Brom-propionyl  chloride,  180. 
Brunner's  glands,  512. 
Buchu  seeds,  114. 
Bull,  spermatozoa  of,  285;  blood  of,  554, 

555. 

Bursse  mucosae,  578. 
Butter-fat,  333. 
Butyric  acid,  102;  from  carbohydrates  in 

the  intestine,  63,  64. 
Butyric  acid  fermentation,  27,  469. 
Butylchloral  hydrate,  34. 

C. 

Cabbage,  iron  and  calcium  content,  370, 
381. 

Cachexia  strumipriva,  605. 

Cadaverine,  154,  170,  259. 

Caffeine,  200,  280. 

Caecum,  elimination  of  iron,  etc.,  389 
et  seq. 

Calcium,  80,  370  et  seq. 

Calcium  chloride,  antidote  for  NaCl 
glucosuria,  80;  effect  on  blood  coagu- 
lation, 538. 

Calcium  salts,  in  foods,  370-372;  in 
rachitis,  371 ;  elimination  of,  392 ; 
influence  on  blood  coagulation,  538. 

Calories,  definition  of,  332,  333. 

Calorific  requirement,  645-647. 

Calorific  value  of  certain  foods,  333,  334, 
336,  661,  662. 

Camphene  glycol,  34. 

Camphor,  32,  34. 

Cane-sugar,  13,  29,  37,  190;  inversion  in 
the  intestine,  61;  behavior  when 
introduced  directly  into  the  blood, 
61;  effect  upon  the  muscles,  323, 
358;  calorific  value,  333,  336. 

Caoutchouc,  339,  312. 

Capric  acid,  102. 

Caproic  acid,  102. 

Caprylic  acid,  102. 

Caramel,  25. 

Carbamate  of  ammonium,  230. 

Carbamic  acids,  232,  425. 

Carbaminobenzoic  acid,  234. 

Carbamic  acid  amide,  232. 

Carbaminoisethionic  acid,  234. 

Carbamo-acetate  of  calcium,  233. 

Carbamo-propionate  of  calcium,  233. 

Carbohemoglobin,  562. 

Carbohydrates,  13-100;  transformation 
into  fat  in  plants,  103;  as  source  of 
heat,  342;  influence  upon  the  protein 
requirement,  342  et  seq.;  influence 
upon  fattening,  345  et  seq.;  influence 
on  respiratory  quotient,  346;  influ- 
ence on  general  metabolism,  347 


Carbohydrate  group  of  the  proteins,  141, 
159,  317. 

Carbohydrate  metabolism,  623,  627,  632. 

Carbon  atom,  asymmetric,  16. 

Carbon  atom  added  to  sugars,  18. 

Carbon  chains  of  amino  acid  radicles,  318, 
324. 

Carbon,  relation  to  nitrogen  in  urine,  321. 

Carbon  dioxide  (Carbonic  acid),  assimi- 
lation of,  15,  51 ;  formation  in  the 
intestines  from  carbohydrates,  63; 
gas  exchange,  420;  gas  pressure  in 
blood,  420  et  seq.;  in  lymph,  435; 
absorption  in  serum,  421 ;  influence 
on  composition  of  blood  components, 
426;  influence  on  absorption  of 
oxygen,  427. 

Carbon  monoxide  glucosuria,  81. 

Carbon-monoxide  hemoglobin,  424,  561. 

Carcinoma,  675. 

Carica  papaya,  168. 

Caries  of  the  teeth,  493. 

Carmine,  elimination  by  the  kidneys,  583. 

Carnine,  660. 

Carrots,  iron  content,  381. 

Carp,  eggs  of  (hematogen),  388;  sperma 
of,  136;  spermatozoa,  285. 

Cartilage,  chondroitin-sulphuric  acid,  49; 
mucoid,  143;  tissue,  611. 

Casein,  134,  206;  from  cow's  milk  174; 
from  goat's  milk,  174;  calorific 
value,  333;  glutamic  acid  content, 
653. 

Castor-oil  seeds,  103,  122. 

Castration  600;  influence  on  osteoma- 
lacia,  378. 

Catalases,  449. 

Catalyzers,  467. 

Catalysis,  467. 

Catechol,  254. 

Catechoyl  sulphuric  acid,  251,  254. 

Cations,  358  et  seq. 

Cats,  rate  of  growth,  371,  404;  blood, 
554,  555;  hemoglobin,  125,  559. 

Cell  metabolism,  311  et  seq.,  349  et  seq. 

Cell  nucleus,  672. 

Cellobiose,  37. 

Cellose,  38. 

Cells,  chief  or  principal,  495;  composition 
of,  329,  330. 

Cell-substance,  resistance  towards  fer- 
ments, 191. 

Cellulase,  482. 

Cellulose,  13,  31,  38,  41,  42,  62,  63,  482. 

Celtis  reticulosa  Miq.,  201. 

Cement,  of  tooth,  493. 

Cephalopoda,  402,  447. 

Cerealose,  39. 

Cerebrin,  613. 

Cerebron,  20,  31,  613. 

Cerebronic  acid,  20,  31,  613. 

Cerebro-spinal  fluid,  615. 

Cerosin,  44. 

Cetin,  102. 

Cetyl  alcohol,  102. 


SUBJECT  INDEX. 


709 


Chemical  energy,  52. 

Chenopodium,  362. 

Cherries,  iron  and  lime  in,  64. 

Cherry-gum,  24,  42. 

Chief  cells,  495. 

Chilodon,  46. 

Chitin,  162. 

Chiton,  402. 

Chloracetyl  chloride,  180. 

Chloracetyl-glycine,  180. 

Chloral,  81. 

Chloral  hydrate,  32,  34. 

Chloride  of  sodium,  361  et  seq. 

Chlorine,  435. 

Chlorine  water  reagent  for  tryptophane, 

152. 

Chloroform,  81,  327. 
Chlorophyll,  52,  396,  397,  565,  566. 
Chlorosis,  386  et  seq. 
Cholalic  acid,  229,  248,  514. 
Choleic  acid,  514. 
Cholera  bacteria,  679. 
Cholesterol,  116,  117,  514,  613. 
Cholic  acid.     See  Cholalic  acid. 
Choline,  112,  113,  615. 
Chondro-albumoid,  138. 
Chondroitin,  143. 

Chondroitin-sulphuric  acid,  49,  138. 
Chondromucoid,  143. 
Chorda  dorsalis,  138. 
Chorda  tympani,  485. 
Chromogens  in  suprarenal  capsule,  601. 
Chromophyll,  52,  565. 
Chyle,  107. 
Chyme,  506. 
Cilianic  acid,  515. 
Circulation,  of  foetus,  410. 
Cladophora,  357. 

Classification  of  proteins,  129  et  seq. 
Cleavage.     See  Hydrolysis. 
Cleavage  processes,  as  source  of   energy, 

74,  411. 

Cleavage  products  of  proteins,  146-170. 
Clostridium  Pasteurianum,  195. 
Clupeine,  136,  175. 
Coagulation    of    proteins,    120,    121;    of 

fibrinogin,  133;  of  blood,  535-544.     , 
Cocoa  beans,  iron  and  lime  content,  370, 

380. 

Cobitis  fossilis,  438, 
Cobra  poison,  115,  117,  547. 
Cocks,  castration  of,  600. 
Coefficient  of  absorption.    See  Absorption. 
Colloid,  608. 
Colloids,  120,  360. 
Colorability  of  tissues,  678. 
Coloring  matters.     See  various  pigments. 
Colostrum,  655. 
Coma  diabeticum,  99. 
Combustion,  in  the  organism,  409  et  seq., 

439-460. 
Comparative    chemical    investigation,    2, 

663  et  seq. 
Complement,  689. 
Composition  of  body  cells,  329,  330. 


Concept,  of  quantity,  11;  of  food,  349-354. 

Conchiolin,  138. 

Configuration,  of  hexoses,  17,  18;  influ- 
ence on  fermentation,  470  et  seq.; 
on  taste,  494. 

Conglutin,  173;  calorific  value,  333;  glu- 
tamic  acid  content,  653. 

Connective  tissue,  47,  611. 

Coniferee,  199. 

Constitution  of  proteins,  171,  178. 

Consumption  of  foodstuffs,  647. 

Contact  action,  467. 

Control  experiment,  8. 

Coprosterol,  117. 

Coregonus  oxyrhynchus,  137. 

Cornea,  143. 

Copper  albuminate,  128. 

Copper  in  hemocyanin,  402. 

Copper  salts,  357. 

Corn,  zein  from,  133. 

Corpora  amylacea,  138. 

Cotton-seed,  albumin  crystals,  123. 

Cow's  blood,  554,  555;  hemoglobin  from, 
559. 

Cow's  milk,  366-380,  404. 

Crab's  muscle,  546,  576. 

Creatine,  235. 

Creatonine,  235. 

Cresol,  p-,  170,  252,  255. 

Cresol-sulphuric  acid,  p-,  254. 

Cretins,  604. 

Crustaceans,  402. 

Crystalline  lens.     See  Lens. 

Crystallization  of  proteins,  122. 

Cucurbita,  103. 

Cupric  oxide,  as  carrier  of  oxygen,  445. 

Curari,  30,  81. 

Cyanamide,  156,  235. 

Cyanhydrine,  18. 

Cyanic  acid,  230,  278. 

Cyanophyceae,  125. 

Cyanuric  acid,  238. 

Cycadese,  198. 

Cyclopterine,  137,  175. 

Cyclopterus  lumpus,  137. 

Cycle,  of  carbon,  51,  200;  of  hydrogen,  53, 
200;  of  oxygen,  51;  of  nitrogen,  194; 
of  sulphur,  200. 

Cyprinines,  137,  175. 

Cyprinus  carpio,  137. 

Cysteine,  158. 

Cysteinic  acid,  158. 

Cystine,  157,  239,  245,  248,  266,  304. 

Cystine  diathesis,  267. 

Cystinuria,  260,  266. 

Cysts,  142. 

Cytosine,  282,  298. 

D. 

Dahlias,  inulin  content,  29. 
Dalton's  law,  413. 

Dandelion  greens,  iron  content  of,  381. 
Dates,  iron  and  lime  content,  370,  380. 
Death  rigor,  133,  617,  618. 


710 


SUBJECT  INDEX. 


Decomposition  of  polypeptids  in  the 
organism,  185;  of  proteins  by  tryp- 
sin,  188,  189,  208;  by  pepsins,  203; 
of  the  purine  bases,  292;  of  the 
pyrimidine  bases,  298 ;  of  albumin,  193, 
260 ;  of  albumin  in  intestines,  209,  212 ; 
in  germinating  seeds,  201,  202. 

Degeneration,  fatty,  327. 

Dehydrocholic  acid,  515. 

Deilephilia  elpenor  and  euphorbias,  447. 

Delomorphous  or  parietal  cells,  496. 

Denaturizing  of  proteins,  120. 

Denitrification,  194. 

Denitrifying  bacteria,  198. 

Dentin,  493. 

Desamidation,  232,  304. 

Development,  rate  of  (relation  to  com- 
position of  milk),  367,  370,  371,  404, 
655. 

Dextrins,  43,  44,  46,  59,  61. 

Dextrine-like  substances  in  urine,  48,  96. 

Dextrose,  29.     See  d-Glucose. 

Diabetes  mellitus,  87  et  seq.,  332,  341. 

Diabetic  puncture,  77. 

Dialanyl-cystine,  179,  185,  474. 

Dialuric  acid,  240. 

Dialysis,  120. 

Diamino  acids,  129. 

Diamino-capronic  acid  a  and  e,  154. 

Diamino-/?-dithiodilactyl  acid,  a,  158. 

Diamino-mono  carboxylic  acids,  154. 

Diamino  hydroxy-mono-carboxylic  acids, 
154. 

Diamino-trihydroxy-dodecanoic  acid,  154, 
318. 

Diamino-valeric  acids,  156. 

Diastase,  39,  40,  476;  of  saliva,  59,  490; 
of  pancreatic  juice,  60,  521 ;  of  plants, 
477;  of  intestinal  juice,  512. 

Dibenzoyl-ornithine,  155. 

Dicalcium  phosphate,  122. 

Diet  for  various  classes  of  people,  644  et  seq. 

Digestibility,  507. 

Digestion,  59-62,  104-110,  203-220,  579, 
638. 

Digitalin,  21. 

Digitonin,  21,  31. 

Digitoxin,  21. 

Diglycyl-glycine,  180-228. 

Dihydrocholesterol,  117. 

Diketopiperazine,  180. 

Dileucyl-cystine,  179,  185,  474. 

Dileucyl-glycyl-glycine,  179,  217,  475. 

Dimethyl-amino-benzajdehyde,  p-,  152. 

Dimethyl-cyclo-octadi-ine  (15),  306. 

Dimethyl-dihydroxy-purines,  280. 

Dimethyl-xanthine,  297. 

Disodium  urate,  299. 

Dionsea  muscipala,  168. 

Dihydroxybenzenes,  252. 

Dihydroxyphenylacetic  acid,  257,  271. 

Dioses,  19. 

Dioxypurine,  280. 

Dioxypyrimidine,  281. 

Dipalmitylolein,  102. 


Diphtheria  toxin,  680. 

Disaccharides,  36-40. 

Disinfection  by  HC1  of  stomach,  218,  219. 

Dissociation,  of  hemoglobin,  416;  of  bicar- 
bonate 422. 

Distearylpalmitin,  102. 

Dog,  ash  of  suckling,  367 ;  rate  of  develop- 
ment, 404. 

Dog's  blood,  oxygen  content,  415;  CO2 
content,  421;  composition,  554-555; 
hemoglobin,  559. 

Dog's  milk,  composition,  366,  404. 

Dolium  galea,  490. 

Doris,  402. 

Drosera,  168. 

Drosophila  funebris,  448. 

Dulcite,  27. 

Duodenum,  absorption  of  iron,  388  et  seq. ; 
digestion  in,  511  et  seq. 

E. 

Earth-worms,  glycogen  in,  46. 

Echinoderms,  46,  493. 

Echinus  eggs,  672. 

Eck's  fistula,  231. 

Edestin,  126,  127,  132,  172. 

Edinger's  theory  of  nervous  exhaustion, 
616. 

Eggs,  composition  of,  659. 

Egg  albumin,  124,  132,  172,  333,  653. 

Egg  globulin,  132. 

Egg-yolk,  370,  377,  381,  387. 

Eteagnacse,  197,  198. 

Elastin,  138,  176. 

Elimination  of  iron,  388;  of  metabolic 
end  products,  579-595. 

Elodea  canadensis,  57. 

Emulsin,  20,  461,  472. 

Emulsions,  103,  105. 

Enamel,  527. 

Endotryptase,  464. 

End-products  of  protein  metabolism,  221- 
250. 

Energy,  chemical,  52;  obtained  by 
cleavage,  74,  412,  441;  obtained  by- 
oxidation,  74,  436-460;  from  food, 
331,  332;  radiant,  52;  conservation 
of,  334;  exchange  of  in  animals  of 
different  sizes,  629. 

Enterokinase,  208,  521. 

Enzymes.     See  Ferments. 

Epiguanine,  298. 

Episarkine,  298. 

Epithelium,  47. 

Erepsin,  167,  513,  531. 

Erucic  acid,  110. 

Erythric  acid,  28. 

Erythritol,  28. 

Erythrose,  28. 

Erythrocytes,  550. 

Esox  lucius,  protamine  in,  137. 

Ether,  cause  of  glucosuria,  81. 

Ethereal  sulphuric  acids,  250,  251. 
r  Ethyl  alcohol.     See  alcohol. 
'  Ethylamine  carbonate,  234. 


SUBJECT  INDEX. 


711 


Ethylbenzene,  243. 

Ethylene  oxide,  113. 

Ethylurea,  234. 

Esters  of  monoamino  acids,  172. 

Evonymus,  56. 

Exact  science,  relation  to  physiological 
chemistry,  4. 

Excitability,  role  of  oxygen,  459. 

Excrements,  534. 

Expired  air,  428. 

Exudates,  578. 

F. 

Faeces,  534. 

Fagine,  114. 

Fasting  values,  628. 

Fat,  as  first  assimilation  product  of 
plants,  56;  formation  from  sugar, 
67;  melting  points,  103;  assimila- 
tion, 109. 

Fats,  101-112;  as  source  of  energy,  338; 
influence  on  protein  requirement, 
342  et  seq.;  on  respiratory  quotient, 
346;  on  general  metabolism,  347; 
source  of  heat,  111;  solvent  of  the 
cells,  112;  from  carbohydrates,  303, 
309;  calorific  value,  333;  from  pro- 
tein, 323;  influence  on  gastric  secre- 
tion, 500;  on  pancreatic  secretion  and 
emptying  of  stomach,  527. 

Fat,  determination  of,  325. 

Fat,  in  secretions,  326;  in  faeces,  624;  in 
icterus,  519. 

Fat  metabolism,  623,  627,  631. 

Fat  migration,  327,  328. 

Fattening,  345  et  seq. 

Fatty  acids,  from  fat,  101 ;  from  lecithine, 
112,  113;  utilization  in  fat  synthesis, 
105;  decomposition,  456. 

Fatty  degeneration,  327. 

Fatty  infiltration,  322,  327,  328. 

Fatty  tissue,  101,  110. 

Fehling's  test,  25. 

Fellic  acid,  516. 

Fermentation,  27;   reactions,  37,  38,  479. 

Ferments,  73,  294,  295,  374,  447,  461- 
483.  See  Diastase,  Lipase,  Rennin, 
Trypsin,  Pepsin,  Erepsin. 

Fibrogenous  substances,  537. 

Fibrin,  133,  173,  535  et  seq. 

Fibrin  ferment,  482,  537;  zymogen  of, 
538. 

Fibrin  globulin,  542. 

Fibrinogen,  133,  537. 

Fibrinoplastic  substance,  537. 

Fibroin,  138. 

Fictitious  meal,  341,  498. 

Ficus  carica,  168. 

Ficus  nmcrocarpa,  168. 

Figs,  iron  and  lime  content,  370,  380. 

Fig-tree,  proteolytic  ferment  from,  168. 

Fish,  protein  from,  653. 

Fish-scales,  138. 

Flagellata,  52. 

Flesh,  composition  of,  660.  See  Beef 
and  Meat. 


Flies,  larvae,  46;  eggs,  326. 

Florideae,  125. 

Fostus,  ash  of,  369. 

Foods,  calorific  value,  333;  inorganic, 
349-436;  organic,  13;  concept  of, 
353;  requirement,  644-652. 

Foodstuffs,  consumption  of,  647;  replace- 
ment of,  331-348;  relative  value  of, 
333,  334,  336. 

Formaldehyde,  14,  56,  201,  446. 

Formamide,  201. 

Formic  acid,  63,  74. 

Frogs,  extirpation  of  pancreas,  83;  mucin 
in  the  spawn,  141;  function  of 
kidneys,  582.  See  also  Mud-frog, 
Nurse-frog,  River-frog. 

Fructose,  26,  27,  29,  38,  42,  66,  95,  190, 
323,  471. 

Fruit-sugar.     See  Fructose. 

Fucose,  19,  24. 

Functional  nervous  diseases,  615. 

Fundulus  heteroclitus,  359. 

Fundus  glands,  495. 

Fungi,  glycogen  in,  47. 

Furfurol,  21. 

Fusel  oil,  470. 

G. 

Galactanes,  31. 

Galactitol,  44. 

Galactonic  acid,  28. 

Galactosamine,  20,  35. 

Galactose,  16,  20,  27,  28,  31,  38,  39,  40, 
44,  148,  613;  fermentation  of,  471. 

Gall-bladder,  516,  517. 

Gas-absorption,  law  of,  413. 

Gas-exchange,  in  formation  of  fats  from 
carbohydrates,  310-311;  in  the  lungs, 
428,  434;  in  the  tissues,  435-438;  in 
work  of  kidneys,  584;  under  various 
conditions,  663-670. 

Gases  in  alveolar  air,  etc.,  428-431. 

Gas-secretion,  in  the  lungs,  431;  in 
swimming-bladder  of  the  fish,  433. 

Gastric  contents.     See  Chyme. 

Gastric  fistula,  164. 

Gastric  juice,  496-507. 

Gastric  lipase,  103,  497. 

Gastropods,  glycogen  in,  46. 

Gelatin,  137,  176 ;  food  value  of,  215;  blood 
coagulation,  547. 

Gelatin-sugar.     See  Galactose. 

General  metabolism,  620-662. 

Generation,  organs  of,  glycogen  in,  47; 
relation  to  other  organs,  597-600. 

Gentiobiose,  37. 

Glands,  activity  seen  under  the  micro- 
scope, 465. 

Glandular  work,  source  of,  341. 

Gliadin,  133,  173,  653. 

Globin,  124,  141,  174,  397,  424,  556. 

Globulins,  127,  132,  172. 

Globuloses,  165. 

Glomerulus  Malpighi,  581. 

Glucase,  60,  61. 

Glucohemia,  77,  78,  85,  92. 


712 


SUBJECT  INDEX. 


Glucolytic  ferment,  73,  447. 

Gluconic  acid,  57,  94. 

Glucoproteids,  20,  141. 

Glucosamine,  20,  31,  35,  94,  141,  159,  488. 

Glucosazon,  26. 

Glucose,  d-,  16,  38,  39,  40,  66,  67,  190,  305, 
323,  333,  336,  445,  471,  480,  481.  See 
also  Grape-sugar  and  Dextrose. 

Glucose- a-glucoside  (Maltose),  481. 

Glucose- /?-glucoside  (Isomaltose),  481. 

Glucosides,  19,  472. 

Glucosuria,  alimentary,  30,  76;  starvation, 
30;  phloridzin,  30,  80;  strychnine, 
etc.,  30,  80;  after  diabetic  puncture, 
77;  injection  of  salt,  80,  359;  extir- 
pation of  pancreas,  82. 

Glucothionic  acid,  49. 

Glucurone,  32. 

Glucuronic  acid,  27,  31-34;  oxidation  in 
diabetes,  94. 

Glucuronic  acid  conjugates,  32-34. 

Glutamic  acid,  149,  304,  470,  653. 

Glutamine,  151,  202. 

Glutenin,  653. 

Gluten  casein,  132. 

Glutin,  137. 

Glyceric  aldehyde,  28. 

Glyceric  acid,  28,  303,  470. 

Glycerol,  14,  22,  28,  101,  112,  303,  314, 
483. 

Glycero-phosphoric  acid,  113,  115. 

Glycerose,  14,  28,  58,  302,  303,  304. 

Glycine.     See  Glycocoll. 

Glycine  anhydride,  179,  186,  228. 

Glycine-ethyl-ester,  181. 

Glyco-apiose,  37. 

Glycocholeic  acid,  248,  514. 

Glycocholic  acid,  248. 

Glycocoll,  5,  147,  148,  229,  242-248,  278, 
294,  458,  494,  514. 

Glycocoll  carbonate  of  calcium,  233. 

Glycogen,  36,  44-49,  66-75,  315. 

Glycol,  28,  113,  114. 

Glycol  aldehyde,  19. 

Glycolose,  19,  28. 

Glycolic  acid,  28. 

Glycosuria.     See  Glucosuria. 

Glycyl-alanine,  474. 

Glycyl-d-alanine,  187. 

Glycyl-alanine  anhydride,  186. 

Glycyl-asparagine,  183. 

Glycyl-aspartic  acid,  182. 

Glycyl-glycine,  179,  180,  185,  217,  228, 
474. 

Glycyl-leucyl-alanine,  474. 

Glycyl-phenyl-alanine,  179,  474. 

Glycyl-Z-tyrosine,  179,  184,  185,  187,  474. 

Glyoxylic  acid,  152,  162,  295. 

Glyoxydiuride.     See  Allantoine. 

Gmelin's  test  for  bile  pigments,  569. 

Goats,  rate  of  development,  371,  404. 

Goat's  blood,  554,  555. 

Goat's  milk,  366,  404,  405. 

Goblet  cells,  142. 

Goitre  region,  604. 


Gold  chloride  solution,  357. 

Gonionemus,  358. 

Goose-blood,  559. 

Goose-fat,  absorption  of,  117. 

Gorgonia  Carolini,  138. 

Gossypose,  40. 

Gout,  298. 

Graham  bread,  iron  and  lime  in,  370,  377. 

Grains,  protein  in,  132,  133. 

Grape,  iron  and  lime  content,  370,  380. 

Grape-sugar,  13,  336,  358,  440.     See  also 

t/-glucose. 
Grave-wax,  326. 
Green-gage  (or  French)  plums,  iron  and 

lime  content,  370,  380. 
Grubs  of  insects,  glycogen  in,  46. 
Guaiacum  test,  446. 
Guanidine,  156,  235. 
Guanine,  22,  280,  283,  294,  297. 
Guanylic  acid,  22,  283. 
Guinea  pigs,  experiments  with,  64,  124, 

368,  371,  393,  559. 
Gulose,  17. 
Gums,  42,  48. 

H. 

Haptophor  groups,  685. 
Hazel  nuts,  iron  in,  381. 
Heat,  coagulation  of  proteins  by,  121; 

equivalent   of  work,   336,   424,   625; 

measurement  of,  335,  625;  sources  of, 

75,  111,  342 ; regulation,  595,  643;  rigor, 

617. 
Helianthus,   inulin   of,   29;  fat  cleavage. 

103. 

Helix,  glycogen  of,  46. 
Helix  pomatia,  glucoproteid  of,  144. 
Helleborin,  21. 
Hemal-lymph-glands,  573. 
Hematin,   124,   141,  386,  392,  416,  558- 

565. 

Hematinic  acids,  564. 
Hematogen,  381,  387. 
Hematoidin,  569. 
Hematopoietic  organs,  398. 
Hematoporphyrin,  387,  396,  564,  573. 
Hemieelluloses,  42. 
Hemin,  396,  563,  565. 
Hemochromogen,  416,  558. 
Hemocyanin,  402. 
Hemoglobin,  381;  in  new-born,  382-385; 

crystals    of,    125;    behavior   in    high 

altitudes,  436;  spectroscopic  behavior, 

560;  combination  with  oxygen,  415; 

chemistry  of,  551-557 ;  analysis  of,  559. 
Hemoglobin  formation,  387-392. 
Hemoglobin-iron  of  new-born,  384,  385. 
Hemolysis,  115,  551,  688-690. 
Hemolysins,  689. 
Hemophilia,  543. 
Hemopyrrole,  564. 

Hemp-seeds,albumincrystalsfrom,122,123. 
Hen,  hemoglobin  of,  559. 
Hen's  egg,  ash  of  the  white,  369,  370,  380, 

659;  ash  of  the  yolk,  369,  370,  659. 


SUBJECT  INDEX. 


713 


Henle's  loop,  581. 

Heptoses,  19. 

Heredity,  670-676. 

Herring,  clupein  in,  136. 

Heterocyclic  araino  acids,  151. 

Heteroxanthine,  297. 

Hexahydrobenzene  (inositol),  306. 

Hexobioses,  37. 

Hexoses,  19. 

High  altitudes,  effect  of,  436. 

Hippomelanin,  145. 

Hippuric  acid  synthesis,  5, 50, 229,242,479. 

Hirudin,  547. 

Histidine,  154,  288. 

Histidyl-histidine,  179. 

Histones,  135,  174. 

Hoffmann's  tyrosine  test,  151. 

Holothuria,  glycogen  of,  46. 

Homogentisic  acid,  257,  271. 

Homothermous  animals,  643. 

Honey,  ash  of,  369,  370,  380. 

Hordein,  653. 

Horn,  138. 

Horse,  rate  of  growth,  371,  404;  hemo- 
globin, 559. 

Horse-blood,  125,  418,421,  554,  555. 

Horse-milk,  366,  404. 

Horse-tallow,  103. 

Horny  layer,  138. 

Human  beings,  ash  of  infants,  368,  369; 
rate  of  growth,  371,  404;  iron  con- 
tent, 393,  394. 

Human  milk,  ash  of,  366,  369,  370,  377, 
380,  404. 

Humin  substances,  146. 

Humor,  vitreous,  143. 

Hunger.     See  Starvation. 

Hydra,  CO2,  assimilation  of,  52. 

Hydrazones,  25. 

Hydrobilirubin,  572. 

Hydrochinon.     See  Quinol. 

Hydrochloric  acid,  203,  204,  219,  220, 
490,  492,  496,  523. 

Hydrocyanic  acid,  18,  220,  238. 

Hydrogen,  200,  438. 

Hydrogen  peroxide,  313,  449. 

Hydrolysis  of  proteins,  146,  partial,  186. 

Hydro- p-cumaric  acid,  254. 

Hydrosol,  120. 

Hydroxylamine,  201. 

Hydroxymandelic  acid,  p-,  170,  254. 

Hydroxynaphtylamine,  446. 

Hydroxyphenyl-  a-aminopropionic  acid, 
151. 

Hydroxyphenyl-ethylamine,  259. 

Hydroxyphenylacetic  acid.  170,  254,  255, 
273. 

Hydroxyphenyl -propionic  acid,  p-,  170, 
254,  255,  259,  273. 

Hydroxyprolin,  151. 

Hydroxypyrrolidin-carboxylic  acid,  151. 

Hydroxy-/?-quinolin-carboxylic  acid,  p-, 
153. 

Hydroxy-benzoic  acids,  252. 

Hydroxybutyric  acid,  <#-,  97. 


Hydroxy-fatty  acids  in  fats,  102. 
Hydroxy-quinolin-sulphate,  252. 
Hydroxy-p-cumaric  acid,  254,  255. 
Hyoglycocholic  acid,  515. 
Hyperglucaemia.     See  Glucohemia. 
Hyperisotonic  solution,  550. 
Hypersecretion  of  gastric  juice,  508. 
Hypisotonic  solution,  550. 
Hypophysis,  609. 
Hypos ulphurous  acid,  249. 
Hypoxanthine,  280,  292,  297. 


I. 


Ichthulin,  144. 

Ichthylepidin,  138. 

Idose,  17. 

Icterus,  518,  570. 

Ileum,  absorption  of  iron  in,  389. 

Illuminating  gas,  81. 

Imadazole,  284. 

Immunity,   509;    of    mucous    membrane, 

494;  acquired,  680. 
Inactivated  serum,  688. 
Indican,  259. 
Indigo,  201. 
Indigo-blue,  258. 
Indigo-red,  259. 
Indigotate,  sodium  sulph-,  582. 
Indirect  conclusions,  4,  307,  313,  314. 
Indirubin,  259. 
Individual  variations,  8. 
Indole,  153,  170,  251,  258,  457. 
Indophenol,  446. 
Indoxyl,  201,  252,  257,  457. 
Indoxyl-glucuronic  acid,  32. 
Indoxyl-sulphuric  acid,  252. 
Indoxyl-sulphate  of  potassium,  252. 
Infants,  ash  of,  368,  369 ;   rate  of  growth, 

371,  404. 

Inorganic  foodstuffs,  349  et  seq. 
Insects,  glycogen  in  the  grubs  of,  46. 
Inspired  air,  volume  of,  429. 
Internal  secretion,  90. 
Innervation,  of  the  liver,  77;  of  the  lungs, 

434 ;  of  the  kidneys,  585. 
Inositol,  93,  306. 
Inorganic  foods,  349-407. 
Insect  blood,  125,  447. 
Inspired  air,  composition  of,  428. 
Intestinal  digestion  of  carbohydrate,  60; 

of  fat,  104 ;  qf  protein,  208. 
Intestinal  flora,  62,  64,  218. 
Intestinal  gases,  438. 
Intestinal  juice,  512  et  seq. 
Intestinal  putrefaction,  218. 
Intestinal  respiration,  438. 
Intestine,    absorption    of    iron    in    small, 

388  et  seq. ;  digestion  and  absorption, 

511  et  seq. ;  elimination  of  iron  in  the 

large,  388  et  seq. 
Inulase,  482. 
Inulin,  29,  41,  44,  95. 
Inversion,  38. 


714 


SUBJECT  INDEX. 


Invertase,  467,  482,  512. 

Invertin,  61,  461. 

Invert-sugar,  29,  38. 

Iodine,  41,  406,  607. 

lodothyrin,  607,  608. 

Ions,  358,  359,  592. 

Iridese,  44. 

Iron,  380-402. 

Iron,  bacteria,  194. 

Iron  content  of  foodstuffs,  380,  381 ;    of 

rabbits,  681 ;  guinea  pigs,  682. 
Isoamylalkohol,  149,  455,  470. 
Isobilianic  acid,  515. 
Isobutyric  acid,  455. 
Isobutyl-acetic  acid,  455. 
Isocholesterol,  117. 
Isodynamics,  law  of,  331,  336. 
Isolactose,  38,  480,  481. 
Isoleucine,  148. 
Isomaltose,  37,  479-481. 
Isomers,  behavior  in  hydrolysis,  471-476. 
Isotonic  solutions,  550. 
Iso valeric  aldehyde,  149-455. 
Isovalerianic  acid,  455. 
Isovalero-nitrile,  149. 
Ixodis-ricinus,  547. 

J. 

Jalap,  rhodeose  in,  19. 

Jecorin,  49. 

Jejunum,  iron  absorption  in,  389  et  seq. 

Jequirity  seeds,  682. 

Johannisbrot  tree,  cane  sugar  in,  38. 

K. 

Kephir  lactase,  38,  480. 

Keratins,  138,  176. 

Ketoses,  19. 

Kidneys,    glycogen    in,  47;    glucothionic 

acid,  49;    elimination   of   sugar,    82; 

hippuric  acid,  246,  247;   elimination 

of    iron,    388;     of    lime,    392,    397; 

function  of,  579-594. 
Kynurenic  acid,  153,  260. 
Kyrins,  177. 

L. 

Laborer,  diet  of,  645,  646. 

Laccase,  447. 

Lactarius  volemus,  29. 

Lactase,  323,  482,  513. 

Lactates,  oxidation  of,  in  diabetes,  93. 

Lactation,  386. 

Lactic  acid,  238,  303,  304;  from  carbo- 
hydrates in  the  intestine,  63;  as 
intermediate  product  in  alcoholic 
fermentation,  483. 

Lactic-acid-ferment,  482. 

Lactic-acid  fermentation,  27,  469. 

Lactobiose,  39. 

Lacto-glucase,  38. 

Lactose,  39. 


Laevulic  acid,  282,  306,  313. 

Lsevulic  aldehyde,  306,  313. 

Laked  blood,  550. 

Lampyris  splendidula,  411. 

Langerhans  cells  in  the  pancreas,  90, 
93. 

Lanolin,  105. 

Large  intestine,  elimination  of  iron  in, 
389  et  seq. 

Latent  period  of  the  stomach,  498. 

Lathrsea  squamaria,  122. 

Laurie  acid,  102. 

Lavosin,  44. 

Laws,  of  isodynamics,  331-348;  of  conser- 
vation of  energy,  334  et  seq. ;  of  the 
minimum,  356;  of  gas-absorption, 
413 ;  of  specific  sense  energy,  494. 

Lecithides,  115. 

Lecithin,  112-116,  403;  content  in  cer- 
tain organs,  114;  cleavage  by  lipase, 
115;  activates,  115;  in  nervous 
tissue,  613. 

Legumin,  132. 

Leguminoses,  196. 

Legumes,  legumin  in,  132. 

Lens,  crystalline,  138. 

Lentils,  iron  content,  381. 

Leptothrix  ochracea,  194. 

LeucaBmia,  290. 

Leucine,  148,  239,  304,  305,  325;  decom- 
position of  the  d-l  form  in  the  organ- 
ism, 453,  454 ;  cleavage  by  fungi,  470 ; 
cleavage  by  yeasts,  470;  taste,  494. 

Leucine-ethyl-ester,  475. 

Leucine  carbonate  of  calcium,  233. 

Leucinimide,  169. 

Leucocytes,  glycogen,  47:  uric  acid,  389; 
in  blood  coagulation,  540;  in  general, 
551  et  seq. 

Leucyl-alanine,  179,  474. 
-alanyl-alanine,  179. 
-asparagine,  183. 
-aspartic  acid,  182. 
-glycine,  179,  474. 
-glycyl-glycine,  179,  181,  474. 
-isoserine,  474. 
-leucine,  179,  186,  228,  474. 
-proline,  179,  474. 
-tetraglycine,  179. 
-Z-tyrosine,  181,  474. 

Levulose,  27.     See  d- Fructose. 

Lichenin,  44. 

Lichens,  53. 

Lieberkiihn's  glands,  512. 

Liebermann's  reaction  for  proteins,  162. 

Life  without  bacteria,  64. 

Ligamentum  muchse,  138. 

Lignification,  42. 

Liliacese,  44. 

Limax,  46. 

Limonene,  118. 

Lipoids,  solubility  of,  112. 

Lipase,  103,  475,  482;  of  stomach,  429; 
of  intestinal  juice,  512. 

Lithium,  407. 


SUBJECT  INDEX. 


715 


Liver,  glycogen,  47;  glucothionic  acid, 
49;  jecorin,  49;  glycogen  storehouse, 
66;  carbohydrate  metabolism,  77; 
behavior  after  pancreas  extirpation, 
84,  636;  in  diabetes  mellitus,  93; 
urea  formation,  231;  uric  acid,  237; 
metabolism  in  diabetes,  353;  iron 
depot,  391;  bile,  513-521;  relation 
to  fibrinogen,  548;  part  played  in 
formation  of  bile-pigments,  569, 
570. 

Liver  atrophy,  264. 

Liver-bile,  516. 

Liver-proteid,  22. 

Loach,  438. 

Localization  of  combustion,  409. 

Luminescence,  53. 

Lump-fish,  protamine  from,  137. 

Lung  arteries,  428,  429. 

Lung  catheter,  429. 

Lungs,  gas  exchange  in,  408-432; 
metabolism  in,  431,  441;  as  glands, 
431;  surface  of,  428;  reducing  power, 
431 ;  glycogen  in,  47. 

Lung  veins,  428. 

Lupines,  133,  150. 

Luteins,  549. 

Lymph,  573-578. 

Lymphagogues,  576. 

Lymph  fistula,  108. 

Lymph  glands,  function  of,  577. 

Lymph  vessels,  glycogen  in,  47. 

Lysine,  154. 

Lysyl-lysine,  179,  259,  305. 

M. 

Mackerel,  scombrin  in,  136. 

Madder,  21. 

Maggots,  sugar  formation  by,  319. 

Magnesium,  402. 

Magnesium  salts,  from  albumin,  123. 

Malt,  39. 

Maltase,    479,    480;    of    intestinal    juice, 

512. 

Maltobiose,  39. 
Maltoglucase,  37. 
Maltose,  37,  39,  46,  59,  96,  480. 
Malt-sugar,  39. 

Mammary  glands,  49,  595,  596-599. 
Man.     See  Human  beings. 
Mandelic  acid,  470. 
Mandelo-nitrile-glucoside,  20,  480. 
Manganese,  402. 
Manganous  oxide,  450,  451. 
Manganese  peroxide,  450,  468. 
Mannans.,  29. 

Manna  tetrasaccharide,  40. 
Mannitol,  27,  93. 
Mannonic  acid,  28. 
Mannonic-acid-lactose,  470. 
Manno-rhamnoses,  36,  190. 
Mannose,  16,  26,  28,  29;  transformation 

into  glucose  and  fructose,   67,    190; 

fermentation  of,  471. 


Mannose  hydrozone,  26. 

Manno-saccharic  acid,  28. 

Mariotte's  law.     See  Boyle's  law. 

Marrow  of  bones,  612. 

Meal  worm,  123. 

Meat,  ash  of,  366,  370,  377,  381;  influ- 
ence on  gastric  secretion,  502;  in 
pancreatic  secretion,  531 ;  composi- 
tion of,  660. 

Meat  broth,  influence  on  gastric  secretion, 
500. 

Meat,  consumption  of,  by  different  races 
of  people,  659. 

Meat  juice,  influence  on  gastric  secretion, 
500. 

Meconium,  218. 

Medulla  oblongata,  77. 

Melanins,  144. 

Melanose,  447. 

Melanotic  sarcoma,  144. 

Melibiase,  482. 

Melibiose,  37. 

Melitriose,  37,  40. 

Melons,  168. 

Membranse  propria?,  138. 

Menstruation,  398. 

Mercaptan,  494. 

Mercapturic  acid,  159-160. 

Mercury  salts,  357. 

Mesitylene,  458. 

Mesitylenic  acid,  458. 

Mesoporphrine,  564,  567. 

Meso-tartaric  acid,  452. 

Mesoxyl-urea,  279. 

Metabolism,  620-662;  of  cells,  49;  with- 
out salts,  354,  356;  influence  of  work 
upon,  626;  effect  of  body  surface, 
628-630;  influence  of  age,  630;  in 
starvation,  630;  during  pregnancy, 
642;  external  conditions,  643;  m 
osteomalacia,  377. 

Metal-albuminates,  128. 

Methemoglobin,  125,  425,  562. 

Methane,  63,  438. 

Methods,  value  of,  11. 

Methylamine,  602. 

Methylene  blue,  411. 

Methyl-glucosides,  472-473. 

Methyl-2-6-dihydroxy-pyrimidine,  281. 

Methylfuran,  306. 

Methylglycocoll,  235. 

Methylguanine,  7-  (epiguanine),  298. 

Methylquanidine-acetic  acid,  235. 

Methyl  imidazole,  286. 

Methyl  indole,  257,  602. 

Methyl  pentosans,  23-65. 

Methyl  pentoses,  19. 

Methyl  propyl-pyrrole,  564. 

Methyl  quinol,  252. 

Methyl  quinolin,  457. 

Methyl  uracil,  281. 

Methyl  xanthine,  297. 

Methyl  xyloside,  473. 

Mice.    See  Mouse. 

Micro-chemical  tests,  105,  390. 


716 


SUBJECT  INDEX. 


Migration  of  material,  in  salmon,  351,  352; 
in  starvation,  352. 

Milk,  milk-sugar  in,  39;  ash  of,  366;  lime 
in,  370 ;  influence  on  gastric  secretion, 
500,  502,  503 ;  influence  on  pancreatic 
secretion,  531;  composition  of,  654; 
relation  of  composition  to  rate  of 
development  of  suckling,  367,  370, 
371,  404,  655. 

Milk-albumin,  132. 

Milk-globulin,  132. 

Milk-sugar,  13,  31,  37,  39,  323;  digestion 
of,  62;  calorific  value,  333;  action  on 
muscle,  358. 

Millon's  reagent,  151. 

Mimicry,  677. 

Molecules,  size  of,  starch,  41 :  proteins,  128. 

Molisch's  sugar  test,  162. 

Mollusks,  46,  402. 

Mono-amino-di-carbo-oxylic  acid,  150. 

Mono-amino-mono-carbo-oxylic  acids,  148, 
151. 

Mono-amino-hydroxy-carbo-oxylic  acids, 
149,  151. 

Mono-amino-acids,  129. 

Mono-methyl-xanthine,  297. 

Mono-sodium  urate,  299,  593. 

Monosaccharides,  19-21. 

Moore's  sugar  test,  25. 

Morbus  Addisonii,  603. 

Morbus  Basedowii,  609. 

Morphine,  80,  677. 

Moss,  Iceland,  44. 

Mouse,  iron  content  of  a,  393. 

Mouth,  485. 

Mountain  sickness,  437. 

Mucins,  141,  142. 

Mucin-like  substances  in  urine,  268. 

Mucic  acids,  28,  39,  94. 

Mucoids,  142. 

Mucous  glands,  485. 

Mud-frog,  sterile  larva?,  64. 

Murcena,  546. 

Musca  lucilia,  478. 

Muscarine,  114. 

Musca  vomitoria,  319. 

Muscle-albumin,  calorific  value,  333, 
336. 

Muscles,  action  of  certain  salts  upon, 
358;  creatine  in,  235;  function  of, 
611. 

Muscles,  glycogen,  46;  jecorin,  50;  glyco- 
gen  stores,  67;  behavior  after  extir- 
pation of  pancreas,  85;  consumption 
of  carbohydrates,  87;  purine  bases, 
292. 

Muscular  force,  source  of,  337. 

Mussels,  conchiolin  of,  138. 

Muscular  work,  67;  influence  on  albumin- 
fattening,  618. 

Muscular  stomach  of  birds,  138,  507. 

Mutual  relations  of  fat,  carbohydrate  and 
protein,  301-348,  358  et  seq. 

Mutton-tallow,  melting-point,  103;  absorp- 
tion of,  108;  assimilation,  110. 


Myogen,  133. 

Myosin,  133. 

Myrostic  acid,  102. 

Myrosin,  20,  461. 

Myxcedema,  605. 

Myxomycetes,  oxygen  requirement  of,  459. 

N. 

Naphthol,  «,  162,  446. 

Naphthoic  acid,  229,  243. 

Naphthuric  acid,  229,  243. 

Navel.     See  Umbilical  cord. 

Naphtylamine,  a,  446. 

Nepente,  168. 

Nephritis,  268. 

Nerves,  facial,  485. 

glossopharyngeal,  485,  494. 

lingual,  486. 

splanchnic,  78. 

sympathetic,  485,  507,  527,  603. 

trigeminal,  495. 

vagus,  78,  434,  498,  521. 

degeneration  of,  616. 

Nervous  diseases,  615,  617. 

Nervous  system,  influence  on  liver, 
77. 

Nervous  tissue,  phosphorus  content,  403; 
function  of,  611  to  614;  affinity  to 
tetanus  toxin,  686. 

Neurine,  114. 

Neurokeratin,  138,  613. 

Neurosis,  459. 

Neutral  fats,  101. 

Nitrates,  193. 

Nitrification,  193. 

Nitrites,  194. 

Nitric  acid,  193. 

Nitric-oxide-hemoglobin,  561. 

Nitro-benzaldehyde,  244,  457. 

Nitro-benzene,  81. 

Nitro-benzoic  acid,  244. 

Nitro-benzyl  alcohol,  34,  458. 

Nitro-hippuric  acid,  243. 

Nitro-phenol,  252. 

Nitro-toluene,  34,  458. 

Nitrogen,  119,  194-200,  438. 

Nitrogen  content  of  blood,  415;  of  faeces, 
624. 

Nitrogen  in  soil,  196. 

Nitrogenous  equilibrium,  342,  637-640. 

Nucleases,  288. 

Nucleic  acids,  144,  275,  276,  300;  from 
yeast,  21;  digestion,  288. 

Nuclein  bases.    See  Purines. 

Nucleic-acid-protamine,  140. 

Nucleins,  141,  275,  387,  388,  403. 

Nucleoalbumins,  133,  173,  397,  403. 

Nucleohistone,  139. 

Nucleoproteids,  140,  275-300. 

Nurse-frog,  353. 

Nutritional  value  of  foods,  621-626. 

Nutrition  without  salts,  354  et  seq. 

Nuts,  conglutin,  133;  fats  from  carbo- 
hydrates, 308. 


SUBJECT  INDEX. 


717 


O. 

Oats,  gliadin  in,  133. 

Obesity,  111. 

Ocean,  denitrifying  bacteria  in,  199. 

Octodecyl  alcohol,  102,  595. 

CEsophageal  fistula,  341. 

GEsophageal  groove,  509. 

Oil  as  first  assimilation-product  of  plants, 
56. 

Oil-bag  of  birds,  102,  595. 

Oil  of  Pennyroyal,  English,  327. 

Oil-plasma,  545. 

Oils,  ethereal,  303. 

Oil-seeds,    fats   from   carbohydrates,    308 
et  seq. 

Oleacae,  56. 

Oleic  acid,  102,  113,  303. 

Oleum   Pulegii.     See  Oil  of   Pennyroyal, 
English. 

Olive  oil,  108. 

Olives,  carbohydrate  and  fat  in,  308. 

Opalins,  glycogen  in,  46. 

Opalisin,  654. 

Optical  activity,  15  et  seq. 

Oranges,  iron  and  lime  in,  370,  380. 

Orcin,  252. 

Organ  pentoses,  22. 

Organs,     experiments    in    surviving,     9; 
hematopoetic,  398. 

Organs  of  generation,  597  et  seq. 

Organs  of  phosphorescence,  411. 

Ornithine,  155,  169,  227,  228,  245. 

Ornithuric  acid,  155,  245. 

Osazones,  26. 

Oscillaria  sancta,  671. 

Osmosis,  357. 

Osseoalbumoid,  138. 

Osteoidal  tissue,  374. 

Osteoclasts,  612. 

Osteomalacia,  377. 

Oteoplastic  tissues,  374. 

Osteoporosis,  375. 

Oval,  433. 

Ovalbumin.     See  Egg  albumin. 

Ovaries,  379,  599. 

Ovimucoid,  143. 

Ovokeratin,  138. 

Oxalic  acid,  28,  279,  295,  444,  457. 

Oxalylurea,  279. 

Ox-blood,  421. 

Ox-muscle,  653. 

Oxidases,  445,  482. 

Oxidation,  animal,  409,  439-460. 

Oxidation  ferments,  445  et  seq. 

Oxidation  power,  93. 

Oxidation  processes,  74,  411,  452. 

Oxidizable  substances,  408. 

Oxy-.     See  Hydroxy. 

Oxydases,  445,  482. 

Oxygen,  408-438 ;  free  in  saliva,  411 ;  actu- 
ation, 442. 

absorption  by  the  blood,   at  different 
temperatures,  417;  at  different  pres- 
sures, 418;  influence  of  CO2,  427. 
capacity  of  the  blood,  427. 


Oxygen,  carriers  of,  445. 

consumption    by   animals    of   different 
size,  629. 

supply  of  foetus,  410,  411;   of   insects, 
411,  412. 

tension  of  lymph,  435. 

tension  curves,  418. 
Oxygenases,  449. 

Oxyhemoglobin,  125,  127,  141,  558-561. 
Oxyneurine,  114. 
Oxyproteic  acid,  270. 
Oxypurine,  6,  280. 
Oxysantonine,  457. 
Ozone,  312,  441. 
Ozonide,  313. 

P. 

Palms,  cellulose  stores  in,  44;  cane-sugar 
content,  38. 

Palmitic  acid,  303 ;  from  lecithin,  113 ;  from 
fat,  102. 

Palmitic-acid-myricyl  ester,  102. 

Pancreas,  nucleic  acid  in,  285;  carbohy- 
drate metabolism,  82,  83,  87;  part 
played  in  digestion,  513  et  seq.', 
glycogen,  47;  glucothionic  acid,  49. 

Pancreas,  extirpation  of,  82. 

Pancreas-nucleoproteid,  21. 

Pancreatic  fistula,  164. 

Pancreatic  juice,  action  on  nucleic  acids, 
288;  absorption  of  fat,  107;  general 
function,  521  et  seq. 

Papayotin,  168. 

Papillionacse,  197. 

Parabanic  acid,  279. 

Paracasein,  207. 

Parachymosin,  207. 

Paraffin  plasma,  545. 

Paralyzers,  468. 

Paramucin,  142. 

Paranuclein,  134. 

Para  nuts,  123. 

Parathyroid  glands,  604,  605,  606. 

Paraxanthine,  297. 

Parotid  gland,  484  et  seq. 

Parthogenesis,  360. 

Partial  pressure,  374. 

Partial  hydrolysis  of  proteins,  186. 

Patella,  402. 

Pathology,  relation  to  physiological 
chemistry,  3. 

Paunch,  509. 

Pears,  iron  and  lime  content,  370,  380. 

Peas,  ash  of,  369,  377,  388. 

Pectases,  482. 

Pecten  ir radians,  148. 

Pectinase,  482. 

Penicillium  glaucum,  470,  472. 

Pentaglycine,  179. 

Pentamethyldiamine,  154,  170,  259. 

Pentosans,  23,  42,  65. 

Pentoses,  19,  21,  323. 

Pentoses  in  organs,  22 ;  in  food,  24. 

Pentosuria,  23,  96. 

Pepsin,  203,  204,  462,  482,  499. 

Pepsin  digestion,  163. 


718 


SUBJECT  INDEX. 


Pepsinogen,  497. 

Peptides.     See  Polypeptides. 

Peptone  blood,  546. 

Peptones,  165,  178,  188,  204,  208,  546. 

Percarbonic  acid,  57. 

Perforating  fibers,  612. 

Periosteum,  612. 

Peroxide  formation,  449,  450. 

Peroxydases,  449. 

Persea-gratissima,  29. 

Perseitol,  29. 

Petroselinum  apiin,  36. 

Phenaceturic  acid,  243,  256. 

Pharmacology,  relation  to  physiological 
chemistry,  677. 

Phenol,  170,  229,  252,  457,  458. 

Phenylacetic  acid,  170,  244. 

Phenol-glucuronic  acid,  32. 

Phenolphtalein,  446. 

Phenolphtalin,  446. 

Phenol-sulphate  of  potassium,  229,  252, 
457. 

Phenol  sulphuric  acid,  252,  254. 

Phenylalanine,  151, 251,  256,  259, 272,  304. 

Phenylaminopropionic  acid,  151. 

Phenyldiaminine,  446. 

Phenylethylamine,  259. 

Phenylhydrazine,  25. 

Phenylpropionic  acid,  170. 

Phloretin,  30,  82. 

Phloretic  acid,  30. 

Phloridzin,  21,  30,  81. 

Phloridzin  poisoning,  31,  327,  587. 

Phloroglucinol,  30. 

Phospho-globulin,  137. 

Phosphoglucoproteid,  44. 

Phosphorescent  organs,  411. 

Phosphoric  acid,  22,  112,  277. 

Phosphoric  acid  amide,  284. 

Phosphorus,  403-406;  behavior  in  organ- 
ism, 403,  444;  content  of  nervous 
tissue,  613. 

Phosphorus  poisoning,  30,  81,  265,  327, 
328,  548. 

Phrynolysin,  690. 

Phycocyan,  125. 

Phylloporphyrin,  568. 

Physcia  parietina,  217. 

Physiology,  relation  to  physiological 
chemistry,  3,  484,  485. 

Physiological  salt  solution,  550. 

Phytocholesterol,  116. 

Phytovitellin,  132,  173. 

Pigment  formation  in  Morbus  Addisonii, 
603. 

Pigments,  569. 

Pigs,  development  of,  370,  404. 

Pig's  blood,  iron  and  lime  content,  370, 
381;  analysis  of,  554,  555;  hemo- 
globin from,  559. 

Pig's  fat,  absorption  of,  108. 

Pig's  milk,  366,  404,  405. 

Pike,  protamine  from,  137. 

Pinene,  188. 

Pine-seeds,  albumin  from,  173. 


Pinguicula,  168. 

Pinna  squamosa,  402. 

Planarians,  52. 

Plant  casein,  173. 

Plant  crytalloids,  122. 

Plasma,  415,  421,  422,  423,  535. 

Plastein,  208. 

Platinum  catalysis,  468. 

Pleurobranchia  Meckelii,  490. 

Plums,  iron  and  lime  content  of,  370,  380. 

Pneumonia,  350. 

Poikilothermous  animals,  643. 

Polydypsia,  83. 

Polypeptides,  178,  179,  183-186,  192,  474, 
475. 

Polyphagia,  83. 

Polyps,  46. 

Polysaccharides,  19,  36-49. 

Polyuria,  83. 

Potash,  content  of  certain  foodstuffs,  366. 

Potatoes,  ash  of,  369,  370,  380. 

Precipitin  formation,  668. 

Preserved  yeasts,  464. 

Primula,  29. 

Principal  cells,  495. 

Problems  of  physiological  chemistry,  1-12. 

Preferments,  465. 

Proline,  151,  152. 

Prolyl-leucine,  179. 

Propionic  acid  from  alanine,  170. 

Propylbenzene,  243. 

Prosecretin,  528. 

Prostate  gland,  599. 

Protagon,  613. 

Protamines,  135-137. 

Protective  substances,  23. 

Proteid  of  the  liver,  22. 

Proteids,  131,  139,  275.     See  also  Proteins. 

Proteins,  119-275. 

Protocatechuic  acid,  252,  254;  from 
adrenalin,  602. 

Protococcus  vulgaris,  28. 

Proton,  226. 

Protoplasm,  456,  672. 

Protozoa,  46. 

Psalterium,  509. 

Pseudomucin,  142. 

Pseudonucleins,  134. 

Ptyalin,  59. 

Ptyalose,  39. 

Pumpkin  seeds,  122. 

Purine  bases,  277,  278,  289-294;  decom- 
position of,  292-297. 

Purine  ring,  279. 

Purine  value,  exogenous  and  endogenous, 
291. 

Pus,  578. 

Pus  cells,  140. 

Putrefaction,  in  the  intestine,  253;  of 
protein,  218. 

Putrefactive  products  of  proteins,  169, 
170. 

Putrescine,  155,  170,  260,  267. 

Pylorus,  function  of,  507. 

Pyridine,  from  adrenalin,  602. 


SUBJECT  INDEX. 


719 


Pyrimidine  bases,  276. 

Pyrimidine  ring,  281. 

Pyrocatechol-sulphuric  acid,  251. 

Pyrogallol,  252,  440. 

Pyrotartaric  acid,  169. 

Pyrrole,  from  adrenalin,  602;  in  Morbus 

Addisonii,  603. 

Pyrrolidine  carboxylic  acid,  151. 
Pyrrole  reaction,  152. 

Q. 

Quantity,  concept  of,  11. 

Quercitrin,  24. 

Quinol,  253,  458. 

Quinoyl  sulphuric  acid,  254. 

Quotient,  respiratory,  346, 627 ;  D  -f- N,  321, 

R. 

Rabbits,    ash    of    young,    368;     rate    of 

development,    370,    404;    blood    of, 

554,  555;    composition  of  milk,  366, 

404;    hemoglobin  content,  383;    iron 

content,  393. 
Racemic  acid,  453. 
Racemic  bodies,  amino  acid  in,  181. 
Rachitis,  371  et  seq. 
Raffinose,  37,  40. 
Rape-seed  oil,  1,  10. 
Raspberries,  iron  and  lime  content,  370, 

380. 

Rats,  hemoglobin  of,  383. 
Reaction,  biological,  668  et  seq. 
Reactions,  of  the  hexoses,  25-27. 
Reabsorption,    in    urinary  tubes,   584    et 

seq. 

Receptors,  683. 

Reduction -power  of  the  lungs,  431. 
Reduction  processes,  411,  442. 
Reflex  action,  490. 
Regeneration,  674. 
Regulation,  mechanism  of,  436. 
Regurgitation,  509. 
Reindeer,  milk  of,  654. 
Relation    of    foodstuffs,  2,    5   et   seq,  301 

et  seq. 
Relation  of  milk  compositions  to  rate  of 

development,  366. 
Relative    value    of   foodstuffs,    333,    334, 

336. 

Renal  calculi,  297. 
Rennet  bag,  509. 
Rennin,  205-207,  482,  495,  497. 
Reproductive  glands,  glycogen  in,  47. 
Reproductive  organs,  597  et  seq. 
Reserve     air,      429;     carbohydrate,     42; 

cellulose,  44. 
Residual  air,  429. 
Resistance  capacity  of  cell-substance 

towards  ferments,  191. 
Respiration,  internal   and   external,    412; 

anaerobic,  412;  cutaneous,  432-437. 
Respiration  calorimeter,  625. 
Respiratory  quotient,  346. 
Retention  cysts,  487. 
Reticulin,  138. 


Reticulum,  509. 

Reversible  fermentation  reactions,  37, 479- 

483. 

Rhamninose,  40,  190. 
Rhamnose,  19,  24,  29,  40,  190. 
Rhamnus  infectoria,  40,  190. 
Rhinantacse,  197. 
Rhizapoda,  46,  459. 
Rhodeose,  19. 
Rhodophycese,  125. 
Ribose,  29. 

Rice,  iron  and  lime  content,  370,  380. 
Ricin,  681. 

Ricinus  communis,  681. 
Rigor  of  death,  133,  617,  618;    of  heat, 

617. 

River-crabs,  tyrosinase  of,  447. 
Roman-snail,  144. 
Root-nodules  or  tubercles,  196. 
Ruberythric  acid,  21. 
Rubia  tinctorum,  21. 
Rumen,  509. 
Ruminants,  509. 
Rumination,  509. 
Rye,  133,  369,  370,  380. 

S. 

Saccharin,  318. 

Saccharic  acid,  27;  d-,  oxidation  in  dia- 
betes, 94. 

Saccharobiose,  38. 

Saccharo-colloids,  41. 

Saccharomyces  apiculatus,  471. 

Saccharomyces  intermedians,  481. 

Saccharomyces  productivus,  471. 

Saccharose,  38. 

Salicin,  21. 

Salicylic  acid,  243,  440,  446. 

Salicylic  aldehyde,  94,  440,  446. 

Salicylic  amide,  252. 

Saliva,  203,  485-494;  action  on  carbo- 
hydrates, 59;  oxygen  content  of,  410. 

Salivary  glands,  function  of,  485-494; 
microscopic  appearance.  487,  488; 
mucin  in,  142. 

Salmine,  136,  175. 

Salmo  fario,  protamine  in,  137. 

Salmonucleic  acid,  285. 

Salmon,  migration  of  matter  in,  130,  287, 
351. 

Salmon  testes,  histon,  135;  salmine,  136. 

Salmon  spawn,  140. 

Salsola,  or  Salt-wort,  364. 

Salt,  common.     See  Sodium  chloride. 

Salt,  preparation  of  substitute  for,  363, 
364. 

Saltpeter,  formation  in  soil,  193. 

Salts,  349  et  seq.;  storage  of,  by  foetus, 
375. 

Salts,  action  of,  upon  muscle,  357  et  seq. 

Salts,  requirement  of,  by  adults,  366;  by 
growing  individuals,  366;  by  suck- 
lings, 376. 

Santonine,  457. 

Saponification,  103. 


720 


SUBJECT  INDEX. 


Saponin,  21,  116. 

Sapotoxin,  31. 

Sarcolemma,  138. 

Sarcoma,  675. 

Sarcosme,  235,  660. 

Schweitzer's  reagent,  41. 

Sciences,  exact,  relation  to  physiological 
chemistry,  4. 

Scombrine,  136,  174. 

Scybala,  534. 

Scyllium  catulus  and  canicula,  83. 

Scymnol,  515. 

Scymnol-sulphuric  acid,  515. 

Scymnus  borealis,  513. 

Sea-moss,  19,  24. 

Sea-urchin,  140. 

Sebaceous  glands,  595. 

Secalin,  44. 

Secretin,  527  et  seq.,  596  et  seq. 

Secretion,  internal,  596  et  seq. 

Sedimentum  lateritium,  573,  592. 

Selachia,  225. 

Seminase,  482. 

Seralbumin  and  Serglobulin.  See  Serum 
albumin  and  Serum  globulin. 

Serine,  149,  239,  304. 

Serous  membranes,  577. 

Serum,  536. 

Serum  albumin,  131,  132,  172,  548; 
crystals,  124,  127;  glutamic  acid  con- 
tent, 653. 

Serum  globulin,  131,  132,  172,  548;  glu- 
tamic acid  content,  653. 

Seryl-serine,  179. 

Sexual  character,  secondary,  599. 

Sexual  organs.     See  Regenerative  organs. 

Schweigger-Seidel's  urinary  tubule,  581. 

Sheath-fish,  protamine  in,  137. 

Sheep,  rate  of  development,  370,  404; 
blood,  554,  555;  milk  of,  366,  404, 
405. 

Side-chains,  683. 

Side-chain  theory,  682-691. 

Silicate  of  soda,  120. 

Silicic  acid,  120. 

Silk,  139;  -fibroin,  176;  -gelatine,  176. 

Silver,  absorption  by  the  cells,  357. 

Silurus  glanus,  137. 

Sinapis  alba,  57. 

Size,    influence    upon    metabolism,     628 

Skatole,  153,  170,  201,  251,  257,  458. 

Skatole-acetic  acid,  153,  170,  259. 

Skatole-amino-acetic  acid,  153,  258. 

Skatole-carboxylic  acid,  153,  170,  259. 

Skatoxyl,  257,  458. 

Skatoxyl-glucuronic  acid,  32. 

Skatoxyl-sulphuric  acid,  251. 

Skin,  432-437. 

Small  intestine,  389-392,  511  et  seq. 

Smell,  489^95. 

Snail,  mucin  from,  142. 

Snail,  Roman,  144. 

Snails,  acid,  490. 

Snake  venom,  690. 


Soaps,  103 ;  influence  on  pancreas,  526. 

Soda,  content  of  foods,  366. 

Sodium  bicarbonate,  423. 

Sodium  carbonate,  423. 

Sodium  chloride,  361-365;  glucosuria 
produced  by,  79,  80;  cycle  of,  525. 

Sodium  phosphate,  423,  593. 
silicate,  120. 
sulphindigotate,  582. 
urate,  299,  593. 

Soil,  nitrogen  in,  196. 

Soja  hispida,  197. 

Sol,  120. 

Solanin,  116. 

Soldiers,  diet  of,  647. 

Sorbite,  27,  448. 

Sorbpse,  448. 

Species,  conception  of,  663-678. 

Specific  composition  of  body-cells,  329, 
330. 

Specific  nature,  of  oxydases,  446;  of 
ferments,  467. 

Spectroscopic  behavior,  of  oxyhemoglobin, 
560;  hemoglobin,  560 ;  carbonic-oxide- 
hemoglobin,  561 ;  nitric  oxide  hemo- 
globin, 561 ;  sulph-hemoglobin,  562. 

Spermaceti,  102,  105,  108. 

Spermatozoa,  135,  140,  285. 

Sperm-whale,  102. 

Sphaerochinus  granularis,  123. 

Sphingosin,  20,  31,  613. 

Spider  poison,  648. 

Spinach,  iron  in,  381,  388. 

Spirogyra,  357. 

Spleen,  glucothionic  acid,  49;  jecorin,  49; 
iron  depot,  390;  influence  on  pan- 
creas, 531;  on  blood-formation,  573; 
function  of,  610,  611. 

Splitting-processes.  See  Cleavage  and 
Hydrolysis. 

Sponge,  46,  138. 

Spongin,  138. 

Squirrels,  hemoglobin,  125,  559. 

Stacchyose,  40. 

Standard  calorific  values  of  foodstuffs,  337. 

Staphylosin,  690. 

Starch,  13,  36,  42;  soluble,  43;  calorific 
value  of,  333,  336;  paste,  43. 

Starvation,  glucosuria,  30;  effect  on 
diabetic  puncture,  77;  migration  of 
matter  during,  352 ;  disappearance  of 
glycogen,  68;  metabolism,  631;  rela- 
tion of  separate  organs  in,  635. 

Steapsin.     See  Lipase. 

Stearic  acid,  from  fats,  102;  from  lecithin, 
113;  formation  of,  303. 

Stereochemistry,  of  sugars,  16-18;  of  poly- 
peptides,  180,  181,  184,  185. 

Stereoisomers,  decomposition  of,  in  the 
organism,  452;  relation  to  cleavage, 
470-476. 

Stercobilin,  534. 

Stomach,  function  of,  495-510;  small, 
496;  fistula,  496;  extirpation  of,  509; 
emptying  of,  507. 


SUBJECT  INDEX. 


721 


Strophantin,  37. 

Strophantobiose,  29. 

Strychnine,   glucosuria,  30,  81;  influence 

upon  the  nervous  system,  459. 
Strawberries,  370,  377,  381. 
Strawberry  extract,  577. 
Sturgeon,  sperma  of,  137;  sturin  in,  136. 
Sturin,  136,  175. 
Sublimate,  corrosive,  81. 
Substance,  fibrogenous  and  fibrinoplastic, 

537. 
Sublingual  and  submaxillary  glands,  485- 

489. 
Succinic    acid,    170,    483;    oxidation    of, 

during  diabetes,  94. 
Sucklings,  ash  of,  368. 
Sugar,  370,  380. 
Sugar  acids,  27,  28. 
Sugar-beet,  38. 
Sugar  center,  77. 
Sugar-cane,  38. 

Sugar-content  of  the  blood,  29. 
Sugar-maple,  38. 
Sugar-millet,  38. 

Sugar  puncture.     See  Diabetic  puncture. 
Sugars,  simple,   19  et  seq. ;  compound,  36 

et  seq.;  formation  from  fat,  310-322; 

formation  from  protein,  316-321. 
Sulphanilcarbamic  acid,  234. 
Sulphanilic  acid,  234. 
Sulph-hemoglobin,  561. 
Sulphocyanic  acid,  250. 
Sulphur,  119,  194,  249,  406. 
Sulphur  bacteria,  194. 
Sulphureted  hydrogen,  170,  194,  401,  438. 
Sulphuric  acid,  249,  457,  490. 
Sulphurous  amino  acids,  156. 
Sunflower-seeds,  123. 
Suprarenal  gland,  600-603. 
Surface-tension,  532. 
Surviving  organs,  experiments  with,  9. 
Sweat-glands,  595. 
Swimming-bladder  of  fishes,  433. 
Symbiosis,  53. 
Synovia!  fluid,  578. 
Synthesis,  of  fat  in  intestinal  wall,   105; 

of  polypeptides,  179;  by  ferments,  37, 

38,  479-483. 
Syntonin,  336. 

T. 

Takadiastase,  38. 
Talose,  18,  472. 
Tape-worm,  glycogen,  46. 
Tannin,  252,  305. 
Tartaric  acids,  28,  94,  453,  470. 
Tartronic  acid,  28,  239. 
Taste,  489-495. 
Taste-buds,  494. 
Taurine,  158,  234,  248,  515. 
Taurochenocholic  acid,  515. 
Taurocholic  acid,  158,  248,  515. 
Teeth,  493. 
Temperature,    during    work    of    salivary 

glands,  486;  of  kidneys,  584. 
Tendon  mucoid,  143. 


Tension,  of  CO2,  421 ;  of  oxygen,  418. 

Tenebrio  molitor,  123. 

Terpenes,  117,  307. 

Testudo  graeca,  433. 

Testes,  123,  600;  of  a  bull,  285. 

Tetanolysin,  690. 

Tetanus  toxin,  116,  687-690. 

Tetraglycine,  179. 

Tetraglycyl-glycine,  474. 

Tetramethylenediamine,  155,  170,  259. 

Tetrasaccharides,  40. 

Tetroses,  19,  37. 

Theobromine,  200,  280. 

Theophylline,  280. 

Thiolactic  acid,  or,  169. 

Thiophenaldehyde,  244. 

Thiophenuric  acid,  244. 

Thiosulphuric  acid,  249. 

Thread  bacteria,  194. 

Thread  fungi,  198. 

Thujone,  34. 

Thujone  hydrate,  34. 

Thymine,  281,  298. 

Thymol,  162,  252. 

Thymus  glands,  histon,  135,  174;  function 
of,  610.. 

Thymus-nucleic  acid,  281,  285. 

Thyreoglobulin,  132,  608. 

Thyroid  gland,  604-609. 

Tissue,  osteoplastic,  374;  osteoidal,  374. 

Tissue-extracts,  10. 

Tissue-fat,  calorific  value,  333. 

Tissue-juices,  influence  on  coagulation  of 
blood,  540. 

Toad  poison,  690. 

Toad-stools,  114. 

Toluene,  243. 

Toluric  acid,  243. 

Toluene  diamine,  570. 

Toluic  acid,  243,  458. 

Tonus,  vascular,  437. 

Tooth-structure,  493. 

Tooth-wort,  albumin  crystals  from,  122. 

Torpedo  marmorata,  83. 
oscellata,  83. 

Toxines,  682-690. 

Toxophor  groups,  684. 

Trachse,  411. 

Tradescentia,  459. 

Tragacanth-gum,  24. 

Transformation  of  nutriment  albumin 
into  body  albumin,  209  et  seq  ;  car- 
bohydrate and  protein,  305  et  seq. ;  fat 
and  carbohydrate,  103,  303  et  seq. ;  fat 
and  protein,  305,  323  et  seq. 

Transudates,  577,  578. 

Trebalose,  37. 

Tribrom-phenol,  252. 

Trichlor-lactic  acid,  278. 

Triglycine,  185. 

Triglycyl-glycine,  474. 

Triglycyl-glycine-ester,  474. 

Trihydroxyglutaric  acid,  28. 

Trimethylamine,  113,  114. 

Trimethylamino  acetic  acid,  114. 


722 


SUBJECT  INDEX. 


Trimethyl-2-,  6-,  dioxypurine,  1-,  3-,  7- 
(caffein),  280. 

Trimethylcarbinol,  34,  229. 

Trimethyl-hydroxy-ethyl-arnmonium  hy- 
droxide, 113. 

Trimethyl- vinyl-ammonium  hydroxide, 
114. 

Triolein,  102. 

Trioses,  19. 

Trioxypurin  (2-,  6-,  8-),  238,  280. 

Tripalmitin,  102. 

Trisaccharides,  40. 

Tristearin,  102. 

Triticonucleic  acid,  23. 

Triton  (Salamander),  674. 

Trommer's  test  for  sugar,  25. 

Trout,  protamine  from,  137. 

Trypsin,  208,  482,  522. 

Trypsin  digestion,  163,  164,  189. 

Trypsinogen,  522. 

Tryptophane,  152,  251,  258,  260. 

Tubulus  contortus,  581. 

Typhoid,  679. 

Tryosine,  151,  202,  251,  254,  255,  256, 
259,  272,  304. 

Tryosinase,  447. 

Tyrosyl-glycine,  Z-,  187. 

U. 

Umbilical  cord,  143. 

Uracil,  281,  298. 

Uraemia,  595. 

Uraminobenzoic  acid.  See  carbamino- 
benzoic  acid. 

Uraminoisethionic  acid.  See  carbamino- 
isethionic. 

Uranium  salts,  cause  of  glucosuria,  81. 

Urate  of  sodium,  acid  and  neutral,  299, 
593. 

Urea,  155,  225-227,  238,  278,  279,  295, 
325;  role  in  solution  of  uric  acid 
594;  formation  of,  228  et  seq.',  oxi- 
dation of  amino  acids,  234;  conju- 
gation with,  234,  457;  behavior  to  red 
corpuscles,  550. 

Urease,  482. 

Uric  acid,  236  et  seq. ;  277,  289 ;  exogenous 
and  endogenous,  291 ;  metabolism, 
291;  solubility  of,  298,  593;  elimi- 
nation from  kidneys,  586  et  seq. 

Uric  acid  diathesis,  298. 

Uricolytical  ferments,  294. 

Urinary  tubes,  function  of,  582. 

Urine,  579  et  seq.;  theory  of  elimination, 
583,  586;  composition  of,  589,  590; 
reaction  of,  591. 

Urobilin,  572. 

Urochloralic  acid,  34. 

Urochrome,  572. 

Uroerythrin,  572. 

Uroferric  acid,  270. 

Uroleucic  acid,  257,  271. 

Uroxanthic  acid,  271. 

Ursocholeic  acid,  516. 


Utilization  of  foodstuffs,  650  et  seq. 
Utricularia,  168. 

V. 

Valeric  acid,  from  celulose,  63. 

Valeric  aldehyde,  d-,  149. 

Value  of  foodstuffs,  333,  334,  336. 

Vampyrella  spirogyrse,  533. 

Vanillin,  oxidation  in  diabetes,  94. 

Variations,  individual,  8. 

Vascular  tonus  in  high  altitudes,  436. 

Vegetable    acids,    56;     oxidation    of   the 

alkali  salts  in  diabetes,  93. 
Vegetable  diet,  649-653. 
Vegetable  mucilages,  42. 
Vegetarianism,  649-652. 
Vignin,  653. 
Vitellin,  134. 
Vitelloses,  165. 
Volemitol,  29. 
Vorticella,  46,  52. 

W. 
Water,  53,  349,  354;   influence  on  gastric 

secretion,  500. 
Whale  (sperm),  102. 
Wheat,  ash  of,  369,  370,  380;  gliadin  and 

gluten  casein,  132. 
Wheat-bran,  381. 
Wheat-flour,  380. 
White-bread,  iron  and  lime  content,  370, 

377,  380. 

White-horse  melanin,  145. 
White  of  egg,  composition  of,  659. 
White-snapper,  protamine  from,  137. 
Wild   raspberries,   iron  and  lime  content, 

370. 
Wild  strawberries,  iron  and  lime  content, 

370,  381. 

Woman's  milk.      See  Human  milk. 
Wood,  pentosans  from,  24. 
Wool-fat,  116. 
Work,  heat  equivalent  of,  335,  336,  624, 

625. 

X. 

Xanthine,  280,  297. 

Xantho-proteic  reaction,  162,  163. 

Xanthorhamnin,  40. 

Xylan,  24. 

Xylitol,  28. 

Xylol,  243,  458. 

Xylose,  1-,  21,  24,  33,  282. 

Y. 

Yeast,  27,  47,  141. 

Yeast-nucleic  acid,  21,  22,  281. 

Yeasts,  expressed  liquor  from,  464. 

Yeasts,  preserved,  464. 

Yolk  of  the  hen's  egg.     See  Egg-yolk. 

Yolk-plates,  123. 

Z. 

Zein,  133,  173,  653. 
Zymase,  464. 
Zymogen,  205,  463,  465,  497. 


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Text-book  of  physio- 
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